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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #50 on: February 01, 2014, 04:07:26 AM »
The following extract about Totten Glacier is taken from the linked website:

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

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

http://ameliashevenell.wordpress.com/2014/01/27/1272014-mysteries-of-east-antarcticas-totten-glacier-system/
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #51 on: February 22, 2014, 06:22:12 PM »
The linked NASA article (see also discussion in replies 49 & 50) finds that the reducing salinity of the ocean water (due to a reduction in the number of local polynas) around the Totten & Moscow U. Ice Shelves is leading to melting and thinning of the Totten Glacier (see the link for further explanations):

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


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

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


The second attached image is from the Modis Terra satellite on Feb 22 2014 and is zoomed in on the Totten Glacier and Ice Shelf.  This image shows a calving event from the Totten Ice Shelf (note the sea ice is retreated off of the ice shelf face in this image); possibly associate with the ocean-ice advection cited in the NASA news article.
« Last Edit: February 23, 2014, 02:51:35 PM by AbruptSLR »
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sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #52 on: February 23, 2014, 05:27:30 AM »
I think the reduction in salinity near the Totten is an effect, not a cause. The winds cause the polynas; if the wind decreases, so does number of polynas and salinity. But there is more going on, Purkey(2013) DOI: 10.1175/JCLI-D-12-00834.1 is excellent. I have not the time right now, but this is fig 5c from the reference and associated colorscale, look where the freshwater is, deep and by EAIS. The whole discussion in Purkey on halosteric change, and (potential temperature) isotherm heave is fascinating.
 

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #53 on: February 23, 2014, 03:04:41 PM »
sidd,

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

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

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

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

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

http://www.pmel.noaa.gov/people/gjohnson/publications.html
« Last Edit: February 23, 2014, 03:15:33 PM by AbruptSLR »
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wili

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Re: EAIS Contributions to SLR by 2100
« Reply #54 on: May 05, 2014, 03:42:38 PM »
This was just posted at ClimateProgress:
http://thinkprogress.org/climate/2014/05/05/3433981/antarctic-melting-sea-levels/

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

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

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

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


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

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

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

http://climatecrocks.com/2014/05/05/new-research-east-antarctic-at-risk-of-unstoppable-melt/
« Last Edit: May 05, 2014, 04:49:44 PM by wili »
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sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #55 on: May 05, 2014, 11:39:38 PM »
Thanks for the reference. I like the term "ice plug" used to describe the thickness of ice required to shift ice sheet profile into irreversible retreat across retrograde bed. I also like the fact that PISM performs as well as Elmer which is a full Stokes model.

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

So just for fun: 3 images:

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

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

sidd


sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #56 on: May 06, 2014, 05:55:08 AM »
I forgot to mention the most important bit in the Mengel paper: this is an amplifier (over century plus timescale)

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

So thats a 60 to 1 amplifier.

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

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

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

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

sidd

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #57 on: May 06, 2014, 04:51:32 PM »
sidd & wili,

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

Best
ASLR
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #58 on: May 15, 2014, 01:23:01 AM »
The linked reference (with a free access pdf) indicates that the West Ragnhild Glacier (marine-terminating) in Dronning Maud Land, East Antarctica, is more sensitive to external forcing (with regard to ice mass loss) than are other glaciers in the region:

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

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

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

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Re: EAIS Contributions to SLR by 2100
« Reply #59 on: July 07, 2014, 06:01:01 PM »
The linked reference (with a free access pdf) indicates how pervasive circum-Antarctic ocean warming associated with changes in the Southern Hemisphere Westerlies (SHW) may threaten EAIS stability:

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

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

ABSTRACT: "The stability of Antarctic ice sheets and their potential contribution to sea level under projected future warming remains highly uncertain. The Last Interglacial (135 000–116 000 years ago) provides a potential analogue, with global temperatures 2 °C higher and rates of sea-level rise >5.6m ka_1, leading to sea levels 6.6– 9.4m higher than present. The source(s) of this sea-level rise remain fiercely debated. Here we report a series of independent model simulations exploring the effects of migrating Southern Hemisphere Westerlies (SHWs) on Southern Ocean circulation and Antarctic ice-sheet dynamics. We suggest that southerly shifts in winds may have significantly impacted the sub-polar gyres, inducing pervasive warming (0.2–0.8 °C in the upper 1200 m) adjacent to sectors of the East Antarctic Ice Sheet (EAIS), which due to their geometries and connectivity to the Southern Ocean are highly sensitive to ocean forcing. We conclude that the EAIS potentially made a substantial, hitherto unsuspected, contribution to interglacial sea levels, and given 21st-century projections in the Southern Annular Mode and associated SHW migration, we highlight how pervasive circum-Antarctic warming may threaten EAIS stability."
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icefisher

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Re: EAIS Contributions to SLR by 2100
« Reply #60 on: September 06, 2014, 11:31:23 PM »
ASLR,  There is another projection of Antarctic ice discharge recently published in (www.earth-syst-dynam.net/5/271/2014/) titled "Projecting Antarctic ice discharge using response functions from SeaRISE ice-sheet models.  This is an open access paper.

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

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #61 on: September 07, 2014, 02:54:02 AM »
icefisher,

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

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

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

Best,
ASLR
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sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #62 on: October 06, 2014, 06:45:56 AM »
Gogineni has a paper out that discusses subglacial topo and ice stucture under Byrd (and Jacobshawn)
Confirms that Byrd trench is >3Km deep. Ouch.

doi: 10.3189/2014JoG14J129

sidd

solartim27

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Re: EAIS Contributions to SLR by 2100
« Reply #63 on: October 07, 2014, 01:04:42 AM »
Article on Live Science discussing the 3 km deep trench under Byrd:
http://www.livescience.com/48096-hidden-trench-discovered-under-glacier.html?cmpid=558455
FNORD

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #64 on: October 07, 2014, 05:43:31 AM »
If you are at the Fall AGU in San Francisco then go see:

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

Abstract:
The Totten Glacier Ice Shelf (TGIS) is the primary outlet of the Aurora Subglacial Basin, draining 6.9 meters of eustatic sea level potential into the Sabrina Coast (SC) alongside the Moscow University Ice Shelf that fringes the coastline. The TGIS and surrounding grounded ice has the largest thinning signal in East Antarctica and the nature of the thinning suggests that it is driven by enhanced basal melting due to ocean processes. Warm Modified Circumpolar Deep Water (MCDW), which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the SC continental shelf in the 400-500 m depth range. Here we show, using new data from recent aerogeophysical flights, that entrances to the cavity exist that are deeper than this range of thermocline depths, indicating that the TGIS is vulnerable to intrusions of MCDW if the vertical structure of cavity inflow is similar to the nearest observations. We provide evidence that a new entry to the cavity has opened likely due to the interplay between thinning ice and subglacial channels that could be related to regional mass loss acceleration observed in 2006. This new connection may increase access of warm water to the east side of the ice shelf, potentially destabilizing the low-lying area to the east of the TGIS.
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sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #65 on: October 07, 2014, 10:54:14 PM »
Some reading for that presentation might include doi:10.1029/2011JF002066 with many of the same authors showing the hydrological connection through the Aurora Subglacial Basin from Totten all the way to Dome C and almost all the way to Lake Vostok, a thousand klicks or more. And recall it's neighbours, as discussed in Mengel(2014) DOI: 10.1038/NCLIMATE2226, Cook and Ninnis, where a small investment in melting the ice plug of 80mm SLR equiv reaps an additional rise of 4000mm. Now consider that the Wilkes basin drained by Cook and Ninnis is larger than Byrd Deeps underlying PIG/Thwaites. Couple Wilkes and Aurora together a la Feldman(2014) doi:10.5194/tcd-8-4885-2014 who shows that draining one ice basin destabilizes neighbours. And remember that Byrd glacier also drains Wilkes through the Transantarctic spine through a trench 3.6 km (Gogineni's latest doi:10.3189/2014JoG14J129 )deep into the Ross Shelf, and has interesting hydrology beneath also.

Another one that scares me is Amery.

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

sidd

Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #66 on: December 06, 2014, 02:02:45 PM »
De Boer et al 2014 model the (E)AIS during the Pliocene:
http://www.the-cryosphere-discuss.net/8/5539/2014/tcd-8-5539-2014-print.pdf

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

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

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

So these models do not seem to reproduce the paleo-data yet, but they're getting closer.

Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #67 on: December 06, 2014, 03:30:04 PM »
Khazendar et al 2014 on Totten Glacier:
http://www.staff.science.uu.nl/~broek112/home.php_files/Publications_MvdB/2013_Khazendar_NatComm.pdf

Observed thinning of Totten Glacier is linked to coastal polynya variability

Abstract
Analysis of ICESat-1 data (2003–2008) shows significant surface lowering of Totten Glacier, the glacier discharging the largest volume of ice in East Antarctica, and less change on nearby Moscow University Glacier. After accounting for firn compaction anomalies, the thinning appears to coincide with fast-flowing ice indicating a dynamical origin. Here, to elucidate these observations, we apply high-resolution ice–ocean modelling. Totten Ice Shelf is simulated to have higher, more variable basal melting rates. We link this variability to the volume of cold water, originating in polynyas upon sea ice formation, reaching the sub-ice-shelf cavity. Hence, we propose that the observed increased thinning of Totten Glacier is due to enhanced basal melting caused by a decrease in cold polynya water reaching its cavity. We support this hypothesis with passive microwave data of polynya extent variability. Considering the widespread changes in sea ice conditions, this mechanism could be contributing extensively to ice-shelf instability.

sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #68 on: December 06, 2014, 10:18:41 PM »
Mr. Linde posted a reference to Fogwill(2014,doi:10.1002/jqs.2683) in a WAIS thread. That paper states:

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

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

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

sidd

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #69 on: January 01, 2015, 07:13:28 PM »
The link to a Jamstec press release (from October 2014) indicates that the EAIS is more susceptible to warming ocean temperatures than was previously realized (see also Reply #66 that supports this conclusion); based on detailed time-series analyses of ice-berg rafted debris collected from a sediment core adjacent to the Wilkes Subglacial Basin (see attached image):

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

Extract: "Based on core samples collected in the Antarctic Ocean, this analysis examined the timing of the EAIS melting mode occurred between 4.3 and 2.2 million years ago. It found out that, prior to 3.5 million years ago, the sea ice melting was related mainly to variance in the obliquity cycle, and since 3.5 million years, it has been related to precession. In other words, the EAIS was sensitive to seawater temperature variations in the Antarctic Ocean during the period older than 3.5 million years, while it has been affected mainly by summer insolation since 3.5 million years ago.
This study results demonstrate how the EAIS volume, in particular melting, is caused when the global seawater temperature was 2 °C higher, as occurred during the early Pliocene. In facing global warming, it gives an important insight into the EAIS behaviors. Also, it is expected to contribute to prediction of future climate changes, because this study indicates that EAIS is not as stable as expected."
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #70 on: January 07, 2015, 10:18:45 PM »
The linked reference provides paleo-evidence that the Wilkes land sub-basin has been eroded during past ice mass loss events, and may be susceptible to future such events.

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

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


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

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sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #71 on: January 07, 2015, 11:23:43 PM »
One thing i do not understand in the recent Pollard(2014) paper: Why is Amery stable ? Thoughts ?

sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #72 on: January 07, 2015, 11:35:28 PM »
One thing i do not understand in the recent Pollard(2014) paper: Why is Amery stable ? Thoughts ?

sidd

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

edit: It may also be more difficult to get the Amery ice shelf to collapse due to hydrofracturing as it is so well confined by the adjoining land mass.
« Last Edit: January 08, 2015, 02:11:48 PM by AbruptSLR »
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #73 on: January 08, 2015, 02:12:41 PM »
The extent of iceberg debris fields identified near the gateway to the Wilkes Subglacial Basin by the linked reference, makes it evident that under Pliocene like conditions "cliff failure (possibly/probably together with hydrofracturing [see Pollard, DeConto & Alley 2015)" was an important type of ice mass loss from this portion of the EAIS, and may soon be again if we continue on a BAU pathway:

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


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

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

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Re: EAIS Contributions to SLR by 2100
« Reply #74 on: January 20, 2015, 10:31:12 PM »
Reinardya et al 2015, Repeated advance and retreat of the East Antarctic Ice Sheet on the continental shelf during the early Pliocene warm period:
http://www.sciencedirect.com/science/article/pii/S0031018215000103

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

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

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Re: EAIS Contributions to SLR by 2100
« Reply #75 on: January 26, 2015, 11:54:30 AM »
Warm ocean water is melting Totten glacier from below:
http://www.abc.net.au/news/2015-01-26/sea-water-melting-totten-glacier-in-antarctica-from-below/6047076

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

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

Tony Worby, also from the research centre, said the study was groundbreaking. "No ship has ever been where the Aurora Australis went on this voyage, the ship managed to get front of the Totten Glacier," he said. "Over the next year or two we'll process all of that data and get a really great sense of how warmer ocean water is affecting the glacier."

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Re: EAIS Contributions to SLR by 2100
« Reply #76 on: January 27, 2015, 08:17:41 AM »
Rintoul comparing Totten to PIG:
http://www.theage.com.au/environment/climate-change/giant-east-antarctic-glacier-melting-with-warmer-oceans-20150127-12ypy4.html

"Pine Island is melting and thinning more rapidly, but Totten is not too far behind," he said.

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #77 on: February 05, 2015, 01:46:25 AM »
The fact that the linked reference connects the rate of iceberg calving from the Wilkes Subglacial Basin during the Pliocene to the austral summer isolation; indicates to me that this provided circumstantial support for the Pollard et al (2015) cliff failure and hydrofracturing mechanism for this part of Antarctic:

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


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

Abstract: "The Pliocene and Early Pleistocene, between 5.3 and 0.8 million years ago, span a transition from a global climate state that was 2–3 °C warmer than present with limited ice sheets in the Northern Hemisphere to one that was characterized by continental-scale glaciations at both poles. Growth and decay of these ice sheets was paced by variations in the Earth’s orbit around the Sun. However, the nature of the influence of orbital forcing on the ice sheets is unclear, particularly in light of the absence of a strong 20,000-year precession signal in geologic records of global ice volume and sea level. Here we present a record of the rate of accumulation of iceberg-rafted debris offshore from the East Antarctic ice sheet, adjacent to the Wilkes Subglacial Basin, between 4.3 and 2.2 million years ago. We infer that maximum iceberg debris accumulation is associated with the enhanced calving of icebergs during ice-sheet margin retreat. In the warmer part of the record, between 4.3 and 3.5 million years ago, spectral analyses show a dominant periodicity of about 40,000 years. Subsequently, the powers of the 100,000-year and 20,000-year signals strengthen. We suggest that, as the Southern Ocean cooled between 3.5 and 2.5 million years ago, the development of a perennial sea-ice field limited the oceanic forcing of the ice sheet. After this threshold was crossed, substantial retreat of the East Antarctic ice sheet occurred only during austral summer insolation maxima, as controlled by the precession cycle."
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Re: EAIS Contributions to SLR by 2100
« Reply #78 on: February 08, 2015, 12:22:02 AM »
Rintoul comparing Totten to PIG:
http://www.theage.com.au/environment/climate-change/giant-east-antarctic-glacier-melting-with-warmer-oceans-20150127-12ypy4.html

"Pine Island is melting and thinning more rapidly, but Totten is not too far behind," he said.

Warm ocean melting East Antarctica's largest glacier
But the voyage found that waters around the glacier were some 1.5 degrees Celsius warmer than other areas visited on the same trip during the southern hemisphere summer.
"We made it to the front of the glacier and we measured temperatures that were warm enough to drive significant melt," Rintoul said.

What scares me is that the more hard data we get the more 'surprises' we find. The question that keeps coming to mind is how can the majority of scientist studying this continue to to put up such low numbers for SLR? Granted the physics say you need x amount of energy for y amount of melt, but there are so many different ways of a glacier to melt and all the different ways seem to be happening at the same time in all parts of the world that I really think we are getting a very low ball number and it will be only when we get to an "Oh ****" year such as what happened in the Arctic in 2007,2012 that we will find out how bad things really are. Mind you by then it will be too late to save a great many cities.
Unlike sea ice, glaciers rarely have a 'rebound' year.
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sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #79 on: February 08, 2015, 06:08:10 AM »
"What scares me is that the more hard data we get the more 'surprises' we find."

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

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

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

Some are breaking ranks. Rignot comes to mind.

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

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

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

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

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

Join the club.

sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #80 on: February 11, 2015, 02:40:13 PM »
Another question that does come to mind is what about those lakes under the ice. Other then being surprised that they are there and how big they are there seems to be very little being said as to how they affect the ice above them and how the dynamics may change if the ocean starts interacting with that water.
Sidd you mentioned the rain, but as a few have mentioned rarely the more the ice melts, the lower the surface altitude gets, the warmer air temps become. Some people talk about the very cold temps at the south pole. Part of that is because the air temps would be cold anyway but you are sitting also on top of 9000 ft of ice. That can mean a change in average temps if that was all gone of a couple of dozen degrees on its own.
Paraphrasing a scientist that I heard (can not remember who it was): The more we learn, the more we find out how little we actually know. ( A closer quote was actually: The difference between someone with a masters degree and a PhD is not the amount of knowledge they have which is very little difference in actual fact, but that the one with the masters thinks they know everything and the one with the PhD discovers they know nothing.)
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sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #81 on: February 11, 2015, 07:53:37 PM »
"but as a few have mentioned rarely the more the ice melts, the lower the surface altitude gets, the warmer air temps become"

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

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Re: EAIS Contributions to SLR by 2100
« Reply #82 on: February 18, 2015, 06:24:37 PM »
Do we have a thread just on general slr? Anyway, here are a couple pieces on it:

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

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

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

http://www.rollingstone.com/politics/news/the-pentagon-climate-change-how-climate-deniers-put-national-security-at-risk-20150212
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Re: EAIS Contributions to SLR by 2100
« Reply #83 on: February 18, 2015, 06:47:51 PM »
Do we have a thread just on general slr?


wili,

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

http://forum.arctic-sea-ice.net/index.php/topic,874.250.html
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Re: EAIS Contributions to SLR by 2100
« Reply #84 on: February 18, 2015, 06:56:14 PM »
Thanks. I'll repost there.
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #85 on: February 26, 2015, 09:50:08 PM »

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


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


Extract: "Our observations of the Jökulhlaup confirmed Law Dome had high geothermal heat emanating from the Earth's crust which was melting the bottom of the ice cap," Professor Goodwin said."
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Re: EAIS Contributions to SLR by 2100
« Reply #86 on: March 16, 2015, 07:17:55 PM »
I am re-posting Chuck Yokota's post in the "What's new in Antarctica?" thread to this thread about the EAIS:

East Antarctica Melting Could be Explained by Oceanic Gateways

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


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

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

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

The ice loss to the ocean may soon be irreversible unless atmospheric and oceanic conditions change so that snowfall outpaces coastal melting. The potential for irreversible ice loss is due to the broadly deepening shape of Totten Glacier’s catchment, the large collection of ice and snow that flows from a deep interior basin to the coastline."
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #87 on: March 16, 2015, 07:25:09 PM »
As a public service, I provide the following reference information about the article on Totten that Chuck Yokota cited:

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


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


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

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Re: EAIS Contributions to SLR by 2100
« Reply #88 on: March 16, 2015, 09:18:03 PM »
Regarding Totten's (in)-stability also see the following Washington Post article & extract:

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

Extract: “What we need now is a confirmation of the findings of the paper from oceanographic data, because it is one thing to find potential pathways for warm water to intrude the cavity, it is another to show that this is actually happening,” observes Eric Rignot, an Antarctica expert at the University of California, Irvine. “This paper comes short of the latter, but other research efforts are underway to get critical oceanographic information near Totten.”
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Re: EAIS Contributions to SLR by 2100
« Reply #89 on: March 17, 2015, 05:15:23 PM »
Regarding Totten's (in)-stability also see the following Washington Post article & extract:

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

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


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

I mean, how could the entire continent NOT become undercut by warmer waters in the near future?
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Re: EAIS Contributions to SLR by 2100
« Reply #90 on: March 17, 2015, 06:45:59 PM »
I mean, how could the entire continent NOT become undercut by warmer waters in the near future?

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

The Pollard et al 2015 paper certainly sounds an alarm about possible abrupt EAIS SLR contributions towards the end of this century (assuming we continue on a BAU pathway for a few more decades).
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #91 on: March 27, 2015, 10:50:50 PM »
The linked reference discusses research by a French team working in Antarctica that looked at the history of the polynya in the lee of the Mertz Glacier going back 250 years.

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


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


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

Also see:
http://gizmodo.com/when-an-iceberg-the-size-of-a-country-breaks-free-what-1694005231
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

wili

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Re: EAIS Contributions to SLR by 2100
« Reply #92 on: April 17, 2015, 07:22:31 PM »
https://www.skepticalscience.com/trouble-at-totten-glacier.html

New Video: The Trouble at Totten Glacier

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

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

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

It’s a realization that, one top expert told us, even seasoned ice sheet veterans find “shattering”.
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #93 on: April 18, 2015, 07:43:33 AM »
Also from the Mooney-piece:
For Richard Alley, a glaciologist at Penn State University, the new research hints at a possible solution to a question that scientists have long had about the planet’s past — and in particular the Pliocene epoch, beginning 5.3 million years ago, when sea levels were dramatically higher, by as much as 40 meters.

“The sea-level indicators from the Pliocene have suggested that an important amount of ice came out of East Antarctica into the ocean,” says Alley. “Sedimentary records offshore pointed in the same way, and recent modeling… shows the strong potential for this to have happened. This new paper adds to the evidence — the pieces are fitting together.”

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #94 on: April 18, 2015, 03:56:49 PM »

New Video: The Trouble at Totten Glacier


wili,

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

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Shared Humanity

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Re: EAIS Contributions to SLR by 2100
« Reply #95 on: April 20, 2015, 04:20:32 AM »
I can't imagine why anyone would  think this portion of the EAIS would not be susceptible to underwater melt.

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


AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #96 on: April 30, 2015, 03:20:17 AM »
The linked article provides a light discussion of the investigation of the East Antarctic bed map in and around the Totten Catchment Basin (see attached map):

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

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

JMP

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Re: EAIS Contributions to SLR by 2100
« Reply #97 on: April 30, 2015, 05:45:58 AM »
Below from the comment section of the article ASLR in Reply #96 (also #86) linked to above:
http://www.jsg.utexas.edu/news/2015/03/east-antarctica-melting-could-be-explained-by-oceanic-gateways

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

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

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

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

“Now we know the ocean is melting ice in an area of the glacier that we thought was totally cut off before,” Greenbaum said. “Knowing this will improve predictions of ice melt and the timing of future glacier retreat.”

Apologies for reposting this link but I had not taken note of this exact aspect previously and it seems significant enough to keep in context and repeat.  That there is a channel three miles wide is astounding to me. Am anxious to know what predictions they might make from this.




« Last Edit: April 30, 2015, 06:06:07 AM by JMP »

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #98 on: April 30, 2015, 08:06:43 PM »
Am anxious to know what predictions they might make from this.


JMP,

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

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

See also:

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

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #99 on: May 01, 2015, 04:49:07 AM »
"three-mile-wide seafloor valley"

Thwaites is ten times that ...