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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #100 on: May 01, 2015, 10:17:16 AM »
"three-mile-wide seafloor valley"

Thwaites is ten times that ...

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

I note also, that the formation of the Thwaites Ice Tongue indicates that "surges" of ice have moved out of this trough repeatedly in the past several hundred years; and I suspect that in the coming multiple decades that the ice in the Totten gateway "seafloor valley" may also "surge" repeatedly (which thins the glacial ice sufficiently that eventually icebergs will be able to float out of the Totten Catchment Basin that are created by Pollard et al style cliff failures and hydrofracturing, assuming that we reach early Pliocene conditions this century).
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Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #101 on: May 01, 2015, 01:07:12 PM »
I was told David Pollard and colleague(s) are about to submit a 'high-profile paper on future changes'. I don't know how long it will take to be published and what the topic is, but it would be interesting if they applied the work for Pollard et al 2015 to the current situation at Totten (and the rest of AIS) and if they could make projections for the coming centuries. Keep an eye out (no idea if it would take weeks or months before publication).
« Last Edit: May 01, 2015, 08:18:38 PM by Lennart van der Linde »

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #102 on: May 01, 2015, 04:39:53 PM »
As previously discussed in Reply #222 of the "Potential Collapse Scenario for the WAIS" thread, Pollard et al 2015 already considered SLR contribution due to hydrofracturing & ice cliff failures from all of the AIS (both the WAIS & the EAIS, under Pliocene conditions), as indicated in the attached image & associated caption (however the Pollard et al 2015 work does not consider the influence of the newly identified "three-mile-wide seafloor valley" subjected to advected CDW into the valley):

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

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

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

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

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

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


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

Expected final online publication date for the Annual Review of Earth and Planetary Sciences Volume 43 is May 30, 2015. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #103 on: May 01, 2015, 05:03:39 PM »
For those who do not have access to Pollard et al (2015), I provide the two additional images from that paper that assumes Pliocene type forcing imposed on modern conditions.  While modern temperatures are not yet as high as Pliocene conditions, our current anthropogenic radiative forcing is already much higher (CO2-equivalent of over 485 ppm on April 1 2015, and rising rapidly) than those during the Pliocene and the Southern Ocean heat content is rising much more rapidly than that for the ocean at-large.  Furthermore, as stated in my last post, Pollard et al (2015) do not consider the recently identified "seafloor valley" in the Totten Gateway.

Finally, I note that while I said that there are a large number of parallels between Thwaites and Totten, I never said that the timing of their potential collapse scenarios were identical (but note that once combined cliff failure & hydrofracturing calving events occur, both gateways are tens of miles wide with regard to the potential float-out of calved icebergs).
« Last Edit: May 01, 2015, 08:17:46 PM by AbruptSLR »
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sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #104 on: May 01, 2015, 08:17:48 PM »
There is a paper out by Harig and Simons doi:10.1016/j.epsl.2015.01.029, latest GRACE data

"Ignoring GIA model uncertainty, over the period 2003–2014, West Antarctica has been losing ice mass at a rate of −121 ± 8 Gt/yr and has experienced large acceleration of ice mass losses along the Amundsen Sea coast of −18 ± 5 Gt/yr^2 , doubling the mass loss rate in the past six years. The Antarctic Peninsula shows slightly accelerating ice mass loss, with larger accelerated losses in the southern half of the Peninsula. Ice mass gains due to snowfall in Dronning Maud Land have continued to add about half the amount of West Antarctica’s loss back onto the continent over the last decade. We estimate the overall mass losses from Antarctica since January 2003 at −92 ± 10 Gt/yr."

Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #105 on: May 01, 2015, 08:45:44 PM »
ASLR,
Thanks for pointing to Alley, Pollard et al 2015. That may be the paper that I was told to watch out for. We'll see.

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

So it seems they're wondering what projections a different study would give that would be more "directly applicable to the future", for example by including current orbital insolation, CO2 rising further beyond 400 ppm and more gradual ocean warming. Would that give the same rate of ice mass loss, or even faster, or maybe slower?

Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #106 on: May 01, 2015, 09:12:36 PM »
It seems Alley et al 2015 is not the paper I was told about. DeConto would be lead author and the paper is expected to be published coming fall or winter.

Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #107 on: May 05, 2015, 07:54:23 PM »
Pollard and DeConto on their 2015 paper with Alley and their upcoming paper on implications for the future:
http://www.theguardian.com/environment/planet-oz/2015/may/05/melting-antarctic-failure-to-cut-emissions-now-could-raise-worlds-oceans-by-several-metres

'David Pollard, of the Earth and Environmental Systems Institute at Penn State University, and co-author Professor Robert DeConto, of the University of Massachusetts, told me while it was “pretty clear” that their findings had implications for the future (to be explored in an upcoming paper by Pollard and DeConto) the study’s real focus was to better understand the past.'

Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #108 on: May 05, 2015, 09:51:49 PM »
This EGU-contribution by DeConto & Pollard should become the announced paper later this year:
http://meetingorganizer.copernicus.org/EGU2015/EGU2015-8104.pdf

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

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

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

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

So they don't say here how fast ice-sheet retreat is in their higher emission scenarios. Maybe they did in their presentation?

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #109 on: May 05, 2015, 10:13:28 PM »
Lennart,

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

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

Best,
ASLR
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Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #110 on: May 05, 2015, 10:25:05 PM »
Yes. And this one by Gasson, DeConto and Pollard looks interesting too:
http://meetingorganizer.copernicus.org/EGU2015/EGU2015-10742.pdf

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

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

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

Here we focus on improving simulation of the Antarctic ablation zone by using an asynchronously coupled RCM to provide climate forcing to an ice sheet model. We use a GCM with a Miocene paleo-geography to provide boundary forcing for the RCM, with atmospheric CO2 at various concentrations. In previous simulations there was limited retreat of the ice sheet away from the continental margin, due to a strong hysteresis mechanism. In these asynchronous simulations there is increased retreat of the Antarctic ice sheet, with continental sectors retreating away from the continental margin. This results in a greater overall decrease in ice volume than for non-asynchronously coupled simulations."

Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #111 on: May 05, 2015, 10:32:15 PM »
There's more here for those interested:
http://meetingorganizer.copernicus.org/EGU2015/session/18158

Next year Neven will need some help in following all these sessions :)

Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #112 on: May 05, 2015, 10:48:24 PM »
Also see Hansen's most recent comments:
http://www.climatecodered.org/2015/05/hansen-says-its-crazy-to-think-that-2.html

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

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

The consequences are almost unthinkable. It would mean that all coastal cities would become dysfunctional, some parts of the cities would still be sticking above the water but they would not be habitable, so the economic implications are incalculable. We really cannot go down that path, this is an issue of intergenerational injustice, it's a moral issue…"

solartim27

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Re: EAIS Contributions to SLR by 2100
« Reply #113 on: June 04, 2015, 02:13:39 AM »
FNORD

Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #114 on: June 10, 2015, 07:49:21 PM »
Rignot on potential EAIS ice loss:
http://climatestate.com/2015/06/09/eric-rignot-observations-suggest-that-ice-sheets-and-glaciers-can-change-faster-sooner-and-in-a-stronger-way-than-anticipated/

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

Rignot: East Antarctica has marine-based sectors like West Antarctica but few of them have retrograde beds, i.e. beds that get deeper inland, so they are more immune to rapid collapse yet they remain serious concerns for sea level rise because they hold together far more ice than West Antarctica. At present, numerical models are simply unable to deal with East Antarctica for a variety of reasons including poor model constraints and insufficient understanding of key processes, e.g. circulation of warm water around the periphery and its impact on ice shelf melt."

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #115 on: July 07, 2015, 02:48:40 AM »
The linked reference discusses the paleo stability (instability) of the Wilkes Land continental margin (EAIS) in response to the early Pliocene ocean warming (which are conditions that the Earth could approximately replicate before 2100):

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

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

Abstract: "We investigate the stability of the East Antarctic Ice Sheet (EAIS) on the Wilkes Land continental margin, Antarctica, utilizing a high-resolution record of ice-rafted debris (IRD) mass accumulation rates (MAR) from Integrated Ocean Drilling Program Site U1359. The relationship between orbital variations in the IRD record and climate drivers was evaluated to capture changes in the dynamics of a marine-based ice sheet in response to early Pliocene warming. Three IRD MAR excursions were observed and confirmed via scanning electron microscope microtextural analysis of sand grains. Time series analysis of the IRD MAR reveals obliquity-paced expansions of the ice sheet to the outer shelf prior to ~4.6 Ma. A decline in the obliquity and a transition into a dominant precession response of IRD MAR occur at ~4.6 Ma along with a decline in the amplitude of IRD MAR maxima to low background levels between ~4.0 and ~3.5 Ma. We speculate that as sea surface temperatures began to peak above 3°C during the early Pliocene climatic optimum, the ice shelves thinned, leading to a greater susceptibility to precession-forced summer insolation and the onset of persistent retreat of a marine-based portion of the EAIS."
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #116 on: August 04, 2015, 06:43:20 PM »
The linked reference uses the Roi Baudouin Ice Shelf (RBIS) in East Antarctica as an example (see the attached image) of how to use satellites to monitor basal ice channels in Antarctic ice shelves.  This information could become vital for predicting possible future major ice shelf calving events, if we continue down a warm pathway for anthropogenic forcing, this century:

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

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

Abstract: "Ice shelves buttress the continental ice flux and mediate ice–ocean interactions. They are often traversed by channels in which basal melting is enhanced, impacting ice-shelf stability. Here, channel evolution is investigated using a transient, three-dimensional full Stokes model and geophysical data collected on the Roi Baudouin Ice Shelf (RBIS), Antarctica. The modeling confirms basal melting as a feasible mechanism for channel creation, although channels may also advect without melting for many tens of kilometers. Channels can be out of hydrostatic equilibrium depending on their width and the upstream melt history. Inverting surface elevation for ice thickness using hydrostatic equilibrium in those areas is erroneous, and corresponding observational evidence is presented at RBIS by comparing the hydrostatically inverted ice thickness with radar measurements. The model shows that channelized melting imprints the flow field characteristically, which can result in enhanced horizontal shearing across channels. This is exemplified for a channel at RBIS using observed surface velocities and opens up the possibility to classify channelized melting from space, an important step towards incorporating these effects in ice–ocean models."
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solartim27

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Re: EAIS Contributions to SLR by 2100
« Reply #117 on: August 20, 2015, 03:35:45 AM »
Should we be concerned about this sudden notch in Totten?  Here is April 18, then Aug 17, and 18th.  I know the sea ice will blow around a lot, but I haven't seen anything like the notch in that area before.  It's about 10 km across, scale bar is in the corner.
FNORD

solartim27

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Re: EAIS Contributions to SLR by 2100
« Reply #118 on: August 20, 2015, 03:57:39 AM »
I had saved a Polar view from Mar 16th, so here that is with the one for Aug 17th.  I couldn't get the scales to match up, but you get the idea.  The berg that shows up in the lower left corner is not a new calving, it's been blowing around down there for a while, not sure where it's from.
FNORD

sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #119 on: August 20, 2015, 05:13:20 AM »
wind driver polynya, i think. AABW forms there

solartim27

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Re: EAIS Contributions to SLR by 2100
« Reply #120 on: August 20, 2015, 06:01:20 AM »
The notch area is also on the Sentinel shot from July 22, but not visible on the last clear Worldview shot from May 2.  My impression was the dark line on Worldview was the demarcation for the ice shelf, as opposed to seasonal sea ice.
FNORD

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #121 on: August 20, 2015, 04:48:29 PM »
wind driver polynya, i think. AABW forms there


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

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

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


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

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


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

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

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

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

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

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

Best,
ASLR
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BornFromTheVoid

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Re: EAIS Contributions to SLR by 2100
« Reply #122 on: August 22, 2015, 02:21:06 PM »
https://www.reddit.com/r/science/comments/3hylyw/science_ama_series_we_are_living_in_concordia/


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

We are based at the French-Italian research station Concordia on the east high Antarctic plateau (75°S, 123°E, 3233m). It is one of the remotest, coldest, driest places on Earth, we are 1200 km from the coast and our nearest neighbour is 600 km away: the Russian station Vostok. The landscape is an immense white, flat surface of compacted snow extending 1000 km in all directions. The snow and ice on which we walk is more than 3 km thick. Living here is like living on another planet, ‘Planet Concordia’ or ‘White Mars’. During the nine months of winter from February to November, the station is completely isolated from the rest of the world. No plane or vehicle can reach us, even in an emergency as the harsh weather conditions make all travel impossible. We have experienced temperatures down to –80°C and three months of complete darkness. The multicultural crew is consists of 13 people: seven for logistics and six scientists. We are five Italians, one Swiss, one English and six French. This year we are three women and ten men from 24 to 56 years old. We must rely on our own skills and teamwork while being prepared to face any kind of emergency through training, fire, rescue and medical exercises. Antarctica is the largest, most extreme, multi-disciplinary, open-air scientific laboratory that helps us understand the mechanisms that regulate our planet, its climate, its history and offers a platform to observe and understand the structure of the universe, as well as charting the adaptation of humans to harsh environments. Thanks to the Antarctic Treaty, nations worldwide collaborate peacefully with respect for this environment in the name of science. We are one of very few stations at the heart of the Antarctic continent, so Concordia stands as an important node in the Earth Observatory Grid, for fields such as meteorology, seismology, geomagnetism and atmospheric chemistry. Lorenzo Moggio: 30 years old, Italian physicist, research fellow at the Bologna Institute of Atmospheric Sciences and Climate of the Italian National Research Council. This is my second winter spent at Concordia, I was here in 2010 as well.
Giampietro Casasanta: 35 years old, Italian physicist with a PhD in Remote Sensing and research fellow at the Rome Bologna Institute of Atmospheric Sciences and Climate of the Italian National Research Council. I am in charge of the Italian glaciology and remote sensing experiments.
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #123 on: September 14, 2015, 10:08:10 PM »
The attached Aqua image from Sept 14 2015 shows that the polynyas at Totten have gotten larger (which might possibly be associated with the advection of warm CDW into the area, or could be strictly associated with winds).
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solartim27

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Re: EAIS Contributions to SLR by 2100
« Reply #124 on: September 15, 2015, 03:17:27 AM »
Wouldn't this be more breakup of the floating ice shelf in front of the glacier, since it is within the grey line that comes up with the coastline overlay?  I was willing to accept the last wind burst I had posted about was a polyna, since I had found comparable retreat in previous years.  I believe this is a new line of retreat.  I'll try to post a gif of what I had seen later.

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

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #125 on: September 15, 2015, 03:36:13 AM »
Wouldn't this be more breakup of the floating ice shelf in front of the glacier, since it is within the grey line that comes up with the coastline overlay?  I was willing to accept the last wind burst I had posted about was a polyna, since I had found comparable retreat in previous years.  I believe this is a new line of retreat.  I'll try to post a gif of what I had seen later.

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

I am a bit tied-up to tell if major calving has occurred, or not.  You might want to check Google Earth as it sometimes shows the grounding line.
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #126 on: September 15, 2015, 09:43:43 PM »
Here is an image of Totten Glacier ice flow velocities from a couple of years ago.  This could support the concept that the Totten Ice Shelf has calved since then.
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Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #127 on: October 26, 2015, 09:05:25 PM »
Chris Mooney on new paper on vulnerability of Totten (Aurora) basin:
http://www.washingtonpost.com/news/energy-environment/wp/2015/10/26/east-antarcticas-biggest-glacier-is-melting-from-below-study-confirms/

Or actually it's not such a new paper, of March this year, by Greenbaum et al.

ChadGreene

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Re: EAIS Contributions to SLR by 2100
« Reply #128 on: October 27, 2015, 06:17:44 PM »
Totten's calving front has undergone some minor seasonal and interannual changes over the past 15 years but there appears to be no major secular trend in the coast line.  Here are MODIS images from February of 2001 and 2015:

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

ftp://sidads.colorado.edu/pub/DATASETS/ICESHELVES/modis_iceshelf_archive/sabri/images/sabri_2015263_0040_modis_ch02.png

solartim27

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Re: EAIS Contributions to SLR by 2100
« Reply #129 on: October 29, 2015, 09:35:08 PM »
Here is a look at Totten from Sep 22 to Oct 26.  No major changes, but it does look like it could be interesting to watch over the summer.
FNORD

Lennart van der Linde

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Re: EAIS Contributions to SLR by 2100
« Reply #130 on: November 27, 2015, 03:27:49 PM »
Jones et al 2015 on Rapid Holocene thinning of an East Antarctic outlet glacier driven by marine ice sheet instability:
http://www.nature.com/ncomms/2015/151126/ncomms9910/full/ncomms9910.html

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

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #131 on: November 27, 2015, 05:22:30 PM »
Jones et al 2015 on Rapid Holocene thinning of an East Antarctic outlet glacier driven by marine ice sheet instability:

Great catch (a valuable reference); however, I don't think that this example fully represents key aspects of more dynamic MISI as it does not appear to fully demonstrate either cliff failures and hydrofracturing together with active advection of warm CDW to the grounding line.  This indicates to me that scientists like Pollard would be better off calibrating their (his) MISI model against the Holocene Optimum case for the Jakobshavn Glacier (see Reply # 171 in the "Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe" thread).
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #132 on: January 04, 2016, 05:13:47 PM »
The linked (open access) reference examines two East Antarctic ice cores focused on improving our understanding of the timing and the duration of the MIS 5 event.  Modeling the MIS 5 correctly is important to future climate model estimates of EAIS and WAIS contributions to SLR:

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

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

Abstract. Two deep ice cores, Dome Fuji (DF) and EPICA Dome C (EDC), drilled at remote dome summits in Antarctica, were volcanically synchronized to improve our understanding of their chronologies. Within the past 216 kyr, 1401 volcanic tie points have been identified. DFO2006 is the chronology for the DF core that strictly follows O2 / N2 age constraints with interpolation using an ice flow model. AICC2012 is the chronology for five cores, including the EDC core, and is characterized by glaciological approaches combining ice flow modelling with various age markers. A precise comparison between the two chronologies was performed. The age differences between them are within 2 kyr, except at Marine Isotope Stage (MIS) 5. DFO2006 gives ages older than AICC2012, with peak values of 4.5 and 3.1 kyr at MIS 5d and MIS 5b, respectively. Accordingly, the ratios of duration (AICC2012 / DFO2006) range between 1.4 at MIS 5e and 0.7 at MIS 5a. When making a comparison with accurately dated speleothem records, the age of DFO2006 agrees well at MIS 5d, while the age of AICC2012 agrees well at MIS 5b, supporting their accuracy at these stages. In addition, we found that glaciological approaches tend to give chronologies with younger ages and with longer durations than age markers suggest at MIS 5d–6. Therefore, we hypothesize that the causes of the DFO2006–AICC2012 age differences at MIS 5 are (i) overestimation in surface mass balance at around MIS 5d–6 in the glaciological approach and (ii) an error in one of the O2 / N2 age constraints by ~ 3 kyr at MIS 5b. Overall, we improved our knowledge of the timing and duration of climatic stages at MIS 5. This new understanding will be incorporated into the production of the next common age scale. Additionally, we found that the deuterium signals of ice, δDice, at DF tends to lead the one at EDC, with the DF lead being more pronounced during cold periods. The lead of DF is by +710 years (maximum) at MIS 5d, −230 years (minimum) at MIS 7a and +60 to +126 years on average.
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #133 on: February 19, 2016, 02:12:33 AM »
I believe that the linked reference is relevant to the EAIS, the GIS, and portions of the WAIS (not including the ASE area), and the reference presents field evidence from the Laurentide Ice Sheet from 22,000 to 7,000 years ago, showing that ice stream flow did not progressively destabilize the larger ice sheet, but rather that ice mass loss proceeded at a relatively steady rate.

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

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

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


See also:
http://www.csmonitor.com/Science/2016/0218/Are-glacial-ice-streams-contributing-to-the-rise-of-ocean-levels
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #134 on: March 24, 2016, 05:02:52 PM »
The linked reference presents satellite information about Totten from 1996 to 2013, which shows that while the grounding line for the glacier is retreating rapidly, there is no imminent danger of marine glacier instability.  The images come from the second linked document because it is an open access source to the Geophy. Res. Lett. paywall for this research:

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

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

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

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

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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #135 on: May 19, 2016, 04:39:04 PM »
With a hat tip to Adam Ash, I provide the linked reference that indicates that Totten is closer to collapse than previously realized:

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


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


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

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

Extract: "The Totten Glacier in East Antarctica has an unstable area that could collapse and contribute to more than two metres of sea level rise beyond what is generally predicted if climate change remains unchecked, researchers say."
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crandles

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Re: EAIS Contributions to SLR by 2100
« Reply #136 on: May 19, 2016, 06:16:07 PM »
BBC says
Scientists tell the journal Nature that should the front of the glacier retreat about 150km from its current position, it will then enter a runaway reversal that takes it 200-250km further inland.


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

Still the more potential unstable situations there are, the more reason to take precautionary measures.

sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #137 on: May 19, 2016, 07:36:04 PM »
The BBC reference is to Aitken(2016) doi:10.1038/nature17447
Nice paper with discussion of geology under the ice, and some carefully argued paleo detail.

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #138 on: May 19, 2016, 07:58:54 PM »
The BBC reference is to Aitken(2016) doi:10.1038/nature17447
Nice paper with discussion of geology under the ice, and some carefully argued paleo detail.


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

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


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


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

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

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


By studying the history of Totten's advances and retreats, researchers have discovered that if climate change continues unabated, the glacier could cross a critical threshold within the next century, entering an irreversible period of very rapid retreat."
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sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #139 on: May 19, 2016, 10:52:44 PM »
After a pleasurable hour or two reading the Aitken paper, i realize it is quite a bold and magisterial work, using a very sophisticated gravitational model, an ice sheet (PISM) model, and several different airborne and paleo data sources. I am unqualified on the geology, so i have consulted a geologist, and i look forward to her thoughts. PISM does not yet include cliff instability and hydrofracture as far as i know, but even so, the broad thesis that the sector behind Totten is unstable and has retreated quickly in the past is quite convincing.

Certainly a paper to read and reread carefully.

sidd

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #140 on: May 26, 2016, 05:38:29 PM »
Scribbler has a nice article on Totten Glacier:

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

Extract: "Totten Glacier… has the largest thinning rate in East Antarctica. Thinning may be driven by enhanced basal melting… Warm modified Circumpolar Deep Water, which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the nearby continental shelf beneath 400 to 500 m of cool Antarctic Surface Water…We identify entrances to the ice-shelf cavity below depths of 400 to 500 m that could allow intrusions of warm water if the vertical structure of inflow is similar to nearby observations. Radar sounding reveals a previously unknown inland trough that connects the main ice-shelf cavity to the ocean. If thinning trends continue, a larger water body over the trough could potentially allow more warm water into the cavity, which may, eventually, lead to destabilization of the low-lying region between Totten Glacier and the similarly deep glacier flowing into the Reynolds Trough"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #141 on: June 17, 2016, 12:22:08 AM »
The linked reference studies the impact of pinning points on ice mass loss from marine glaciers in Dronning Maud Land, East Antarctica (see first image), and conclude that while the likely SLR contribution this century from this area (see second image) is meaningful but slower than that from the WAIS (with continued global warming), and that including the dynamic influence of the pinning points in their model actually increased the SLR contribution this century by about 10% over models without the pinning points.  Thus the dynamic influence of pinning points should be assess for other Antarctic marine glaciers:

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

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

Abstract. The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart, because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by (more stable) grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouin ice shelves over the next millennia. Overall, the sub-ice shelf melting substantially impacts the sea level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the collapse of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrates that the onset of the marine ice-sheet retreat and subsequent promontory collapse is controlled by small pinning points within the ice shelves, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning has a small effect on the total amount of sea level rise but locally affects the timing of grounding-line migration, advancing the collapse of a promontory by hundreds of years. On the other hand, omitting the same pinning point in data assimilation decreases the sea level contribution by 10 % and delays the promontory collapse by almost a millennium. This very subtle influence of pinning points on ice dynamics acts on kilometre scale and calls for a better knowledge of the Antarctic margins that will improve sea-level predictions.
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #142 on: August 18, 2016, 04:43:29 PM »
While not of immediate concern w.r.t. SLR the linked reference discusses the evolution of seasonal supraglacial meltwater lakes on Langhovde Glacier, Dronning Maud Land, East Antarctica (see first image), between 2000 and 2013, and the continued evolution of such supraglacial East Antarctic lakes could eventually feed the hydrofracturing and cliff failure mechanisms identified by DeConto & Pollard (see second image) by, or shortly after, 2100:

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

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

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


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

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

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

Richard Alley, a glaciologist at Penn State who was not involved in the study, noted in an email comment that seeing some Antarctic surface melt is not too surprising. “Across many sensors and studies, there is summertime melting on the surface of Antarctica around the edges, and sometimes in some places extending farther inland than you might think,” he said.
However, Alley continued, we should be very concerned about such melting increasing. Alley referred to a study from earlier this year, by Rob DeConto of the University of Massachusetts, Amherst, and David Pollard of Penn State, which found that surface melt is one factor that could greatly speed total Antarctic ice loss, by increasing the tendency for “hydrofracture” to occur, in which meltwater helps to break apart ice shelves."
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― Leon C. Megginson

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #143 on: August 27, 2016, 08:14:57 PM »
The linked open access reference studies AABW production in the Cape Darnley Polyna, adjoining Prydz Bay in East Antarctica. The reference concludes that: "Given the growing number of reports of accelerating and irreversible mass loss from Antarctica’s major ice sheets linked to increased oceanic heat input, it is likely that Antarctica’s AABW production is already compromised and will decrease further into the future."  The reference implies that the AABW is the "canary in the coal mine" for Hansen et al (2016)'s slowing of the global thermohaline circulation, which should result in a positive ice-climate feedback that may increase the planetary energy imbalance as indicated by the attached Figure 7 from Hansen et al (2016):


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

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

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

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

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

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

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

“While this particular area may not be the hotspot for this kind of activity, the fact that we have all the main players makes it a very unique lab experiment to try to understand how it works,” Williams said. “It provides observational evidence which should renew efforts to look for this happening in more key areas of Antarctica where we do know there’s accelerating melt occurring and where bottom water production is important as well.”"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

FishOutofWater

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Re: EAIS Contributions to SLR by 2100
« Reply #144 on: August 28, 2016, 10:35:48 PM »
Purkey & Johnson had a paper a few years back that showed that deepwater all around Antarctica was in decline.Warmer intermediate waters are replacing it volumetrically. Othere papers have shown the decline of deepwater formation in the Weddell sea. In the last month extremely intense storms opened up a polynya there but it closed back up quickly because the water column there is more stable than it was in the 1970s when the polynya was self maintaining once it opened. Fresher surface water, produced by glacial melting from below is the likely culprit in the increased water column stability in the Weddell sea.

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

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

The tropics are about to go crazy in the north Atlantic because there's more heat stored there than anyone has ever seen before now.

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #145 on: October 03, 2016, 04:05:17 PM »
The linked (open access) reference confirms earlier findings that the Wilkes marine glacial basin is unstable once triggered (see attached images); which could then destabilize other portions of the East Antarctic Ice Sheet:

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

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

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

Extract: "We focus on three idealised scenarios, each of which represents a hypothetical collapse of the Wilkes Basin: WILKES, WEST and EAST. The locations of meltwater input within these experiments are shown in Fig. 2. In all of the experiments, a freshwater flux of 0.048 Sv is applied for 900 years. This is based on the estimate of Mengel and Levermann (2014), and is equivalent to an increase of ~3.8m in global sea level."
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #146 on: October 18, 2016, 12:43:22 PM »
More specifics about the Wilkens Ice Shelf:


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


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

Abstract. Ice shelves serve as important buttresses for upstream areas. Several large ice shelves on the Antarctic Peninsula have disintegrated or retreated, which implied dynamic consequences for upstream ice. The present study aims to assess dynamic changes on Wilkins Ice Shelf during multi-stage ice-front retreat in the last decade. A total area of 2135 ± 75 km2 was lost in the period 2008–2009. The present study uses time-series of SAR satellite observations (1994/96, 2006–2010) in order to derive variations in multi-temporal surface flow from intensity offset tracking methods. Spatial patterns of horizontal strain rate and stress components were inferred during different ice-front retreat stages. These fields are used to explain the different break-up stages and to evaluate the ice-shelf stability. For this purpose, we apply criteria which were forwarded to explain and assess past ice-shelf retreat.
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #147 on: November 29, 2016, 05:46:47 PM »
The linked Scribbler article is entitled: "Did Föhn Winds Just Melt Two Miles of East Antarctic Surface Ice in One Day? "

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

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

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

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

Though it is now certain that the large blue blotch in this satellite image is not a melt pond, a bluish coloration appearing over a broad swath of the above region in both the November 27 and November 28 image frames appears to indicate the presence of surface melt. So the downsloping wind related warming may well have produced a more subtle surface melt for this region of East Antarctica."
« Last Edit: November 29, 2016, 10:23:53 PM by AbruptSLR »
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #148 on: December 09, 2016, 07:03:27 PM »
The linked reference indicates that satellite data from the last two decades indicates that East Antarctic ice dynamics has higher rates of ice mass loss than scientists have previously acknowledged, and offers an approach to use future satellite data to better estimate this rate of ice mass loss:

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

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

Abstract. Mass balance changes of the Antarctic ice sheet are of significant interest due to its sensitivity to climatic changes and its contribution to changes in global sea level. While regional climate models successfully estimate mass input due to snowfall, it remains difficult to estimate the amount of mass loss due to ice dynamic processes. It's often been assumed that changes in ice dynamic rates only need to be considered when assessing long term ice sheet mass balance; however, two decades of satellite altimetry observations reveal that the Antarctic ice sheet changes unexpectedly and much more dynamically than previously expected. Despite available estimates on ice dynamic rates obtained from radar altimetry, information about changes in ice dynamic rates are still limited, especially in East Antarctica. Without understanding ice dynamic rates it is not possible to properly assess changes in ice sheet mass balance, surface elevation or to develop ice sheet models. In this study we investigate the possibility of estimating ice dynamic rates by removing modelled rates of surface mass balance, firn compaction and bedrock uplift from satellite altimetry and gravity observations. With similar rates of ice discharge acquired from two different satellite missions we show that it is possible to obtain an approximation of ice dynamic rates by combining altimetry and gravity observations. Thus, surface elevation changes due to surface mass balance, firn compaction and ice dynamic rates can be modelled and correlate with observed elevation changes from satellite altimetry.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #149 on: December 12, 2016, 06:29:57 PM »
Most climate models do not include wind-albedo interaction that is currently inducing surface melting in portions of East Antarctica, but the linked reference documents field evidence for this mechanism that could contribute to a faster rate of EAIS destabilization with global warming then currently projected:

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

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

Abstract: "Surface melt and subsequent firn air depletion can ultimately lead to disintegration of Antarctic ice shelves causing grounded glaciers to accelerate and sea level to rise. In the Antarctic Peninsula, foehn winds enhance melting near the grounding line, which in the recent past has led to the disintegration of the most northerly ice shelves. Here, we provide observational and model evidence that this process also occurs over an East Antarctic ice shelf, where meltwater-induced firn air depletion is found in the grounding zone. Unlike the Antarctic Peninsula, where foehn events originate from episodic interaction of the circumpolar westerlies with the topography, in coastal East Antarctica high temperatures are caused by persistent katabatic winds originating from the ice sheet’s interior. Katabatic winds warm and mix the air as it flows downward and cause widespread snow erosion, explaining >3 K higher near-surface temperatures in summer and surface melt doubling in the grounding zone compared with its surroundings. Additionally, these winds expose blue ice and firn with lower surface albedo, further enhancing melt. The in situ observation of supraglacial flow and englacial storage of meltwater suggests that ice-shelf grounding zones in East Antarctica, like their Antarctic Peninsula counterparts, are vulnerable to hydrofracturing."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson