Arctic Sea Ice : Forum

Cryosphere => Antarctica => Topic started by: AbruptSLR on April 26, 2013, 05:57:05 PM

Title: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 26, 2013, 05:57:05 PM
I am opening this thread to discuss the possible East Antarctic Ice Sheet, EAIS, contributions to SLR by 2100.  While the EAIS is generally more stable than the WAIS the two accompanying figures make it clear that significant areas of East Antarctica have bed elevations below sea level and are thus possibly subject to accelerated ice mass loss due to possible interaction with ocean water.  In subsequent posts I plan to provide information regarding some of the less stable areas of the EAIS, including discussions of areas that could become activated if/when the WAIS collapses.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 26, 2013, 06:16:22 PM
An article within Australian Antarctic Magazine, Issue 21: 2011, entitled: "Model simulations investigate Totten thinning" indicates:

"Enhanced oceanic heat flux and changing ocean dynamics are believed to be the key factors in making the Totten Glacier one of the fastest thinning glaciers in East Antarctica. To investigate this, a model of the ocean circulation beneath and around the Totten Glacier is currently being developed by scientists at the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC) and the Australian Antarctic Division.
The Totten Glacier is located approximately 400 km east of Casey station, on the eastern side of Law Dome, and discharges up to 70 Gt/year of fresh glacial meltwater into the ocean. This is equivalent to 100 times the volume of Sydney Harbour every year. It has a maximum thickness of over 2.5 km at its grounding line – the region at which the glacier departs the continental ice sheet and begins to float – and is nearly 200 m thick at the calving front, 150 km to the north. Recent measurements show that the Totten Glacier is thinning at up to 1.9 m per year, a three-fold increase over the past 10 years. The direct cause of this alarming statistic isn't yet known, but is believed to be ocean driven.
The leading hypothesis is that relatively warm water derived from Circumpolar Deep Water (CDW), is mixed and modified and flows southwards onto the continental shelf, enhancing the melting of the glacier.
Once on the continental shelf, and with the appropriate bathymetric pathways to reach the glacier, the modified CDW, which is denser than the surrounding shelf water masses, is able to sink to the grounding line of the glacier and cause increased melting and rapid glacier acceleration. This is also suspected to be the key cause of the increased melting of other ice shelves showing rapid thinning, such as the Pine Island Glacier in the Amundsen Sea region of West Antarctica.
Since the ice shelf acts to slow glacier flow, ice shelf thinning by increased melting could lead to rapid acceleration of the Totten Glacier, similar to what was observed in the wake of the disintegration of the Larsen A and B ice shelves on the Antarctic Peninsula (Australian Antarctic Magazine 14: 22-23, 2008). Observations suggest a transport of modified CDW onto the continental shelf region near the Totten Glacier, but are too sparse to be definitive. Modelling is an obvious way to address the difficulty in obtaining high-resolution observations of the ocean near the Totten Glacier.
At the ACE CRC we are developing a numerical model to examine the thermodynamic interaction between floating ice shelves and the ocean on Antarctica's coastal margins (see Australian Antarctic Magazine 19: 6, 2010 for more details).
The output from the ice shelf-ocean model includes the time-evolution of ocean currents, and salinity and temperature of the water. From this, the melt rates of the ice shelves and the dynamics of massive water bodies can be determined.
The circulation and water temperature in the open ocean and under the Totten and Dalton ice shelves is illustrated in Figure 1 (the second attached image). This shows the depth averaged ocean currents for March 2006, coloured for ocean temperature. Warm modified CDW can be seen to flow onto the shelf break and towards the eastern side of the front of the ice shelf. The fresh meltwater then flows out of western side and continues westwards around Law Dome.
The melt rate of the Totten Glacier ice shelf is calculated within the model. Figure 2 (the third attached figure) shows the melt rate (in metres per year) under the Totten ice shelf, with depth-averaged currents overlaid. Melt rates of more than 50 m per year are observed occurring at the deepest part of the ice shelf."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 27, 2013, 05:13:29 AM
To clarify the location, and behavior, of the EAIS glacier that I am going to be talking about in this thread, I provide here both the first image from Rignot et al 2011, with ice velocities for 2008-2009, and I repost the second image of changes in ice surface elevations (per Aviso) prior to June of 2012.  In addition to the previously discussed Totten Glacier, these two figures make it clear that the following EAIS glaciers are currently losing ice mass: (a) Totten; (b) Denman; (c) the glacier upstream of the Cook Ice Shelf; (d) Rennick; (e) Lambert; (f) the glacier upstream of the West Ice Shelf; (g) Ninnis; (h) the glacier upstream of the Moscow University Ice Shelf; (i) Frost; (j) Dibble; and (k) Mertz.  Also, these two figures make it clear that as the WAIS is lost the following EAIS glaciers will be activated: (a) Byrd; (b) Bailey; (c) Slessor; (d) Recovery; and (e) Support Force.

Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 27, 2013, 06:12:03 AM
For additional background on the EAIS glaciers that are currently losing ice mass, I provide the following information from Wikipedia (see also Ref 1):

Totten Glacier is a large (about 40 miles long and 20 miles wide) glacier off the Budd Coast of Wilkes Land in Australian Antarctica. It drains northeastward from the continental ice but turns northwestward at the coast where it terminates in a prominent tongue close east of Cape Waldron.  Scientists studying the effects of global warming have proposed that sea water encroachment in the area could destabilize a significant portion of the East Antarctic Ice Sheet (see Ref 1).

Denman Glacier is a glacier 7 to 10 miles (11 to 16 km) wide, descending north some 70 miles (110 km), which debouches into the Shackleton Ice Shelf east of David Island, Queen Mary Land.

Rennick Glacier is broad glacier, nearly 200 miles long, which is one of the largest in Antarctica. It rises on the polar plateau westward of Mesa Range and is 20 to 30 miles wide, narrowing to 10 miles near the coast. It takes its name from Rennick Bay where the glacier reaches the sea.
 
Lambert Glacier is a major glacier in East Antarctica. At about 60 miles (100 km) wide, over 250 miles (400 km) long, and about 2,500 m deep, it holds the Guinness world record for the world's largest glacier. It drains 8% of the Antarctic ice sheet to the east and south of the Prince Charles Mountains and flows northward to the Amery Ice Shelf.

Ninnis Glacier (68°22′S 147°0′E68.367°S 147.000°E) is a large, heavily hummocked and crevassed glacier descending steeply from the high interior to the sea in a broad valley, on George V Coast in Antarctica.

Frost Glacier (67°5′S 129°0′E67.083°S 129.000°E) is a channel glacier flowing to the head of Porpoise Bay, Antarctica.

Dibble Glacier (66°17′S 134°36′E66.283°S 134.600°E) is a prominent channel glacier flowing from the continental ice and terminating in a prominent tongue at the east side of Davis Bay.

Mertz Glacier (67°30′S 144°45′E67.500°S 144.750°E) is a heavily crevassed glacier in George V Coast of East Antarctica. It is the source of a glacial prominence that historically has extended northward into the Southern Ocean, the Mertz Glacial Tongue.

Cook Ice Shelf is an ice shelf about 55 miles (90 km) wide, occupying a deep recession of the coastline between Cape Freshfield and Cape Hudson, to the east of Deakin Bay. The generic term has been amended, as the bay is permanently filled by an ice shelf.  Scientists studying the effects of global warming have proposed that sea water encroachment in the area could destabilize a significant portion of the East Antarctic Ice Sheet (see Ref 1).

Moscow University Ice Shelf (67°0′S 121°0′E67.000°S 121.000°E) is a narrow ice shelf, about 120 miles (193 km) long, which fringes Sabrina Coast between Totten Glacier and Paulding Bay. Dalton Iceberg Tongue extends north from the east part of the shelf.

Ref 1: Pearce, Fred (2007). With Speed and Violence: Why scientists fear tipping points in climate change. Beacon Press Books. ISBN 978-0-8070-8576-9.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 27, 2013, 04:20:21 PM
As indicated by the various images already posted it is clear that the Totten / Moscow University Ice Shelf area is one of the most critical in the EAIS and is already losing ice mass as also confirmed by the ocean salinity measures immediately offshore of this area as indicated in the first image.  The importance of this area is confirmed by the research effort being expended to study ice mass loss from this area as indicated by the data that will become publically available in July 2013 at the following websites:

http://gcmd.nasa.gov/records/AADC_AAS_3121.html (http://gcmd.nasa.gov/records/AADC_AAS_3121.html)
https://data.aad.gov.au/index.cfm (https://data.aad.gov.au/index.cfm)

In advance of the release of this data, the following provides a summary of this effort and contact information.


Mass balance of the Totten basin in East Antarctica: Estimation and calibration from ground, air and space-based observations (TOT-Cal)

Abstract: Linked to this record are a report providing further details about the project, as well as the data from the project.

Public Summary
Regions of Antarctica are undergoing significant change in response to the Earth's changing climate. This project will provide a state of the art contemporary insight into the changing behaviour of the Totten drainage basin in East Antarctica - an area of vital importance in understanding ice/ocean/atmosphere and climate interactions in the Australian region of Antarctica. We will estimate the contribution of the Totten Glacier drainage basin to present-day sea level rise and simultaneously provide a critical validation of the European Space Agency (ESA) CryoSat-2 satellite mission over this region.

Project #3121 investigated the mass balance of the Totten basin and provided an Australian contribution to the validation of CryoSat-2 data over Law Dome and the Totten Glacier. With field seasons in 2010/11 and 2011/12, the project gathered a range of in situ data using field and airborne data collection techniques. These data include geodetic quality GPS observations from up to 6 quasi-permanent GPS sites from which ice velocity, tropospheric water vapour and in some cases, tidal motion are derived. These sites were equipped with temperature and atmospheric pressure sensors, and in some cases, acoustic snow accumulation sensors. GPS equipped skidoo surveys were undertaken over the survey region on Law Dome to facilitate the generation of a validation surface to compare against airborne LiDAR and ASIRAS based DEMs. In the 2011/12 season, AWI collaborators achieved 4 days of survey flights in Polar-6, obtaining LiDAR and ASIRAS data over specific flight lines spanning Law Dome and the Totten Glacier.

Project objectives:
This project will provide a state-of-the-art contemporary insight into the most recent changes in the surface elevation of the Totten drainage basin in East Antarctica, whilst simultaneously providing a critical and unique contribution to the calibration and validation of the new European Space Agency (ESA) CryoSat-2 satellite mission and the Australian Antarctic Division (AAD) LiDAR/RADAR system. The present-day mass balance change of Antarctica plays a key role in understanding the effects of global warming on the Earth system, in particular the contribution of melting Antarctic ice to present-day sea level rise. The Totten Glacier is known to be undergoing significant surface lowering and is perhaps the most significant basin in the East Antarctic (e.g., Shepherd and Wingham, 2007). The basin itself drains approximately 1/8th of the East Antarctic Ice Sheet (EAIS) and, as a marine-based system, is analogous to the West Antarctic Ice Sheet (WAIS) whose changing mass balance dominates the Antarctic contribution to global sea level rise(Lemke et al., 2007). The TOT-Cal project will independently lead Australian research in understanding the contribution of Antarctic ice to changing sea-levels by focusing new data on this key drainage basin of international scientific interest. Importantly, this region can be reached with relative ease by AAD logistics - it is located literally at the doorstep of the Australian Casey station, in close proximity to the Wilkins intercontinental airstrip. With international interest focused on this region, this project provides a showcase of AAD short-stay logistics in support of vital time-critical research and a major new ESA satellite mission that will undoubtedly play a major role in cryospheric science into the future.

The TOT-Cal project will draw upon key resources and personnel within the University of Tasmania (UTAS), Australian National University (ANU), Laboratoire d'Etudes en Geophysique et Oceanographie Spatiales (LEGOS, France), Scripps Institution of Oceanography (SIO, USA) and the AAD, requiring the collection and analysis of field based, airborne and satellite data over a multi-season campaign. It builds upon and extends related past, existing and planned Australian Antarctic Science (AAS), Australian Research Council (ARC) and International Polar Year (IPY) projects, addressing three specific questions:

1) What is the present-day mass balance of the Totten drainage basin and what is its contribution to global sea level change? This will be assessed through a combination of airborne LiDAR/RADAR observations, satellite altimetry observations including Seasat (1978), Geosat (1985-1989), ERS-1 (1992-1996), ERS-2 (1995-2005), Envisat-RA2 (2002 to present), ICESat (2003-present) and CryoSat-2 (expected launch 2009), space gravity observations (GRACE), along with ground-based validation experiments.

2) What are the accuracies and uncertainty characteristics of the altimetry measurement systems? (In other words, what is the expected accuracy of the altimetry-derived mass balance estimates?) With an emphasis on the new CryoSat-2 and AAD LiDAR/RADAR systems, this will be assessed through repeated ground and airborne experiments, providing direct contribution to the CryoSat-2 international Calibration, Validation and Retrieval Team (CVRT), whilst also providing an important cross-calibration of synchronous ICESat, Envisat and CryoSat-2 data. Of particular focus will be the understanding of the different surface interactions between the incident radar and laser waveforms (both satellite and airborne) with the surface snow/ice characteristics (topography, firn, seasonal changes, etc).

3) What is the magnitude of the present-day Glacial Isostatic Adjustment (GIA) in the region that needs to be removed from the space-based geodetic observations in order to estimate mass balance using a space geodetic approach? Present uncertainty in the magnitude of GIA is a dominant error source in the mass balance error budget and requires an analysis of recent models and in-situ geodetic evidence in order to fully understand and minimise this error contribution.

Each of the objectives set out above will be assessed with data acquired over the coming three summer seasons, leading into participating in the larger period of logistics support around the Totten Glacier in 2011/12. This also enables this project to provide state-of-the-art estimates of surface lowering to the Australian AAD/ACECRC modelling team (R.Warner et al) for integration into dynamic ice models in the subsequent years of this project. These estimates will be fundamental in improving conventional forward ice models which to date, are not able to predict the observed changes in the Totten Glacier (van der Veen et al. 2008). The timing of the work outlined in this proposal is critical given the CryoSat-2 launch (expected late 2009) and the impending conclusion of the GRACE mission, this research needs to be undertaken now for the field seasons indicated in order to maximise the scientific impact and provide the necessary complement to other planned AAS projects that will operate over the same future field seasons.

Public summary of the season progress:
2010/11 was the first field season for this project. Valuable GPS field data were acquired in the Law Dome and Totten Glacier regions to assist with providing an Australian contribution to the validation of the CryoSat-2 ice monitoring satellite mission, and to further understand ice shelf/ocean interactions and climate change in this region. Planned airborne surveys by the German AWI Polar-5 aircraft were unable to be completed due to poor weather. Collaboration with the 'Investigating the Cryospheric Evolution of the Central Antarctic Plate' project (ICECAP - UTexas) yielded important airborne scanning laser altimeter elevation data over the Law Dome site.
Name: DATA OFFICER AADC
Phone: +61 3 6232 3244
Fax: +61 3 6232 3351
Email: metadata at aad.gov.au
Contact Address:
Australian Antarctic Division
203 Channel Highway
City: Kingston
Province or State: Tasmania
Postal Code: 7050
Country: Australia

Personnel
CHRISTOPHER WATSON
Role: INVESTIGATOR
Role: TECHNICAL CONTACT
Email: cwatson at utas.edu.au
Contact Address:
University of Tasmania
City: Sandy Bay
Province or State: Tasmania
Postal Code: 7005
Country: Australia

Temporal Coverage
Start Date: 2009-09-30
Stop Date: 2012-03-31
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 27, 2013, 04:35:48 PM
For those sophisticated enough to use either the "Global Glacier Inventory" and - or the "Randolph Glacier Inventory", to make their own potential ice mass loss assessment, I provide the following links where the best know information is available to further characterize these critical East Antarctic glaciers (and others):

https://nsidc.org/pipermail/glims/2012/000527.html (https://nsidc.org/pipermail/glims/2012/000527.html)

http://www.glims.org/RGI/randolph.html (http://www.glims.org/RGI/randolph.html)

For those less sophisticated at manipulating massive databases I provide the following from:

Climatic Change
DOI 10.1007/s10584-011-0037-5
Exploring high-end scenarios for local sea level rise to develop flood protection strategies for a low-lying delta—the Netherlands as an example

by Caroline A. Katsman et al, 2011

This paper includes the following statements about SLR contributions from the EAIS this century:

"2. the three marine-based glacier basins in East Antarctica that are showing recent thinning (Pritchard et al. 2009): Totten Glacier, the glacier which feeds Cook Ice Shelf around 150 E, and Denman Glacier (EAIS-g) and
3. the northern Antarctic Peninsula (n-AP), an area that has suffered recent
increases in atmospheric temperature, increased glacier

The severe scenario is based on an emerging collapse of the ASE and EAIS-g as a result of marine ice sheet Climatic Change
EAIS-g  SLR contribution by 2100: 0.19m (for discharge as analogous to ASE)

During a collapse, the retreat of the ice and the contribution to sea level rise is not limited by the acceleration of the glaciers taking ice to the oceans, as suggested by the investigations of the upper bound of the AIS contribution to sea level rise by Pfeffer et al. (2008). For a marine ice sheet it is possible for the edge of the ice sheet to migrate inland, into increasingly deep ice, and this could cause a collapse of West Antarctic Ice Sheet at rates that are higher than could be achieved by glacier acceleration alone. It is generally thought that a full-scale collapse would be promoted by the removal of ice shelves that fringe the grounded ice sheet and act to buttress it. On the Antarctic Peninsula, loss of Larsen B Ice Shelf resulted in a speed-up of the glaciers that formerly fed it by factors of two to eight times (Scambos et al. 2004). If we imagine glacier acceleration at the upper end of this range we can come close to the rates of loss that could be described as a collapse. If the loss of ice from the glaciers across ASE increases to eight times the balance value, akin to what was observed after the loss of Larsen B ice shelf, it would result in an additional contribution of 3 mm/yr to sea level rise. If this type of behavior followed an ice-shelf loss, it could, in theory dominate for much of the latter part of the century, giving a total contribution to sea level rise by 2100 on the order of 0.25 m (Table 2).  If the marine glacier basins in EAIS-g were to follow the progress of the ASE glaciers, effectively producing a 50% excess in discharge over 30 years (from 2000), and then following exponential growth to 2100, this would imply around 0.19 m global mean sea level contribution in the period 2000–2100. In this severe scenario, the contribution from the n-AP glaciers is unlikely to be a significant fraction of the total. We note that the ice thickness on the n-AP (Pritchard and Vaughan 2007) is poorly surveyed, but is unlikely to contain more than 0.10 m global mean sea level equivalent. The potential contribution from this area is therefore unlikely to be substantially greater than 0.05 m. For the purposes of this scenario, we assume that this 0.05 m is lost by 2100. The total sea level contribution for the severe scenario due to changing ice dynamics is then 0.49 m. To this estimate, we add again the
global mean sea level change of −0.08 m projected in response to an increase in accumulation (IPCC AR4), and arrive at an upper estimate of 0.41 m.

Climatic Change
The modest and severe scenarios discussed above serve as the lower and higher end of the high-end projection for the contribution of the AIS to global mean sea level rise. It amounts to −0.01 to 0.41 m (Table 2, Fig. 1). Pfeffer et al. (2008) estimated the AIS contribution at 0.13–0.15 m (low estimate) and 0.62 m (high estimate). The latter is considerably higher than ours, as a consequence of the entirely different starting-point that is chosen in the two studies.  While Pfeffer et al. (2008) focus on kinematic constraints on the contribution by estimating an upper limit to the discharge of the glaciers, our approach focuses on the possible impacts of marine ice sheet instabilities. Based on their kinematic approach, Pfeffer et al. (2008) obtained their estimate for ASE (which is 0.05 to 0.15 m larger than ours) by setting an upper limit on the speed at which glaciers can transport ice to the sea. They assume a (not well-justified) increase in velocity to the highest value ever observed for an outlet glacier (Howat et al. 2007, an observation from Greenland), and maintain this for the remainder of the century. In contrast, we consider the consequences of a collapse of the ice sheet in response to the loss of the adjacent ice shelf by analogy with recent events at Larsen B ice shelf (Scambos et al. 2004). In our opinion, the latter scenario is more likely based on established vulnerability of the ASE Embayment to marine ice sheet instability (Vaughan 2008). Also as a consequence of the different approaches chosen, the two papers consider different regions in East Antarctica in their estimates. While Pfeffer et al. (2008) estimate a contribution for the largest outlet glacier (the Amery/Lambert drainage basin, Rignot et al. 2008), we estimate the contributions from the marine-based glaciers prone to marine ice sheet instability (Pritchard et al. 2009). Finally, part of the difference between the two estimates can be explained by the fact that Pfeffer et al. (2008) only consider SMB changes on the Antarctic Peninsula (assessed at +0.01 m) while we take into account the projected accumulation changes over the entire continent (assessed at −0.08 m). The two estimates for the dynamic contribution from the Antarctic Peninsula hardly differ."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 27, 2013, 05:02:02 PM
I note here that when I created my  RCP 8.5 95% CL abrupt sea level rise projections shown in the "Philosophical" thread that I used estimates such as those presented by Caroline A. Katsman et al, 2011 for my estimates of EAIS contributions to SLR by 2100.  Nevertheless, I would like to note here that at that time the impressive images of atmospheric methane content over East Antarctica presented by A4R in the "Antarctic Methane" thread (as I cannot get this image to attach you will need to go to the "Antarctic Methane" thread to see it) were not available.  These very high atmospheric methane contents (as high as 2163 ppb on April 4, 2013) directly over East Antarctica could have the following possibly severe consequences:
1.  The accummulation of GHG and methane inparticular near the South Pole can reduce the atmospheric pressure, which in-turn can both accelerate the circumpolar wind velocities, but can also induce these high velocity circumpolar winds to migrate southward.
2.  Such changes in the circumpolar winds can change the circulation pattern of the "un-named" gyre shown in the first attached image off the coast of the Totten Glacier - Moscow University Ice Shelf area.
3.  The changes in the "un-named" gyre can entain warm CDW (as has been documented to have happened for the Weddell Gyre), which could potentially bring such warm CDW into direct contact with the grounding lines of the glaciers - ice sheets in this critical area.
4.  The upwelling mechanism shown in the second attached figure could then drive advection that could accelerate the grounding line retreats for the glaciers - ice sheets in this area; possibly at rates considerable faster than previously estimated by researchers such as Caroline A. Katsman.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 28, 2013, 06:49:12 AM
The Transantarctic Mountains, TAM, divide East Antarctica from West Antarctica; thus if/when the WAIS collapses, many glaciers in the TAM will become activated.  Therefore, I provide the following summaries from Wikipedia for those not familiar with this subject:

"The Transantarctic Mountains (TAM) comprise a mountain range in Antarctica which extend, with some interruptions, across the continent from Cape Adare in northern Victoria Land to Coats Land. These mountains divide East Antarctica and West Antarctica. They include a number of separately named mountain groups, which are often again subdivided into smaller ranges.

The Byrd Glacier is a major glacier in Antarctica, about 136 km long and 24 km wide, draining an extensive area of the polar plateau and flowing eastward between the Britannia Range and Churchill Mountains to discharge into the Ross Ice Shelf at Barne Inlet.

The Slessor Glacier is a glacier at least 120 km (75 mi) long and 80 km (50 mi) wide, flowing west into the Filchner Ice Shelf to the north of the Shackleton Range.

Bailey Ice Stream (79°0′S 30°0′W79.000°S 30.000°W) is an ice stream on the northern margin of the Theron Mountains, flowing west-southwest to the Filchner Ice Shelf.

The Recovery Glacier (81°10′S 28°00′W81.167°S 28.000°W) is a glacier flowing west along the southern side of the Shackleton Range in Antarctica.  The Recovery Ice Stream that drains part of the East Antarctic Ice Sheet into the glacier is nearly 800 km (500 mi) long and feeds the Filchner Ice Shelf over the Weddell Sea. The area contains four subglacial lakes, causing the ice flow rate to vary dramatically, ranging between 2 and 50 meters per year. The ice stream drains about 35 billion tons of water and ice into the ocean each year, while the entire East Antarctic ice sheet releases about 57 t (56 long tons; 63 short tons) a year.

Support Force Glacier is a major glacier in the Pensacola Mountains, draining northward between the Forrestal Range and Argentina Range to the Filchner-Ronne Ice Shelf.

Shackleton Glacier is a major Antarctic glacier, over 96 km (60 mi) long and from 8 to 16 km (5 to 10 mi) wide, descending from the polar plateau from the vicinity of Roberts Massif and flowing north through the Queen Maud Mountains to enter the Ross Ice Shelf between Mount Speed and Waldron Spurs. The Roberts Massif is a remarkable snow-free massif exceeding 2,700 metres (8,860 ft) and about 155 km2 (60 sq mi) in area.

The Nimrod Glacier is a major glacier about 135 km (85 mi) long, flowing from the polar plateau in a northerly direction through the Transantarctic Mountains between the Geologists and Miller Ranges, then northeasterly between the Churchill Mountains and Queen Elizabeth Range, and finally spilling into Shackleton Inlet and the Ross Ice Shelf between Capes Wilson and Lyttelton.

Mulock Glacier in Antarctica is a heavily crevassed glacier which flows into the Ross Ice Shelf 40 km south of the Skelton Glacier in the Ross Dependency, Antarctica.

The Beardmore Glacier in Antarctica is one of the largest glaciers in the world, with a length exceeding 160 km (100 mi). The glacier is one of the main passages from the Ross Ice Shelf through the Queen Alexandra and Commonwealth ranges of the Transantarctic Mountains to the Antarctic Plateau, and was one of the early routes to the South Pole. Beardmore Glacier has a steep upward incline

The Scott Glacier (85°45′S 153°0′W85.750°S 153.000°W) is a major glacier, 120 miles (190 km) long, that drains the East Antarctic Ice Sheet through the Queen Maud Mountains to the Ross Ice Shelf. The Scott Glacier is one of a series of major glaciers flowing across the Transantarctic Mountains, with the Amundsen Glacier to the west and the Leverett and Reedy glaciers to the east.

Amundsen Glacier (85°35′S 159°00′W85.583°S 159.000°W) is a major Antarctic glacier, about 6 to 10 km (4 to 6 mi) wide and 128 km (80 mi) long, originating on the polar plateau where it drains the area to the south and west of Nilsen Plateau, and descending through the Queen Maud Mountains to enter the Ross Ice Shelf just west of the MacDonald Nunataks.

The Priestley Glacier is a major valley glacier, about 96 km (60 mi) long, originating at the edge of the polar plateau of Victoria Land. The glacier drains southeast between the Deep Freeze and Eisenhower ranges to enter the northern end of the Nansen Ice Sheet.

Liv Glacier is a steep valley glacier, 64 km (40 mi) long, emerging from the Antarctic Plateau just southeast of Barnum Peak and draining north through the Queen Maud Mountains to enter Ross Ice Shelf between Mayer Crags and Duncan Mountains.

The Reedy Glacier is a major glacier in Antarctica, over 160 km (100 mi) long and from 10 to 19 km (6 to 12 mi) wide, descending from the polar plateau to the Ross Ice Shelf between the Michigan Plateau and Wisconsin Range, and marking the limits of the Queen Maud Mountains on the west and the Horlick Mountains on the east.

Foundation Ice Stream is a major ice stream in Antarctica's Pensacola Mountains. The ice stream drains northward for 150 miles (240 km) along the west side of the Patuxent Range and the Neptune Range to enter the Ronne Ice Shelf westward of Dufek Massif.

Aviator Glacier is major valley glacier in Antarctica that is over 60 miles (96 km) long and 5 miles (8 km) wide, descending generally southward from the plateau of Victoria Land along the west side of Mountaineer Range, and entering Lady Newnes Bay between Cape Sibbald and Hayes Head where it forms the Aviator Glacier Tongue."
Title: Re: EAIS Contributions to SLR by 2100
Post by: pikaia on April 28, 2013, 11:07:26 AM
While melting of the Antarctic ice would cause a rise in average sea levels, there would actually be a large REDUCTION in sea level near to the lost ice (because the ice's gravity attracts the surrounding water). Has this been taken into consideration?

Jerry Mitrovica, Harvard University (http://www.youtube.com/watch?v=RhdY-ZezK7w#)
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on April 28, 2013, 11:09:12 PM
I, too, have been looking to the East. Amery,Totten and Denman, and the Moscow U shelf are the ones i try and watch. And once Ross weakens, Byrd will race.

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 29, 2013, 03:15:33 AM
Pikaia,

Yes, all of my projections consider the "finger print" effect of the gravitational influences of ice mass loss.

Sidd,

Thanks for the expression of mutual interest.

ASLR
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 29, 2013, 03:59:35 AM
I would like to make the following observations:

1.  The first attached image show that the Transantarctic Mountains (TAM) are not continuous, and thus as/when the WAIS collapses, many areas of the EAIS that are not currently moving, will become active with new ice streams in the future.

2.  As the ocean water off the coast of the Totten Glacier - Moscow University Ice Shelf increase in temperature due to the increasing entrainment of warm CDW with the "un-named gyre" there will be more frequency ice surface melting events in this area in the future.

3.  The second attached figure showing the monthly Antarctic sea ice extent for March 2013; which indicates that not only are the sea ice extents anomalously large in both the Weddell, and Ross, Seas areas (due to the presence of ice meltwater in these waters), but to a lesser extent so is the sea ice extent off of the coast of the Totten Glacier - Moscow University Ice Shelf areas; and with time (possibly accelerated by the continued presence of high atmospheric methane content concentrations over the EAIS) the Totten Glacier - Moscow University Ice Shelf area may become more like the Ross, Weddell, Seas areas (due to increased ice mass loss form local glacial ice).

4.  The SLR projections that I included in the RSLR graphs in the "Philosophical" thread  from 2100 to 2200 for the RCL 95% CL case illustrate a reasonable rate of RSLR with at least half of the indicated SLR being contributed from the EAIS ice mass loss.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 30, 2013, 06:08:38 PM
In a recent (2013) interview with Jason Box, Mother Jones magazine made the following statement:

"Box also provided a large-scale perspective on how much sea level rise humanity has already probably set in motion from the burning of fossil fuels. The answer is staggering: 69 feet, including water from both Greenland and Antarctica, as well as other glaciers based on land from around the world."

Such a statement implies that the EAIS is already committed to make a make contribution to future SLR, and the only remaining question is how fast this contribution to SLR will occur.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 04, 2013, 11:21:36 PM
I have not yet addressed the possible contributions of subglacial hydrology to potentially destabilize key portions of the EAIS (particularly when working synergistically with the previously discussed ocean - ice interactions).  To begin this post I present the abstract from: Evidence of a hydrological connection between the ice divide and ice sheet margin in the Aurora Subglacial Basin, East Antarctica, by Wright et al 2012, DOI: 10.1029/2011JF002066

"Subglacial hydrology in East Antarctica is poorly understood, yet may be critical to the manner in which ice flows. Data from a new regional airborne geophysical survey (ICECAP) have transformed our understanding of the topography and glaciology associated with the 287,000 km2 Aurora Subglacial Basin in East Antarctica. Using these data, in conjunction with numerical ice sheet modeling, we present a suite of analyses that demonstrate the potential of the 1000 km-long basin as a route for subglacial water drainage from the ice sheet interior to the ice sheet margin. We present results from our analysis of basal topography, bed roughness and radar power reflectance and from our modeling of ice sheet flow and basal ice temperatures. Although no clear-cut subglacial lakes are found within the Aurora Basin itself, dozens of lake-like reflectors are observed that, in conjunction with other results reported here, support the hypothesis that the basin acts as a pathway allowing discharge from subglacial lakes near the Dome C ice divide to reach the coast via the Totten Glacier."

The attached image from: A dynamic early East Antarctic Ice Sheet suggested by ice-covered fjord landscapes by Young et al, 2011, doi:10.1038/nature10114; show where the Aurora Subglacial Basin (ASB) is located and how its bottom topology feed basal meltwater down towards the Totten Glacier (which as noted in previous posts is a major source of concern regarding ice mass loss from the EAIS), which could serve to accelerate the ice mass loss from this area.  Furthermore, the Young et al 2011 paper notes that the Aurora Basin contains several paleo-fjords; which, indicate that in the past the EAIS had on at least two occasions retreated into this subglacial basin.  This clearly raises concerns about the potential SLR contributions from this area (including the Totten and Moscow University Ice Shelf areas) during this century.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 05, 2013, 08:44:39 PM
I thought that I would post this image from an article on Lake Vostok (which is isolated and thus not of particular interest w.r.t. ice mass loss), because is shows the multitude of subglacial lakes and rivers that feed directly beneath Totten Glacier (but it is relevant to the question of ice mass loss from various parts of Antarctica).
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 12, 2013, 11:49:44 PM
I thought that I would post this image here from Shepherd et al 2012 to provide an idea of the trends of ice mass loss from EAIS relative to the WAIS, GIS and the Antarctic Peninsula; however, should the rate of snowfall in East Antarctica remain stable, or decrease, then the ice mass loss trend for the EAIS could become more negative with time.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 26, 2013, 07:25:41 PM
I provide the following abstract from the Nineteenth WAIS Workshop, 2012, regarding the risk of calving from the Amery Ice Shelf:

Intermittent rift propagation in the Amery Ice Shelf
C. C. Walker, J. N. Bassis, R. J. Czerwinski, H. A. Fricker

The Amery Ice Shelf features five prominent rifts within 30 km of its calving front. Through observation using available MODIS and MISR data, we produce a time series of changes in rift length for the period 2002-2012. We find that all five are actively propagating, but with a complex spatio-temporal pattern of variability in which some rifts propagate in tandem while others appear to tradeoff. Temporal variability in rift propagation is dominated by large episodic bursts. These bursts, analogous to the much smaller propagation events detected from field observations, are not synchronous across all five rifts nor do the timing of propagation events exhibit any correlation with observed proxies for environmental forcing (e.g., atmospheric temperatures, sea-ice extent). However, we find that several propagation events take place after the predicted arrival from tsunamis originating in the Indian Ocean. This is especially apparent following the December 2004 Sumatra earthquake and three other earthquakes in the Sumatra/W. Indonesia area. This connection is bolstered by the observation of similar effects at other ice shelves, e.g., a large iceberg calving after the sudden propagation of two front-initiated rifts at Larsen C after the December 2004 tsunami. In comparing rift propagation at Amery with 67 rifts on 11 other ice shelves around Antarctica, we find that with the exception of the occasional tsunami triggered propagation event, the extreme variability on the Amery Ice Shelf is highly atypical. We postulate that the pronounced activity on the Amery is due to the fact that it last had a large calving event in 1963/64, and is approaching its pre-calved position. This suggests that the AIS is poised for another major calving event and the highly dynamic propagation we observe is the precursor to such an event."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on June 22, 2013, 02:28:55 AM
The following extract is from an article from the following website that discusses the very high rate of ice mass loss from East Antarctic ice shelves:

http://www.csmonitor.com/Environment/2013/0614/East-Antarctic-ice-shelves-melting-at-surprising-pace-study-suggests (http://www.csmonitor.com/Environment/2013/0614/East-Antarctic-ice-shelves-melting-at-surprising-pace-study-suggests)

"Several small ice shelves along the East Antarctic coast appear to be melting at surprisingly high rates, some at rates comparable to those of shelves in West Antarctica, long a center of concern over the impact of climate change on the region's vast ice sheet and sea-level rise.
This is an unexpected result of a new study that documents the current status of ice shelves around Antarctica's coastline and the relative influence of the factors melting them.
It's unclear if the unexpected melt rates represent a trend. Conditions off the East Antarctic coast have been less-well studied than those off of West Antarctica, notes Stanley Jacobs, a researcher at Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y., and a member of the team reporting its results in the current issue of the journal Science."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on July 13, 2013, 02:23:18 AM
In multiple posts I have advised that wind scour of snow needs to be considered when evaluating surface mass balance for Antarctica.  The following reference (abstract and attached image) quantify this matter, and identify that the wind scour primarily occurs in the East Antarctic, and: "…. across the continent, the snow mass input is overestimated by 11–36.5 Gt yr−1 in present surface-mass-balance calculations."

Influence of persistent wind scour on the surface mass balance of Antarctica
By: Indrani Das, Robin E. Bell, Ted A. Scambos, Michael Wolovick, Timothy T. Creyts, Michael Studinger, Nicholas Frearson, Julien P. Nicolas, Jan T. M. Lenaerts & Michiel R. van den Broeke Nature Geoscience; 6,367–371(2013)doi:10.1038/ngeo1766
 
"Abstract: Accurate quantification of surface snow accumulation over Antarctica is a key constraint for estimates of the Antarctic mass balance, as well as climatic interpretations of ice-core records1, 2. Over Antarctica, near-surface winds accelerate down relatively steep surface slopes, eroding and sublimating the snow. This wind scour results in numerous localized regions (≤200 km2) with reduced surface accumulation. Estimates of Antarctic surface mass balance rely on sparse point measurements or coarse atmospheric models that do not capture these local processes, and overestimate the net mass input in wind-scour zones3. Here we combine airborne radar observations of unconformable stratigraphic layers with lidar-derived surface roughness measurements to identify extensive wind-scour zones over Dome A, in the interior of East Antarctica. The scour zones are persistent because they are controlled by bedrock topography. On the basis of our Dome A observations, we develop an empirical model to predict wind-scour zones across the Antarctic continent and find that these zones are predominantly located in East Antarctica. We estimate that ~ 2.7–6.6% of the surface area of Antarctica has persistent negative net accumulation due to wind scour, which suggests that, across the continent, the snow mass input is overestimated by 11–36.5 Gt yr−1 in present surface-mass-balance calculations."

The full caption for the attached image is: "Wind-scour zones (yellow) are predicted to form over areas of slope threshold (MSWD≥0.002) and an accumulation to wind speed ratio (A/W)≤9.12 (C2 threshold). The A/W ratio colour scale shows the continent-wide extent of the C1 (A/W = 6.66, light blue shade) and C2 (A/W = 9.12, dark blue shade) thresholds. The thresholds of A/W ratio from Dome A are consistent over a large section of East Antarctica."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on July 21, 2013, 08:04:11 PM
The article at the following website contains the following quotes, indicating that portions of the EAIS are less stable that previously assumed:

http://www.nbcnews.com/science/message-mud-east-antarctic-meltdown-could-cause-massive-sea-rise-6C10687020 (http://www.nbcnews.com/science/message-mud-east-antarctic-meltdown-could-cause-massive-sea-rise-6C10687020)

"Cook and colleagues suggest that much of the ice that melted was in basins that were below sea level, putting it in direct contact with the seawater. As the ocean warmed, the ice was more vulnerable to melting.

That interpretation fits with recent airborne surveys that revealed large under-ice fjords in this part of Antarctica that appeared geologically young and carved by ice, and not as a result of plate tectonics, according to Duncan Young, a geophysicist at the University of Texas at Austin, who flew some of the surveys.

"This work reinforces that result," he told NBC News in an email. The new study is also "a shot in favor" of the argument that the East Antarctic ice sheet is less stable than previously believed, "which may be significant for future sea level change estimates," said Duncan, who was not involved in the new research.

Given the similarity between the Pliocene's estimated atmospheric carbon dioxide levels and those of today, scientists consider the epoch an analog for understanding how the present-day climate will evolve.

"What the study shows is that there is a clear record of rapid(-ish) sea level response to past climate shifts," Ted Scambos, an Antarctic ice expert at the National Snow and Ice Data Center in Boulder, Colo., said in an email to NBC News. He was not involved in the new research.

While the East Antarctic basins are covered in ice today, they might begin to melt as the oceans continue to warm, Scambos said. He noted that a mile-thick, Colorado-sized chunk of ice sloughing into the ocean would have a "big impact" on sea levels.

"And what we're seeing in other parts of Antarctica and Greenland today tells us that the transitions can be very abrupt by geologic standards," Scambos said. "They are mercifully more manageable by human standards, at least if we decide to start managing.""

Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on August 05, 2013, 12:42:13 AM
The attached pdf discusses the "Loose Tooth Rift System" which is part of the Amery Ice Shelf; and which may calf two large icebergs sometime after 2015.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on August 19, 2013, 11:30:33 PM
The following weblink provide access to a pdf for the following reference about the floating portion of the Totten Glacier and the Moscow University Ice Shelf:

Greenbaum, J and Roberts, Jason and Soderlund, K and Young, D and Richter, T and Warner, RC and Young, NW and van Ommen, TD and Siegert, M and Blankenship, D, Seafloor shapes of the floating portion of Totten Glacier and Moscow University Ice Shelf, East Antarctica, Book of Abstracts - 26th International Forum for Research into Ice Shelf Processes - FRISP, 12 June 2012, Sweden, pp. 16-17. (2012)

http://ecite.utas.edu.au/84492 (http://ecite.utas.edu.au/84492)
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on August 28, 2013, 11:47:17 PM
Obviously, the following linked article supports the risk of rapid ice mass loss from the Pacific coast portion of the EAIS:


http://www.nature.com/nature/journal/v500/n7464/full/nature12382.html (http://www.nature.com/nature/journal/v500/n7464/full/nature12382.html)

Rapid, climate-driven changes in outlet glaciers on the Pacific coast of East Antarctica;
by: B. W. J. Miles, C. R. Stokes, A. Vieli & N. J. Cox; Nature; 500, pp 63–566doi:10.1038/nature12382

"Observations of ocean-terminating outlet glaciers in Greenland and West Antarctica indicate that their contribution to sea level is accelerating as a result of increased velocity, thinning and retreat. Thinning has also been reported along the margin of the much larger East Antarctic ice sheet, but whether glaciers are advancing or retreating there is largely unknown, and there has been no attempt to place such changes in the context of localized mass loss or climatic or oceanic forcing. Here we present multidecadal trends in the terminus position of 175 ocean-terminating outlet glaciers along 5,400 kilometres of the margin of the East Antarctic ice sheet, and reveal widespread and synchronous changes. Despite large fluctuations between glaciers—linked to their size—three epochal patterns emerged: 63 per cent of glaciers retreated from 1974 to 1990, 72 per cent advanced from 1990 to 2000, and 58 per cent advanced from 2000 to 2010. These trends were most pronounced along the warmer western South Pacific coast, whereas glaciers along the cooler Ross Sea coast experienced no significant changes. We find that glacier change along the Pacific coast is consistent with a rapid and coherent response to air temperature and sea-ice trends, linked through the dominant mode of atmospheric variability (the Southern Annular Mode). We conclude that parts of the world’s largest ice sheet may be more vulnerable to external forcing than recognized previously."
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on August 29, 2013, 03:36:03 PM
Miles(2013) last sentence:

" ... the vulnerability of large parts of the EAIS margin requires urgent reassessment."

Could not  agree more. Was a little dissapointed that the study area did not include Amery or Byrd.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on August 31, 2013, 07:35:08 PM
Sidd,
The following link leads to a several year old pdf focused on the glaciers feeding into the Amery Ice Shelf (entitled: Mass budgets of the Lambert, Mellor and Fisher glaciers and basal fluxes beneath their flowbands on Amery Ice Shelf):

http://media.asf.alaska.edu/asfmainsite/documents/ramp/Wen_Amery_MassBudget.pdf (http://media.asf.alaska.edu/asfmainsite/documents/ramp/Wen_Amery_MassBudget.pdf)

Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on September 01, 2013, 09:22:37 PM
Thanx. I am on the road now, but will read carefully when I return home.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 05, 2013, 05:53:32 AM
In August 2013 the Australian Antarctic Division annouced that the Totten Glacier has the largest ice mass discharge of any EAIS glacier, with a discharge of 70 billion tonnes/yr of ice.

https://twitter.com/AusAntarctic/status/366697252443541504
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 05, 2013, 06:00:23 AM
Per Chris Rapley, the outgoing head of the British Antarctic Survey, and the information at the following link confirms that not only is ice mass loss from WAIS accelerating faster than previously expected; but also that ice discharge from both Totten (see previous post) and Cook Glaciers are exceeding previous expectations.

http://www.reuters.com/article/2007/08/22/environment-climate-antarctica-dc-idUSL2210716920070822 (http://www.reuters.com/article/2007/08/22/environment-climate-antarctica-dc-idUSL2210716920070822)
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 07, 2013, 08:18:03 PM
The following three interrelated abstracts are taken from the proceedings of the following IGSOC sponsored symposia.  The abstracts discuss how increasing surface melting on the East Antarctic coastal ices shelves could result in an abrupt collapse of these coastal ice shelves this century, which has the risk of increased SLR this century indicated in the following extracted text:  "Potential loss of East Antarctic ice shelves and their buttressing effect, as seen along the Antarctic Peninsula, could easily double the discharge of ice from major East Antarctic outlet glaciers, which would be enough ice to double the rate at which sea-level currently rises."

International Symposium on Changes in Glaciers and Ice Sheets: observations, modelling and environmental interactions; 28 July–2 August; Beijing, China; Contact: Secretary General, International Glaciological Society


http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm (http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm)



Ice dolines in East Antarctica: ice–ocean interactions from surface meltwater drainage events
Stefan W. VOGEL, Alex D. FRASER, Petra HEIL, Ben GALTON-FENZI, David ALEXANDER
Corresponding author: Stefan W. Vogel
Corresponding author e-mail: stefan.vogel@aad.gov.au
"Surface melting and meltwater streams are common features on outlet glaciers along the East Antarctic coast during summer. One of the big questions about surface melting in Antarctica is what happens to the meltwater? With Antarctic winters being long and cold, most meltwater likely refreezes in the snowpack with little to no impact on the overall mass balance of the ice sheet. One mechanism for surface meltwater to reach the ocean and mass being lost from the ice sheet is drainage through ice shelves. Ice dolines are longitudinal surface depressions, which are believed to be the remains of meltwater lakes that have drained through the ice. Dolines have been reported from various parts of Antarctica and pose a plausible mechanism through which significant amounts of fresh water may reach the ocean beneath ice shelves with potential impact on the sea-ice environment, Antarctic bottom water formation and ocean circulation in general. Here we revisit the topic of surface meltwater drainage and report on the evolution of Amery Ice Shelf dolines and on a very recent doline drainage event on the Mawson coast. Satellite observations indicate that dolines may be a standing feature, which reforms as the original feature moves with the flow of ice downstream. In addition to the water draining during the lake drainage events both features (Amery and Mawson coast) are at the receiving end of larger meltwater catchment areas and bear the potential that significant amounts of surface meltwater drains year after year through hidden openings at the bottom of the partially snow-covered dolines."

 
Surface melting and melt features on the Amery Ice Shelf – implications for ice-shelf, ice-sheet stability
Stefan W. VOGEL, Alex D. FRASER, Petra HEIL
Corresponding author: Stefan W. Vogel
Corresponding author e-mail: stefan.vogel@aad.gov.au
"A general notion about Antarctica is that it is dry and cold. Yet along its coastline significant melting is observed each summer. In various places meltwater has been responsible for changes in the dynamic of glaciers, ice sheet and ice shelves. One spectacular event was the collapse of the Larsen B Ice Shelf. Here meltwater ponding had a destabilizing effect on the ice shelf. Meltwater draining through an ice sheet can enhance lubrication of the glacier bed, leading to flow acceleration and enhanced ice discharge. Freshwater input to the sub-ice-shelf environment may enhance thermohaline circulation with the potential of enhancing the draw of warmer water masses into the sub-ice-shelf cavity. Here we present initial results investigating surface melting and surface melt distribution on the Lambert Graben–Amery Ice Shelf. Clearly visible from space, each year a network of lakes and rivers forms on the surface of the Amery Ice Shelf south of Jetty Peninsula (~70.5° S). Surface melt features are absent in the front half of the Amery Ice Shelf likely due to high snow accumulation. Microwave imagery as well as snow temperature data indicate melting with meltwater percolation into and refreezing inside the snow cover. Closer examination of satellite imagery shows an extensive surface hydrological network covering the back of the Amery Ice Shelf transporting meltwater over large distances. During high melt years supraglacial lakes can reach tens of kilometres in length and >1 km in width. The most southern surface lake is found adjacent to Cumpston Massif on Mellor Glacier (73.5° S). This is a significant distance upstream from the ice-shelf grounding zone and raises the possibility that surface melting under 21st century climate warming scenarios could enhance lubrication of East Antarctic outlet glaciers. "


East Antarctic surface melting – biggest 21st century sea-level change threat?
Stefan W. VOGEL, Alex D. FRASER, Petra HEIL, Rob MASSOM, Neal YOUNG, Mike CRAVEN
Corresponding author: Stefan W. Vogel
Corresponding author e-mail: stefan.vogel@aad.gov.au
"Antarctica: driest and coldest place on Earth. The East Antarctic coastline in summer, however, provides a contrasting picture. Along the coast surface melting and an extensive network of meltwater streams are the dominant features in summer. While Greenland melting is at the forefront of science and extensive attention is given to its interannual variability as well its impact on ice dynamics, Antarctic melting has received comparably little attention, with most of the attention coming from broad-scale remote-sensing applications. Direct measurements validating remote-sensing applications are however scarce as are estimates of surface accumulation/ablation and the fate of meltwater during winter. With surface melting already being widespread at present, surface melting in Antarctica will only increase under 21st century warming scenarios, raising the question as to when the East Antarctic margin will catch up with the Antarctic Peninsula and/or Greenland. This presentation provides a visual overview of melting along the East Antarctic margin and discusses the potential impact of surface melting on ice dynamics, ice-shelf stability and the Southern Ocean environment. In general surface meltwater can have a destabilizing effect on ice shelves, while freshwater flux into the ocean impacts thermohaline circulation, sea-ice production and the Southern Ocean ecosystem in general. Potential loss of East Antarctic ice shelves and their buttressing effect, as seen along the Antarctic Peninsula, could easily double the discharge of ice from major East Antarctic outlet glaciers, which would be enough ice to double the rate at which sea-level currently rises."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 07, 2013, 08:34:26 PM
The following abstracts are taken from the proceedings of the following IGSOC sponsored symposia and are all relevant to the topic of the continuing degradation of the Amery Ice Shelf (and abutting glaciers).  These abstracts taken together with those referenced in the immediately prior post, indicate the importance of the Amery Ice Shelf and of the glacier drainage basins feeding into this ice shelf:


International Symposium on Changes in Glaciers and Ice Sheets: observations, modelling and environmental interactions; 28 July–2 August; Beijing, China; Contact: Secretary General, International Glaciological Society


http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm (http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm)


Development of an ice thickness model over the southern extremity of the Amery Ice Shelf and re-assessment of the mass budget of Lambert Glacier basin
Jiahong WEN, Long HUANG, Fan YANG, Weili WANG, V. Damm
Corresponding author: Jiahong Wen
Corresponding author e-mail: jhwen@shnu.edu.cn
"The previous results of mass budgets of the Lambert Glacier basin differ greatly due mainly to the ice thickness data from different sources and approaches (e.g. Wen and others, 2007; Yu and others, 2010). In this paper we use a geographic information system environment to combine the ice thickness data from the BEDMAP project and the PCMEGA expedition (the Prince Charles Mountains expedition of Germany and Australia during the Antarctic season 2002/03) to generate a digital ice thickness model (DITM) over the southern extremity of the Amery Ice Shelf and re-estimate the mass budget of Lambert Glacier gasin including Lambert, Mellor and Fisher Glaciers. The DITM shows that the thickest ice up to 2789 m is located at the transition zone from grounded ice to floating ice shelf of the Mellor flowband. The overall ice thickness along the grounding line is slightly larger than that presented by Yu and others (2010) interpolating data from the BEDMAP project, but much smaller than that derived assuming hydrostatic equilibrium (Wen and others, 2007). The ice flux through the southern grounding of the Amery Ice Shelf is 36.6 ± 2 Gt a–1, which is similar to the result of 38.9 ± 2.8 Gt a–1 provided by Yu and others (2010), but much smaller than that of 54.0 ± 5.4 Gt a–1 (Wen and others, 2007). The Lambert Glacier basin is in a positive mass balance."


Distributed temperature logging on the Amery Ice Shelf – challenges and scientific opportunities
Roland WARNER, Stefan W. VOGEL, Mike CRAVEN, Alan ELCHEIKH, Adam CHRISTENSEN, Adam TREVERROW, Shavawn DONOGHUE, Kelly BRUNT, Jeremy RIDGEN, Steve CANN, David TULLOH, Scott TYLER, Ian ALLISON, Ben GALTON FENZI
Corresponding author: Stefan W. Vogel
Corresponding author e-mail: stefan.vogel@aad.gov.au
"Antarctic ice shelves are coupled to the climate of the Southern Ocean by the sub-ice ocean circulation, with interactions ranging from substantial basal melting to the accretion of thick layers of marine ice. They are vulnerable to increased melting from a warming ocean and from changes in ocean currents. Hidden beneath kilometre thick ice, sub-ice-shelf processes are difficult to study. During the 2009/2010 field season the AMSIOR team installed two fibre-optic cables through the Amery Ice Shelf as part of a sub-ice ocean observation network. Optical fibre light-scattering properties can be used for distributed temperature sensing (DTS). DTS measurements provide continuous temperature profiles at a resolution of ~1 m. Here we discuss the opportunities DTS systems provide for sub-ice and englacial temperature monitoring as well as the challenges that come with installing and operating a DTS system in Antarctica, including system set-up and calibration challenges."





Platelet ice and marine ice layer formation processes beneath the Amery Ice Shelf
Stefan W. VOGEL, Mike CRAVEN, Roland WARNER, Laura HERRAIZ BORREGUERO, Ben GALTON FENZI
Corresponding author: Stefan W. Vogel
Corresponding author e-mail: stefan.vogel@aad.gov.au
"Frazil/platelet ice formation processes are an elusive process hidden beneath a dark ice-covered ocean. Frazil and platelet ice are important for sea-ice formation as well as the formation of marine ice at the base of ice shelves. Craven and others (in preparation) report frazil/platelet-ice-induced mooring uplifts in the order of 10–20 dbar. Detailed analysis of the oceanographic data (temperature, salinity and pressure) surrounding these serendipitous events provides new insight into ice-shelf boundary layer processes, the formation of frazil/platelet ice through the year and marine ice accretion processes. In general the observed mooring uplift events follow periods of cooling and are associated with periods of supercooling in the ice-shelf boundary layer. While conditions favourable for frazil ice formation and platelet ice growth develop slowly, these events end abruptly with changes in thermal conditions. While the formation of frazil ice and the actual growth of platelet ice require a significant amount of thermal heat deficit, coagulation and attachment of ice suspended in the water column requires only small changes in the thermal budget to cause disaggregation. The frontal part of the Amery Ice Shelf (AM01 and AM04) appears to be dominated by seasonal cyclicity. Here periods of accumulation (5–10 cm d–1) at a long-term net accumulation of 1–3 m a–1 are followed by periods of erosion. In the centre of the ice shelf (AM05) on the other hand ice formation and associated mooring uplifts are observed year round."

Observation and analysis of ice-flow velocity on Lambert Glacier–Amery Ice Shelf using interferometric and GPS data
Chunxia ZHOU, Fanghui DENG, Zemin WANG, Dongchen E, Shengkai ZHANG
Corresponding author: Chunxia Zhou
Corresponding author e-mail: zhoucx@whu.edu.cn
"Ice-flow velocity is a fundamental parameter of the ice dynamic model which indicates how the ice is transported from the interior regions to the ocean and how ice mass evolves with time. The Lambert Glacier–Amery Ice Shelf system (LAS) is the largest ice stream system in East Antarctica. The ice streams of LAS flow towards to the sea through a narrow drainage area, the length of which is only 1/60 of the Antarctic coastline. So study of the ice velocity of LAS is of great importance for the ice dynamic changes and mass balance in Antarctica. During the Chinese National Antarctic Research Expedition (CHINARE), multi-term GPS observations were carried out on the Amery Ice Shelf with the support of helicopters. Meanwhile, the SAR interferometry technique is significant to estimate ice sheet and glacier surface motion. This paper discusses ice-flow velocity estimation with InSAR pairs and validation with GPS data of LAS. ERS-1/2 tandem SAR data and Envisat ASAR data were adopted for ice-flow velocity estimation in this study. The D-InSAR and speckle tracking methods were utilized for ice velocity derivation. In order to generate a 2-D ice velocity map with high accuracy, the combination of the displacement in the range direction estimated by D-InSAR with the displacement in the azimuth direction calculated by speckle tracking was applied for most image pairs. It can be seen from the ice velocity map that several tributary ice streams coming separately from Fisher Glacier, Mellor Glacier and Lambert Glacier flowed towards to the Amery Ice Shelf and converged into the mainstream. The ice velocity at the meeting point reached as high as 800 m a–1, while the ice velocity along the mainstream decreased to about 350 m a–1 and then increased quickly near the front edge of the Amery Ice Shelf. The ice velocity near the edge was about 1500 m a–1. Taking static nunataks and rocks as checking points, the average velocity error in LAS was about 8 m a–1. Our results also showed close agreement with the in situ measurements near the meeting point and the front of the Amery Ice shelf."


Response of the Amery Ice Shelf basal melting to ocean temperature change Fan YANG, Jiahong WEN, Weili WANG, T.H. Jacka
Corresponding author: Jiahong Wen
Corresponding author e-mail: jhwen@shnu.edu.cn
"The relationship between ice-shelf basal melting beneath the Amery Ice Shelf, East Antarctica, and ocean temperature is studied using a numerical model. The basal melting and freezing rates under the ice shelf, a column-averaged ice density model, sea-water temperature and salinity measurements and projected Southern Ocean temperate rise over the 21st century are employed in the analysis. The difference between the ocean temperature and the sea-water freezing point under the ice shelf is numerically modeled. Our results show that the basal melting rate increases quadratically as the ocean offshore from the ice-shelf front warms. Near the grounding zone where the strongest thermal forcing exists, we find the basal melting rate increases by 12.5 m a–1, associated with a 1° rise in ocean temperature, in good agreement with previous studies. However, we find no correlation between changes in basal freezing/melting rate and ocean temperature in the marine ice zone. The different response patterns of the basal melting/freezing to variations in ocean temperature between the melting area and the refreezing marine ice area may suggest an important role for frazil dynamics. Considering the sensitivity of melting rate and thermal forcing, the net basal melting of the Amery Ice Shelf within the next three decades may be greater than 81 km3 a–1."



GRACE RL05-based ice-mass change in the typical regions of Antarctica from 2004 to 2012
Xiaoleij JU, Yunzhong SHEN, Zizhan ZHANG
Corresponding author: Yunzhong Shen
Corresponding author e-mail: yzshen@tongji.edu.cn
"As the biggest ice sheet in the world, the mass change of Antarctica plays an important role in global climate change. Gravity Recovery and Climate Experiment (GRACE) provides a good way to monitor mass variation of the Antarctic ice sheet. In April 2012, the new RL05 data with better spatial resolution, better accuracy and periodical characteristics were officially released by CSR, JPL and GFZ. By using the newly released data we analyzed the mass change from 2004 to 2012 in the typical areas, e.g. Antarctic Peninsula (AP, West Antarctica) and Lambert–Amery System (LAS, East Antarctica). Based on the RL05 data of CSR, JPL and GFZ, the AP mass change rates are –16.41 ± 2.92 Gt a–1 (2004–2012), –15.99 ± 2.79 Gt a–1 (2004–2012) and –16.44 ± 2.12 Gt a–1 (2005–2012) and the LAS mass change rates are –1.81 ± 5.04 Gt a–1 (2004–2012), –5.92 ± 7.76 Gt a–1 (2004–2012) and 6.95 ± 8.90 Gt a–1 (2005–2012), respectively. The results show that the mass changes derived from CSR, JPL and GFZ data are of great differences, with larger uncertainties for the LAS. However, the mass changes in the AP derived from the three agencies are much closer to each other and the uncertainties are significantly smaller than the mass change rates."



Measurement of ice-flow velocity at the Amery Ice Shelf from optical and interferometric SAR satellite imagery
Yi LIU, Shuang LIU, Huan XIE, Weian WANG, Fei YAN, Marco SCAIONI, Xiaohua TONG, Rongxing LI
Corresponding author: Yi Liu
Corresponding author e-mail: cnliuyi@qq.com
Antarctica plays an important role for explotion of the relationship between global climate change and sea-level rise. Ice-flow velocity is one of the most fundamental measurements for studying the dynamics of ice sheets and for calculating the mass balance of ice sheets. The Amery Ice Shelf (AIS), which is one of the largest ice shelves in Antarctica, has been studied over the past 50 years. A number of research papers have reported velocity measurements in this area. Among them, most results are based on two methods: field survey and remote sensing. The field survey is less cost-effective and sometimes depends on opportunities, while the remote-sensing method mostly uses optical and interferometric SAR satellite imagery. Accordingly, there are two approaches: feature-based and interferometry-based techniques. The former is usually based on the method of normalized cross correlation, which can cover large areas with lower costs, but may be subject to errors caused by mismatches. The latter is often concerned with the lack of imagery data because of the strict requirements of building interferometric pairs. In this paper, we propose a combined optical/SAR imagery approach to calculate glacier ice-flow velocity based on Landsat ETM+ and SAR imagery. First, we compared the advantages of several interest point operators and presented an integrated method by combing these operators together for feature extraction. Second, we developed a coarse-to-fine match method to match these extracted point features from optical imagery. Third, we proposed a new loopy-belief-propagation (LBP) method to densify the matched points. Finally, in some local areas, we used the interferometry method to obtain a more accurate result of ice-flow velocities based on interferometric SAR by using ERS-1/2 tandem data. We tested our proposed method in the Amery Ice Shelf region. The results showed that our proposed method combines the complementary advantages of the two individual techniques and obtains the measurement of ice-flow velocities more accurately and effectively."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 07, 2013, 08:54:35 PM
The following two abstracts are taken from the proceedings of the following IGSOC sponsored symposia, and they discuss the details, mechanisms and consequence of a major 2010 calving event for the ice tongue of the Mertz Glacier, East Antarctica:


International Symposium on Changes in Glaciers and Ice Sheets: observations, modelling and environmental interactions; 28 July–2 August; Beijing, China; Contact: Secretary General, International Glaciological Society


http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm (http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm)


Dynamics of Mertz Glacier and its ice tongue, East Antarctica: implications of its calving and changes at various timescales B. LEGRÉSY, B.K. GALTON-FENZI, L.G. LESCARMONTIER, E. COUGNON, C. MAYET, L. TESTUT, N. YOUNG, R. MASSOM, R. WARNER, R. COLEMAN
Corresponding author: B. Legresy
Corresponding author e-mail: benoit.legresy@legos.obs-mip.fr
"In February 2010, the tongue of Mertz Glacier calved, releasing an 80 km × 30 km iceberg. We had anticipated this calving event and started observing its development as well as gathering data to monitor the dynamics of the glacier. Here, we present the main characteristics of Mertz Glacier in the context of this calving event. In addition to regular collection of satellite images, a number of observations have been made within the Cooperative Research into Antarctic Calving (CRACICE) project. For investigations of the glacier dynamics and rift development we have used the following data types: ERS SAR interferometry, RADARSAT and Envisat SAR images, Landsat and SPOT images, SPOT stereo imagery, airborne ice thickness radar profiles and in situ GPS measurements. We improved the ocean bathymetry using airborne gravimetry, iceberg movements and grounding points, and new bathymetric soundings. We used numerical model studies to integrate and compare the various derived information. We compare the basal melt/freeze rates derived from an ice/ocean model (ROMS) with that from mass balance of the glacier tongue. We use the ocean circulation in the Mertz region derived from a barotropic model (TUGO), together with continuous GPS measurements of the movement and flexure of the ice tongue, to assess the response of the glacier tongue to ocean forcing. They are found to be a main driver of the rifting and calving. We describe the sequence of events in the calving process. We evaluate the various forces acting on the ice tongue. We evaluate the dynamics changes with regard to climate variability as well as pre-/post-calving situations both toward the glacier and toward its glacial and oceanic environment."


Crevasse changes over the Antarctic Mertz Ice Shelf before disintegration
Xianwei WANG, Xiao CHENG
Corresponding author: Xianwei Wang
Corresponding author e-mail: wangxianwei0304@163.com
"Crevasse depth and central large rifts on the Mertz Ice Shelf were investigated from laser altimetry data (ICESat/GLAS) and remotely sensed images (Landsat and ENVISAT-ASAR). The smaller footprint of ICESat/GLAS enables its application in large crevasse depth detection. The method to calculate crevasse depth based on track observation of GLA12 data was proposed. The histogram of crevasse depth on the Mertz Ice Shelf from 2003 to 2009 showed nearly the same annual distribution, indicating the almost stable situation. The crevasse depth range from 2 to 10 m takes more than 70% every year, with the remaining 30% greater than 10 m and smaller than 56 m. The area of large rift in the right side along the ice shelf advancing showed an increasing trend (4.05 to 19.4 km2) from 1989 to 2003 and a decreasing trend (19.05 to 17.6 km2) from 2003 to 2009. However, a large rift in the left side along the ice shelf advancing occurred at about 2002 and the area increased to 11.38 km2 at the end of 2009. Deep crevasses on the surface and expansion of the central large rift made the Mertz Ice Shelf fragile and disintegrated after collision by an iceberg."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 07, 2013, 09:19:10 PM
The following abstracts are taken from the proceedings of the following IGSOC sponsored symposia, and they all relate to China's finding related to Dome A, East Antarctica:

International Symposium on Changes in Glaciers and Ice Sheets: observations, modelling and environmental interactions; 28 July–2 August; Beijing, China; Contact: Secretary General, International Glaciological Society


http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm (http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm)



Proxies in Antarctic ice cores of climate change over the southern Indian Ocean: a review
Cunde XIAO
Corresponding author: Cunde Xiao
Corresponding author e-mail: cdxiao@lzb.ac.cn
"Several shallow ice cores were retrieved from the Chinese Antarctic traverse route (Zhongshan to Dome A) of the International Trans-Antarctic Scientific Expedition (ITASE) program. These ice cores cover time periods from decades to thousands of years. Ice cores from the coastal and medium-altitudinal terrains of the ice sheet contain promising climatic proxies. For example, water stable isotopes from the DT001 ice core indicate changes of sea surface temperature (SST) over the north ocean of Prydz Bay, southern Indian Ocean (SIO). Sea salts from the ice core are a reliable proxy of sea-level pressure (SLP) of high SIO. Methylsulfonate (MS–) and sodium (Na+) in the LGB69 ice core are indicators of sea-ice extent (SIE) over the SIO sector. Quantitatively, SIE is a function of MS– (Na+) and meridional wind strength. Three modes of Antarctic climate, i.e. Southern Annular Mode (SAM), Trans-Polar Index (TPI) and Antarctic Circumpolar Wave (ACW), are identified using proxies in ice cores from the coastal regions. Records in other ice cores from the SIO sector of the ice sheet (such as Law Dome) also support some aspects of the above results."

Characterization of surface, englacial and basal ice-sheet condition in the region of Dome A, East Antarctica: an optical site for deep ice core drilling
Bo SUN, Xiangbin CUI, Jingxue GUO, Xueyuan TANG, Leibao LIU
Corresponding author: Bo Sun
Corresponding author e-mail: sunbo@pric.gov.cn
"The CHINARE science plan is for deep ice coring to be drilled in the Dome A region of East Antarctica. We present glaciological characteristics of Dome Argus, East Antarctica, and systematically discuss the merits and possible ventures of its potential as a deep ice-core site. According to recent observations by high-precision GPS in the Dome A region, the horizontal velocity of the ice surface is close to zero. A shallow ice core from Dome A indicates the mean accumulation rate of 23.2 mm w.e. a–1 over the last 3000 years. Ground-based ice-penetrating radar surveys generated a subglacial topography digital elevation model (DEM), covering the central 30 km × 30 km region at Dome A, with a 150 m × 150 m grid resolution. Radar stratigraphy shows that internal ice layers are stable and the isochronous layers are not anomalous. Using a two-parameter roughness index of the bedrock elevation, calculated results of the roughness index from the base of Dome A indicate that the features of the subglacial topography of Dome A correspond to lower rates of deposition from erosion, indicating that the bottom has a colder and slower ice flow. A full-Stokes ice-flow model using the finite-element code Elmer for the vicinity of Dome A suggests that the basal temperature is below the pressure-melting point, constraining through the radar isochronous layers with both geothermal heat flux and the ice fabric."

Spatial and temporal variability of surface mass balance (1999–2011) from Zhongshan station to Dome A, East Antarctica
Minghu DING, Cunde XIAO, Jiawen REN
Corresponding author: Minghu Ding
Corresponding author e-mail: dingminghu@cams.cma.gov.cn
"Stake measurements have been carried out along a 1248 km traverse from Zhongshan station to Dome A, East Antarctica. Spatial analysis suggests that the post-depositional process might be the most important factor influencing surface micro-morphology, and precipitation is another. Thus the representiveness of firn/ice core in different areas differs largely with each other and it should be discussed with local climate features. An overall estimation showed that the Lambert Glacier basin might be experiencing a slight loss trend, with a –0.5% annual average accumulation rate from 1999. This loss mainly happens in the coastal and Dome areas, yet the surface mass balance of the middle part from 202 to 800 km is still increasing."


A full-Stokes anisotropic ice-flow model for Dome A, Antarctica Thomas ZWINGER, Liyun ZHAO, John MOORE, Dong ZHANG, Xueyuan TANG, Carlos MARTIN, Bo SUN
Corresponding author: Liyun Zhao
Corresponding author e-mail: zhaoly69@gmail.com
"Chinese scientists will start to drill a deep ice core at Kunlun station near Dome A in the near future. It is important to know the basal temperature of ice and estimate the age of the ice core. We apply a three-dimensional thermomechanically coupled full-Stokes model to a 70 km2 × 70 km2 domain around Kunlun station, using the package Elmer/Ice. We make simulations using isotropic and different prescribed anisotropic fabrics which strongly affect the vertical advection which as a consequence controls both the basal temperature and age profile. Parts of the bed in the domain reach pressure-melting point, which seems to be consistent with radar observations in the Gamburtsev Mountains. We determine melt rates in those areas and also assess basal age by using steady-state velocity results."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 07, 2013, 11:14:36 PM
The following abstract is taken from the proceedings of the following IGSOC sponsored symposia.  This abstract discusses the unique nature of the surface snow and the near-surface winds on the East Antarctic Plateau (and the wind scour can affect SLR):

International Symposium on Changes in Glaciers and Ice Sheets: observations, modelling and environmental interactions; 28 July–2 August; Beijing, China; Contact: Secretary General, International Glaciological Society


http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm (http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm)

Wind glaze, wind scour and megadunes in East Antarctica
Ted A. SCAMBOS
Corresponding author: Ted A. Scambos
Corresponding author e-mail: teds@nsidc.org
"The East Antarctic Plateau is host to unique interactions between surface snow and near-surface winds, producing widespread regions of very low net accumulation termed wind glaze (near-zero accumulation), wind scour (slightly negative accumulation) and snow megadunes (alternating bands of high accumulation and wind glaze). These regions have been mapped by both their remote-sensing characteristics and by prediction based on surface slope, regional accumulation and regional wind direction. Profound changes occur in the firn below wind glaze regions due to the prolonged period of exposure to annual temperature oscillations. The alternating dune and glaze surfaces have potential impacts on ice-core interpretation through post-deposition effects on snow chemistry and isotopes. These features represent a kind of new facies in the ice sheet, in effect a variation of the dry-snow zone that is nearly unrepresented in Greenland."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 08, 2013, 07:21:23 PM
The following abstracts come from the linked sources and are relevant to East Antarctica:

www.igsoc.org/symposia/2013/kansas/proceedings/procsfiles/procabstracts_63.htm (http://www.igsoc.org/symposia/2013/kansas/proceedings/procsfiles/procabstracts_63.htm)
Contact: Secretary General, International Glaciological Society


67A017
Model meets radar data: about a migrating ice divide in eastern Dronning Maud Land, Antarctica
Reinhard DREWS, Kenichi MATSUOKA, Carlos MARTIN, Denis CALLENS, Frank PATTYN
Corresponding author: Reinhard Drews
Corresponding author e-mail: rdrews@ulb.ac.be
Ice rises are grounded topographic highs in the coastal margin of Antarctica. They originate from a locally elevated bedrock topography and are typically enclosed by fast-flowing ice shelves. Radar data collected near the dome or below the ice divides show that the internal stratigraphy arches upwards due to the non-linear ice rheology, which stiffens ice at low deviatoric stresses. The arch (or Raymond bump) characteristics allow us to deduce the history of the divide position – and with it the history of the flow regime including a potential change in the dynamics of the surrounding ice shelves. We present data from Derwael Ice Rise (70.5° S, 26.5° E) which buttresses and deviates Western Ragnhild Glacier, one of the main ice streams in Dronning Maud Land. Combining different radar systems (400 MHz, 5 MHz) we visualize the bedrock and the internal layering three- dimensionally. The data reveal spatially varying accumulation rates as well as multiple isochrone arches, which appear unrelated to the flat bedrock and exhibit a varying bump-amplitude versus depth function below the current ice divide. More importantly, we also observe relict arches in the flanks, which indicate that the divide most likely migrated to its current position. Using numerical models (higher order and full Stokes) together with the radar stratigraphy and the derived accumulation rates we aim to explain the relict arches as a result of changing boundary conditions induced by a changing geometry of the surrounding Roi Baudoin ice shelf. We hypothesize that the relict arches bear witness to a larger-scale change in ice flow that may encompass variations of Western Ragnhild Glacier. If this holds true, this sector of East Antarctica may be more susceptible to changes than previously assumed.


67A071
Extending East Antarctic ice-core chronology with radar layer stratigraphy
Marie G.P. CAVITTE, Donald D. BLANKENSHIP, Duncan A. YOUNG, Dusty M. SCHROEDER, Martin J. SIEGERT, Emmanuel LE MEUR
Corresponding author: Marie G.P. Cavitte
Corresponding author e-mail: mariecavitte@gmail.com
Airborne radar-sounding surveys collected by the University of Texas Institute of Geophysics (UTIG) with a 60 MHz system are used to trace englacial layering between the two deep East Antarctic ice cores: EPICA Dome C and Vostok. As a result of their isochronal properties, these englacial reflectors are used to connect the two cores continuously. Eleven layers spanning the last two 100 ka glacial cycles have been successfully connected, thereby providing a direct stratigraphic comparison of the two deep age–depth timescales over a 2200 m depth interval and a distance of 500 km. The coherent radar system used allows the identification of a layer depth to a precision much smaller than range resolution owing to strong signal-to-noise ratios of the layer strengths. These radar depth uncertainties can be can be converted to age uncertainties using the ice-core sites integrated in the radar surveys. We show that radar layer dating can therefore serve a useful role in recalibrating ice-core timescales with large age uncertainties. We also give a first-order recalibration of the EPICA Dome C EDC3 timescale using a radar-extended Vostok O2/N2 chronology (Suwa and Bender, 2008). In addition, the radar transects between Vostok and EDC3 show that aeolian stratigraphic reworking has a strong impact on layer depth accuracy, which impacts layers only in the last glacial cycle where ice-core chemistry is very reliable. As ice-core chemistry uncertainties increase in the penultimate glacial cycle, radar layering is apparently undisrupted by aeolian reworking, and the radar-extended EDC3 chronology is both reliable and characterized by smaller uncertainties than those for the existing geochemistry.
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on September 08, 2013, 10:11:01 PM
Re: Drews et al. (2013), IGSOC symposium:

This is why I am not a professional glaciologist. Once it is pointed out, this is quite obvious. I had not previously considered this effect. The abstract points out that they move in response to ice flow changes in the glaciers fed by the catchments they delineate. In which case we ought to watch ice divides around the Amundsen sector, Byrd, MU, Totten, and Amery.

How fast can ice divides move ? I had thought of them as static in the timescales we were considering. And as far as I know, this is not in the models ? CICE and such have static divides that gradually decrease in elevation, don't they ?  And Gregoire in his paper on saddle collapse also had static divides i think. I already watch the saddle at 67N on GIS like a hawk.

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 09, 2013, 01:42:19 AM
Sidd,

One of the main reason that I post so many different references is because I am learning new concepts all the time; and it appears to me that the professional glaciologists are are learning new things (especially about the AIS and the PIG/Thwaites Glacier) all the time.  As I commented in the "Misconception" thread the divide between the PIG Basin and the TG Basin is very likely to change within the next few decades (especially considering the MacGegor et al 2013 paper that I recently discussed in the PIG/Thwaites 2012 to 2060 thread). 

Risk assessments are all about postulating and addressing the "Unknown Unknowns", and I believe that society is in for many more surprises by 2100 (many of which I do not believe society will be prepared for; which they might be if they followed the "Precautionary Principle".

Best,
ASLR
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on September 19, 2013, 03:16:53 PM
Two quotes from the new paper by Hansen et al 2013 that are particularly noteworthy, at least to me, living in Holland:
http://m.rsta.royalsocietypublishing.org/content/371/2001/20120294.full.pdf (http://m.rsta.royalsocietypublishing.org/content/371/2001/20120294.full.pdf)

“The empirical data support a high sensitivity of the sea level to global temperature change, and they provide strong evidence against the seeming lethargy and large hysteresis effects that occur in at least some ice sheet models [p.22].”

“The amount of CO2 required to melt most of Antarctica in the MMCO [Middle Miocene Climatic Optimum, about 16 million years ago] was only approximately 450–500 ppm, conceivably only about 400 ppm. These CO2 amounts are smaller than suggested by ice sheet/climate models, providing further indication that the ice sheet models are excessively lethargic, i.e. resistant to climate change [p.23].”

So we could be very close to melting all of the ice on Earth, resulting in about 70m of SLR. Maybe that would take as little as a few millennia and could be very hard to stop, if we don't succeed in decarbonizing our economy very fast and/or in geoengineering our way out of this prospect. About 10m of SLR, including contributions from EAIS, could be possible in the coming three centuries, which may be inevitable in the longer term anyhow, but could still be slowed down substantially by fast decarbonization.

How Holland and the world could or would adapt to 10m of SLR over the coming centuries is an interesting question, but it looks like it would be a lot more expensive than rapidly decarbonizing. Which of course would also mitigate the need for adaptation to earlier and maybe even more urgent pressures, like food and water shortages, heat waves, droughts, fires, storms, floods, diseases, migration and conflicts over all kinds of resources.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 19, 2013, 05:31:33 PM
Lennart,

I agree with all of you points; however, you did not point out that we are already committed to about 2m of SLR with a few hundred years even if we decarbonize quickly (which I personnally doubt that we will do); and consequently, in addition to decarbonization, and possible geoengineering (which is dangerous), we will also need to take some adaptive measures just to deal with SLR that we are already committed to.

Best, ASLR
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on September 19, 2013, 09:46:39 PM
ASLR,

I agree, and implicitly meant to say as much when I wrote:
"About 10m of SLR, including contributions from EAIS, could be possible in the coming three centuries, which may be inevitable in the longer term anyhow, but could still be slowed down substantially by fast decarbonization."

To me 5-10m of SLR over several centuries to millennia seems impossibe to avoid by now, even with very rapid decarbonization. And 2m in the coming two to three centuries certainly seems like a best case scenario.

I still have hope for strong mitigation, but the odds for success don't look good, indeed. But who knows, maybe we'll surprise ourselves over the coming years and decades.

Yes we can, right?
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 19, 2013, 10:29:49 PM
Yes we can!
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on September 20, 2013, 03:08:34 PM
I'm not sure if the following two papers have been posted here before, but they give further support to the apparent vulnerability of the EAIS at current CO2-levels.

Dwyer & Chandler 2009, Phil. Trans. R. Soc.;
Mid-Pliocene sea level and continental ice volume based on coupled benthic Mg/Ca palaeotemperatures and oxygen isotopes:
http://rsta.royalsocietypublishing.org/content/367/1886/157.full.pdf+html (http://rsta.royalsocietypublishing.org/content/367/1886/157.full.pdf+html)

ABSTRACT:
"Ostracode magnesium/calcium (Mg/Ca)-based bottom-water temperatures were combined with benthic foraminiferal oxygen isotopes in order to quantify the oxygen isotopic composition of seawater, and estimate continental ice volume and sea-level variability during the Mid-Pliocene warm period, ca 3.3–3.0 Ma. Results indicate that, following a low stand of approximately 65 m below present at marine isotope stage (MIS) M2 (ca 3.3 Ma), sea level generally fluctuated by 20–30 m above and below a mean value similar to presentday sea level. In addition to the low-stand event atMIS M2, significant low stands occurred at MIS KM2 (K40 m), G22 (K40 m) and G16 (K60 m). Six high stands ofC10 m or more above present day were also observed; four events (C10, C25,C15 and C30 m) from MIS M1 to KM3, a high stand of C15 m at MIS K1, and a high stand of C25 m at MIS G17. These results indicate that continental ice volume varied significantly during the Mid-Pliocene warm period and that at times there were considerable reductions of Antarctic ice."

Kenneth G. Miller, James D. Wright, James V. Browning, Andrew Kulpecz, Michelle Kominz, Tim R. Naish, Benjamin S. Cramer, Yair Rosenthal, W. Richard Peltier and Sindia Sosdian 2012, Geology;
High tide of the warm Pliocene: Implications of global sea level for Antarctic deglaciation:
http://geology.rutgers.edu/images/Publications_PDFS/Miller_2012.pdf (http://geology.rutgers.edu/images/Publications_PDFS/Miller_2012.pdf)

ABSTRACT:
"We obtained global sea-level (eustatic) estimates with a peak of ∼22 m higher than present for the Pliocene interval 2.7–3.2 Ma from backstripping in Virginia (United States), New Zealand, and Enewetak Atoll (north Pacific Ocean), benthic foraminiferal δ18O values, and Mg/Ca-δ18O estimates. Statistical analysis indicates that it is likely (68% confidence interval) that peak sea level was 22 ± 5 m higher than modern, and extremely likely (95%) that it was 22 ± 10 m higher than modern. Benthic foraminiferal δ18O values appear to require that the peak was <20–21 m. Our estimates imply loss of the equivalent of the Greenland and West Antarctic ice sheets, and some volume loss from the East Antarctic Ice Sheet, and address the long-standing controversy concerning the Pliocene stability of the East Antarctic Ice Sheet."

So this last study indicates there seems to be about 84% chance that sea level will rise at least 17m in the long term, if current CO2 levels are not reduced over the coming centuries.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on October 24, 2013, 01:44:07 AM
Here is an article about an East Antarctic glacier that is on the move and contributing to SLR:

http://www.the-cryosphere-discuss.net/7/4913/2013/tcd-7-4913-2013.html (http://www.the-cryosphere-discuss.net/7/4913/2013/tcd-7-4913-2013.html)

Callens, D., Matsuoka, K., Steinhage, D., Smith, B., and Pattyn, F.: Transition of flow regime along a marine-terminating outlet glacier in East Antarctica, The Cryosphere Discuss., 7, 4913-4936, doi:10.5194/tcd-7-4913-2013, 2013.

Abstract. We present results of a~multi-methodological approach to characterize the flow regime of West Ragnhild Glacier, the widest glacier in Dronning Maud Land, Antarctica. A new airborne radar survey points to substantially thicker ice (> 2000 m) than previously thought. According to the new data, West Ragnhild Glacier discharges 13–14 Gt yr−1. Therefore, it is one of the three major outlet glaciers in Dronning Maud Land. Glacier-bed topography is distinct between the upstream and downstream section. In the downstream section (< 65 km upstream of the grounding line), the glacier overlies a wide and flat basin well below the sea level while the upstream region is more mountainous. Spectrum analysis of the bed topography reveals a clear contrast between these two regions, suggesting that the downstream area is sediment covered. The bed returned power varies by 30 dB within 20 km near the bed flatness transition, which suggests that water content at bed/ice interface increases over a short distance downstream, hence pointing to water-rich sediment. Ice flow speed observed in the downstream part of the glacier (~ 250 m yr−1) can only be explained if basal motion accounts for ~ 60% of the surface motion. All above lines of evidence (sediment bed, wetness and basal motion) and the relative flat grounding zone give the potential for West Ragnhild Glacier to be more sensitive to external forcing compared to other major outlet glaciers in this region which are more stable due to their bed geometry (e.g. Shirase Glacier).
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 07, 2013, 08:43:45 PM
Per Colorado Bob's post on the ASI blog:

http://www.sciencedaily.com/releases/2013/12/131206143614.htm (http://www.sciencedaily.com/releases/2013/12/131206143614.htm)

"A new NASA-led study has discovered an intriguing link between sea ice conditions and the melting rate of Totten Glacier, the glacier in East Antarctica that discharges the most ice into the ocean. The discovery, involving cold, extra salty water -- brine -- that forms within openings in sea ice, adds to our understanding of how ice sheets interact with the ocean, and may improve our ability to forecast and prepare for future sea level rise. ......."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 13, 2013, 04:45:14 PM
To date, I have not yet talked about the potential SLR contribution that the Recovery Catchment basin could make, as currently it is stable; however, as the article at the following link makes clear the projected introduction of warm water into the Weddell sea could eventually tigger between 3 and 4 m of SLR contribution from this basin (possibly by 2200?):

http://www.bbc.co.uk/news/science-environment-25173121 (http://www.bbc.co.uk/news/science-environment-25173121)

Note that: (a) little is known about the bed condition of this basin so it is now difficult to say how fast it may lose ice mass if tiggered by the introduction of warm ocean currents beneath the FRIS; and (b) while most of this ice lies in the EAIS, it may well be triggered by activity (warm currents and/or local retreat of the FRIS) in the FRIS area.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 13, 2013, 05:16:13 PM
Further to my prior post about the stability of the Recovery Catchment Basin, I thought that it would be helpful to provide the accompanying three images, that help to illustrate why researchers are sufficiently concerned about this area to spend their limited research budgets on expensive field programs like the ICEGRAV project.

The first image is a re-posting (from the FRIS folder) of projections of warm ocean currently that should begin melting the ice at the grounding line of the Recovery Ice Stream within the next few decades.

The second image shows the multiple (at least four) subglacial lakes, causing the ice flow rate to vary dramatically, ranging between 2 and 50 meters per year.  The presence of such subglacial hydrological features indicate potential instability of this ice feature.

The third image, while not current or numerically accurate, indicates that that relatively speaking the subglacial basal heating beneath the Recovery Ice Stream has the highest estimated geothermal heating of any region of Antarctica; which could promote future ice mass loss.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 13, 2013, 05:31:03 PM
The discussion at the following web-article (including the quote below), makes it clear that the researchers are concerned that the high geothermal heat source beneath the Recovery Ice Steam, many contribute to the creation of subglacial "swamps" (shallow bodies of subglacial water), such has have been found beneath the Thwaites Glacier.  If the ICEGRAV project finds such subglacial "swamps" then once the gateway basal ice is melted by the projected warm ocean currents, then the "swamps" may reduce basal friction sufficiently to allow for rapid acceleration of the ice flows in this basin"

http://phys.org/news/2013-12-secrets-climate-ancient-supercontinents.html (http://phys.org/news/2013-12-secrets-climate-ancient-supercontinents.html)

Dr Ferraccioli says, "I've always thought this area is an Achilles heel for East Antarctica, but until we have the data we won't know that for sure. Preliminary results from our survey suggest that there's a lot of water there. But subglacial lakes are not the only form of water; it's possible that there are shallower bodies of water that don't form distinct lakes. So now there's the question of how continuous are these features?"
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 13, 2013, 07:40:20 PM
Regarding the first figure in my reply #44, showing the projected future introduction of warm ocean current beneath the Filchner Ice Shelf after about 2080 (due to projected changes in sea ice and associated local wind driven ocean currents); I would like to re-post the accompanying figure from the FRIS thread, indicating that warm ocean water is already (today) promoting more rapid sub-ice-shelf basal melting near the face/front of the Filchner Ice Shelf, FIS.  If this trend continous (or more likely accelerates) calving from the face of the FIS could accelerate over the next few decades; which may accelerate the introduction of warm ocean currents to the grounding line of the Recovery Ice Stream.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 14, 2013, 01:16:48 AM
The linked article talks about a past IceBridge mission to investigate the Recovery Glacier area, showing multiple subglacial lakes, see attached figure:

http://blogs.ei.columbia.edu/2012/10/29/a-recovery-mission/ (http://blogs.ei.columbia.edu/2012/10/29/a-recovery-mission/)
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 14, 2013, 05:05:02 PM
While all of these images are re-posts, I thought that many readers would like to have them compiled in this string of posts about the Recovery Glacier/Ice Stream:

The first image from Bedmap2, shows that a region of near circular rised bed elevation is associated with the area of high geothermal basal flux; indicating that it is likely that a hotspot in the mantle exists in this location which is raising-up the bed elevation in a similar manner to the hotspot beneath Marie Byrd Land (associated with recent volcanic activity).  Furthermore, the Bedmap2 image show how deep the bed elevation is beneath Recovery Glacier, which indicates that the 2 to 3km thick glacier would have an unstable calving face when the grounding line retreats into these deep areas, as discussed by Bassis et al 2013 (see reference at the end of this post).

The second image from Bassis et al 2013 shows that marine glaciers (such as Jakobshaven, and Thwaites) that have a thickness of over 1km have grounding lines with inherent geometric instability.  Therefore, once the grounding line of the Recover Glacier retreats into the deep areas shown in the Bedmap2 image, the grounding line is likely to retreat abruptly.

The third image shows that even through the gateway to the Recovery Glacier/Ice Stream is at about 80 degrees South latitude (as compared to the 75 degrees Slouth latitude for the Thwaites Glacier), still in a warm austral summer such as the austral summer of 2005, surface melting occurs, so that in the future (after about 2050) meltwater could enter increasingly frequent crevasses near the Recovery Glacier calving face; thus further accelerating the possibly abrupt rate of ice mass loss associated with the calving mechanism discussed by Bassis et. al. 2013.

Bassis, J.N., and Jacobs,S., (2013), "Diverse calving patterns linked to glacier geometry", Nature Geoscience, 6, 833–836, doi:10.1038/ngeo1887.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on January 16, 2014, 02:33:53 AM
The following link leads to a NASA article providing more details as to why the Totten Glacier is losing ice mass so rapidly:

http://www.jpl.nasa.gov/news/news.php?release=2013-352 (http://www.jpl.nasa.gov/news/news.php?release=2013-352)
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on February 01, 2014, 04:07:26 AM
The following extract about Totten Glacier is taken from the linked website:

"Recent satellite observations indicate that the Totten ice drainage system is thinning in response to undermelting by intruding warm ocean waters. While this process is observed elsewhere in Antarctica (e.g. the rapidly retreating Pine Island Glacier in West Antarctica), the Totten Glacier system is potentially Antarctica’s most important glacial drainage system due to its large size; it is three times larger than any system in West Antarctica. Thus, the system could transfer large volumes of glacial meltwater to the oceans at faster rates than any other marine based ice system on Earth. Sparse regional oceanographic data supports warm water intrusion, but no sampling has ever been conducted in front of the Totten Glacier, where warm water could impact the mass balance of the glacier system most directly. For these reasons the NSF has elevated this project to one of its top priorities, for this austral field season.

During the expedition, USF researchers will generate detailed bathymetric maps of the seafloor to improve understanding of ice and ocean coupling as well as regional navigation. The team will also collect 25-meter long marine sediment cores from the continental shelf using the N. B. Palmer’s jumbo piston corer. These cores will allow researchers to reconstruct past periods of instability of the Totten Glacier system in order to evaluate what forces the system to retreat and advance."

http://ameliashevenell.wordpress.com/2014/01/27/1272014-mysteries-of-east-antarcticas-totten-glacier-system/ (http://ameliashevenell.wordpress.com/2014/01/27/1272014-mysteries-of-east-antarcticas-totten-glacier-system/)
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on February 22, 2014, 06:22:12 PM
The linked NASA article (see also discussion in replies 49 & 50) finds that the reducing salinity of the ocean water (due to a reduction in the number of local polynas) around the Totten & Moscow U. Ice Shelves is leading to melting and thinning of the Totten Glacier (see the link for further explanations):

http://www.jpl.nasa.gov/news/news.php?release=2013-352 (http://www.jpl.nasa.gov/news/news.php?release=2013-352)


The caption for the first attached annotated Aqua image from Sept 25 2013 is:

"This image shows the Totten Glacier ice shelf in East Antarctica (the wrinkled white area at top left) on Sept. 25, 2013. Two large open-water polynyas appear on the sea ice below and to the right of the shelf, as well as several smaller ones. The open-water areas are bright black. The stippled diagonal line from lower left to upper right is the outer edge of the sea ice, with cloud cover to the right of that line. The image is from the Moderate Resolution Imaging Spectroradiometer instrument on NASA's Aqua satellite. Credit: NASA"


The second attached image is from the Modis Terra satellite on Feb 22 2014 and is zoomed in on the Totten Glacier and Ice Shelf.  This image shows a calving event from the Totten Ice Shelf (note the sea ice is retreated off of the ice shelf face in this image); possibly associate with the ocean-ice advection cited in the NASA news article.
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on February 23, 2014, 05:27:30 AM
I think the reduction in salinity near the Totten is an effect, not a cause. The winds cause the polynas; if the wind decreases, so does number of polynas and salinity. But there is more going on, Purkey(2013) DOI: 10.1175/JCLI-D-12-00834.1 is excellent. I have not the time right now, but this is fig 5c from the reference and associated colorscale, look where the freshwater is, deep and by EAIS. The whole discussion in Purkey on halosteric change, and (potential temperature) isotherm heave is fascinating.
 
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on February 23, 2014, 03:04:41 PM
sidd,

Thanks for your comment/correction.  I have changed my prior post to indicate that the reduction in salinity is due to a reduction in the number of local polynas (which as you point out can be correlated to the winds), as supported by the quotes from the article below (I should probably not post when I am in a hurry, but if I did that my number of posts would be decreased by a factor of 10):

"The team then examined a data set of passive microwave measurements from the Defense Meteorological Satellite Program. These showed that in the latter part of the study period, the extent of polynyas (and therefore the production of cold brine) decreased significantly. ICESat observations showed that at the same time, the thinning of Totten Glacier increased, as the team's hypothesis predicted it would.

 If there are more winters with reduced polynya extents, Khazender points out, the cavity under Totten can fill with warmer ocean water rather than cold brine. "If that happens, the glacier's flow could be significantly destabilized, causing it to discharge even more ice into the ocean," he said."

Thanks also for the Purkey & Johnson (2013) figure; which to me indicates that there are multiple mechanisms changing simultaneously around Antarctica and the Southern Ocean, with changes in AABW, CDW, meltwater, wind patterns, advective patterns, etc.

For those who want a free access version of the Purkey & Johnson, 2013 (as well as other Johnson papers), you can find it (them) here:

http://www.pmel.noaa.gov/people/gjohnson/publications.html (http://www.pmel.noaa.gov/people/gjohnson/publications.html)
Title: Re: EAIS Contributions to SLR by 2100
Post by: wili on May 05, 2014, 03:42:38 PM
This was just posted at ClimateProgress:
http://thinkprogress.org/climate/2014/05/05/3433981/antarctic-melting-sea-levels/ (http://thinkprogress.org/climate/2014/05/05/3433981/antarctic-melting-sea-levels/)

East Antarctic Melting Could Raise Sea Levels By 10 To 13 Feet, Study Finds

Quote
A region of East Antarctica is more vulnerable than previously thought to a massive thaw that could result in world sea levels rising for thousands of years, a study found Sunday.

The study, published in the journal Nature Climate Change, looked at the 600-mile Wilkes Basin in East Antarctica, which, if it melted, has enough ice to raise sea levels by 10 to 13 feet. Researchers found that the region was vulnerable to melting because it’s held in place by a small “ice plug” that may melt over the next few centuries, meaning East Antarctica could “become a large contributor to future sea-level rise on timescales beyond a century,” according to the article.

“East Antarctica’s Wilkes Basin is like a bottle on a slant. Once uncorked, it empties out,” Matthias Mengel, lead author of the study, said in a statement.

Here's a link to the abstract of the study itself, with figures: http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2226.html (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2226.html)

(Apologies if this was already posted elsewhere and I missed it.)

ETA: ClimateCrock has a video on this now, too. (Thanks to dorlomin at POForums for this link.)

http://climatecrocks.com/2014/05/05/new-research-east-antarctic-at-risk-of-unstoppable-melt/ (http://climatecrocks.com/2014/05/05/new-research-east-antarctic-at-risk-of-unstoppable-melt/)
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on May 05, 2014, 11:39:38 PM
Thanks for the reference. I like the term "ice plug" used to describe the thickness of ice required to shift ice sheet profile into irreversible retreat across retrograde bed. I also like the fact that PISM performs as well as Elmer which is a full Stokes model.

That said, let me whine a little: where is the hydrology ?it is rolled up into various basal treatments, but I fear this is not enough, we need something like Elmer but with with fine detail  as in Hughes(2014 doi:10.5194/tcd-8-2043-2014 open access) which is a very nice force balance method including subglacial lake drainage and refilling, (this treatment unfortunately, cannot give longterm behavior.) Also more unfortunately, we cant just run Elmer at fine enough detail today to possibly model the full complexity of the networks depicted in Livingstone (2013 doi:10.5194/tc-7-1721-2013 open access)  Nor can they reproduce fine structure on the surface, as depicted in a section of Hughes (2014 ) fig 1 which is the third image below

So just for fun: 3 images:

Image 1)fig 1 from Mengel showing depth of bedrock, which is not the full description of hydrology
Image 2)fig 1 from Livingstone showing hydrology, which depends on surface slope as well
Image 3)surface streams from fig1 Hughes(2014)

and do note the other hole in this bathtub going left into the Ross is Byrd (which is dealt with extensively in Hughes(2014)

sidd

Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on May 06, 2014, 05:55:08 AM
I forgot to mention the most important bit in the Mengel paper: this is an amplifier (over century plus timescale)

Consider: Net radiative imbalance is all (90%) going into the ocean, causing thermal sea level rise of about 1 mm/yr. This is not much sea level bang for the buck, but if you put it all into melting land based ice that would be about 60mm/yr (curiously enough this is about the annual swing in arctic sea ice volume ...)

So thats a 60 to 1 amplifier.

Now consider further, according to Mengel et al., if you put enough heat to melt 8 cm worth of SLR into Cook and Ninnis, you will then get 400cm of SLR out. Another amplification of 50.

And of course the ice plug is right by the ocean at the war front, so the ocean can eat it away easily.

Then, just to rub salt in they point out that this implies a heat flux from the ocean comparable to that seen in the West Amundsen Embayment where our friends PIG and Thwaites are fidgeting.

"The corresponding heat flux of 1.3 TW–2.6 TW is comparable to estimates for the present heat flux into the Amundsen embayment and towards the Dotson and Getz ice shelves."

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 06, 2014, 04:51:32 PM
sidd & wili,

A great series of posts, on the serious fragility of the AIS over a period of centuries.  I am very curious to see what happens to the rate of Antarctic ice mass loss, if/when we get a strong El Nino; and we may find-out later by the end of the coming austral summer.

Best
ASLR
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 15, 2014, 01:23:01 AM
The linked reference (with a free access pdf) indicates that the West Ragnhild Glacier (marine-terminating) in Dronning Maud Land, East Antarctica, is more sensitive to external forcing (with regard to ice mass loss) than are other glaciers in the region:

Callens, D., Matsuoka, K., Steinhage, D., Smith, B., Witrant, E., and Pattyn, F., (2014), "Transition of flow regime along a marine-terminating outlet glacier in East Antarctica", The Cryosphere, 8, 867-875, doi:10.5194/tc-8-867-2014

http://www.the-cryosphere.net/8/867/2014/tc-8-867-2014.html (http://www.the-cryosphere.net/8/867/2014/tc-8-867-2014.html)

"Abstract. We present results of a multi-methodological approach to characterize the flow regime of West Ragnhild Glacier, the widest glacier in Dronning Maud Land, Antarctica. A new airborne radar survey points to substantially thicker ice (>2000 m) than previously thought. With a discharge estimate of 13–14 Gt yr−1, West Ragnhild Glacier thus becomes of the three major outlet glaciers in Dronning Maud Land. Its bed topography is distinct between the upstream and downstream section: in the downstream section (<65 km upstream of the grounding line), the glacier overlies a wide and flat basin well below the sea level, while the upstream region is more mountainous. Spectral analysis of the bed topography also reveals this clear contrast and suggests that the downstream area is sediment covered. Furthermore, bed-returned power varies by 30 dB within 20 km near the bed flatness transition, suggesting that the water content at bed/ice interface increases over a short distance downstream, hence pointing to water-rich sediment. Ice flow speed observed in the downstream part of the glacier (~250 m yr−1) can only be explained through very low basal friction, leading to a substantial amount of basal sliding in the downstream 65 km of the glacier. All the above lines of evidence (sediment bed, wetness and basal motion) and the relatively flat grounding zone give the potential for West Ragnhild Glacier to be more sensitive to external forcing compared to other major outlet glaciers in this region, which are more stable due to their bed geometry (e.g. Shirase Glacier)."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on July 07, 2014, 06:01:01 PM
The linked reference (with a free access pdf) indicates how pervasive circum-Antarctic ocean warming associated with changes in the Southern Hemisphere Westerlies (SHW) may threaten EAIS stability:

Fogwill, C., C. Turney, K. Meissner, N. Golledge, P. Spence , J. Roberts, M. England, L. Carter, (2014), "Testing the sensitivity of the East Antarctica Ice Sheet to Southern Ocean dynamics: past changes and future implications", Journal of Quaternary Science, 29 (1), 91-98, DOI: 10.1002/jqs.2683

http://web.science.unsw.edu.au/~paulspence/EAIC.pdf (http://web.science.unsw.edu.au/~paulspence/EAIC.pdf)

ABSTRACT: "The stability of Antarctic ice sheets and their potential contribution to sea level under projected future warming remains highly uncertain. The Last Interglacial (135 000–116 000 years ago) provides a potential analogue, with global temperatures 2 °C higher and rates of sea-level rise >5.6m ka_1, leading to sea levels 6.6– 9.4m higher than present. The source(s) of this sea-level rise remain fiercely debated. Here we report a series of independent model simulations exploring the effects of migrating Southern Hemisphere Westerlies (SHWs) on Southern Ocean circulation and Antarctic ice-sheet dynamics. We suggest that southerly shifts in winds may have significantly impacted the sub-polar gyres, inducing pervasive warming (0.2–0.8 °C in the upper 1200 m) adjacent to sectors of the East Antarctic Ice Sheet (EAIS), which due to their geometries and connectivity to the Southern Ocean are highly sensitive to ocean forcing. We conclude that the EAIS potentially made a substantial, hitherto unsuspected, contribution to interglacial sea levels, and given 21st-century projections in the Southern Annular Mode and associated SHW migration, we highlight how pervasive circum-Antarctic warming may threaten EAIS stability."
Title: Re: EAIS Contributions to SLR by 2100
Post by: icefisher on September 06, 2014, 11:31:23 PM
ASLR,  There is another projection of Antarctic ice discharge recently published in (www.earth-syst-dynam.net/5/271/2014/ (http://www.earth-syst-dynam.net/5/271/2014/)) titled "Projecting Antarctic ice discharge using response functions from SeaRISE ice-sheet models.  This is an open access paper.

 Abstract: The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical ice discharge from Antarctica.  Basal ice-shelf melting induced by a warming ocean has been identified as a major cause for additional ice flow across the grounding line.  Here we attempt to estimate the oceanic response and the ice-sheet model response.  The uncertainty in the global mean temperature increase is obtained from historically constrained emulations with the MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model.  The oceanic forcing is derived from scaling of the subsurface with the atmospheric warming from 19 comprehensive climate models of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models from the EU-project Ice2Sea.  The dynamic ice-sheet response is derived from linear response functions for basal ice-shelf melting for four different Antarctic drainage regions using experiments from the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models.  The resulting uncertainty range for the historic Antarctic contribution to global sea-level rise from 1992 to 2011 agrees with the observed contribution for this period if we use the three ice-sheet models with an explicit representation of ice-shelf dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature.  The median of the additional ice loss for the 21st century is computed to 0.07m (66% range: 0.02-0.14m; 90% range: 0.0-0.23m) of global sea-level equivalent for the low-emission RCP-2.6 and 0.15m (66% range: 0.07-0.28m; 90% range: 0.04-0.43m) for RCP-8.5.  All probability distributions are highly skewed towards high values.  The applied ice-sheet models are coarse resolution with limitations in the representation of grounding-line motion.  Within the constraints of the applied methods, the uncertainty induced from different ice-sheet models is smaller than that induced by the external forcing to the ice sheets.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 07, 2014, 02:54:02 AM
icefisher,

Thanks for the link.  I provide some discussion about this reference in Reply #171 of the "Potential Collapse Scenario for the WAIS" thread at the following link:

http://forum.arctic-sea-ice.net/index.php/topic,31.150.html#lastPost (http://forum.arctic-sea-ice.net/index.php/topic,31.150.html#lastPost)

It is good to cross reference these links in the various threads, and it will be interest to see what SLR projection are issued by AR6, if/when that document is issued.

Best,
ASLR
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on October 06, 2014, 06:45:56 AM
Gogineni has a paper out that discusses subglacial topo and ice stucture under Byrd (and Jacobshawn)
Confirms that Byrd trench is >3Km deep. Ouch.

doi: 10.3189/2014JoG14J129

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: solartim27 on October 07, 2014, 01:04:42 AM
Article on Live Science discussing the 3 km deep trench under Byrd:
http://www.livescience.com/48096-hidden-trench-discovered-under-glacier.html?cmpid=558455 (http://www.livescience.com/48096-hidden-trench-discovered-under-glacier.html?cmpid=558455)
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on October 07, 2014, 05:43:31 AM
If you are at the Fall AGU in San Francisco then go see:

Jamin Stevens Greenbaum1, Donald D Blankenship1, Duncan A Young1, Alan Aitken2, Thomas G Richter, Jason L Roberts, Roland Charles Warner, Tas D van Ommen and Martin John Siegert, (2014), "Increasing Ocean Access to Totten Glacier, East Antarctica"

Abstract:
The Totten Glacier Ice Shelf (TGIS) is the primary outlet of the Aurora Subglacial Basin, draining 6.9 meters of eustatic sea level potential into the Sabrina Coast (SC) alongside the Moscow University Ice Shelf that fringes the coastline. The TGIS and surrounding grounded ice has the largest thinning signal in East Antarctica and the nature of the thinning suggests that it is driven by enhanced basal melting due to ocean processes. Warm Modified Circumpolar Deep Water (MCDW), which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the SC continental shelf in the 400-500 m depth range. Here we show, using new data from recent aerogeophysical flights, that entrances to the cavity exist that are deeper than this range of thermocline depths, indicating that the TGIS is vulnerable to intrusions of MCDW if the vertical structure of cavity inflow is similar to the nearest observations. We provide evidence that a new entry to the cavity has opened likely due to the interplay between thinning ice and subglacial channels that could be related to regional mass loss acceleration observed in 2006. This new connection may increase access of warm water to the east side of the ice shelf, potentially destabilizing the low-lying area to the east of the TGIS.
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on October 07, 2014, 10:54:14 PM
Some reading for that presentation might include doi:10.1029/2011JF002066 with many of the same authors showing the hydrological connection through the Aurora Subglacial Basin from Totten all the way to Dome C and almost all the way to Lake Vostok, a thousand klicks or more. And recall it's neighbours, as discussed in Mengel(2014) DOI: 10.1038/NCLIMATE2226, Cook and Ninnis, where a small investment in melting the ice plug of 80mm SLR equiv reaps an additional rise of 4000mm. Now consider that the Wilkes basin drained by Cook and Ninnis is larger than Byrd Deeps underlying PIG/Thwaites. Couple Wilkes and Aurora together a la Feldman(2014) doi:10.5194/tcd-8-4885-2014 who shows that draining one ice basin destabilizes neighbours. And remember that Byrd glacier also drains Wilkes through the Transantarctic spine through a trench 3.6 km (Gogineni's latest doi:10.3189/2014JoG14J129 )deep into the Ross Shelf, and has interesting hydrology beneath also.

Another one that scares me is Amery.

EAIS is not as stable as is supposed, and far larger than WAIS. If EAIS lets go we are quickly and seriously screwed. Best keep at least as close an eye on it as WAIS.

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on December 06, 2014, 02:02:45 PM
De Boer et al 2014 model the (E)AIS during the Pliocene:
http://www.the-cryosphere-discuss.net/8/5539/2014/tcd-8-5539-2014-print.pdf (http://www.the-cryosphere-discuss.net/8/5539/2014/tcd-8-5539-2014-print.pdf)

Simulating the Antarctic ice sheet in the Late-Pliocene warm period: PLISMIP-ANT, an ice-sheet model intercomparison project

Abstract
In the context of future climate change, understanding the nature and behaviour of ice sheets during warm intervals in Earth history is of fundamental importance. The Late-Pliocene warm period (also known as the PRISM interval: 3.264 to 3.025 million years before present) can serve as a potential analogue for projected future climates. Although Pliocene ice locations and extents are still poorly constrained, a significant contribution to sea-level rise should be expected from both the Greenland ice sheet and the West and East Antarctic ice sheets based on palaeo sea-level reconstructions. Here, we present results from simulations of the Antarctic ice sheet by means of an international Pliocene Ice Sheet Modeling Intercomparison Project (PLISMIP-ANT). For the experiments, ice-sheet models including the shallow ice and shelf approximations have been used to simulate the complete Antarctic domain (including grounded and floating ice). We compare the performance of six existing numerical ice-sheet models in simulating modern control and Pliocene ice sheets by a suite off our sensitivity experiments. Ice-sheet model forcing fields are taken from the HadCM3 atmosphere–ocean climate model runs for the pre-industrial and the Pliocene. We include an overview of the different ice-sheet models used and how specific model configurations influence the resulting Pliocene Antarctic ice sheet. The six ice-sheet models simulate a comparable present-day ice sheet, although the models are setup with their own parameter settings. For the Pliocene simulations using the Bedmap1 bedrock topography, some models show a small retreat of the East Antarctic ice sheet, which is thought to have happened during the Pliocene for the Wilkes and Aurora basins. This can be ascribed to either the surface mass balance, as the HadCM3 Pliocene climate shows a significant increase over the Wilkes and Aurora basin, or the initial bedrock topography. For the latter, our simulations with the recently published Bedmap2 bedrock topography indicate a significantly larger contribution to Pliocene sea-level rise from the East Antarctic ice sheet for all six models relative to the simulations with Bedmap1.

And from their conclusion:
"Our simulations of the Late-Pliocene warm period with Bedmap1 do not show a retreat of the EAIS from the Wilkes and Aurora basins as has been suggested by studies of marine sediments (e.g. Williams et al., 2010; Cook et al., 2013). Thus far transient simulations through the Late-Pliocene were not capable of simulating a significant retreat either (Pollard and DeConto, 2012b; de Boer et al., 2014). On the other hand, the experiments using the Bedmap2 initial ice sheet do suggest that an additional contribution from the EAIS should be considered likely. Our simulations indicate significantly less ice over the Wilkes and Aurora basins and a more considerable and less biased contribution to Pliocene sea level relative to the simulations with Bedmap1. These sensitivity experiments show the importance of including an accurate data set of bedrock topography for ice sheet models, which is in line with Mengel and Levermann (2014)."

So these models do not seem to reproduce the paleo-data yet, but they're getting closer.
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on December 06, 2014, 03:30:04 PM
Khazendar et al 2014 on Totten Glacier:
http://www.staff.science.uu.nl/~broek112/home.php_files/Publications_MvdB/2013_Khazendar_NatComm.pdf (http://www.staff.science.uu.nl/~broek112/home.php_files/Publications_MvdB/2013_Khazendar_NatComm.pdf)

Observed thinning of Totten Glacier is linked to coastal polynya variability

Abstract
Analysis of ICESat-1 data (2003–2008) shows significant surface lowering of Totten Glacier, the glacier discharging the largest volume of ice in East Antarctica, and less change on nearby Moscow University Glacier. After accounting for firn compaction anomalies, the thinning appears to coincide with fast-flowing ice indicating a dynamical origin. Here, to elucidate these observations, we apply high-resolution ice–ocean modelling. Totten Ice Shelf is simulated to have higher, more variable basal melting rates. We link this variability to the volume of cold water, originating in polynyas upon sea ice formation, reaching the sub-ice-shelf cavity. Hence, we propose that the observed increased thinning of Totten Glacier is due to enhanced basal melting caused by a decrease in cold polynya water reaching its cavity. We support this hypothesis with passive microwave data of polynya extent variability. Considering the widespread changes in sea ice conditions, this mechanism could be contributing extensively to ice-shelf instability.
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on December 06, 2014, 10:18:41 PM
Mr. Linde posted a reference to Fogwill(2014,doi:10.1002/jqs.2683) in a WAIS thread. That paper states:

"We propose that the sensitivity of these sectors of the ice sheet relates to two major factors: firstly the coincidence of EAIS basins with concave ice-sheet surface profiles; secondly, the basins’ connectivity to the ocean. The basins’ bed topography and ice-sheet geometry control the mass flux from the ice sheet; those which have a weak or sliding bed have a faster flow regime, resulting in a concave surface profile (Cuffey and Paterson, 2010). In contrast, basins where ice is flowing slowly with little or no basal sliding exhibit a parabolic, or convex, surface profile and much lower ice fluxes. Our results imply that basins with concave surface profiles are particularly susceptible to ocean forcing, bringing about greater rates of surface lowering than in other areas ..."

"Similarly, the extensive Lambert/Amery Basin is connected to the open ocean through the Amery Ice Shelf into Prydz Bay and, as with the EAIS outlets in the eastern Weddell Sea, the basin has a concave profile which continues deep into the interior of the ice sheet ..."

The latter, Amery, is one (like NEGIS up north) that scares me. Look at that big concave hole at two o'clock and the projected ocean warming right in front of it.

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on January 01, 2015, 07:13:28 PM
The link to a Jamstec press release (from October 2014) indicates that the EAIS is more susceptible to warming ocean temperatures than was previously realized (see also Reply #66 that supports this conclusion); based on detailed time-series analyses of ice-berg rafted debris collected from a sediment core adjacent to the Wilkes Subglacial Basin (see attached image):

http://www.jamstec.go.jp/e/about/press_release/20141027/ (http://www.jamstec.go.jp/e/about/press_release/20141027/)

Extract: "Based on core samples collected in the Antarctic Ocean, this analysis examined the timing of the EAIS melting mode occurred between 4.3 and 2.2 million years ago. It found out that, prior to 3.5 million years ago, the sea ice melting was related mainly to variance in the obliquity cycle, and since 3.5 million years, it has been related to precession. In other words, the EAIS was sensitive to seawater temperature variations in the Antarctic Ocean during the period older than 3.5 million years, while it has been affected mainly by summer insolation since 3.5 million years ago.
This study results demonstrate how the EAIS volume, in particular melting, is caused when the global seawater temperature was 2 °C higher, as occurred during the early Pliocene. In facing global warming, it gives an important insight into the EAIS behaviors. Also, it is expected to contribute to prediction of future climate changes, because this study indicates that EAIS is not as stable as expected."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on January 07, 2015, 10:18:45 PM
The linked reference provides paleo-evidence that the Wilkes land sub-basin has been eroded during past ice mass loss events, and may be susceptible to future such events.

L. Tauxe, S. Sugisaki, F. Jiménez-Espejo, C. Escutia, C.P. Cook, T. van de Flierdt & M. Iwai, (2015), "Geology of the Wilkes land sub-basin and stability of the East Antarctic Ice Sheet: Insights from rock magnetism at IODP Site U1361", Earth and Planetary Science Letters, Volume 412, 15 February 2015, Pages 61–69, doi:10.1016/j.epsl.2014.12.034

http://www.sciencedirect.com/science/article/pii/S0012821X1400795X (http://www.sciencedirect.com/science/article/pii/S0012821X1400795X)


Abstract: "IODP Expedition 318 drilled Site U1361 on the continental rise offshore of Adélie Land and the Wilkes subglacial basin. The objective was to reconstruct the stability of the East Antarctic Ice Sheet (EAIS) during Neogene warm periods, such as the late Miocene and the early Pliocene. The sedimentary record tells a complex story of compaction, and erosion (thus hiatuses). Teasing out the paleoenvironmental implications is essential for understanding the evolution of the EAIS. Anisotropy of magnetic susceptibility (AMS) is sensitive to differential compaction and other rock magnetic parameters like isothermal remanence and anhysteretic remanence are very sensitive to changes in the terrestrial source region. In general, highly anisotropic layers correspond with laminated clay-rich units, while more isotropic layers are bioturbated and have less clay. Layers enriched in diatoms are associated with the latter, which also have higher Ba/Al ratios consistent with higher productivity. Higher anisotropy layers have lower porosity and moisture contents and have fine grained magnetic mineralogy dominated by maghemite, the more oxidized form of iron oxide, while the lower anisotropy layers have magnetic mineralogies dominated by magnetite. The different magnetic mineralogies support the suggestion based on isotopic signatures by Cook et al. (2013) of different source regions during low productivity (cooler) and high productivity (warmer) times. These two facies were tied to the coastal outcrops of the Lower Paleozoic granitic terranes and the Ferrar Large Igneous Province in the more inland Wilkes Subglacial Basin respectively. Here we present evidence for a third geological unit, one eroded at the boundaries between the high and low clay zone with a “hard” (mostly hematite) dominated magnetic mineralogy. This unit likely outcrops in the Wilkes subglacial basin and could be hydrothermally altered Beacon sandstone similar to that detected by Craw and Findlay (1984) in Taylor Valley or the equivalent to the Elatina Formation in the Adelaide Geosyncline in Southern Australia (Schmidt and Williams, 2013). Correlation of the “hard” events with global oxygen isotope stacks of Zachos et al. (2001) and Lisiecki and Raymo (2005) suggest that the source region was eroded during times with higher global ice volume."

Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on January 07, 2015, 11:23:43 PM
One thing i do not understand in the recent Pollard(2014) paper: Why is Amery stable ? Thoughts ?

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on January 07, 2015, 11:35:28 PM
One thing i do not understand in the recent Pollard(2014) paper: Why is Amery stable ? Thoughts ?

sidd

My thought is that there is insufficient advection of warm CDW to the grounding line, but I have not studied Amery as much as I have other basins.

edit: It may also be more difficult to get the Amery ice shelf to collapse due to hydrofracturing as it is so well confined by the adjoining land mass.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on January 08, 2015, 02:12:41 PM
The extent of iceberg debris fields identified near the gateway to the Wilkes Subglacial Basin by the linked reference, makes it evident that under Pliocene like conditions "cliff failure (possibly/probably together with hydrofracturing [see Pollard, DeConto & Alley 2015)" was an important type of ice mass loss from this portion of the EAIS, and may soon be again if we continue on a BAU pathway:

M. O. Patterson, R. McKay, T. Naish, C. Escutia, F. J. Jimenez-Espejo, M. E. Raymo, S. R. Meyers, L. Tauxe, H. Brinkhuis, & IODP Expedition 318 Scientists, (2014), "Orbital forcing of the East Antarctic ice sheet during the Pliocene and Early Pleistocene", Nature Geoscience, Volume: 7, Pages: 841–847, doi:10.1038/ngeo2273


http://www.nature.com/ngeo/journal/v7/n11/abs/ngeo2273.html (http://www.nature.com/ngeo/journal/v7/n11/abs/ngeo2273.html)

Abstract: "The Pliocene and Early Pleistocene, between 5.3 and 0.8 million years ago, span a transition from a global climate state that was 2–3 °C warmer than present with limited ice sheets in the Northern Hemisphere to one that was characterized by continental-scale glaciations at both poles. Growth and decay of these ice sheets was paced by variations in the Earth’s orbit around the Sun. However, the nature of the influence of orbital forcing on the ice sheets is unclear, particularly in light of the absence of a strong 20,000-year precession signal in geologic records of global ice volume and sea level. Here we present a record of the rate of accumulation of iceberg-rafted debris offshore from the East Antarctic ice sheet, adjacent to the Wilkes Subglacial Basin, between 4.3 and 2.2 million years ago. We infer that maximum iceberg debris accumulation is associated with the enhanced calving of icebergs during ice-sheet margin retreat. In the warmer part of the record, between 4.3 and 3.5 million years ago, spectral analyses show a dominant periodicity of about 40,000 years. Subsequently, the powers of the 100,000-year and 20,000-year signals strengthen. We suggest that, as the Southern Ocean cooled between 3.5 and 2.5 million years ago, the development of a perennial sea-ice field limited the oceanic forcing of the ice sheet. After this threshold was crossed, substantial retreat of the East Antarctic ice sheet occurred only during austral summer insolation maxima, as controlled by the precession cycle."
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on January 20, 2015, 10:31:12 PM
Reinardya et al 2015, Repeated advance and retreat of the East Antarctic Ice Sheet on the continental shelf during the early Pliocene warm period:
http://www.sciencedirect.com/science/article/pii/S0031018215000103 (http://www.sciencedirect.com/science/article/pii/S0031018215000103)

Highlights
• Deposition on the Antarctic shelf interpreted using micromorphology.
• Diatom assemblage from shelf site indicates Pliocene age sediments.
• The site was open marine three times and covered by ice at least four times.
• Proxies from the rise can be linked with grounding line migration from the shelf.
• EAIS is more sensitive to climatic and oceanic forcing than previously suggested.

Abstract
Diatom analysis of a sediment core recovered at IODP Site U1358 on the continental shelf off the Adélie Coast indicated that the lower section of the core contained an assemblage dating back to the Thalassiosira innura Zone of the lower Pliocene that ranges from 4.2 to 5.12 Ma. Based on lithological descriptions at both a macro- and micro-scale of this early Pliocene part of the core, four facies were interpreted from the diamictons representing the progressive advance and retreat of the grounding line over the site. Facies 1a and 1b contain a distinct directional signal from the orientation of the a-axis of clasts with several phases of fabric development along with both brittle and ductile deformation features that are common in sediments that have been subglacially deformed. Facies 1c and 1d are finely laminated and were deposited in open marine conditions. The four facies within the depositional model provide for the first time direct evidence for ice advancing across the shelf adjacent to the Wilkes Subglacial Basin on at least four occasions separated by three periods of open marine conditions indicating retreat of grounded ice inland of the site during a warmer than present early Pliocene. The times of open marine conditions are correlated with previous findings from the neighbouring rise sites that also indicated an oscillating ice margin. This has significant implications because firstly it suggests a dynamic East Antarctic Ice Sheet (EAIS) that is probably far more sensitive to climatic and oceanic forcing even during relatively short time periods than had previously been thought. Secondly it suggests that proxies used to interpret the advance and retreat of the grounding line from the rise can be linked with direct evidence of grounding line migration from the shelf. It also has important implications for the future behaviour and sensitivity of the EAIS under present continuing warming conditions. Together with results from the rise, this paper provides a crucial ice extent target for a new ice sheet model of this region during the Pliocene.
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on January 26, 2015, 11:54:30 AM
Warm ocean water is melting Totten glacier from below:
http://www.abc.net.au/news/2015-01-26/sea-water-melting-totten-glacier-in-antarctica-from-below/6047076 (http://www.abc.net.au/news/2015-01-26/sea-water-melting-totten-glacier-in-antarctica-from-below/6047076)

Quote
Steve Rintoul from the Australian Climate and Environment Cooperative Research Centre said the results indicated the glacier was being melted by the sea water beneath it. "The measurements we collected provide the first evidence that warm water reaches the glacier and may be driving that melt of the glacier from below," he said. The glacier holds enough water to raise the sea level by six metres and scientists said it had been thinning over the past 15 years...

But he said it was too soon to tell if the glacier was melting as a result of a changing global climate. "What our observations can't tell us is how things have changed over time, because this is the first time anyone has made measurements in this area," he said. "The measurements we've collected here are crucial for setting a benchmark that can be used to assess future change."

Tony Worby, also from the research centre, said the study was groundbreaking. "No ship has ever been where the Aurora Australis went on this voyage, the ship managed to get front of the Totten Glacier," he said. "Over the next year or two we'll process all of that data and get a really great sense of how warmer ocean water is affecting the glacier."
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on January 27, 2015, 08:17:41 AM
Rintoul comparing Totten to PIG:
http://www.theage.com.au/environment/climate-change/giant-east-antarctic-glacier-melting-with-warmer-oceans-20150127-12ypy4.html (http://www.theage.com.au/environment/climate-change/giant-east-antarctic-glacier-melting-with-warmer-oceans-20150127-12ypy4.html)

"Pine Island is melting and thinning more rapidly, but Totten is not too far behind," he said.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on February 05, 2015, 01:46:25 AM
The fact that the linked reference connects the rate of iceberg calving from the Wilkes Subglacial Basin during the Pliocene to the austral summer isolation; indicates to me that this provided circumstantial support for the Pollard et al (2015) cliff failure and hydrofracturing mechanism for this part of Antarctic:

M. O. Patterson, R. McKay, T. Naish, C. Escutia, F. J. Jimenez-Espejo, M. E. Raymo, S. R. Meyers,, L. Tauxe, H. Brinkhuis, IODP Expedition 318 Scientists. "Orbital forcing of the East Antarctic ice sheet during the Pliocene and Early Pleistocene." Nature Geosciences. DOI: 10.1038/NGEO2273


http://www.nature.com/ngeo/journal/v7/n11/abs/ngeo2273.html (http://www.nature.com/ngeo/journal/v7/n11/abs/ngeo2273.html)

Abstract: "The Pliocene and Early Pleistocene, between 5.3 and 0.8 million years ago, span a transition from a global climate state that was 2–3 °C warmer than present with limited ice sheets in the Northern Hemisphere to one that was characterized by continental-scale glaciations at both poles. Growth and decay of these ice sheets was paced by variations in the Earth’s orbit around the Sun. However, the nature of the influence of orbital forcing on the ice sheets is unclear, particularly in light of the absence of a strong 20,000-year precession signal in geologic records of global ice volume and sea level. Here we present a record of the rate of accumulation of iceberg-rafted debris offshore from the East Antarctic ice sheet, adjacent to the Wilkes Subglacial Basin, between 4.3 and 2.2 million years ago. We infer that maximum iceberg debris accumulation is associated with the enhanced calving of icebergs during ice-sheet margin retreat. In the warmer part of the record, between 4.3 and 3.5 million years ago, spectral analyses show a dominant periodicity of about 40,000 years. Subsequently, the powers of the 100,000-year and 20,000-year signals strengthen. We suggest that, as the Southern Ocean cooled between 3.5 and 2.5 million years ago, the development of a perennial sea-ice field limited the oceanic forcing of the ice sheet. After this threshold was crossed, substantial retreat of the East Antarctic ice sheet occurred only during austral summer insolation maxima, as controlled by the precession cycle."
Title: Re: EAIS Contributions to SLR by 2100
Post by: LRC1962 on February 08, 2015, 12:22:02 AM
Rintoul comparing Totten to PIG:
http://www.theage.com.au/environment/climate-change/giant-east-antarctic-glacier-melting-with-warmer-oceans-20150127-12ypy4.html (http://www.theage.com.au/environment/climate-change/giant-east-antarctic-glacier-melting-with-warmer-oceans-20150127-12ypy4.html)

"Pine Island is melting and thinning more rapidly, but Totten is not too far behind," he said.
Warm ocean melting East Antarctica's largest glacier (http://phys.org/news/2015-01-ocean-east-antarctica-largest-glacier.html)
Quote
But the voyage found that waters around the glacier were some 1.5 degrees Celsius warmer than other areas visited on the same trip during the southern hemisphere summer.
"We made it to the front of the glacier and we measured temperatures that were warm enough to drive significant melt," Rintoul said.
What scares me is that the more hard data we get the more 'surprises' we find. The question that keeps coming to mind is how can the majority of scientist studying this continue to to put up such low numbers for SLR? Granted the physics say you need x amount of energy for y amount of melt, but there are so many different ways of a glacier to melt and all the different ways seem to be happening at the same time in all parts of the world that I really think we are getting a very low ball number and it will be only when we get to an "Oh ****" year such as what happened in the Arctic in 2007,2012 that we will find out how bad things really are. Mind you by then it will be too late to save a great many cities.
Unlike sea ice, glaciers rarely have a 'rebound' year.
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on February 08, 2015, 06:08:10 AM
"What scares me is that the more hard data we get the more 'surprises' we find."

Not just the data, but also the theory. As we refine our theoretical understanding, the future looks grimmer. Consider how much more we know now than even in 2007, when Schoof published his strong analysis of Weertmann instability. Bassis on the fundamental limit of about a kilometer high ice cliff being the limit before collapse, or the recent study on collapse propagation between neighbouring basins, or the Rignot or the Pollard analysis on timescales for WAIS collapse, or the saddle collapse mechanism from Gregoire all come immediately to my recall, among a very great many others.

Not that the data is at all reassuring, for example, the recent discovery of warm water eating Totten and I await, cringing, for similar discoveries at Amery.

"The question that keeps coming to mind is how can the majority of scientist studying this continue to to put up such low numbers for SLR? "

Some are breaking ranks. Rignot comes to mind.

"Granted the physics say you need x amount of energy for y amount of melt,..."

Precisely. For a long time the assumption was diffusive timescales ...

" ... but there are so many different ways of a glacier to melt and all the different ways seem to be happening at the same time in all parts of the world ..."

Nature is cleverer than we. The more mundane effects like increasing surface slope in ablation zones increasing gravitational stress and ice velocities was well known. The Gregoire saddle collapse mechanism might, perhaps, have been foreseen, by a wiser head than mine. But, for a long time i thought that oceanic heat would only affect glaciers at grounding line. But of course, in Greenland we have increasing rain, which is good way to move heat into the ice sheet through the air, and the southern ocean freshening/sea ice increase demonstrates to me that the Antarctic ice sheet can steal heat from way further north than i thought possible until i saw it happening.

" ... that I really think we are getting a very low ball number ..."

Join the club.

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: LRC1962 on February 11, 2015, 02:40:13 PM
Another question that does come to mind is what about those lakes under the ice. Other then being surprised that they are there and how big they are there seems to be very little being said as to how they affect the ice above them and how the dynamics may change if the ocean starts interacting with that water.
Sidd you mentioned the rain, but as a few have mentioned rarely the more the ice melts, the lower the surface altitude gets, the warmer air temps become. Some people talk about the very cold temps at the south pole. Part of that is because the air temps would be cold anyway but you are sitting also on top of 9000 ft of ice. That can mean a change in average temps if that was all gone of a couple of dozen degrees on its own.
Paraphrasing a scientist that I heard (can not remember who it was): The more we learn, the more we find out how little we actually know. ( A closer quote was actually: The difference between someone with a masters degree and a PhD is not the amount of knowledge they have which is very little difference in actual fact, but that the one with the masters thinks they know everything and the one with the PhD discovers they know nothing.)
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on February 11, 2015, 07:53:37 PM
"but as a few have mentioned rarely the more the ice melts, the lower the surface altitude gets, the warmer air temps become"

This is the Gregoire instability, and i expect it to become visible at the saddle in GIS at 67 N within my lifetime. ELA (equilibrium line altitude) exceeded saddle altitude in 2012, i believe.

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: wili on February 18, 2015, 06:24:37 PM
Do we have a thread just on general slr? Anyway, here are a couple pieces on it:

An oldie-but-goodie lecture by Jeremy Jackson that recently came to my attention again:

https://www.youtube.com/watch?v=TAtCQ7REXAc (https://www.youtube.com/watch?v=TAtCQ7REXAc)

Something recent from the main stream-ish press, Rolling Stone:

http://www.rollingstone.com/politics/news/the-pentagon-climate-change-how-climate-deniers-put-national-security-at-risk-20150212 (http://www.rollingstone.com/politics/news/the-pentagon-climate-change-how-climate-deniers-put-national-security-at-risk-20150212)
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on February 18, 2015, 06:47:51 PM
Do we have a thread just on general slr?

wili,

The thread on general SLR is in the Consequence folder located here:

http://forum.arctic-sea-ice.net/index.php/topic,874.250.html (http://forum.arctic-sea-ice.net/index.php/topic,874.250.html)
Title: Re: EAIS Contributions to SLR by 2100
Post by: wili on February 18, 2015, 06:56:14 PM
Thanks. I'll repost there.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on February 26, 2015, 09:50:08 PM

The linked article discusses a Jökulhlaup, or sudden outburst of basal melt water, observed in the austral winter of 2014,from beneath the ice cap, erupted near Robinsons Ridge near Law Dome, East Antarctica.  Per the extract below, this indicates that there is high geothermal heat at the bottom of the glaciers in this area:


http://phys.org/news/2015-02-rare-antarctic-sub-glacial-eruption.html (http://phys.org/news/2015-02-rare-antarctic-sub-glacial-eruption.html)


Extract: "Our observations of the Jökulhlaup confirmed Law Dome had high geothermal heat emanating from the Earth's crust which was melting the bottom of the ice cap," Professor Goodwin said."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on March 16, 2015, 07:17:55 PM
I am re-posting Chuck Yokota's post in the "What's new in Antarctica?" thread to this thread about the EAIS:

East Antarctica Melting Could be Explained by Oceanic Gateways

http://www.utexas.edu/news/2015/03/16/east-antarctica-melting-could-be-explained-by-oceanic-gateways/ (http://www.utexas.edu/news/2015/03/16/east-antarctica-melting-could-be-explained-by-oceanic-gateways/)


AUSTIN,Texas — Researchers at The University of Texas at Austin’s Institute for Geophysics (UTIG) in the Jackson School of Geosciences have discovered two seafloor gateways that could allow warm ocean water to reach the base of Totten Glacier, East Antarctica’s largest and most rapidly thinning glacier. The discovery, reported in the March 16 edition of the journal Nature Geoscience, probably explains the glacier’s extreme thinning and raises concerns about how it will affect sea level rise.

Totten Glacier is East Antarctica’s largest outlet of ice to the ocean and has been thinning rapidly for many years. Although deep, warm water has been observed seaward of the glacier, until now there was no evidence that it could compromise coastal ice. The result is of global importance because the ice flowing through Totten Glacier alone is sufficient to raise global sea level by at least 11 feet, equivalent to the contribution of the West Antarctic Ice Sheet if it were to completely collapse.

“We now know there are avenues for the warmest waters in East Antarctica to access the most sensitive areas of Totten Glacier,” said lead author Jamin Greenbaum, a UTIG Ph.D. candidate.

The ice loss to the ocean may soon be irreversible unless atmospheric and oceanic conditions change so that snowfall outpaces coastal melting. The potential for irreversible ice loss is due to the broadly deepening shape of Totten Glacier’s catchment, the large collection of ice and snow that flows from a deep interior basin to the coastline."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on March 16, 2015, 07:25:09 PM
As a public service, I provide the following reference information about the article on Totten that Chuck Yokota cited:

J. S. Greenbaum, D. D. Blankenship, D. A. Young, T. G. Richter, J. L. Roberts, A. R. A. Aitken, B. Legresy, D. M. Schroeder, R. C. Warner, T. D. van Ommen & M. J. Siegert (2015), "Ocean access to a cavity beneath Totten Glacier in East Antarctica", Nature Geoscience, doi:10.1038/ngeo2388


http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2388.html (http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2388.html)


Abstract: "Totten Glacier, the primary outlet of the Aurora Subglacial Basin, has the largest thinning rate in East Antarctica. Thinning may be driven by enhanced basal melting due to ocean processes, modulated by polynya activity. Warm modified Circumpolar Deep Water, which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the nearby continental shelf beneath 400 to 500 m of cool Antarctic Surface Water. Here we derive the bathymetry of the sea floor in the region from gravity and magnetics data as well as ice-thickness measurements. We identify entrances to the ice-shelf cavity below depths of 400 to 500 m that could allow intrusions of warm water if the vertical structure of inflow is similar to nearby observations. Radar sounding reveals a previously unknown inland trough that connects the main ice-shelf cavity to the ocean. If thinning trends continue, a larger water body over the trough could potentially allow more warm water into the cavity, which may, eventually, lead to destabilization of the low-lying region between Totten Glacier and the similarly deep glacier flowing into the Reynolds Trough. We estimate that at least 3.5 m of eustatic sea level potential drains through Totten Glacier, so coastal processes in this area could have global consequences."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on March 16, 2015, 09:18:03 PM
Regarding Totten's (in)-stability also see the following Washington Post article & extract:

http://www.washingtonpost.com/news/energy-environment/wp/2015/03/16/the-melting-of-antarctica-was-already-really-bad-it-just-got-worse/ (http://www.washingtonpost.com/news/energy-environment/wp/2015/03/16/the-melting-of-antarctica-was-already-really-bad-it-just-got-worse/)

Extract: “What we need now is a confirmation of the findings of the paper from oceanographic data, because it is one thing to find potential pathways for warm water to intrude the cavity, it is another to show that this is actually happening,” observes Eric Rignot, an Antarctica expert at the University of California, Irvine. “This paper comes short of the latter, but other research efforts are underway to get critical oceanographic information near Totten.”
Title: Re: EAIS Contributions to SLR by 2100
Post by: jai mitchell on March 17, 2015, 05:15:23 PM
Regarding Totten's (in)-stability also see the following Washington Post article & extract:

http://www.washingtonpost.com/news/energy-environment/wp/2015/03/16/the-melting-of-antarctica-was-already-really-bad-it-just-got-worse/ (http://www.washingtonpost.com/news/energy-environment/wp/2015/03/16/the-melting-of-antarctica-was-already-really-bad-it-just-got-worse/)

Extract: “What we need now is a confirmation of the findings of the paper from oceanographic data, because it is one thing to find potential pathways for warm water to intrude the cavity, it is another to show that this is actually happening,” observes Eric Rignot, an Antarctica expert at the University of California, Irvine. “This paper comes short of the latter, but other research efforts are underway to get critical oceanographic information near Totten.”

The fact that so much attention was made on the (relatively) easily accessible WAIS and the alarms were ringing about PIG and Thwaites, but when one looked east, there was a big veil of "we don't know yet" made me always wonder what kind of idiots they take us for?

I mean, how could the entire continent NOT become undercut by warmer waters in the near future?
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on March 17, 2015, 06:45:59 PM
I mean, how could the entire continent NOT become undercut by warmer waters in the near future?

I think that the policymakers think that so long as abrupt sea level rise does not occur on their personal watch, then where's the problem? 

The Pollard et al 2015 paper certainly sounds an alarm about possible abrupt EAIS SLR contributions towards the end of this century (assuming we continue on a BAU pathway for a few more decades).
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on March 27, 2015, 10:50:50 PM
The linked reference discusses research by a French team working in Antarctica that looked at the history of the polynya in the lee of the Mertz Glacier going back 250 years.

P. Campagne, Xavier Crosta, M.N. Houssais, D. Swingedouw, S. Schmidt, A. Martin, E. Devred, S. Capo, V. Marieu, I. Closset & G. Massé (2015), "Glacial ice and atmospheric forcing on the Mertz Glacier Polynya over the past 250 years", Nature Communications, Volume: 6, Article number: 6642, doi:10.1038/ncomms7642


http://www.nature.com/ncomms/2015/150324/ncomms7642/full/ncomms7642.html (http://www.nature.com/ncomms/2015/150324/ncomms7642/full/ncomms7642.html)


Abstract: "The Mertz Glacier Polynya off George V Land, East Antarctica, is a source of Adélie Land Bottom Water, which contributes up to ~25% of the Antarctic Bottom Water. This major polynya is closely linked to the presence of the Mertz Glacier Tongue that traps pack ice upstream. In 2010, the Mertz Glacier calved a massive iceberg, deeply impacting local sea ice conditions and dense shelf water formation. Here we provide the first detailed 250-year long reconstruction of local sea ice and bottom water conditions. Spectral analysis of the data sets reveals large and abrupt changes in sea surface and bottom water conditions with a ~70-year cyclicity, associated with the Mertz Glacier Tongue calving and regrowth dynamics. Geological data and atmospheric reanalysis, however, suggest that sea ice conditions in the polynya were also very sensitive to changes in surface winds in relation to the recent intensification of the Southern Annular Mode."

Also see:
http://gizmodo.com/when-an-iceberg-the-size-of-a-country-breaks-free-what-1694005231 (http://gizmodo.com/when-an-iceberg-the-size-of-a-country-breaks-free-what-1694005231)
Title: Re: EAIS Contributions to SLR by 2100
Post by: wili on April 17, 2015, 07:22:31 PM
https://www.skepticalscience.com/trouble-at-totten-glacier.html (https://www.skepticalscience.com/trouble-at-totten-glacier.html)

New Video: The Trouble at Totten Glacier

Quote
Chris Mooney wrote recently in the Washington Post, “A hundred years from now, humans may remember 2014 as the year that we first learned that we may have irreversibly destabilized the great ice sheet of West Antarctica, and thus set in motion more than 10 feet of sea level rise.”

He added, “Meanwhile, 2015 could be the year of the double whammy — when we learned the same about one gigantic glacier of East Antarctica, which could set in motion roughly the same amount all over again.”

The decades-long unfolding of this story – that vast areas of ice once thought to be invulnerable on time scales meaningful to humans, may in fact already be in the process of disintegration – is one that that the vast majority of humanity still does not understand, and that the media has been unwilling to track. 

It’s a realization that, one top expert told us, even seasoned ice sheet veterans find “shattering”.
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on April 18, 2015, 07:43:33 AM
Also from the Mooney-piece:
Quote
For Richard Alley, a glaciologist at Penn State University, the new research hints at a possible solution to a question that scientists have long had about the planet’s past — and in particular the Pliocene epoch, beginning 5.3 million years ago, when sea levels were dramatically higher, by as much as 40 meters.

“The sea-level indicators from the Pliocene have suggested that an important amount of ice came out of East Antarctica into the ocean,” says Alley. “Sedimentary records offshore pointed in the same way, and recent modeling… shows the strong potential for this to have happened. This new paper adds to the evidence — the pieces are fitting together.”
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 18, 2015, 03:56:49 PM

New Video: The Trouble at Totten Glacier


wili,

Thanks for the link to the new video.  Attached is a screen capture from the video of the newly identified pathway for warm CDW to access the Totten grounding line.

Best,
ASLR
Title: Re: EAIS Contributions to SLR by 2100
Post by: Shared Humanity on April 20, 2015, 04:20:32 AM
I can't imagine why anyone would  think this portion of the EAIS would not be susceptible to underwater melt.

http://upload.wikimedia.org/wikipedia/commons/b/b7/AntarcticBedrock.jpg (http://upload.wikimedia.org/wikipedia/commons/b/b7/AntarcticBedrock.jpg)

Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 30, 2015, 03:20:17 AM
The linked article provides a light discussion of the investigation of the East Antarctic bed map in and around the Totten Catchment Basin (see attached map):

http://theconversation.com/melting-moments-a-look-under-east-antarcticas-biggest-glacier-40960 (http://theconversation.com/melting-moments-a-look-under-east-antarcticas-biggest-glacier-40960)

Title: Re: EAIS Contributions to SLR by 2100
Post by: JMP on April 30, 2015, 05:45:58 AM
Below from the comment section of the article ASLR in Reply #96 (also #86) linked to above:
http://www.jsg.utexas.edu/news/2015/03/east-antarctica-melting-could-be-explained-by-oceanic-gateways (http://www.jsg.utexas.edu/news/2015/03/east-antarctica-melting-could-be-explained-by-oceanic-gateways)

Quote
"Because much of the California-sized interior basin lies below sea level, its overlying thicker ice is susceptible to rapid loss if warm ocean currents sufficiently thin coastal ice. Given that previous work has shown that the basin has drained its ice to the ocean and filled again many times in the past, this study uncovers a means for how that process may be starting again.

The Totten Glacier catchment (outlined in blue) is a collection basin for ice and snow that flows through the glacier. It’s estimated to contain enough material to raise sea levels by at least 11 feet.

“We’ve basically shown that the submarine basins of East Antarctica have similar configurations and coastal vulnerabilities to the submarine basins of West Antarctica that we’re so worried about, and that warm ocean water, which is having a huge impact in West Antarctica, is affecting East Antarctica, as well,” Blankenship said.

The deeper of the two gateways identified in the study is a three-mile-wide seafloor valley extending from the ocean to beneath Totten Glacier in an area not previously known to be floating. Identifying the valley was unexpected because satellite analyses conducted by other teams had indicated the ice above it was resting on solid ground. Special analysis of ice-penetrating radar data shows the bottom of the ice over the valley is smoother and brighter than elsewhere in the area — tell-tale signs that the ice is floating and being eroded by the ocean.

“Now we know the ocean is melting ice in an area of the glacier that we thought was totally cut off before,” Greenbaum said. “Knowing this will improve predictions of ice melt and the timing of future glacier retreat.”
Apologies for reposting this link but I had not taken note of this exact aspect previously and it seems significant enough to keep in context and repeat.  That there is a channel three miles wide is astounding to me. Am anxious to know what predictions they might make from this.




Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on April 30, 2015, 08:06:43 PM
Am anxious to know what predictions they might make from this.

JMP,

As there appears to be a large number of parallels between potential collapse responses for the Thwaites Glacier Catchment Basin and the Totten Glacier Catchment Basin, I suggest that you review my discussions in: "Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe" at the first following link:

http://forum.arctic-sea-ice.net/index.php/topic,72.0.html (http://forum.arctic-sea-ice.net/index.php/topic,72.0.html)

See also:

http://forum.arctic-sea-ice.net/index.php/topic,21.0.html (http://forum.arctic-sea-ice.net/index.php/topic,21.0.html)

Best,
ASLR
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on May 01, 2015, 04:49:07 AM
"three-mile-wide seafloor valley"

Thwaites is ten times that ...
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 01, 2015, 10:17:16 AM
"three-mile-wide seafloor valley"

Thwaites is ten times that ...

While I do not have time to assemble a point by point comparison between the Thwaites and the Totten Catchment Basins; however, regarding the "three-mile-wide seafloor valley" that allows CDW access into the Totten gateway (and where there is a subglacial cavity beneath the grounded ice in this "three-mile-wide seafloor valley"), I was comparing this "seafloor valley" to the "trough" shown in the attached composite image of the Thwaites gateway; which also had a subglacial cavity beneath the grounded ice that was carved by warm CDW, before the 2012 "surge" of the Thwaites Ice Tongue infilled this former subglacial cavity in the Thwaites gateway "trough" (or seafloor valley).

I note also, that the formation of the Thwaites Ice Tongue indicates that "surges" of ice have moved out of this trough repeatedly in the past several hundred years; and I suspect that in the coming multiple decades that the ice in the Totten gateway "seafloor valley" may also "surge" repeatedly (which thins the glacial ice sufficiently that eventually icebergs will be able to float out of the Totten Catchment Basin that are created by Pollard et al style cliff failures and hydrofracturing, assuming that we reach early Pliocene conditions this century).
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on May 01, 2015, 01:07:12 PM
I was told David Pollard and colleague(s) are about to submit a 'high-profile paper on future changes'. I don't know how long it will take to be published and what the topic is, but it would be interesting if they applied the work for Pollard et al 2015 to the current situation at Totten (and the rest of AIS) and if they could make projections for the coming centuries. Keep an eye out (no idea if it would take weeks or months before publication).
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 01, 2015, 04:39:53 PM
As previously discussed in Reply #222 of the "Potential Collapse Scenario for the WAIS" thread, Pollard et al 2015 already considered SLR contribution due to hydrofracturing & ice cliff failures from all of the AIS (both the WAIS & the EAIS, under Pliocene conditions), as indicated in the attached image & associated caption (however the Pollard et al 2015 work does not consider the influence of the newly identified "three-mile-wide seafloor valley" subjected to advected CDW into the valley):

Pollard, D., R.M. DeConto and R.B. Alley (2015) "Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure", Earth Plan. Sci. Lett., 412, 112-121

http://www.sciencedirect.com/science/article/pii/S0012821X14007961 (http://www.sciencedirect.com/science/article/pii/S0012821X14007961)

Caption for the Image: "Ice distributions in a warm-climate simulation. The simulation starts from modern conditions, with a step-function change to a generic past warm climate applied at year 0. Atmospheric temperatures and precipitation are from a Regional Climate Model simulation with hot austral summer orbit, CO2=400ppmv, and ocean temperatures are increased uniformly by 2◦C above modern. Color scale: Grounded ice elevations, m. Pink scale: floating ice thicknesses, m. The run is initialized from a previous simulation equilibrated to modern climate (panel (a), 0 yr). Both new mechanisms (cliff failure and melt-driven hydrofracturing) are active."

It is conceivable that the paper that Lennart is referring to is the following (with the pdf now available behind a paywall):

Alley, R.B., S. Anandakrishnan. K. Christianson, H.J. Horgan, A. Muto, B.R. Parizek, D. Pollard and R.T. Walker (2015) "Oceanic forcing of ice-sheet retreat: West Antarctica and more", Ann. Rev. Earth Plan. Sci., 43, 7.1-7.25.

http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105344?journalCode=earth (http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105344?journalCode=earth)


Abstract: "Ocean-ice interactions have exerted primary control on the Antarctic Ice Sheet and parts of the Greenland Ice Sheet, and will continue to do so in the near future, especially through melting of ice shelves and calving cliffs. Retreat in response to increasing marine melting typically exhibits threshold behavior, with little change for forcing below the threshold but a rapid, possibly delayed shift to a reduced state once the threshold is exceeded. For Thwaites Glacier, West Antarctica, the threshold may already have been exceeded, although rapid change may be delayed by centuries, and the reduced state will likely involve loss of most of the West Antarctic Ice Sheet, causing >3 m of sea-level rise. Because of shortcomings in physical understanding and available data, uncertainty persists about this threshold and the subsequent rate of change. Although sea-level histories and physical understanding allow the possibility that ice-sheet response could be quite fast, no strong constraints are yet available on the worst-case scenario. Recent work also suggests that the Greenland and East Antarctic Ice Sheets share some of the same vulnerabilities to shrinkage from marine influence."

Expected final online publication date for the Annual Review of Earth and Planetary Sciences Volume 43 is May 30, 2015. Please see http://www.annualreviews.org/catalog/pubdates.aspx (http://www.annualreviews.org/catalog/pubdates.aspx) for revised estimates.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 01, 2015, 05:03:39 PM
For those who do not have access to Pollard et al (2015), I provide the two additional images from that paper that assumes Pliocene type forcing imposed on modern conditions.  While modern temperatures are not yet as high as Pliocene conditions, our current anthropogenic radiative forcing is already much higher (CO2-equivalent of over 485 ppm on April 1 2015, and rising rapidly) than those during the Pliocene and the Southern Ocean heat content is rising much more rapidly than that for the ocean at-large.  Furthermore, as stated in my last post, Pollard et al (2015) do not consider the recently identified "seafloor valley" in the Totten Gateway.

Finally, I note that while I said that there are a large number of parallels between Thwaites and Totten, I never said that the timing of their potential collapse scenarios were identical (but note that once combined cliff failure & hydrofracturing calving events occur, both gateways are tens of miles wide with regard to the potential float-out of calved icebergs).
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on May 01, 2015, 08:17:48 PM
There is a paper out by Harig and Simons doi:10.1016/j.epsl.2015.01.029, latest GRACE data

"Ignoring GIA model uncertainty, over the period 2003–2014, West Antarctica has been losing ice mass at a rate of −121 ± 8 Gt/yr and has experienced large acceleration of ice mass losses along the Amundsen Sea coast of −18 ± 5 Gt/yr^2 , doubling the mass loss rate in the past six years. The Antarctic Peninsula shows slightly accelerating ice mass loss, with larger accelerated losses in the southern half of the Peninsula. Ice mass gains due to snowfall in Dronning Maud Land have continued to add about half the amount of West Antarctica’s loss back onto the continent over the last decade. We estimate the overall mass losses from Antarctica since January 2003 at −92 ± 10 Gt/yr."
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on May 01, 2015, 08:45:44 PM
ASLR,
Thanks for pointing to Alley, Pollard et al 2015. That may be the paper that I was told to watch out for. We'll see.

You're right of course that Pollard et al 2015 already included Totten and the rest of EAIS. In that paper they also say:
"our study is not directly applicable to the future because of our step-function climate change, Pliocene-like climate, and homogeneous ocean warming."

So it seems they're wondering what projections a different study would give that would be more "directly applicable to the future", for example by including current orbital insolation, CO2 rising further beyond 400 ppm and more gradual ocean warming. Would that give the same rate of ice mass loss, or even faster, or maybe slower?
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on May 01, 2015, 09:12:36 PM
It seems Alley et al 2015 is not the paper I was told about. DeConto would be lead author and the paper is expected to be published coming fall or winter.
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on May 05, 2015, 07:54:23 PM
Pollard and DeConto on their 2015 paper with Alley and their upcoming paper on implications for the future:
http://www.theguardian.com/environment/planet-oz/2015/may/05/melting-antarctic-failure-to-cut-emissions-now-could-raise-worlds-oceans-by-several-metres (http://www.theguardian.com/environment/planet-oz/2015/may/05/melting-antarctic-failure-to-cut-emissions-now-could-raise-worlds-oceans-by-several-metres)

'David Pollard, of the Earth and Environmental Systems Institute at Penn State University, and co-author Professor Robert DeConto, of the University of Massachusetts, told me while it was “pretty clear” that their findings had implications for the future (to be explored in an upcoming paper by Pollard and DeConto) the study’s real focus was to better understand the past.'
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on May 05, 2015, 09:51:49 PM
This EGU-contribution by DeConto & Pollard should become the announced paper later this year:
http://meetingorganizer.copernicus.org/EGU2015/EGU2015-8104.pdf (http://meetingorganizer.copernicus.org/EGU2015/EGU2015-8104.pdf)

It says:
"Modeling Antarctica’s contribution to sea-level rise during the Last Interglacial and the future: differing roles of oceanic versus atmospheric warming

A hybrid ice sheet-shelf model with freely migrating grounding lines is extended by accounting for surface meltwater enhancement of ice shelf calving; and the structural stability of thick, marine-terminating (tidewater) grounding lines. The ice model is coupled to a high-resolution atmospheric model with imposed and simulated ocean temperatures, and applied to past and future climate scenarios. When forced by greenhouse gas and orbital forcing representing the Last Interglacial (LIG; 130 to 115ka), the model simulates an Antarctic global mean sea-level contribution of up to +5m, in agreement with observed estimates. Most of the ice sheet response is driven by circum-Antarctic oceanic warming, rather than atmospheric warming, implying meridional overturning ocean dynamics were an important factor in the timing of Antarctic ice sheet retreat. A long, coupled climate-icesheet simulation through the entire LIG shows that two peaks in sea level (early and late in the interglacial) are possible, but depend on the timing of Southern Ocean warming relative to local insolation maxima.

Using the same atmosphere and ice-model physics used in the LIG simulations, future simulations are run following RCP2.6, 4.5, and 8.5 greenhouse-gas scenarios extended to the year 2500 CE. Ocean temperatures in each scenario are prescribed from offline simulations using the NCAR CCSM4 with 0.5º ocean resolution. As expected, the magnitude and rate of Antarctic ice sheet retreat are highly dependent on which future greenhouse gas scenario is followed, but even the lower emission scenarios produce an Antarctic contribution of several meters within the next several centuries. Once atmospheric CO2 concentrations exceed 2x preindustrial levels, we find that hydrofracturing by surface melt on ice shelves can trigger large-scale ice sheet retreat, regardless of circum-Antarctic ocean warming. Hence, unlike the LIG, atmospheric (not ocean) warming has the potential to become the primary mechanism driving future retreat of the Antarctic ice sheet. In simulations without atmospheric warming, we find small amounts of ocean warming can still produce large-scale retreat of the West Antarctic Ice Sheet, although the timescale of ocean-driven retreat is slower than atmospherically driven retreat.

In sum, these results suggest past Pleistocene episodes of Antarctic ice loss were primarily driven by Southern Ocean warming, which in itself has serious implications for future commitment to sea-level rise given current rates of ocean heat uptake. However, we also find that atmospheric warming and surface melt on ice shelves (driving hydrofracturing and ice shelf breakup) will take over as the dominant driver of future Antarctic ice loss if greenhouse gas emissions continue unabated, making the LIG and other Pleistocene interglacials poor mechanistic analogues for future sea-level rise."

So they don't say here how fast ice-sheet retreat is in their higher emission scenarios. Maybe they did in their presentation?
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 05, 2015, 10:13:28 PM
Lennart,

Thank you very much for the DeConto & Pollard EGU-2015 reference.  The following quote from the abstract indicates that once the effective CO2 equivalent concentration gets to 560ppm; hydrofracturing will begin in the WAIS, and I assume that this model assumes that ECS is about 3.1C.  Thus as ECS may be 4.1C, and as the current CO2 equivalent is about 485ppm, and as the effective CO2 equivalent is currently over 425ppm; it seems plausible to me that such hydrofracturing could begin in the WAIS between 2030 and 2040, depending on how fast we clean-up aerosol emissions (a negative forcing) and how fast we reduce GHG emissions.

Quote: "Once atmospheric CO2 concentrations exceed 2x preindustrial levels, we find that hydrofracturing by surface melt on ice shelves can trigger large-scale ice sheet retreat, regardless of circum-Antarctic ocean warming."

Best,
ASLR
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on May 05, 2015, 10:25:05 PM
Yes. And this one by Gasson, DeConto and Pollard looks interesting too:
http://meetingorganizer.copernicus.org/EGU2015/EGU2015-10742.pdf (http://meetingorganizer.copernicus.org/EGU2015/EGU2015-10742.pdf)

"Miocene Antarctic ice sheet simulations using an asynchronously coupled RCM-ISM

Both direct and indirect evidence suggests that there was fluctuation of the Antarctic ice sheet over the past 34 million years. For example, sediment provenance studies suggest retreat into the Wilkes Subglacial Basin during the Pliocene and possibly earlier, in the Miocene. Indirect evidence, such as from the oxygen isotope record from benthic formanifera, suggests fluctuations in ice volume exceeding 50 m in sea level equivalence during the Miocene. Ice sheet models have struggled to achieve such large-scale retreat under the relatively modest atmospheric CO2 concentrations suggested by proxy records.

Attempts to resolve this data-model conflict have recently focused on simulating retreat into the marine basins of Antarctica, with retreat into the Wilkes Subglacial Basin during the Pliocene simulated in 2 recent ice sheet modeling studies using different approaches. Although retreat into the subglacial basins may explain approximately 20 m of ice volume fluctuation from Antarctica, it is still lower than the magnitudes suggested by the oxygen isotope record for the Miocene.

Here we focus on improving simulation of the Antarctic ablation zone by using an asynchronously coupled RCM to provide climate forcing to an ice sheet model. We use a GCM with a Miocene paleo-geography to provide boundary forcing for the RCM, with atmospheric CO2 at various concentrations. In previous simulations there was limited retreat of the ice sheet away from the continental margin, due to a strong hysteresis mechanism. In these asynchronous simulations there is increased retreat of the Antarctic ice sheet, with continental sectors retreating away from the continental margin. This results in a greater overall decrease in ice volume than for non-asynchronously coupled simulations."
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on May 05, 2015, 10:32:15 PM
There's more here for those interested:
http://meetingorganizer.copernicus.org/EGU2015/session/18158 (http://meetingorganizer.copernicus.org/EGU2015/session/18158)

Next year Neven will need some help in following all these sessions :)
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on May 05, 2015, 10:48:24 PM
Also see Hansen's most recent comments:
http://www.climatecodered.org/2015/05/hansen-says-its-crazy-to-think-that-2.html (http://www.climatecodered.org/2015/05/hansen-says-its-crazy-to-think-that-2.html)

"The paleoclimate evidence indicates the ice sheets are much more sensitive than the glaciologist, the modellers of ice sheets have indicated and furthermore we now have satellite data over the last 12 years that confirms that ice sheet disintegration is a non-linear process that should not have been surprising, and I have been saying that for 10 years, but now this satellite data confirms that.

The ice sheets are losing mass faster and faster with a doubling the of about 10 years. If that continues, we would get sea-level rises of several metres within 40 to 50 years.

The consequences are almost unthinkable. It would mean that all coastal cities would become dysfunctional, some parts of the cities would still be sticking above the water but they would not be habitable, so the economic implications are incalculable. We really cannot go down that path, this is an issue of intergenerational injustice, it's a moral issue…"
Title: Re: EAIS Contributions to SLR by 2100
Post by: solartim27 on June 04, 2015, 02:13:39 AM
Short article on the ICECAP project at Totten Glacier:

http://skepticalscience.com/melting-moments-look-under-east-antarctica-biggest-glacier.html (http://skepticalscience.com/melting-moments-look-under-east-antarctica-biggest-glacier.html)
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on June 10, 2015, 07:49:21 PM
Rignot on potential EAIS ice loss:
http://climatestate.com/2015/06/09/eric-rignot-observations-suggest-that-ice-sheets-and-glaciers-can-change-faster-sooner-and-in-a-stronger-way-than-anticipated/ (http://climatestate.com/2015/06/09/eric-rignot-observations-suggest-that-ice-sheets-and-glaciers-can-change-faster-sooner-and-in-a-stronger-way-than-anticipated/)

"Machens: There are signs that East Antarctica might not be that stable, as previously thought. Does this mean we have to revise figures?

Rignot: East Antarctica has marine-based sectors like West Antarctica but few of them have retrograde beds, i.e. beds that get deeper inland, so they are more immune to rapid collapse yet they remain serious concerns for sea level rise because they hold together far more ice than West Antarctica. At present, numerical models are simply unable to deal with East Antarctica for a variety of reasons including poor model constraints and insufficient understanding of key processes, e.g. circulation of warm water around the periphery and its impact on ice shelf melt."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on July 07, 2015, 02:48:40 AM
The linked reference discusses the paleo stability (instability) of the Wilkes Land continental margin (EAIS) in response to the early Pliocene ocean warming (which are conditions that the Earth could approximately replicate before 2100):

Melissa A. Hansen, Sandra Passchier, Boo-Keun Khim, Buhan Song &Trevor Williams (2015), "Threshold behavior of a marine-based sector of the East Antarctic Ice Sheet in response to early Pliocene ocean warming", Paleoceanography, DOI: 10.1002/2014PA002704

http://onlinelibrary.wiley.com/doi/10.1002/2014PA002704/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2014PA002704/abstract)

Abstract: "We investigate the stability of the East Antarctic Ice Sheet (EAIS) on the Wilkes Land continental margin, Antarctica, utilizing a high-resolution record of ice-rafted debris (IRD) mass accumulation rates (MAR) from Integrated Ocean Drilling Program Site U1359. The relationship between orbital variations in the IRD record and climate drivers was evaluated to capture changes in the dynamics of a marine-based ice sheet in response to early Pliocene warming. Three IRD MAR excursions were observed and confirmed via scanning electron microscope microtextural analysis of sand grains. Time series analysis of the IRD MAR reveals obliquity-paced expansions of the ice sheet to the outer shelf prior to ~4.6 Ma. A decline in the obliquity and a transition into a dominant precession response of IRD MAR occur at ~4.6 Ma along with a decline in the amplitude of IRD MAR maxima to low background levels between ~4.0 and ~3.5 Ma. We speculate that as sea surface temperatures began to peak above 3°C during the early Pliocene climatic optimum, the ice shelves thinned, leading to a greater susceptibility to precession-forced summer insolation and the onset of persistent retreat of a marine-based portion of the EAIS."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on August 04, 2015, 06:43:20 PM
The linked reference uses the Roi Baudouin Ice Shelf (RBIS) in East Antarctica as an example (see the attached image) of how to use satellites to monitor basal ice channels in Antarctic ice shelves.  This information could become vital for predicting possible future major ice shelf calving events, if we continue down a warm pathway for anthropogenic forcing, this century:

Drews R., 2015. Evolution of ice-shelf channels in Antarctic ice shelves, The Cryosphere, 9, 1169-1181, doi:10.5194/tc-9-1169-2015

http://www.the-cryosphere.net/9/1169/2015/tc-9-1169-2015.html (http://www.the-cryosphere.net/9/1169/2015/tc-9-1169-2015.html)

Abstract: "Ice shelves buttress the continental ice flux and mediate ice–ocean interactions. They are often traversed by channels in which basal melting is enhanced, impacting ice-shelf stability. Here, channel evolution is investigated using a transient, three-dimensional full Stokes model and geophysical data collected on the Roi Baudouin Ice Shelf (RBIS), Antarctica. The modeling confirms basal melting as a feasible mechanism for channel creation, although channels may also advect without melting for many tens of kilometers. Channels can be out of hydrostatic equilibrium depending on their width and the upstream melt history. Inverting surface elevation for ice thickness using hydrostatic equilibrium in those areas is erroneous, and corresponding observational evidence is presented at RBIS by comparing the hydrostatically inverted ice thickness with radar measurements. The model shows that channelized melting imprints the flow field characteristically, which can result in enhanced horizontal shearing across channels. This is exemplified for a channel at RBIS using observed surface velocities and opens up the possibility to classify channelized melting from space, an important step towards incorporating these effects in ice–ocean models."
Title: Re: EAIS Contributions to SLR by 2100
Post by: solartim27 on August 20, 2015, 03:35:45 AM
Should we be concerned about this sudden notch in Totten?  Here is April 18, then Aug 17, and 18th.  I know the sea ice will blow around a lot, but I haven't seen anything like the notch in that area before.  It's about 10 km across, scale bar is in the corner.
Title: Re: EAIS Contributions to SLR by 2100
Post by: solartim27 on August 20, 2015, 03:57:39 AM
I had saved a Polar view from Mar 16th, so here that is with the one for Aug 17th.  I couldn't get the scales to match up, but you get the idea.  The berg that shows up in the lower left corner is not a new calving, it's been blowing around down there for a while, not sure where it's from.
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on August 20, 2015, 05:13:20 AM
wind driver polynya, i think. AABW forms there
Title: Re: EAIS Contributions to SLR by 2100
Post by: solartim27 on August 20, 2015, 06:01:20 AM
The notch area is also on the Sentinel shot from July 22, but not visible on the last clear Worldview shot from May 2.  My impression was the dark line on Worldview was the demarcation for the ice shelf, as opposed to seasonal sea ice.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on August 20, 2015, 04:48:29 PM
wind driver polynya, i think. AABW forms there

solartim27,
Sidd is most likely correct that what you are showing is most likely wind-driven polynyas, that typically generate AABW and thus would normally stabilize Totten by delivering cold saline water near its grounding line.  However, I believe that the actual situation is much more complicated and chaotic, due to the growing potential for the advection of warm CDW into the grounding line area.

The linked NASA article (see also discussion in replies 49 & 50) finds that the reducing salinity of the ocean water (due to a reduction in the number of local polynas) around the Totten & Moscow U. Ice Shelves is leading to melting and thinning of the Totten Glacier (see the link for further explanations):

http://www.jpl.nasa.gov/news/news.php?release=2013-352 (http://www.jpl.nasa.gov/news/news.php?release=2013-352)


The caption for the first attached annotated Aqua image from Sept 25 2013 is:

"This image shows the Totten Glacier ice shelf in East Antarctica (the wrinkled white area at top left) on Sept. 25, 2013. Two large open-water polynyas appear on the sea ice below and to the right of the shelf, as well as several smaller ones. The open-water areas are bright black. The stippled diagonal line from lower left to upper right is the outer edge of the sea ice, with cloud cover to the right of that line. The image is from the Moderate Resolution Imaging Spectroradiometer instrument on NASA's Aqua satellite. Credit: NASA"


The second attached image is from the Modis Terra satellite on Feb 22 2014 and is zoomed in on the Totten Glacier and Ice Shelf.  This image shows a calving event from the Totten Ice Shelf (note the sea ice is retreated off of the ice shelf face in this image); possibly associate with the ocean-ice advection cited in the NASA news article.

Extract: "The team then examined a data set of passive microwave measurements from the Defense Meteorological Satellite Program. These showed that in the latter part of the study period, the extent of polynyas (and therefore the production of cold brine) decreased significantly. ICESat observations showed that at the same time, the thinning of Totten Glacier increased, as the team's hypothesis predicted it would.

 If there are more winters with reduced polynya extents, Khazender points out, the cavity under Totten can fill with warmer ocean water rather than cold brine. "If that happens, the glacier's flow could be significantly destabilized, causing it to discharge even more ice into the ocean," he said."

To summarize, to me it appears that there are multiple mechanisms changing simultaneously around Antarctica and the Southern Ocean, with changes in AABW, CDW, meltwater, wind patterns, advective patterns, etc., which result in changing sea ice patterns, changing polynyas patterns and changing local wind patterns.

If you want a free access version of the Purkey & Johnson, 2013 (as well as other Johnson papers), you can find it (them) here, so that you can learn about the changing trends for the AABW, CDW, meltwater etc. for the Southern Ocean:

http://www.pmel.noaa.gov/people/gjohnson/publications.html (http://www.pmel.noaa.gov/people/gjohnson/publications.html)

Best,
ASLR
Title: Re: EAIS Contributions to SLR by 2100
Post by: BornFromTheVoid on August 22, 2015, 02:21:06 PM
https://www.reddit.com/r/science/comments/3hylyw/science_ama_series_we_are_living_in_concordia/ (https://www.reddit.com/r/science/comments/3hylyw/science_ama_series_we_are_living_in_concordia/)


Science AMA Series: We are living in Concordia station, Antarctica, researching glaciology, climate and physiology. We haven’t seen the Sun for 4 months and 4 months to go before fresh supplies are flown in. The temperature outside is –67.8°C. AMA!

We are based at the French-Italian research station Concordia on the east high Antarctic plateau (75°S, 123°E, 3233m). It is one of the remotest, coldest, driest places on Earth, we are 1200 km from the coast and our nearest neighbour is 600 km away: the Russian station Vostok. The landscape is an immense white, flat surface of compacted snow extending 1000 km in all directions. The snow and ice on which we walk is more than 3 km thick. Living here is like living on another planet, ‘Planet Concordia’ or ‘White Mars’. During the nine months of winter from February to November, the station is completely isolated from the rest of the world. No plane or vehicle can reach us, even in an emergency as the harsh weather conditions make all travel impossible. We have experienced temperatures down to –80°C and three months of complete darkness. The multicultural crew is consists of 13 people: seven for logistics and six scientists. We are five Italians, one Swiss, one English and six French. This year we are three women and ten men from 24 to 56 years old. We must rely on our own skills and teamwork while being prepared to face any kind of emergency through training, fire, rescue and medical exercises. Antarctica is the largest, most extreme, multi-disciplinary, open-air scientific laboratory that helps us understand the mechanisms that regulate our planet, its climate, its history and offers a platform to observe and understand the structure of the universe, as well as charting the adaptation of humans to harsh environments. Thanks to the Antarctic Treaty, nations worldwide collaborate peacefully with respect for this environment in the name of science. We are one of very few stations at the heart of the Antarctic continent, so Concordia stands as an important node in the Earth Observatory Grid, for fields such as meteorology, seismology, geomagnetism and atmospheric chemistry. Lorenzo Moggio: 30 years old, Italian physicist, research fellow at the Bologna Institute of Atmospheric Sciences and Climate of the Italian National Research Council. This is my second winter spent at Concordia, I was here in 2010 as well.
Giampietro Casasanta: 35 years old, Italian physicist with a PhD in Remote Sensing and research fellow at the Rome Bologna Institute of Atmospheric Sciences and Climate of the Italian National Research Council. I am in charge of the Italian glaciology and remote sensing experiments.
Our tasks are to maintain and assure the scientific instruments work, retrieve the data run a first analysis and send it to Europe on a daily basis. We measure radiative balances at Earth’s surface, Meterological variables, optical and physical properties of aerosols, properties of clouds. We have at our disposal broadband and spectral radiometers in the shortwave, longwave and ultraviolet part of the electromagnetic spectrum, particle counters and sizers, lidar, sodar, sonic anemometers, automatic weather stations and sounding stations equipped with: barometers, anemometers, thermo-hygrometers, GPS and radio transmitters/receivers. Beth Healey: British medical doctor. I am running studies for the European Space Agency on the crew and myself to see how we adapt to living in this extreme environment. Our nine-month isolation living completely cut off from the world with low air pressure is similar in many ways to the stress astronauts will endure during a long spaceflight. I am running experiments on morale, eyesight, blood pressure and even searching for new life! http://www.esa.int/concordia (http://www.esa.int/concordia)[1] We will be back at 1pm ET to answer your questions, Ask Us Anything about life here and the science we do!
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 14, 2015, 10:08:10 PM
The attached Aqua image from Sept 14 2015 shows that the polynyas at Totten have gotten larger (which might possibly be associated with the advection of warm CDW into the area, or could be strictly associated with winds).
Title: Re: EAIS Contributions to SLR by 2100
Post by: solartim27 on September 15, 2015, 03:17:27 AM
Wouldn't this be more breakup of the floating ice shelf in front of the glacier, since it is within the grey line that comes up with the coastline overlay?  I was willing to accept the last wind burst I had posted about was a polyna, since I had found comparable retreat in previous years.  I believe this is a new line of retreat.  I'll try to post a gif of what I had seen later.

When do the coastlines get updated?  Hardly anything matches.  I can see how you don't want to be adjusting for seasonal advance and retreat, but there are some areas that have been off from the earliest images I can access.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 15, 2015, 03:36:13 AM
Wouldn't this be more breakup of the floating ice shelf in front of the glacier, since it is within the grey line that comes up with the coastline overlay?  I was willing to accept the last wind burst I had posted about was a polyna, since I had found comparable retreat in previous years.  I believe this is a new line of retreat.  I'll try to post a gif of what I had seen later.

When do the coastlines get updated?  Hardly anything matches.  I can see how you don't want to be adjusting for seasonal advance and retreat, but there are some areas that have been off from the earliest images I can access.

I am a bit tied-up to tell if major calving has occurred, or not.  You might want to check Google Earth as it sometimes shows the grounding line.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on September 15, 2015, 09:43:43 PM
Here is an image of Totten Glacier ice flow velocities from a couple of years ago.  This could support the concept that the Totten Ice Shelf has calved since then.
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on October 26, 2015, 09:05:25 PM
Chris Mooney on new paper on vulnerability of Totten (Aurora) basin:
http://www.washingtonpost.com/news/energy-environment/wp/2015/10/26/east-antarcticas-biggest-glacier-is-melting-from-below-study-confirms/ (http://www.washingtonpost.com/news/energy-environment/wp/2015/10/26/east-antarcticas-biggest-glacier-is-melting-from-below-study-confirms/)

Or actually it's not such a new paper, of March this year, by Greenbaum et al.
Title: Re: EAIS Contributions to SLR by 2100
Post by: ChadGreene on October 27, 2015, 06:17:44 PM
Totten's calving front has undergone some minor seasonal and interannual changes over the past 15 years but there appears to be no major secular trend in the coast line.  Here are MODIS images from February of 2001 and 2015:

ftp://sidads.colorado.edu/pub/DATASETS/ICESHELVES/modis_iceshelf_archive/sabri/images/sabri_2001048_0050_modis_ch02.png

ftp://sidads.colorado.edu/pub/DATASETS/ICESHELVES/modis_iceshelf_archive/sabri/images/sabri_2015263_0040_modis_ch02.png
Title: Re: EAIS Contributions to SLR by 2100
Post by: solartim27 on October 29, 2015, 09:35:08 PM
Here is a look at Totten from Sep 22 to Oct 26.  No major changes, but it does look like it could be interesting to watch over the summer.
Title: Re: EAIS Contributions to SLR by 2100
Post by: Lennart van der Linde on November 27, 2015, 03:27:49 PM
Jones et al 2015 on Rapid Holocene thinning of an East Antarctic outlet glacier driven by marine ice sheet instability:
http://www.nature.com/ncomms/2015/151126/ncomms9910/full/ncomms9910.html (http://www.nature.com/ncomms/2015/151126/ncomms9910/full/ncomms9910.html)

Abstract
Outlet glaciers grounded on a bed that deepens inland and extends below sea level are potentially vulnerable to ‘marine ice sheet instability’. This instability, which may lead to runaway ice loss, has been simulated in models, but its consequences have not been directly observed in geological records. Here we provide new surface-exposure ages from an outlet of the East Antarctic Ice Sheet that reveal rapid glacier thinning occurred approximately 7,000 years ago, in the absence of large environmental changes. Glacier thinning persisted for more than two and a half centuries, resulting in hundreds of metres of ice loss. Numerical simulations indicate that ice surface drawdown accelerated when the otherwise steadily retreating glacier encountered a bedrock trough. Together, the geological reconstruction and numerical simulations suggest that centennial-scale glacier thinning arose from unstable grounding line retreat. Capturing these instability processes in ice sheet models is important for predicting Antarctica’s future contribution to sea level change.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on November 27, 2015, 05:22:30 PM
Jones et al 2015 on Rapid Holocene thinning of an East Antarctic outlet glacier driven by marine ice sheet instability:

Great catch (a valuable reference); however, I don't think that this example fully represents key aspects of more dynamic MISI as it does not appear to fully demonstrate either cliff failures and hydrofracturing together with active advection of warm CDW to the grounding line.  This indicates to me that scientists like Pollard would be better off calibrating their (his) MISI model against the Holocene Optimum case for the Jakobshavn Glacier (see Reply # 171 in the "Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe" thread).
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on January 04, 2016, 05:13:47 PM
The linked (open access) reference examines two East Antarctic ice cores focused on improving our understanding of the timing and the duration of the MIS 5 event.  Modeling the MIS 5 correctly is important to future climate model estimates of EAIS and WAIS contributions to SLR:

Fujita, S., Parrenin, F., Severi, M., Motoyama, H., and Wolff, E. W.: Volcanic synchronization of Dome Fuji and Dome C Antarctic deep ice cores over the past 216 kyr, Clim. Past, 11, 1395-1416, doi:10.5194/cp-11-1395-2015, 2015.

http://www.clim-past.net/11/1395/2015/cp-11-1395-2015.html (http://www.clim-past.net/11/1395/2015/cp-11-1395-2015.html)
http://www.clim-past.net/11/1395/2015/cp-11-1395-2015.pdf (http://www.clim-past.net/11/1395/2015/cp-11-1395-2015.pdf)

Abstract. Two deep ice cores, Dome Fuji (DF) and EPICA Dome C (EDC), drilled at remote dome summits in Antarctica, were volcanically synchronized to improve our understanding of their chronologies. Within the past 216 kyr, 1401 volcanic tie points have been identified. DFO2006 is the chronology for the DF core that strictly follows O2 / N2 age constraints with interpolation using an ice flow model. AICC2012 is the chronology for five cores, including the EDC core, and is characterized by glaciological approaches combining ice flow modelling with various age markers. A precise comparison between the two chronologies was performed. The age differences between them are within 2 kyr, except at Marine Isotope Stage (MIS) 5. DFO2006 gives ages older than AICC2012, with peak values of 4.5 and 3.1 kyr at MIS 5d and MIS 5b, respectively. Accordingly, the ratios of duration (AICC2012 / DFO2006) range between 1.4 at MIS 5e and 0.7 at MIS 5a. When making a comparison with accurately dated speleothem records, the age of DFO2006 agrees well at MIS 5d, while the age of AICC2012 agrees well at MIS 5b, supporting their accuracy at these stages. In addition, we found that glaciological approaches tend to give chronologies with younger ages and with longer durations than age markers suggest at MIS 5d–6. Therefore, we hypothesize that the causes of the DFO2006–AICC2012 age differences at MIS 5 are (i) overestimation in surface mass balance at around MIS 5d–6 in the glaciological approach and (ii) an error in one of the O2 / N2 age constraints by ~ 3 kyr at MIS 5b. Overall, we improved our knowledge of the timing and duration of climatic stages at MIS 5. This new understanding will be incorporated into the production of the next common age scale. Additionally, we found that the deuterium signals of ice, δDice, at DF tends to lead the one at EDC, with the DF lead being more pronounced during cold periods. The lead of DF is by +710 years (maximum) at MIS 5d, −230 years (minimum) at MIS 7a and +60 to +126 years on average.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on February 19, 2016, 02:12:33 AM
I believe that the linked reference is relevant to the EAIS, the GIS, and portions of the WAIS (not including the ASE area), and the reference presents field evidence from the Laurentide Ice Sheet from 22,000 to 7,000 years ago, showing that ice stream flow did not progressively destabilize the larger ice sheet, but rather that ice mass loss proceeded at a relatively steady rate.

C. R. Stokes, M. Margold, C. D. Clark & L. Tarasov (18 February 2016), "Ice stream activity scaled to ice sheet volume during Laurentide Ice Sheet deglaciation", Nature, Volume: 530, Pages: 322–326, doi:10.1038/nature16947

http://www.nature.com/nature/journal/v530/n7590/full/nature16947.html (http://www.nature.com/nature/journal/v530/n7590/full/nature16947.html)

Abstract: "The contribution of the Greenland and West Antarctic ice sheets to sea level has increased in recent decades, largely owing to the thinning and retreat of outlet glaciers and ice streams. This dynamic loss is a serious concern, with some modelling studies suggesting that the collapse of a major ice sheet could be imminent or potentially underway in West Antarctica, but others predicting a more limited response. A major problem is that observations used to initialize and calibrate models typically span only a few decades, and, at the ice-sheet scale, it is unclear how the entire drainage network of ice streams evolves over longer timescales. This represents one of the largest sources of uncertainty when predicting the contributions of ice sheets to sea-level rise. A key question is whether ice streams might increase and sustain rates of mass loss over centuries or millennia, beyond those expected for a given ocean–climate forcing. Here we reconstruct the activity of 117 ice streams that operated at various times during deglaciation of the Laurentide Ice Sheet (from about 22,000 to 7,000 years ago) and show that as they activated and deactivated in different locations, their overall number decreased, they occupied a progressively smaller percentage of the ice sheet perimeter and their total discharge decreased. The underlying geology and topography clearly influenced ice stream activity, but—at the ice-sheet scale—their drainage network adjusted and was linked to changes in ice sheet volume. It is unclear whether these findings can be directly translated to modern ice sheets. However, contrary to the view that sees ice streams as unstable entities that can accelerate ice-sheet deglaciation, we conclude that ice streams exerted progressively less influence on ice sheet mass balance during the retreat of the Laurentide Ice Sheet."


See also:
http://www.csmonitor.com/Science/2016/0218/Are-glacial-ice-streams-contributing-to-the-rise-of-ocean-levels (http://www.csmonitor.com/Science/2016/0218/Are-glacial-ice-streams-contributing-to-the-rise-of-ocean-levels)
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on March 24, 2016, 05:02:52 PM
The linked reference presents satellite information about Totten from 1996 to 2013, which shows that while the grounding line for the glacier is retreating rapidly, there is no imminent danger of marine glacier instability.  The images come from the second linked document because it is an open access source to the Geophy. Res. Lett. paywall for this research:

Li, X., E. Rignot, M. Morlighem, J. Mouginot, and B. Scheuchl (2015), Grounding Line Retreat of Totten
Glacier, East Antarctica 1996 to 2013, Geophys. Res. Lett., 42, doi: 10.1002/2015GL065701.

http://onlinelibrary.wiley.com/doi/10.1002/2015GL065701/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2015GL065701/abstract)

Abstract: "Totten Glacier, East Antarctica, a glacier that holds a 3.9 m sea level change equivalent, has thinned and lost mass for decades. We map its grounding line positions in 1996 and 2013 using differential radar interferometry (InSAR) data and develop precise, high-resolution topographies of its ice surface and ice draft using NASA Operation IceBridge data, InSAR data, and a mass conservation method. We detect a 1 to 3 km retreat of the grounding line in 17 years. The retreat is asymmetrical along a two-lobe pattern, where ice is only grounded a few 10 m above sea level, or ice plain, which may unground further with only modest amounts of ice thinning. The pattern of retreat indicates ice thinning of 12 m in 17 years or 0.7±0.1 m/yr at the grounding line on average. Sustained thinning will cause further grounding line retreat but may not be conducive to a marine instability."

See also:
http://www.wmo.int/pages/prog/sat/meetings/documents/PSTG-5_Doc_13-01_BScheuchl-Ice-Sheets-Final.pdf (http://www.wmo.int/pages/prog/sat/meetings/documents/PSTG-5_Doc_13-01_BScheuchl-Ice-Sheets-Final.pdf)

Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 19, 2016, 04:39:04 PM
With a hat tip to Adam Ash, I provide the linked reference that indicates that Totten is closer to collapse than previously realized:

J. S. Greenbaum, D. D. Blankenship, D. A. Young, T. G. Richter, J. L. Roberts, A. R. A. Aitken, B. Legresy, D. M. Schroeder, R. C. Warner, T. D. van Ommen & M. J. Siegert  (2015), "Ocean access to a cavity beneath Totten Glacier in East Antarctica", Nature Geoscience, Volume: 8, Pages: 294–298, doi:10.1038/ngeo2388


http://www.nature.com/ngeo/journal/v8/n4/full/ngeo2388.html (http://www.nature.com/ngeo/journal/v8/n4/full/ngeo2388.html)


Abstract: "Totten Glacier, the primary outlet of the Aurora Subglacial Basin, has the largest thinning rate in East Antarctica. Thinning may be driven by enhanced basal melting due to ocean processes, modulated by polynya activity. Warm modified Circumpolar Deep Water, which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the nearby continental shelf beneath 400 to 500 m of cool Antarctic Surface Water. Here we derive the bathymetry of the sea floor in the region from gravity and magnetics data as well as ice-thickness measurements. We identify entrances to the ice-shelf cavity below depths of 400 to 500 m that could allow intrusions of warm water if the vertical structure of inflow is similar to nearby observations. Radar sounding reveals a previously unknown inland trough that connects the main ice-shelf cavity to the ocean. If thinning trends continue, a larger water body over the trough could potentially allow more warm water into the cavity, which may, eventually, lead to destabilization of the low-lying region between Totten Glacier and the similarly deep glacier flowing into the Reynolds Trough. We estimate that at least 3.5 m of eustatic sea level potential drains through Totten Glacier, so coastal processes in this area could have global consequences."

See also:
http://www.abc.net.au/news/2016-05-19/warning-on-tipping-point-for-east-antarctic-glacier/7425362 (http://www.abc.net.au/news/2016-05-19/warning-on-tipping-point-for-east-antarctic-glacier/7425362)

Extract: "The Totten Glacier in East Antarctica has an unstable area that could collapse and contribute to more than two metres of sea level rise beyond what is generally predicted if climate change remains unchecked, researchers say."
Title: Re: EAIS Contributions to SLR by 2100
Post by: crandles on May 19, 2016, 06:16:07 PM
BBC says
Quote
Scientists tell the journal Nature that should the front of the glacier retreat about 150km from its current position, it will then enter a runaway reversal that takes it 200-250km further inland.

http://www.bbc.co.uk/news/science-environment-36327250 (http://www.bbc.co.uk/news/science-environment-36327250)
So they don't seem to be pushing this as imminent even if 0.5m thinning a year does sound like quite a fast rate of thinning.

Still the more potential unstable situations there are, the more reason to take precautionary measures.
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on May 19, 2016, 07:36:04 PM
The BBC reference is to Aitken(2016) doi:10.1038/nature17447
Nice paper with discussion of geology under the ice, and some carefully argued paleo detail.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 19, 2016, 07:58:54 PM
The BBC reference is to Aitken(2016) doi:10.1038/nature17447
Nice paper with discussion of geology under the ice, and some carefully argued paleo detail.

As a public service, I provide the following information on the reference cited by sidd & indirectly by crandles:

A. R. A. Aitken, J. L. Roberts, T. D. van Ommen, D. A. Young, N. R. Golledge, J. S. Greenbaum, D. D. Blankenship & M. J. Siegert (19 May 2016), "Repeated large-scale retreat and advance of Totten Glacier indicated by inland bed erosion", Nature, Volume: 533, Pages: 385–389, doi:10.1038/nature17447


http://www.nature.com/nature/journal/v533/n7603/full/nature17447.html (http://www.nature.com/nature/journal/v533/n7603/full/nature17447.html)


Abstract: "Climate variations cause ice sheets to retreat and advance, raising or lowering sea level by metres to decametres. The basic relationship is unambiguous, but the timing, magnitude and sources of sea-level change remain unclear; in particular, the contribution of the East Antarctic Ice Sheet (EAIS) is ill defined, restricting our appreciation of potential future change. Several lines of evidence suggest possible collapse of the Totten Glacier into interior basins during past warm periods, most notably the Pliocene epoch, causing several metres of sea-level rise. However, the structure and long-term evolution of the ice sheet in this region have been understood insufficiently to constrain past ice-sheet extents. Here we show that deep ice-sheet erosion—enough to expose basement rocks—has occurred in two regions: the head of the Totten Glacier, within 150 kilometres of today’s grounding line; and deep within the Sabrina Subglacial Basin, 350–550 kilometres from this grounding line. Our results, based on ICECAP aerogeophysical data, demarcate the marginal zones of two distinct quasi-stable EAIS configurations, corresponding to the ‘modern-scale’ ice sheet (with a marginal zone near the present ice-sheet margin) and the retreated ice sheet (with the marginal zone located far inland). The transitional region of 200–250 kilometres in width is less eroded, suggesting shorter-lived exposure to eroding conditions during repeated retreat–advance events, which are probably driven by ocean-forced instabilities. Representative ice-sheet models indicate that the global sea-level increase resulting from retreat in this sector can be up to 0.9 metres in the modern-scale configuration, and exceeds 2 metres in the retreated configuration."

See also:
http://phys.org/news/2016-05-scientists-extensive-ice-loss-huge.html (http://phys.org/news/2016-05-scientists-extensive-ice-loss-huge.html)

Extract: "Current rates of climate change could trigger instability in a major Antarctic glacier, ultimately leading to more than 2m of sea-level rise.


By studying the history of Totten's advances and retreats, researchers have discovered that if climate change continues unabated, the glacier could cross a critical threshold within the next century, entering an irreversible period of very rapid retreat."
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on May 19, 2016, 10:52:44 PM
After a pleasurable hour or two reading the Aitken paper, i realize it is quite a bold and magisterial work, using a very sophisticated gravitational model, an ice sheet (PISM) model, and several different airborne and paleo data sources. I am unqualified on the geology, so i have consulted a geologist, and i look forward to her thoughts. PISM does not yet include cliff instability and hydrofracture as far as i know, but even so, the broad thesis that the sector behind Totten is unstable and has retreated quickly in the past is quite convincing.

Certainly a paper to read and reread carefully.

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on May 26, 2016, 05:38:29 PM
Scribbler has a nice article on Totten Glacier:

https://robertscribbler.com/2016/05/25/tottering-totten-and-the-coming-multi-meter-sea-level-rise/

Extract: "Totten Glacier… has the largest thinning rate in East Antarctica. Thinning may be driven by enhanced basal melting… Warm modified Circumpolar Deep Water, which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the nearby continental shelf beneath 400 to 500 m of cool Antarctic Surface Water…We identify entrances to the ice-shelf cavity below depths of 400 to 500 m that could allow intrusions of warm water if the vertical structure of inflow is similar to nearby observations. Radar sounding reveals a previously unknown inland trough that connects the main ice-shelf cavity to the ocean. If thinning trends continue, a larger water body over the trough could potentially allow more warm water into the cavity, which may, eventually, lead to destabilization of the low-lying region between Totten Glacier and the similarly deep glacier flowing into the Reynolds Trough"
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on June 17, 2016, 12:22:08 AM
The linked reference studies the impact of pinning points on ice mass loss from marine glaciers in Dronning Maud Land, East Antarctica (see first image), and conclude that while the likely SLR contribution this century from this area (see second image) is meaningful but slower than that from the WAIS (with continued global warming), and that including the dynamic influence of the pinning points in their model actually increased the SLR contribution this century by about 10% over models without the pinning points.  Thus the dynamic influence of pinning points should be assess for other Antarctic marine glaciers:

Favier, L., Pattyn, F., Berger, S., and Drews, R.: Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica, The Cryosphere Discuss., doi:10.5194/tc-2016-144, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-144/ (http://www.the-cryosphere-discuss.net/tc-2016-144/)

Abstract. The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart, because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by (more stable) grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouin ice shelves over the next millennia. Overall, the sub-ice shelf melting substantially impacts the sea level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the collapse of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrates that the onset of the marine ice-sheet retreat and subsequent promontory collapse is controlled by small pinning points within the ice shelves, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning has a small effect on the total amount of sea level rise but locally affects the timing of grounding-line migration, advancing the collapse of a promontory by hundreds of years. On the other hand, omitting the same pinning point in data assimilation decreases the sea level contribution by 10 % and delays the promontory collapse by almost a millennium. This very subtle influence of pinning points on ice dynamics acts on kilometre scale and calls for a better knowledge of the Antarctic margins that will improve sea-level predictions.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on August 18, 2016, 04:43:29 PM
While not of immediate concern w.r.t. SLR the linked reference discusses the evolution of seasonal supraglacial meltwater lakes on Langhovde Glacier, Dronning Maud Land, East Antarctica (see first image), between 2000 and 2013, and the continued evolution of such supraglacial East Antarctic lakes could eventually feed the hydrofracturing and cliff failure mechanisms identified by DeConto & Pollard (see second image) by, or shortly after, 2100:

Emily S. Langley, Amber A. Leeson, Chris R. Stokes & Stewart S. R. Jamieson (8 August 2016), "Seasonal Evolution of Supraglacial Lakes on an East Antarctic Outlet Glacier", Geophysical Research Letters, DOI: 10.1002/2016GL069511

http://onlinelibrary.wiley.com/doi/10.1002/2016GL069511/full (http://onlinelibrary.wiley.com/doi/10.1002/2016GL069511/full)

Abstract: "Supraglacial lakes are known to influence ice melt and ice flow on the Greenland ice sheet and potentially cause ice shelf disintegration on the Antarctic Peninsula. In East Antarctica, however, our understanding of their behaviour and impact is more limited. Using >150 optical satellite images and meteorological records from 2000-2013, we provide the first multi-year analysis of lake evolution on Langhovde Glacier, Dronning Maud Land (69°11'S, 39°32'E). We observe 7,990 lakes and 855 surface channels up to 18.1 km inland (~ 670 m a.s.l.) from the grounding line, and document three pathways of lake demise: (i) refreezing, (ii) drainage to the en-/sub-glacial environment (on the floating ice), and (iii) overflow into surface channels (on both the floating and grounded ice). The parallels between these mechanisms, and those observed on Greenland/the Antarctic Peninsula, suggest that lakes may similarly affect rates and patterns of ice melt, ice flow and ice shelf disintegration in East Antarctica."


https://www.washingtonpost.com/news/energy-environment/wp/2016/08/17/these-stunning-blue-lakes-just-gave-us-a-new-reason-to-worry-about-antarctica/?utm_term=.09ab23913d58 (https://www.washingtonpost.com/news/energy-environment/wp/2016/08/17/these-stunning-blue-lakes-just-gave-us-a-new-reason-to-worry-about-antarctica/?utm_term=.09ab23913d58)

Extract: "In a new study, scientists who study the largest ice mass on Earth — East Antarctica — have found that it is showing a surprising feature reminiscent of the fastest melting one: Greenland.
More specifically, the satellite-based study found that atop the coastal Langhovde Glacier in East Antarctica’s Dronning Maud Land, large numbers of “supraglacial” or meltwater lakes have been forming — nearly 8,000 of them in summer between the year 2000 and 2013. Moreover, in some cases, just as in Greenland, these lakes appear to have then been draining down into the floating parts of the glacier, potentially weakening it and making it more likely to fracture and break apart.
This is the first time that such a drainage phenomenon has been observed in East Antarctica, the researchers say — though it was previously spotted on the warmer Antarctic Peninsula and was likely part of what drove spectacular events there like the shattering of the Larsen B ice shelf in 2002.

When glaciers lose large parts of their ice shelves, they become less stable and flow faster towards the ocean, contributing to an increased rate of global sea level rise.
“The size of the lakes … are probably not big enough to do much at present, but if climate warming continues in the future, we can only expect the size and number of these lakes to increase. So that’s what we’re looking at,” Jamieson said.
He added that the mid-sized Langhovde Glacier is not special when it comes to East Antarctic meltwater lakes — other parts of coastal Antarctica see them too. The reason the study focused on Langhovde is simply that there was a lot of satellite and temperature data available.

Richard Alley, a glaciologist at Penn State who was not involved in the study, noted in an email comment that seeing some Antarctic surface melt is not too surprising. “Across many sensors and studies, there is summertime melting on the surface of Antarctica around the edges, and sometimes in some places extending farther inland than you might think,” he said.
However, Alley continued, we should be very concerned about such melting increasing. Alley referred to a study from earlier this year, by Rob DeConto of the University of Massachusetts, Amherst, and David Pollard of Penn State, which found that surface melt is one factor that could greatly speed total Antarctic ice loss, by increasing the tendency for “hydrofracture” to occur, in which meltwater helps to break apart ice shelves."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on August 27, 2016, 08:14:57 PM
The linked open access reference studies AABW production in the Cape Darnley Polyna, adjoining Prydz Bay in East Antarctica. The reference concludes that: "Given the growing number of reports of accelerating and irreversible mass loss from Antarctica’s major ice sheets linked to increased oceanic heat input, it is likely that Antarctica’s AABW production is already compromised and will decrease further into the future."  The reference implies that the AABW is the "canary in the coal mine" for Hansen et al (2016)'s slowing of the global thermohaline circulation, which should result in a positive ice-climate feedback that may increase the planetary energy imbalance as indicated by the attached Figure 7 from Hansen et al (2016):


G. D. Williams, L. Herraiz-Borreguero, F. Roquet, T. Tamura, K. I. Ohshima, Y. Fukamachi, A. D. Fraser, L. Gao, H. Chen, C. R. McMahon, R. Harcourt & M. Hindell (August 23 2016), "The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay", Nature Communications, Volume: 7, Article number: 12577, doi:10.1038/ncomms12577

http://www.nature.com/ncomms/2016/160823/ncomms12577/full/ncomms12577.html (http://www.nature.com/ncomms/2016/160823/ncomms12577/full/ncomms12577.html)

Abstract: "A fourth production region for the globally important Antarctic bottom water has been attributed to dense shelf water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011–2013 that provide the first complete assessment of dense shelf water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf water (salinity 34.65–34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley bottom water. Elsewhere, dense water formation is hindered by the freshwater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic bottom water to increased freshwater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic bottom water formation in a warming climate."

Extract: "There has been a lot of attention recently on the decadal-scale impact of icescape changes to AABW, resulting from major ice front calving events in polynyas regions, such as along Adélie Land after the calving of the Mertz Glacier. This study suggests the more ubiquitous process of enhanced ocean/ice shelf interaction could be a far greater long-term threat to AABW production. Given the growing number of reports of accelerating and irreversible mass loss from Antarctica’s major ice sheets linked to increased oceanic heat input, it is likely that Antarctica’s AABW production is already compromised and will decrease further into the future."

See also:
https://www.washingtonpost.com/news/energy-environment/wp/2016/08/23/how-elephant-seals-in-antarctica-are-helping-to-reveal-another-threat-caused-by-melting-ice/?utm_term=.42f9a2381634 (https://www.washingtonpost.com/news/energy-environment/wp/2016/08/23/how-elephant-seals-in-antarctica-are-helping-to-reveal-another-threat-caused-by-melting-ice/?utm_term=.42f9a2381634)

Extract: "The new study “significantly improves our understanding of the details of bottom water production around Antarctica,” said Rahmstorf, who was not involved in the new research, by email. “Scientists have long feared that global warming will slow down this vital process of deep and bottom water production, both in the North Atlantic and in Antarctic waters. With too much global warming, a critical threshold could be crossed where this process grinds to a halt, with incalculable and potentially catastrophic consequences for marine life and climate.” 

Rahmstorf isn’t the only researcher concerned about this issue, either. It’s a key component of a recent paper led by former NASA scientist James Hansen, now at Columbia University’s Earth Institute. The paper outlines a dire scenario in which even 2 degrees Celsius of warming above pre-industrial levels could lead to “dangerous” global consequences.
One of the paper’s key points is that rapid melting of both the Antarctic and Greenland ice sheets may not only contribute to dramatic sea-level rise in the next century, but also affect the world’s oceans in profound ways — including freshening the water at the poles and contributing to a slowdown of the oceans’ overturning circulation.
The new paper “tends to confirm one of the principal phenomena that we were drawing attention to: the effect of freshwater from ice shelves reducing [Antarctic bottom water] formation,” Hansen told The Post by email. “We concluded that this process, slowing down on Antarctic bottom water formation, has already begun.”

“While this particular area may not be the hotspot for this kind of activity, the fact that we have all the main players makes it a very unique lab experiment to try to understand how it works,” Williams said. “It provides observational evidence which should renew efforts to look for this happening in more key areas of Antarctica where we do know there’s accelerating melt occurring and where bottom water production is important as well.”"
Title: Re: EAIS Contributions to SLR by 2100
Post by: FishOutofWater on August 28, 2016, 10:35:48 PM
Purkey & Johnson had a paper a few years back that showed that deepwater all around Antarctica was in decline.Warmer intermediate waters are replacing it volumetrically. Othere papers have shown the decline of deepwater formation in the Weddell sea. In the last month extremely intense storms opened up a polynya there but it closed back up quickly because the water column there is more stable than it was in the 1970s when the polynya was self maintaining once it opened. Fresher surface water, produced by glacial melting from below is the likely culprit in the increased water column stability in the Weddell sea.

And the new paper you cite finds a similar slowdown in deepwater formation caused by increasing surface fresh water linked to glacial melt.

Yes, Hansen's paper is verifying. Less heat is being lost around Antarctica and more heat is building up in the northern hemisphere than the IPCC forecast.

The tropics are about to go crazy in the north Atlantic because there's more heat stored there than anyone has ever seen before now.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on October 03, 2016, 04:05:17 PM
The linked (open access) reference confirms earlier findings that the Wilkes marine glacial basin is unstable once triggered (see attached images); which could then destabilize other portions of the East Antarctic Ice Sheet:

Phipps, S. J., Fogwill, C. J., and Turney, C. S. M.: Impacts of marine instability across the East Antarctic Ice Sheet on Southern Ocean dynamics, The Cryosphere, 10, 2317-2328, doi:10.5194/tc-10-2317-2016, 2016.

http://www.the-cryosphere.net/10/2317/2016/ (http://www.the-cryosphere.net/10/2317/2016/)

Abstract. Recent observations and modelling studies have demonstrated the potential for rapid and substantial retreat of large sectors of the East Antarctic Ice Sheet (EAIS). This has major implications for ocean circulation and global sea level. Here we examine the effects of increasing meltwater from the Wilkes Basin, one of the major marine-based sectors of the EAIS, on Southern Ocean dynamics. Climate model simulations reveal that the meltwater flux rapidly stratifies surface waters, leading to a dramatic decrease in the rate of Antarctic Bottom Water (AABW) formation. The surface ocean cools but, critically, the Southern Ocean warms by more than 1 °C at depth. This warming is accompanied by a Southern Ocean-wide “domino effect”, whereby the warming signal propagates westward with depth. Our results suggest that melting of one sector of the EAIS could result in accelerated warming across other sectors, including the Weddell Sea sector of the West Antarctic Ice Sheet. Thus, localised melting of the EAIS could potentially destabilise the wider Antarctic Ice Sheet.

Extract: "We focus on three idealised scenarios, each of which represents a hypothetical collapse of the Wilkes Basin: WILKES, WEST and EAST. The locations of meltwater input within these experiments are shown in Fig. 2. In all of the experiments, a freshwater flux of 0.048 Sv is applied for 900 years. This is based on the estimate of Mengel and Levermann (2014), and is equivalent to an increase of ~3.8m in global sea level."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on October 18, 2016, 12:43:22 PM
More specifics about the Wilkens Ice Shelf:


Rankl, M., Fürst, J. J., Humbert, A., and Braun, M. H.: Dynamic changes on Wilkins Ice Shelf during the 2006–2009 retreat derived from satellite observations, The Cryosphere Discuss., doi:10.5194/tc-2016-218, in review, 2016


http://www.the-cryosphere-discuss.net/tc-2016-218/ (http://www.the-cryosphere-discuss.net/tc-2016-218/)

Abstract. Ice shelves serve as important buttresses for upstream areas. Several large ice shelves on the Antarctic Peninsula have disintegrated or retreated, which implied dynamic consequences for upstream ice. The present study aims to assess dynamic changes on Wilkins Ice Shelf during multi-stage ice-front retreat in the last decade. A total area of 2135 ± 75 km2 was lost in the period 2008–2009. The present study uses time-series of SAR satellite observations (1994/96, 2006–2010) in order to derive variations in multi-temporal surface flow from intensity offset tracking methods. Spatial patterns of horizontal strain rate and stress components were inferred during different ice-front retreat stages. These fields are used to explain the different break-up stages and to evaluate the ice-shelf stability. For this purpose, we apply criteria which were forwarded to explain and assess past ice-shelf retreat.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on November 29, 2016, 05:46:47 PM
The linked Scribbler article is entitled: "Did Föhn Winds Just Melt Two Miles of East Antarctic Surface Ice in One Day? "

https://robertscribbler.com/2016/11/28/did-fohn-winds-just-melt-two-miles-of-east-antarctic-surface-ice-in-one-day/

Extract: "It’s right there in the satellite image. A swatch of blue that seems to indicate an approximate 2-mile long melt lake formed over the surface of East Antarctica in just one day. If confirmed, this event would be both odd and concerning. A part of the rising signal that melt stresses for the largest mass of land ice on the planet are rapidly increasing.

While scientists and environmentalists are understandably concerned about ocean warming melting the undersides of sea-fronting West Antarctic glaciers — resulting in risks for rapid sea level rise for the near future, another consequence of global warming is also starting have a more visible impact on the frozen and now thawing continent. Surface melt, which was hitherto unheard of for most of East Antarctica, is now starting to pop up with increasing frequency."

Edit: The article was updated as follows: "Layer analysis of the November 27 MODIS satellite image in bands M  1-12 reveals two cloud shadows near the suspect melt pond (an issue that commentators Hendrick and Sammy raise in discussion below). The separate true color image provides comparison and generates the impression that the suspect melt pond is simply a remnant cloud shadow from the kidney-shaped cloud in the M 1-12 band image.

Though it is now certain that the large blue blotch in this satellite image is not a melt pond, a bluish coloration appearing over a broad swath of the above region in both the November 27 and November 28 image frames appears to indicate the presence of surface melt. So the downsloping wind related warming may well have produced a more subtle surface melt for this region of East Antarctica."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 09, 2016, 07:03:27 PM
The linked reference indicates that satellite data from the last two decades indicates that East Antarctic ice dynamics has higher rates of ice mass loss than scientists have previously acknowledged, and offers an approach to use future satellite data to better estimate this rate of ice mass loss:

Kallenberg, B., Tregoning, P., Hoffmann, J. F., Hawkins, R., Purcell, A., and Allgeyer, S.: A new approach to estimate ice dynamic rates using satellite observations in East Antarctica, The Cryosphere Discuss., doi:10.5194/tc-2016-269, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-269/ (http://www.the-cryosphere-discuss.net/tc-2016-269/)

Abstract. Mass balance changes of the Antarctic ice sheet are of significant interest due to its sensitivity to climatic changes and its contribution to changes in global sea level. While regional climate models successfully estimate mass input due to snowfall, it remains difficult to estimate the amount of mass loss due to ice dynamic processes. It's often been assumed that changes in ice dynamic rates only need to be considered when assessing long term ice sheet mass balance; however, two decades of satellite altimetry observations reveal that the Antarctic ice sheet changes unexpectedly and much more dynamically than previously expected. Despite available estimates on ice dynamic rates obtained from radar altimetry, information about changes in ice dynamic rates are still limited, especially in East Antarctica. Without understanding ice dynamic rates it is not possible to properly assess changes in ice sheet mass balance, surface elevation or to develop ice sheet models. In this study we investigate the possibility of estimating ice dynamic rates by removing modelled rates of surface mass balance, firn compaction and bedrock uplift from satellite altimetry and gravity observations. With similar rates of ice discharge acquired from two different satellite missions we show that it is possible to obtain an approximation of ice dynamic rates by combining altimetry and gravity observations. Thus, surface elevation changes due to surface mass balance, firn compaction and ice dynamic rates can be modelled and correlate with observed elevation changes from satellite altimetry.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 12, 2016, 06:29:57 PM
Most climate models do not include wind-albedo interaction that is currently inducing surface melting in portions of East Antarctica, but the linked reference documents field evidence for this mechanism that could contribute to a faster rate of EAIS destabilization with global warming then currently projected:

J. T. M. Lenaerts, et. al.  (2016), "Meltwater produced by wind–albedo interaction stored in an East Antarctic ice shelf", Nature Climate Change, doi:10.1038/nclimate3180

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3180.html (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3180.html)

Abstract: "Surface melt and subsequent firn air depletion can ultimately lead to disintegration of Antarctic ice shelves causing grounded glaciers to accelerate and sea level to rise. In the Antarctic Peninsula, foehn winds enhance melting near the grounding line, which in the recent past has led to the disintegration of the most northerly ice shelves. Here, we provide observational and model evidence that this process also occurs over an East Antarctic ice shelf, where meltwater-induced firn air depletion is found in the grounding zone. Unlike the Antarctic Peninsula, where foehn events originate from episodic interaction of the circumpolar westerlies with the topography, in coastal East Antarctica high temperatures are caused by persistent katabatic winds originating from the ice sheet’s interior. Katabatic winds warm and mix the air as it flows downward and cause widespread snow erosion, explaining >3 K higher near-surface temperatures in summer and surface melt doubling in the grounding zone compared with its surroundings. Additionally, these winds expose blue ice and firn with lower surface albedo, further enhancing melt. The in situ observation of supraglacial flow and englacial storage of meltwater suggests that ice-shelf grounding zones in East Antarctica, like their Antarctic Peninsula counterparts, are vulnerable to hydrofracturing."
Title: Re: EAIS Contributions to SLR by 2100
Post by: kiwichick16 on December 16, 2016, 08:52:20 PM
observations re Totten glacier

https://www.washingtonpost.com/news/energy-environment/wp/2016/12/16/warm-ocean-water-is-slamming-into-and-melting-the-biggest-glacier-in-east-antarctica/?utm_term=.2252571233c4 (https://www.washingtonpost.com/news/energy-environment/wp/2016/12/16/warm-ocean-water-is-slamming-into-and-melting-the-biggest-glacier-in-east-antarctica/?utm_term=.2252571233c4)
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 16, 2016, 09:30:43 PM
observations re Totten glacier

For those of you who hesitate to click on links, I provide the following information; which helps to quantify the extent of recent ocean-ice interaction with the Totten Ice Shelf.

Stephen Rich Rintoul, Alessandro Silvano,  Beatriz Pena-Molino,  Esmee van Wijk,  Mark Rosenberg,  Jamin Stevens Greenbaum and Donald D. Blankenship (16 Dec 2016), "Ocean heat drives rapid basal melt of the Totten Ice Shelf", Science Advances, Vol. 2, no. 12, e1601610, DOI: 10.1126/sciadv.1601610

http://advances.sciencemag.org/content/2/12/e1601610 (http://advances.sciencemag.org/content/2/12/e1601610)

Abstract: "Mass loss from the West Antarctic ice shelves and glaciers has been linked to basal melt by ocean heat flux. The Totten Ice Shelf in East Antarctica, which buttresses a marine-based ice sheet with a volume equivalent to at least 3.5 m of global sea-level rise, also experiences rapid basal melt, but the role of ocean forcing was not known because of a lack of observations near the ice shelf. Observations from the Totten calving front confirm that (0.22 ± 0.07) × 106 m3 s−1 of warm water enters the cavity through a newly discovered deep channel. The ocean heat transport into the cavity is sufficient to support the large basal melt rates inferred from glaciological observations. Change in ocean heat flux is a plausible physical mechanism to explain past and projected changes in this sector of the East Antarctic Ice Sheet and its contribution to sea level."
Title: Re: EAIS Contributions to SLR by 2100
Post by: georged on December 17, 2016, 12:18:43 PM

Observations from the Totten calving front confirm that (0.22 ± 0.07) × 106 m3 s−1 of warm water enters the cavity through a newly discovered deep channel.

If my math is right, that's 220,000 cumec/s. Which is equivalent to 1000 of this: http://www.greatlaketaupo.com/things-to-do/must-do/huka-falls/ (http://www.greatlaketaupo.com/things-to-do/must-do/huka-falls/)
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 17, 2016, 04:38:55 PM
The linked article is entitled: "East Antarctica is Melting From Above and Below".

http://www.climatecentral.org/news/east-antarctica-melting-climate-change-20986 (http://www.climatecentral.org/news/east-antarctica-melting-climate-change-20986)

Extract: "East Antarctica is remote even by Antarctic standards. Harsh winds and ocean currents have largely cut off the region from the rest of the world.

That’s left its massive stores of ice largely intact, especially compared to West Antarctica where a massive meltdown is underway that could raise seas by 10 or more feet in the coming centuries. But as carbon pollution warms the air and the ocean, there are signs that the region’s stability is under threat. Two new studies of different ice shelves — tongues of ice that essentially act as bathtub plugs — have seen major melting that could portend a less stable future for the region."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on January 03, 2017, 06:28:08 PM

The linked reference is entitled: "Validation of satellite altimetry by kinematic GNSS in central East Antarctica", and it discusses how radar altimetry was used to improve the accuracy of ice-surface elevations in the central East Antarctica area.

Schröder, L., Richter, A., Fedorov, D. V., Eberlein, L., Brovkov, E. V., Popov, S. V., Knöfel, C., Horwath, M., Dietrich, R., Matveev, A. Y., Scheinert, M., and Lukin, V.: Validation of satellite altimetry by kinematic GNSS in central East Antarctica, The Cryosphere Discuss., doi:10.5194/tc-2016-282, in review, 2017.

http://www.the-cryosphere-discuss.net/tc-2016-282/ (http://www.the-cryosphere-discuss.net/tc-2016-282/)

Abstract. Ice-surface elevation profiles of more than 30.000 km in total length are derived from kinematic GNSS observations on sledge convoy vehicles along traverses between Vostok station and the East Antarctic coast. The profiles have accuracies between 4 and 9 cm. They are used to validate elevation datasets from both radar and laser satellite altimetry as well as four digital elevation models. A crossover analysis with three different Envisat radar altimetry datasets yields a clear preference for the relocation method over the direct method of slope correction and for threshold retrackers over functional fit algorithms. The validation of Cryosat-2 low-resolution mode and SARIn mode datasets documents the progress made from baseline B to C elevation products. ICESat laser altimetry data are demonstrated to be accurate to a few decimeters over wide range of surface slopes. A crossover adjustment above subglacial Lake Vostok combining ICESat elevation data with our GNSS profiles yields a new set of ICESat laser campaign biases and provides new, independent evidence for the stability of the ice-surface elevation above the lake. The evaluation of digital elevation models reveals the importance of radar altimetry for the reduction of interpolation errors.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on January 16, 2017, 06:11:38 PM
The linked article is entitled: "Epic Antarctic voyage maps seafloor to predict ocean rise as glacier the size of California melts".  It will be interesting to eventually read about what the research team finds-out about the long-term melting patterns for Totten.

https://www.theguardian.com/world/2017/jan/15/totten-glacier-antarctic-voyage-to-map-seafloor-hobart-invstigator (https://www.theguardian.com/world/2017/jan/15/totten-glacier-antarctic-voyage-to-map-seafloor-hobart-invstigator)

Extract: "In East Antarctica, 3,000km south of the West Australian town of Albany, an ice shelf the size of California is melting from below.

The concerning trend was confirmed by Australian scientists in December, who reported that warming ocean temperatures were causing the rapid melt of the end of the Totten glacier, which is holding back enough ice to create a global sea rise of between 3.5 metres and six metres.

On Saturday, a team of international scientists left Hobart aboard the Australian research ship Investigator to map the seafloor ahead of the glacier to trace its history back to the last ice age, in the hopes of predicting its future melting patterns."
Title: Re: EAIS Contributions to SLR by 2100
Post by: solartim27 on January 21, 2017, 05:12:10 AM
This post got me thinking of Amery, and I found an old Sentinel from Nov 2015 to compare. 
Some calving of the Amery ice shelf in Prydz Bay, near the 'loose tooth'.
Not the best match for the gif, I tried to align the blue masking layer, darker image is 2017.   The big rift change makes me think we may be getting another huge berg floating about soon (it's all relative, 2018 or 19 time frame?).
http://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SSH_20170115T151915_FB58_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SSH_20170115T151915_FB58_S_1.final.jpg) (62 MB)

S1A_EW_GRDM_1SSH_20151109T152805_82F0_S_1.final.jpg
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on January 23, 2017, 07:39:44 PM
The linked reference indicates that East Antarctic ice shelves are more vulnerable than previously thought, with continued anthropogenic global warming:
 
Martin Siegert (2017), "Glaciology: Vulnerable Antarctic ice shelves", Nature Climate Change, Volume: 7, Pages: 11–12, doi:10.1038/nclimate3189

http://www.nature.com/nclimate/journal/v7/n1/full/nclimate3189.html (http://www.nature.com/nclimate/journal/v7/n1/full/nclimate3189.html)

Summary: "The decay of floating ice shelves around Antarctica speeds up ice flow from the continent and contributes to increased sea-level rise. Now, meltwater attributed to warm winds has been discovered on an East Antarctic ice shelf, suggesting greater vulnerability than previously thought."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on August 15, 2017, 12:52:06 AM
The linked article discussed modeling work at UAF that indicates that certain marine glaciers in East Antarctica are less stable than previously thought, and draws particular attention to Totten:

Title: "High-Performance Computing Tracking Earth’s Most Massive Ice Shelves"

https://edgylabs.com/high-performance-computing-ice-shelves/

Extract: "Glaciers are an indispensable climatic indicator for scientists and meteorologists, giving them insight into past climatic events and helping them to make projections in the future.

For over a decade, climatologists at the University of Alaska Fairbanks (UAF) have been working on ice sheet modeling to track ice sheet progress.

UAF created their own open-source Parallel Ice Sheet Model (PISM).

East Antarctica is the world’s largest ice sheet, roughly the size of the U.S. Until recently, the glaciers of East Antarctica, unlike those of the 10-times smaller West Antarctica, were thought to be more stable, because they’re isolated and very cold.

However, a new study by an international group of climatologists suggests otherwise.

It turns out that Totten, the largest glacier in East Antarctica, is melting and retreating at an alarming rate. This glacier alone threatens to raise sea levels."
Title: Re: EAIS Contributions to SLR by 2100
Post by: Daniel B. on August 15, 2017, 03:38:28 PM
That conclusion stands in contrast from others:

https://www.the-cryosphere-discuss.net/tc-2017-75/tc-2017-75.pdf (https://www.the-cryosphere-discuss.net/tc-2017-75/tc-2017-75.pdf)

"However, the much larger Totten Glacier and the tributaries of the Moscow University Ice Shelf that drain a large fraction of the East Antarctic Ice Sheet show localized areas of ice speed variations but little change in discharge. This result is consistent with recent findings of Li et al. (2016) showing that the Totten Glacier increase in velocity between 2001 and 2007, likely in response to elevated ocean temperature, but has been relatively stable since.

The finding of Li, et. al. can be found here:

http://onlinelibrary.wiley.com/doi/10.1002/2016GL069173/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016GL069173/abstract)
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on August 15, 2017, 05:07:26 PM
The linked reference discusses estimates of representative terrestrial heat flow in central East Antarctica.  Such knowledge is important to help determine the stability of the associated glaciers.  However, such values are not appropriate for use when modeling the stability of large East Antarctic marine glaciers like Totten (which likely has higher rates of geothermal heat flux):

Goodge, J. W.: Crustal heat production and estimate of terrestrial heat flow in central East Antarctica, with implications for thermal input to the East Antarctic ice sheet, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-134, (https://doi.org/10.5194/tc-2017-134,) in review, 2017.

https://www.the-cryosphere-discuss.net/tc-2017-134/ (https://www.the-cryosphere-discuss.net/tc-2017-134/)

Abstract. Terrestrial heat flow is a critical first-order factor governing the thermal condition and, therefore, mechanical stability of Antarctic ice sheets, yet heat flow across Antarctica is poorly known. Previous estimates of terrestrial heat flow come from inversion of seismic and magnetic geophysical data, by modeling temperature profiles in ice boreholes, and by calculation from heat production values reported for exposed bedrock. Although accurate estimates of surface heat flow are important as an input parameter for ice-sheet growth and stability models, there are no direct measurements of terrestrial heat flow in East Antarctica coupled to either subglacial sediment or bedrock. Bedrock outcrop is limited to coastal margins and rare inland exposures, yet valuable estimates of heat flow in central East Antarctica can be extrapolated from heat production determined by the geochemical composition of glacial rock clasts eroded from the continental interior. In this study, U, Th and K concentrations in a suite of Proterozoic (1.2–2.0 Ga) granitoids sourced within the Byrd and Nimrod glacial drainages of central East Antarctica indicate average upper crustal heat production (Ho) of about 2.6 ± 1.9 μW m-3. Assuming typical mantle and lower crustal heat flux for stable continental shields, and a length scale for the distribution of heat production in the upper crust, the heat production values determined for individual samples yield estimates of surface heat flow (qo) ranging from 33–84 mW m-2 and an average of 48.0 ± 13.6 mW m-2. Estimates of heat production obtained for this suite of glacially-sourced granitoids therefore indicate that the interior of the East Antarctic ice sheet is underlain in part by Proterozoic continental lithosphere with average surface heat flow, providing constraints on both geodynamic history and ice-sheet stability. The ages and geothermal characteristics of the granites indicate that crust in central East Antarctica resembles that in the Proterozoic Arunta and Tenant Creek inliers of Australia, but is dissimilar to other areas characterized by anomalously high heat flow in the Central Australian Heat Flow Province. Age variation within the sample suite indicates that central East Antarctic lithosphere is heterogeneous, yet the average heat production and heat flow of four age subgroups cluster around the group mean, indicating minor variation in thermal contribution to the overlying ice sheet from upper crustal heat production. Despite their minor differences, ice-sheet models may favor a geologically realistic model of crustal heat flow represented by such a distribution of ages and geothermal characteristics.
Title: Re: EAIS Contributions to SLR by 2100
Post by: Daniel B. on August 16, 2017, 03:42:54 PM
We could argue all day about which estimates are most important in determining the stability of the Trotten glacier.  We will not know the answer, until the change in ice mass reveals itself.  This will help in modeling other glaciers on the EAIS.  Trotted is just a small part of the total ice sheet, and may or may not be indicative of the larger.
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on August 18, 2017, 12:33:05 AM
Impressive work on the Law glacier by Bader et al.  indicating long term stability at least on that side of the polar plateau. The optimistic headline in the phys.org article overstates the case. An error in the article is publication date, which was apparently in February.

https://phys.org/news/2017-08-validates-east-antarctic-ice-sheet.html

doi:10.1016/j.quascirev.2016.12.005

--
Abstract: Till in an extensive blue ice moraine in the central Transantarctic Mountains at Mt. Achernar shows
relatively continuous deposition by East Antarctic derived ice throughout the last glacial cycle. The most
recently exposed material along the active margin of the Law Glacier (Zone 1) has hummocky topog-
raphy that transitions into to a relatively flat region (Zone 2), followed by a series of ~2 m high
continuous, parallel/sub-parallel ridges and troughs (Zones 3e5). The entire moraine is ice-cored. Past
surface changes of <40 m are indicated by a lateral moraine at the base of Mt. Achernar and substantial
topographic relief across Zone 3.

Pebble lithology and detrital zircon geochronology were analyzed on samples along a 6.5 km transect
across the moraine which formed from sub- and englacial debris. Beacon and Ferrar Supergroup rocks
comprise most rock types on the moraine surface. Overall, pebbles in Zones 1, 4 and 5 are dominated by
igneous rocks of the Ferrar dolerite, whereas Zones 2 and 3 have ~40% more Beacon Supergroup sedi-
mentary rocks. Zone 4 is characterized by distinctly colored lithologic bands, 5e20 m wide, that alternate
between dominant Beacon and Ferrar rock types. When combined with surface exposure ages, we
conclude that Zones 2 and 3 contain sediment accumulated through the last glacial maximum (LGM). In
contrast to pebble data, the U-Pb zircon data from till across all zones show little variability and are
consistent with a Beacon Supergroup source, as samples show significant populations from the Prote-
rozoic, ~550-600 Ma and ~950-1270 Ma, as well as the late Archean ~2700-2770 Ma. The Mackellar,
Fairchild, and lower Buckley Formations are interpreted as dominant sources of the detrital zircons. The
zircon data lack the spatio-temporal variability indicated by the pebble fraction because the local Ferrar dolerite is not zircon bearing, highlighting the broader importance of using multiple techniques when interpreting provenance changes over time.

Rather than reflecting major changes in ice flow path over time, the provenance changes are inter-
preted to indicate relative stability of the East Antarctic ice sheet, as the Law Glacier tapped into and
eroded successively lower stratigraphic units of the Beacon Supergroup. This has important implications
for interpreting offshore provenance records.
--

Very nice. Unfortunately paywalled. I attach figs 3b,c and part of 9 to give a flavor. They conclude:

" ... that is, provenance changes can be explained solely by Law Glacier tapping into successively lower stratigraphic units of the Beacon Supergroup, rather than indicating significant changes within East Antarctic ice sheet catchment boundaries. This has important implications for interpreting long temporal record from cores, such as ANDRILL. For instance, provenance analysis of a core collected downstream of an outlet glacier, such as the Law/Lennox-King Glacier system ... "

sidd

Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on November 01, 2017, 08:49:28 PM
The linked reference concludes: "Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."  This is not good news:

Chad A. Greene, Donald D. Blankenship, David E. Gwyther, Alessandro Silvano and
Esmee van Wijk (01 Nov 2017), "Wind causes Totten Ice Shelf melt and acceleration",
Science Advances, Vol. 3, no. 11, e1701681, DOI: 10.1126/sciadv.1701681

http://advances.sciencemag.org/content/3/11/e1701681

Abstract: "Totten Glacier in East Antarctica has the potential to raise global sea level by at least 3.5 m, but its sensitivity to climate change has not been well understood. The glacier is coupled to the ocean by the Totten Ice Shelf, which has exhibited variable speed, thickness, and grounding line position in recent years. To understand the drivers of this interannual variability, we compare ice velocity to oceanic wind stress and find a consistent pattern of ice-shelf acceleration 19 months after upwelling anomalies occur at the continental shelf break nearby. The sensitivity to climate forcing we observe is a response to wind-driven redistribution of oceanic heat and is independent of large-scale warming of the atmosphere or ocean. Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."
Title: Re: EAIS Contributions to SLR by 2100
Post by: Daniel B. on November 02, 2017, 09:40:29 PM
The linked reference concludes: "Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."  This is not good news:

Chad A. Greene, Donald D. Blankenship, David E. Gwyther, Alessandro Silvano and
Esmee van Wijk (01 Nov 2017), "Wind causes Totten Ice Shelf melt and acceleration",
Science Advances, Vol. 3, no. 11, e1701681, DOI: 10.1126/sciadv.1701681

http://advances.sciencemag.org/content/3/11/e1701681

In other words, they don’t know.

Abstract: "Totten Glacier in East Antarctica has the potential to raise global sea level by at least 3.5 m, but its sensitivity to climate change has not been well understood. The glacier is coupled to the ocean by the Totten Ice Shelf, which has exhibited variable speed, thickness, and grounding line position in recent years. To understand the drivers of this interannual variability, we compare ice velocity to oceanic wind stress and find a consistent pattern of ice-shelf acceleration 19 months after upwelling anomalies occur at the continental shelf break nearby. The sensitivity to climate forcing we observe is a response to wind-driven redistribution of oceanic heat and is independent of large-scale warming of the atmosphere or ocean. Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on November 03, 2017, 10:16:13 PM
The linked reference concludes: "Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."  This is not good news:

Chad A. Greene, Donald D. Blankenship, David E. Gwyther, Alessandro Silvano and
Esmee van Wijk (01 Nov 2017), "Wind causes Totten Ice Shelf melt and acceleration",
Science Advances, Vol. 3, no. 11, e1701681, DOI: 10.1126/sciadv.1701681

http://advances.sciencemag.org/content/3/11/e1701681

In other words, they don’t know.

Abstract: "Totten Glacier in East Antarctica has the potential to raise global sea level by at least 3.5 m, but its sensitivity to climate change has not been well understood. The glacier is coupled to the ocean by the Totten Ice Shelf, which has exhibited variable speed, thickness, and grounding line position in recent years. To understand the drivers of this interannual variability, we compare ice velocity to oceanic wind stress and find a consistent pattern of ice-shelf acceleration 19 months after upwelling anomalies occur at the continental shelf break nearby. The sensitivity to climate forcing we observe is a response to wind-driven redistribution of oceanic heat and is independent of large-scale warming of the atmosphere or ocean. Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."

While scientists many not know everything about projecting future impacts of climate change on the Totten Glacier and Ice Shelf, your post indicates that you know even less.
Title: Re: EAIS Contributions to SLR by 2100
Post by: Daniel B. on November 04, 2017, 02:53:04 PM
The linked reference concludes: "Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."  This is not good news:

Chad A. Greene, Donald D. Blankenship, David E. Gwyther, Alessandro Silvano and
Esmee van Wijk (01 Nov 2017), "Wind causes Totten Ice Shelf melt and acceleration",
Science Advances, Vol. 3, no. 11, e1701681, DOI: 10.1126/sciadv.1701681

http://advances.sciencemag.org/content/3/11/e1701681

In other words, they don’t know.

Abstract: "Totten Glacier in East Antarctica has the potential to raise global sea level by at least 3.5 m, but its sensitivity to climate change has not been well understood. The glacier is coupled to the ocean by the Totten Ice Shelf, which has exhibited variable speed, thickness, and grounding line position in recent years. To understand the drivers of this interannual variability, we compare ice velocity to oceanic wind stress and find a consistent pattern of ice-shelf acceleration 19 months after upwelling anomalies occur at the continental shelf break nearby. The sensitivity to climate forcing we observe is a response to wind-driven redistribution of oceanic heat and is independent of large-scale warming of the atmosphere or ocean. Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."

While scientists many not know everything about projecting future impacts of climate change on the Totten Glacier and Ice Shelf, your post indicates that you know even less.

And this coming from the person who just parrots others opinions!  Perhaps if you took the time to listen to those with whom you disagree, you may learn something.  “There is none so blind as he you will not see.”
Title: Re: EAIS Contributions to SLR by 2100
Post by: Shared Humanity on November 04, 2017, 04:16:52 PM


While scientists many not know everything about projecting future impacts of climate change on the Totten Glacier and Ice Shelf, your post indicates that you know even less.

ASLR....

I've not bothered to read Daniel B's response to this comment as I have him on ignore. He is a troll and a not very bright one at that. I consider you one of this site's top resident experts, a source of links to research that can help any visitor gain an appreciation of the challenges we face with regards to climate change. Responding to this clown is a waste of your time.
Title: Re: EAIS Contributions to SLR by 2100
Post by: Shared Humanity on November 04, 2017, 06:52:52 PM
Oh....and please keep on doing the work that you do.
Title: Re: EAIS Contributions to SLR by 2100
Post by: oren on November 05, 2017, 12:32:32 AM
Daniel B., I just have had enough with you. I've seen some posts from you that I disliked as they all seemed biased in one direction and sometimes derailing the discussions. But I did give you the benefit of the doubt until today. Quotingthe whole post by ASLR, one of the most respected posters on the site, just to stick an unexplained slur in the middle, and then when rebuked you resort to an ad hominem attack, there can be no other verdict but that you are an intentional troll. Best begone.
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on November 05, 2017, 02:14:56 AM
Perhaps use a killfile, rather than posting insults ? And perhaps we discuss the paper forawhile ?

Recall that the antarctic circumpolar wind drives the antarctic circumpolar current toward the east in deep ocean, while over the continental shelf further south a westward wind drives the Antarctic coastal current from east toward the west. This result is surprising in that westward wind stress over the shelf would naively, from Ekman pumping arguments, be supposed to depress thermocline and circumpolar deep water exchange, and hence ice melt beneath Totten. They find that when you look closely at local wind patterns that may not be the case.

"Over the continental shelf, westward winds are expected to induce southward transport of surface water, depress isotherms, and could therefore prevent mCDW from surmounting the continental shelf (28, 29), yet we provide evidence that competing processes prevail."

They use ice shelf velocity (from MOSDIS) as a proxy for bottom melt and ERA interim reanalysis for wind. They calculate upwelling due to Ekman pumping from the surface wind velocity.  They use data from February 2001 to September 2014. They find the the Totten ice shelf accelerates 19 months after upwelling increases in certain areas around the mouth of Totten.

What of the future ? Models indicate that the Antarctic Circumpolar winds and antarctic coastal currents eastward strengthen. But the effect on westward coastal winds and coastal current is not clear.

"Projections show an intensification of the wind-driven Antarctic Circumpolar Current and an increase in upwelling, particularly along the East Antarctic continental slope (36, 38, 39). It is possible that westward winds along the coast could weaken in conjunction with a southward migration of the divergence zone (39), in which case mCDW delivery to TIS could be tempered by a weakened coastal current; however, projections of coastal westward winds near TIS are few, and their relationships to SAM or atmospheric greenhouse gas have not been validated."

They continue:

"Wind patterns over the Southern Ocean are expected to evolve throughout the 21st century, and a shifting regime of upwelling could precipitate a marked response in Totten Glacier, unlocking the door to at least 3.5 m of eustatic sealevel potential (13) in the vast ice basin it drains."

But it not clear exactly what those shifting regimes of upwelling will be, since there are no climate models yet that have the skill or resolution for local regions around Totten over small timescales. So I think the last sentence of the abstract is too strong.

"Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."

They should have stopped after the comma, since it is not clearly projected that surface coastal winds will increase. All that is projected clearly is that the Antarctic circumpolar winds and current will increase.

I think this is an ingenious paper, and I don't have major quibbles with linking ice shelf velocity to bottom melt, but i think that the calculation from surface wind stress to upwelling is not so well supported and must await longer time series measurements of ocean upwelling over a larger area. (They do have float data from a single float for 2015 and have shown some correlation but that is just for that year along that float track using the -0.4C isotherm depth as as proxy for upwelling.)  Projections for the future must likewise await models with finer temporal and spatial resolution and accuracy. That said, I dont see how the strengthened ACC in the deep ocean forcing more CDW upward wont find a way to the bottom of Totten and the rest, but that's just me.

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: Daniel B. on November 05, 2017, 02:42:45 AM
Daniel B., I just have had enough with you. I've seen some posts from you that I disliked as they all seemed biased in one direction and sometimes derailing the discussions. But I did give you the benefit of the doubt until today. Quotingthe whole post by ASLR, one of the most respected posters on the site, just to stick an unexplained slur in the middle, and then when rebuked you resort to an ad hominem attack, there can be no other verdict but that you are an intentional troll. Best begone.

Funny how you ignored Abrupts slur and as hominem, but took offense when I responded back.  I guess it just goes to show your own bias.  Perhaps you are the troll.
Title: Re: EAIS Contributions to SLR by 2100
Post by: Daniel B. on November 05, 2017, 02:56:30 AM
Sidd,
That was precisely the issue that I had with this paper.  Too much conjecture, based on uncertainty.  Logically, it makes sense that greater upwelling will negatively affect the stability of the Trotten.  However, they seemed to lack any hard data to support their conclusions.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on November 05, 2017, 03:23:27 AM
Projections for the future must likewise await models with finer temporal and spatial resolution and accuracy. That said, I dont see how the strengthened ACC in the deep ocean forcing more CDW upward wont find a way to the bottom of Totten and the rest, but that's just me.

sidd

sidd,

So long as scientific papers cite all of their assumptions and limitations, they do not need to await the development of better models before presenting their results; otherwise, science will not make much progress.  The reason for publishing uncertain results is both to help guide future models and to provide some degree of warning before Totten reaches a tipping point where global warming will not matter, but the marine glacier will be lost due gravity.

That said, of course more data and better models are a good idea, but an even better idea would be to stop anthropogenic radiative forcing and then to take atmospheric CO2 concentrations back to 350ppm per James Hansen's advice.

Best,
ASLR
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on November 05, 2017, 03:46:27 AM
The linked SciAm article provides some more insights into the Greene et al (2017) paper:

Title: "How Wind Might Nudge a Sleeping Giant in Antarctica"

https://www.scientificamerican.com/article/how-wind-might-nudge-a-sleeping-giant-in-antarctica/

Extract: "Climate projections suggest that the upwelling of warm water may increase over the next century, Greene noted.

"Upwelling is driven not purely by the broad-scale magnitude of wind, but by the gradient in wind—how strong the wind is at one latitude versus how strong it is at a different latitude," he explained. "And CO2 in the atmosphere is modeled to increase the wind gradient around Antarctica, and then therefore increase upwelling around Antarctica."

What that actually means for the future of the sleeping giant is unclear for now. How the flow of ice could change in real time is closely tied to the region's underwater topography, which affects how quickly the glacier retreats as the ice shelf melts. These are issues scientists are still investigating.

"In all reality, Totten isn't going to destabilize in our lifetimes and then dump that 11 feet of sea-level rise into the ocean," Greene said. In fact, the increasingly unstable glaciers of West Antarctica remain a far bigger near-term concern among scientists for now."
Title: Re: EAIS Contributions to SLR by 2100
Post by: oren on November 05, 2017, 07:52:31 AM
...
I think this is an ingenious paper, and I don't have major quibbles with linking ice shelf velocity to bottom melt, but i think that the calculation from surface wind stress to upwelling is not so well supported and must await longer time series measurements of ocean upwelling over a larger area. (They do have float data from a single float for 2015 and have shown some correlation but that is just for that year along that float track using the -0.4C isotherm depth as as proxy for upwelling.)  Projections for the future must likewise await models with finer temporal and spatial resolution and accuracy. That said, I dont see how the strengthened ACC in the deep ocean forcing more CDW upward wont find a way to the bottom of Totten and the rest, but that's just me.

sidd
Thank you sidd for the well-explained criticism of the paper.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on November 05, 2017, 09:43:23 AM
Sidd,
That was precisely the issue that I had with this paper.  Too much conjecture, based on uncertainty.  Logically, it makes sense that greater upwelling will negatively affect the stability of the Trotten.  However, they seemed to lack any hard data to support their conclusions.

The linked reference provides direct evidence that ocean currents are currently driving rapid basal ice melt for the Totten Ice Shelf:

Stephen Rich Rintoul, Alessandro Silvano,  Beatriz Pena-Molino,  Esmee van Wijk,  Mark Rosenberg,  Jamin Stevens Greenbaum and Donald D. Blankenship (16 Dec 2016), "Ocean heat drives rapid basal melt of the Totten Ice Shelf", Science Advances, Vol. 2, no. 12, e1601610, DOI: 10.1126/sciadv.1601610

http://advances.sciencemag.org/content/2/12/e1601610

Abstract: "Mass loss from the West Antarctic ice shelves and glaciers has been linked to basal melt by ocean heat flux. The Totten Ice Shelf in East Antarctica, which buttresses a marine-based ice sheet with a volume equivalent to at least 3.5 m of global sea-level rise, also experiences rapid basal melt, but the role of ocean forcing was not known because of a lack of observations near the ice shelf. Observations from the Totten calving front confirm that (0.22 ± 0.07) × 106 m3 s−1 of warm water enters the cavity through a newly discovered deep channel. The ocean heat transport into the cavity is sufficient to support the large basal melt rates inferred from glaciological observations. Change in ocean heat flux is a plausible physical mechanism to explain past and projected changes in this sector of the East Antarctic Ice Sheet and its contribution to sea level."
Title: Re: EAIS Contributions to SLR by 2100
Post by: Shared Humanity on November 05, 2017, 04:46:43 PM
There you go....quoting him so I have to read his comment.

Thanks for the link to research indicating a mechanism exists at Totten that has been found to operate at most, if not all, marine terminating glaciers.
Title: Re: EAIS Contributions to SLR by 2100
Post by: VaughnAn on November 05, 2017, 08:08:31 PM
Abrupt SLR, as a long time lurker who reads most of your posts, I think it is a good time to thank you for your contribution to this Forum.  Yes, we do not understand all the details about Totten Glacier, however there are some pretty good indications of where it is headed.  Please ignore the troll(s) and continue your informative posts.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on November 06, 2017, 01:23:30 AM
Abrupt SLR, as a long time lurker who reads most of your posts, I think it is a good time to thank you for your contribution to this Forum.  Yes, we do not understand all the details about Totten Glacier, however there are some pretty good indications of where it is headed.  Please ignore the troll(s) and continue your informative posts.

Thank you.  Maybe a good many of my posts primarily present new climate change data (including projections from imperfect models), but to paraphrase a great author, it is not possible to make brick without clay.
Title: Re: EAIS Contributions to SLR by 2100
Post by: wili on November 06, 2017, 10:45:09 PM
... multi-meter sea level rise this Century is not out of the question

https://robertscribbler.com/2017/11/06/sleeping-ice-giants-stir-east-antarcticas-totten-glacier-accelerates-toward-southern-ocean/#comment-128987

Sleeping Ice Giants Stir — East Antarctica’s Totten Glacier Accelerates Toward Southern Ocean
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on November 07, 2017, 05:10:56 PM

Sleeping Ice Giants Stir — East Antarctica’s Totten Glacier Accelerates Toward Southern Ocean


wili,

Thanks for the link to the Scribbler article on Totten.  I post two images from that article (the first showing the general area of Totten and the second showing the upwelling zone in 2002 which fluctuates with the winds), in order to provide context for my repost of the third image that shows the location of an un-named gyre offshore of Totten that clearly interacts with the upwelling zone.  Specifically, such gyre can entrain CDW and advect it into the upwelling zone that lifts the relatively warm CDW up onto the continental shelf where it can be guided to the grounding line for Totten based on bottom bathymetry.

Best,
ASLR
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 13, 2017, 10:33:15 PM
Marine glaciers in the Aurora subglacial basin are less stable than consensus science previously thought:

Gulick et al. (2017), "Initiation and long-term instability of the East Antarctic Ice Sheet", Nature, nature.com/articles/doi:10.1038/nature25026

http://www.nature.com/articles/nature25026

Abstract: "Antarctica’s continental-scale ice sheets have evolved over the past 50 million years. However, the dearth of ice-proximal geological records limits our understanding of past East Antarctic Ice Sheet (EAIS) behaviour and thus our ability to evaluate its response to ongoing environmental change. The EAIS is marine-terminating and grounded below sea level within the Aurora subglacial basin, indicating that this catchment, which drains ice to the Sabrina Coast, may be sensitive to climate perturbations. Here we show, using marine geological and geophysical data from the continental shelf seaward of the Aurora subglacial basin, that marine-terminating glaciers existed at the Sabrina Coast by the early to middle Eocene epoch. This finding implies the existence of substantial ice volume in the Aurora subglacial basin before continental-scale ice sheets were established about 34 million years ago. Subsequently, ice advanced across and retreated from the Sabrina Coast continental shelf at least 11 times during the Oligocene and Miocene epochs. Tunnel valleys associated with half of these glaciations indicate that a surface-meltwater-rich sub-polar glacial system existed under climate conditions similar to those anticipated with continued anthropogenic warming. Cooling since the late Miocene resulted in an expanded polar EAIS and a limited glacial response to Pliocene warmth in the Aurora subglacial basin catchment. Geological records from the Sabrina Coast shelf indicate that, in addition to ocean temperature, atmospheric temperature and surface-derived meltwater influenced East Antarctic ice mass balance under warmer-than-present climate conditions. Our results imply a dynamic EAIS response with continued anthropogenic warming and suggest that the EAIS contribution to future global sea-level projections may be under-estimated."

See also:

Title: "East Antarctic Ice Sheet has history of instability"

https://phys.org/news/2017-12-east-antarctic-ice-sheet-history.html

Extract: "The new results came from geophysical and geological data collected during the first-ever oceanographic survey of East Antarctica's Sabrina Coast. The glaciers in this region may be particularly susceptible to climate change because they flow from the Aurora Basin, a region of East Antarctica that mostly lies below sea level.

Co-lead author Sean Gulick, a research professor at the University of Texas Institute for Geophysics (UTIG) and the UT Department of Geological Sciences (DGS), said the study found that glaciers from the Aurora Basin have been stable only for the past few million years.
"It turns out that for much of the East Antarctic Ice Sheet's history, it was not the commonly perceived large stable ice sheet with only minor changes in size over millions of years," he said. "Rather, we have evidence for a very dynamic ice sheet that grew and shrank significantly between glacial and interglacial periods. There were also often long intervals of open water along the Sabrina Coast, with limited glacial influence.""

&

https://news.nationalgeographic.com/2017/12/east-antarctic-ice-retreat-global-warming/

Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on December 14, 2017, 12:35:00 AM
The last sentence of the Gulick paper reminds me of Mercer's warning about the 0C isotherm.

"Our findings suggest that ice in the ASB catchment may respond dramatically to anthropogenic climate forcing if regional atmospheric warming results in surface meltwater production."

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 17, 2017, 06:13:15 PM
Here is more evidence that portions of the East Antarctic marine glaciers near Law Dome are starting to 'wake-up' due to a combination of increasing ocean heat content (in the CDW) and upwelling due to changes in the westerly winds.  I note that once such activity removes the associated 'ice plugs' (that currently guard the Aurora subglacial basin) the rate of ice mass loss will largely depend on the unknown rates for ice cliff failures and hydrofracturing. I also note that one of the images in the linked pdf highlights Agulhas Leakage that is already occurring as the Antarctic ozone hole has already contracted the Antarctic Circumpolar Current southwards:

Catherine C. Walker, Alex S. Gardner & Johan Nilsson (2017 AGU presentation), "The sleeping giant wakes its neighbors? Observations of recent glacier change near Law Dome, East Antarctica in response to a changing ocean"

https://fallmeeting.agu.org/2017/files/2017/12/Melting-Cryosphere-Wednesday-8AM-slides.pdf

Title: Re: EAIS Contributions to SLR by 2100
Post by: Hyperion on December 19, 2017, 04:23:27 AM
Hmmm.
I have to wonder how many of these tunnels are still uncharted and at what rate inflow might be increasing. That 220,000 cubic meters per second for just one channel discovered, as serious as it sounds may be just be a drop in the bucket compared to totals when you look at that "neighbors" png for example ASLR.
And If this is a self reinforcing feedback where once these currents have bored past the sill ridges into the inland deepening basin, increased exposed ice surface area can increase the velocity both of the incoming denser warm water, and the freshened by melt outgoing surface layer then trouble it surely is. Particularly if as mentioned surface melt becomes common on the top of the ice. If, as we have seen in Greenland the soggy aquifer that persists below the frozen crust of winter then a massive change in the thermal gradient down through the ice sheet is the result. With average surface temperatures annually well below freezing then a stable situation exists with geothermal heat holding the base at melting point and colder temperature as you rise towards the surface. With temps pinned at melting point at the top and bottom, inevitably the whole thickness of the sheet will ease toward melting point, and structural stability of the bottom becomes highly questionable.
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on December 20, 2017, 05:00:59 PM
You will notice that in the attached image from the conservative DeConto & Pollard (2016) analysis, that in panel "c" the "T" stands for Totten Glacier collapsing (due to cliff failures and hydrofracturing) before 2100, with RCP 8.5 radiative forcing:

Caption: "Figure 4 | Future ice-sheet simulations and Antarctic contributions to GMSL from 1950 to 2500 driven by a high-resolution atmospheric model and 1° NCAR CCSM4 ocean temperatures. a, Equivalent CO₂ forcing applied to the simulations, following the RCP emission scenarios in ref. 36, except limited to 8 × PAL (preindustrial atmospheric level, where 1 PAL = 280 p.p.m.v.). b, Antarctic contribution to GMSL. c, Rate of sea-level rise and approximate timing of major retreat and thinning in the Antarctic Peninsula (AP), Amundsen Sea Embayment (ASE) outlet glaciers, AS–BS, Amundsen Sea–Bellingshausen Sea; the Totten (T), Siple Coast (SC) and Weddell Sea (WS) grounding zones, the deep Thwaites Glacier basin (TG), interior WAIS, the Recovery Glacier, and the deep EAIS basins (Wilkes and Aurora). d, Antarctic contribution to GMSL over the next 100 years for RCP8.5 with and without a +3 °C adjustment in ocean model temperatures in the Amundsen and Bellingshausen seas as shown in Extended Data Fig. 5d. e–g, Ice-sheet snapshots at 2500 in the RCP2.6 (e), RCP4.5 (f) and RCP8.5 (g) scenarios. Ice-free land surfaces are shown in brown. h, Close-ups of the Amundsen Sea sector of WAIS in RCP8.5 with bias-corrected ocean model temperatures."
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on January 30, 2018, 11:34:53 PM
The linked reference discusses some of the complexities associated with modeling fracture and calving on the Totten Ice Shelf:

Cook, S., Åström, J., Zwinger, T., Galton-Fenzi, B. K., Greenbaum, J. S., and Coleman, R.: 2018, Modelled fracture and calving on the Totten Ice Shelf, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-3

https://www.the-cryosphere-discuss.net/tc-2018-3/

Abstract. The Totten Ice Shelf (IS) has a large drainage basin, much of which is grounded below sea level, leaving the glacier vulnerable to retreat through the Marine Ice Shelf Instability mechanism. The ice shelf has also been shown to be sensitive to changes in calving rate, as a very small retreat of the calving front from its current position is predicted to cause a change in flow at the grounding line. Therefore understanding the processes behind calving on the Totten IS is key to predicting its future sea level rise contribution. Here we use the Helsinki Discrete Element Model (HiDEM) to show that calving on the Totten IS is controlled not only by locally produced fractures at the calving front, but is also influenced by basal fractures which are likely produced at the grounding line. Our model results show that regrounding points may be key areas of basal crevasse production, and can produce basal crevasses in both an along and across flow orientation. As well as affecting calving, along flow basal crevasses at the grounding line may be a possible precursor to basal channels. We use two additional models to examine the evolution of basal fractures as they advect downstream, demonstrating that both strain and ocean melt have the potential to deform narrow fractures into the broad basal features observed near the calving front. The wide range of factors which influence fracture patterns and calving on this glacier will be a challenge for predicting its future mass loss.
Title: Re: EAIS Contributions to SLR by 2100
Post by: solartim27 on March 20, 2018, 08:00:01 PM
Bad news that the Totten grounding line is much farther back then previously thought.  Cool video.
https://twitter.com/AusAntarctic/status/975896368865689600
Title: Re: EAIS Contributions to SLR by 2100
Post by: Shared Humanity on March 21, 2018, 01:18:39 AM
Yep. EAIS is far more susceptible to warm waters than 1st believed.

https://news.sky.com/story/sea-level-warning-as-scientists-find-larger-part-of-massive-totten-glacier-floating-11298094
Title: Re: EAIS Contributions to SLR by 2100
Post by: jmshelton on March 21, 2018, 07:59:13 PM
Was looking for a little more on the Totten Glacier and found another article:
https://phys.org/news/2018-03-sea-giant-antarctic-glacier-thought.html (https://phys.org/news/2018-03-sea-giant-antarctic-glacier-thought.html)
Title: Re: EAIS Contributions to SLR by 2100
Post by: AbruptSLR on August 01, 2018, 09:10:17 PM
The linked reference helps to quantify the recent ice mass loss of the Totten and Moscow University Glaciers:

Yara Mohajerani et al. (25 July 2018), "Mass Loss of Totten and Moscow University Glaciers, East Antarctica, Using Regionally Optimized GRACE Mascons", Geophysical Research Letters, https://doi.org/10.1029/2018GL078173

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL078173

Abstract: "Totten and Moscow University glaciers, in the marine‐based sector of East Antarctica, contain enough ice to raise sea level by 5 m. Obtaining precise measurements of their mass balance is challenging owing to large area of the basins and the small mass balance signal compared to West Antarctic glaciers. Here we employ a locally optimized processing of Gravity Recovery and Climate Experiment (GRACE) harmonics to evaluate their mass balance at the sub‐basin scale and compare the results with mass budget method (MBM) estimates using regional atmospheric climate model version 2.3 (RACMO2.3) or Modèle Atmosphérique Régional version 3.6.4 (MAR3.6.4). The sub‐basin mass loss estimate for April 2002 to November 2015 is 14.8 ± 4.3 Gt/yr, which is weakly affected by glacial isostatic adjustment uncertainties (±1.4 Gt/yr). This result agrees with MBM/RACMO2.3 (15.8 ± 2.0 Gt/yr), whereas MBM/MAR3.6.4 underestimates the loss (6.6 ± 1.6 Gt/yr). For the entire drainage, the mass loss for April 2002 to August 2016 is 18.5 ± 6.6 Gt/yr, or 15 ± 4% of its ice flux. These results provide unequivocal evidence for mass loss in this East Antarctic sector."
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on September 17, 2018, 11:20:57 PM
More troubling signs in the east: Cook glacier fluctuating quickly, more snesitive than thought. Drains the Wilkes basin. Lotsa SLR locked away there.

open access:
https://www.the-cryosphere-discuss.net/tc-2018-107/

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: sidd on September 19, 2018, 10:38:19 PM
More paleo evidence that Wilkes land destabilized in the Eemian and the Holsteinian:

"The key finding from our new data set is that the Wilkes Subglacial Basin has been susceptible to ice loss not only during warm Pliocene intervals [Ref. 5] with CO2 levels of approximately 400 p.p.m., but also during the late Pleistocene despite CO2 levels [Ref. 25] remaining below 300 p.p.m. Hence, we provide data-based evidence in support of recent ice sheet models that simulate margin retreat and ice loss during late Pleistocene interglacials [Refs. 2,3,9] (Fig. 1b)"

"Based on the ice sheet response during past interglacial periods, we estimate that substantial ice loss within the Wilkes Subglacial Basin would be likely to occur with approximately 2 °C warming (above pre-industrial) if sustained for a few millennia."

doi: 10.1038/s41586-018-0501-8

https://phys.org/news/2018-09-sustained-moderate-east-antarctic-ice.html

sidd
Title: Re: EAIS Contributions to SLR by 2100
Post by: bligh8 on July 27, 2019, 08:44:09 PM
https://www.researchgate.net/publication/308389094_Windblown_Pliocene_diatoms_and_East_Antarctic_Ice_Sheet_retreat

Windblown Pliocene diatoms and East Antarctic Ice Sheet retreat

Article (PDF Available) in Nature Communications 7:12957 · September 2016 with 113 Reads
DOI: 10.1038/ncomms12957

Robert M DeDonto, David Pollard, Richard B Alley, Reed P Sherer

Marine diatoms in tillites along the Transantarctic Mountains (TAMs) have been used to suggest a diminished East Antarctic Ice Sheet (EAIS) during Pliocene warm periods. Updated ice-sheet modelling shows significant Pliocene EAIS retreat, creating marine embayments into the Wilkes and Aurora basins that were conducive to high diatom productivity and rapid accumulation of diatomaceous sediments. Here we show that subsequent isostatic uplift exposed accumulated unconsolidated marine deposits to wind erosion. We report new atmospheric modelling utilizing Pliocene climate and derived Antarctic landscapes indicating that prevailing mid-altitude winds transported diatoms towards the TAMs, dominantly from extensive emerged coastal deposits of the Aurora Basin. This result unifies leading ideas from competing sides of a contentious debate about the origin of the diatoms in the TAMs and their link to EAIS history, supporting the view that parts of the EAIS are vulnerable to relatively modest warming, with possible implications for future sea-level rise.

The new model presented here implies significant EAIS retreat
during the Pliocene with wind patterns that can explain the
source and mechanism for emplacement of Pliocene marine
diatoms in the TAMs by aeolian processes. Webb et al.10 initiated
an important discussion regarding dynamic behaviour of the
EAIS during the Pliocene. Although their interpretation of a
glacial origin for the diatoms in the Sirius tillites and the extent of
retreat that they inferred is not supported, we suggest that these
Pliocene marine diatoms nevertheless provide evidence of
significant EAIS retreat from the current coastline during
Pliocene warm intervals—enough to have had a significant
global impact on sea level. When this debate began, decades ago,
it was already understood that constraining past ice-sheet
dynamics is important for forecasting future behaviour in a
warming world.

More within the open access article

bligh