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AbruptSLR

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EAIS Contributions to SLR by 2100
« 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.
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #1 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."
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #2 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.

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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #3 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.
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #4 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
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
« Last Edit: June 11, 2013, 11:00:32 PM by AbruptSLR »
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #5 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

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."
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #6 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.
« Last Edit: April 27, 2013, 05:10:01 PM by AbruptSLR »
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #7 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."
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― Leon C. Megginson

pikaia

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Re: EAIS Contributions to SLR by 2100
« Reply #8 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

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Re: EAIS Contributions to SLR by 2100
« Reply #9 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.

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Re: EAIS Contributions to SLR by 2100
« Reply #10 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
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Re: EAIS Contributions to SLR by 2100
« Reply #11 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.
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Re: EAIS Contributions to SLR by 2100
« Reply #12 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.
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Re: EAIS Contributions to SLR by 2100
« Reply #13 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.
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Re: EAIS Contributions to SLR by 2100
« Reply #14 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).
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Re: EAIS Contributions to SLR by 2100
« Reply #15 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.
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Re: EAIS Contributions to SLR by 2100
« Reply #16 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."
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Re: EAIS Contributions to SLR by 2100
« Reply #17 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

"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."
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Re: EAIS Contributions to SLR by 2100
« Reply #18 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."
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Re: EAIS Contributions to SLR by 2100
« Reply #19 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

"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.""

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Re: EAIS Contributions to SLR by 2100
« Reply #20 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.
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Re: EAIS Contributions to SLR by 2100
« Reply #21 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
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Re: EAIS Contributions to SLR by 2100
« Reply #22 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

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."
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Re: EAIS Contributions to SLR by 2100
« Reply #23 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.

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Re: EAIS Contributions to SLR by 2100
« Reply #24 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

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Re: EAIS Contributions to SLR by 2100
« Reply #25 on: September 01, 2013, 09:22:37 PM »
Thanx. I am on the road now, but will read carefully when I return home.

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Re: EAIS Contributions to SLR by 2100
« Reply #26 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
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Re: EAIS Contributions to SLR by 2100
« Reply #27 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
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Re: EAIS Contributions to SLR by 2100
« Reply #28 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



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."
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Re: EAIS Contributions to SLR by 2100
« Reply #29 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


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."
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Re: EAIS Contributions to SLR by 2100
« Reply #30 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


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."
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Re: EAIS Contributions to SLR by 2100
« Reply #31 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



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."
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Re: EAIS Contributions to SLR by 2100
« Reply #32 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

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."
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Re: EAIS Contributions to SLR by 2100
« Reply #33 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
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.
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Re: EAIS Contributions to SLR by 2100
« Reply #34 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

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Re: EAIS Contributions to SLR by 2100
« Reply #35 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
« Last Edit: September 19, 2013, 03:50:06 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #36 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

“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.

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #37 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #38 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?

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #39 on: September 19, 2013, 10:29:49 PM »
Yes we can!
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #40 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

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

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.

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Re: EAIS Contributions to SLR by 2100
« Reply #41 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

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).
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Re: EAIS Contributions to SLR by 2100
« Reply #42 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

"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. ......."
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Re: EAIS Contributions to SLR by 2100
« Reply #43 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

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.
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Re: EAIS Contributions to SLR by 2100
« Reply #44 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.
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Re: EAIS Contributions to SLR by 2100
« Reply #45 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

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?"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: EAIS Contributions to SLR by 2100
« Reply #46 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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: EAIS Contributions to SLR by 2100
« Reply #47 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/
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: EAIS Contributions to SLR by 2100
« Reply #48 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.
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Re: EAIS Contributions to SLR by 2100
« Reply #49 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson