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Stephan

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Re: Potential Collapse Scenario for the WAIS
« Reply #500 on: March 25, 2018, 08:43:49 PM »
Thank you sidd for this information.

oren

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Re: Potential Collapse Scenario for the WAIS
« Reply #501 on: March 26, 2018, 07:48:15 AM »
Stephan, bear in mind the retreat is not monotonous. It goes forward and back. It's also not uniform, due to bed topography and other factors. I think I saw a map somewhere up-thread that showed the grounding line of one or more of the glaciers for different years.

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #502 on: March 30, 2018, 10:22:55 PM »
It is good idea to keep an eye on Recovery/Slessor/Baily for their possible ice mass loss later this century:

Anja Diez et al. (30 March 2018), "Basal Settings Control Fast Ice Flow in the Recovery/Slessor/Bailey Region, East Antarctica', Geophysical Research Letters, https://doi.org/10.1002/2017GL076601

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076601

Abstract: "The region of Recovery Glacier, Slessor Glacier, and Bailey Ice Stream, East Antarctica, has remained poorly explored, despite representing the largest potential contributor to future global sea level rise on a centennial to millennial time scale. Here we use new airborne radar data to improve knowledge about the bed topography and investigate controls of fast ice flow. Recovery Glacier is underlain by an 800 km long trough. Its fast flow is controlled by subglacial water in its upstream and topography in its downstream region. Fast flow of Slessor Glacier is controlled by the presence of subglacial water on a rough crystalline bed. Past ice flow of adjacent Recovery and Slessor Glaciers was likely connected via the newly discovered Recovery‐Slessor Gate. Changes in direction and speed of past fast flow likely occurred for upstream parts of Recovery Glacier and between Slessor Glacier and Bailey Ice Stream. Similar changes could also reoccur here in the future."
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sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #503 on: April 02, 2018, 10:38:21 PM »
I and others have posted links to this paper which discusses PIG, Thwaites in some detail. PIG retreat seems to have slowed, attributed to less available warm CDW, but Thwaites has retreated faster. In the supplementary thay have a picture of the grounding lines which i attach. My earlier comment on this paper is at:

https://forum.arctic-sea-ice.net/index.php/topic,622.msg148216.html

doi: 10.1038/s41561-018-0082-z

I attach fig s3. The "further retreat" grounding line is arrived at as follows:

"We also consider a ‘further retreat’ scenario, which is designed to account for potential inland migration of the grounding line since 2011 and thus to provide an upper bound on retreat rates since 2011. However, it should be noted that a recent survey confirmed that substantial further retreat has not occurred [38]. The ‘further retreat’ scenario is designed as follows: the coordinates of the 2011 grounding-line observation are advected upstream over the time from its acquisition (2011) to the end of our observational period (2016); the direction is chosen to be opposite to the flow direction according to the MEaSUREs velocity observations; the magnitude of advection speed is chosen to be 1,500 m/yr as this roughly equals the maximum rates obtained from the InSAR analysis in the Amundsen Sea Embayment 11,12 . Finally, the average rate of grounding-line retreat in the ‘further retreat’ scenario was determined using all Bedmap2 grid cells that lie in the area between the 2011 and the inland advected grounding lines, as well as in the respective cross sections on Pine Island and Thwaites glaciers. Here, it was necessary to choose option 1 for the assumed direction of grounding-line motion (that is, the direction of the flow velocity; see above). The ‘further retreat’ scenario allows us to assess the maximum impact that an inaccurate groundingline position (for example, due to considerable but unmapped retreat since 2011) has on our results."

sidd

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #504 on: April 02, 2018, 11:37:45 PM »
In the Konrad paper there is discussion of the complexities of glacier flow and grounding line movement:

"Retreat at Pine Island Glacier appears to have stagnated at 40 m/yr ±​ 30 m/yr  during the CryoSat-2 period, after it migrated inland at a rate of around 1,000 m/yr between 1992 and 2011 as documented by the previous studies [11] (Fig. 2b). The recent stagnation coincides with a deceleration of thinning from 5 m/yr around 2009 to less than 1 m/yr across a 20 km section inland of the 2011 grounding line [35] , which in principle explains the reduced retreat rate. However, the slowdown in surface lowering could also be due to further ungrounding, and so we first examine this possibility. To maintain contact with the upstream parts of the ~120-km-long central trunk, which are in our data thinning at a maximum rate of 2 m/yr (Supplementary Fig. 3), the grounding line would have had to retreat by at least 15 km since 2011 (more than double that of the previous two decades [11,12] ), at a time when thinning has abated across the lower reaches of the glacier. This leads us to conclude that the main trunk’s grounding line has stabilized, potentially due to the absence of warm sub-shelf water [36] that drove retreat until 2011. This finding is supported by two recent studies [37,38] , which also report a substantial reduction in the pace of retreat since 2011"

sidd

Shared Humanity

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Re: Potential Collapse Scenario for the WAIS
« Reply #505 on: April 03, 2018, 12:38:35 AM »
Good news

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #506 on: April 03, 2018, 01:03:17 AM »
Good news

Just to be clear, it has been widely known for many years that the rate of retreat of the PIG grounding line has stagnated since about 2011; and that PIG grounding line behavior has already been factored in to advanced ice mass loss projections from the WAIS, including those from DeConto & Pollard.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #507 on: April 03, 2018, 06:43:24 AM »
Thwaites worries me more than PIG.

sidd

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #508 on: April 03, 2018, 05:34:08 PM »
Thwaites worries me more than PIG.

sidd

Of course I agree; however, the attached Sentinel 1 image from April 2 2018, showing a major calving event for the Southwest Tributary Glacier's Ice Shell, illustrates how the rapid degradation of the Pine Island Ice Shell, PIIS, can reduce the ice shelf buttressing on the SW Tributary Glacier.  This in turn should accelerate the ice flow velocity of the SW Tributary Glacier, thus reducing the associate marginal shear on the northeast margin of the Thwaites Glacier.  Thus I would say that we are currently witnessing the destabilization of the Thwaites Glacier in real time.
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FrostKing70

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Re: Potential Collapse Scenario for the WAIS
« Reply #509 on: April 03, 2018, 06:24:06 PM »
What is defined as a "major calving event"?   

Is it area, volume or other?

How big is this calving event?

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #510 on: April 03, 2018, 06:38:31 PM »
What is defined as a "major calving event"?   

Is it area, volume or other?

How big is this calving event?

I believe that what qualifies as a major calving event is subjective, based on the size of the ice shelf in consideration.  I consider this event major because it extends across the entire calving front of the SW Tributary Glacier.  The area of the calved iceberg is roughly 30 sq km.

Furthermore, this calving event should markedly reduce the buttressing action of the ice shelf on the SW Tributary Glacier, so that should also qualify it as a major event w.r.t. the behavior of the associated marine glacier.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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solartim27

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Re: Potential Collapse Scenario for the WAIS
« Reply #511 on: April 03, 2018, 11:41:02 PM »
Not to mention the rift in PIG expanding.  Here's a higher res image from today
https://www.polarview.aq/images/105_S1jpgfull/S1A_IW_GRDH_1SSH_20180403T084646_B9CD_S_1.final.jpg
FNORD

solartim27

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Re: Potential Collapse Scenario for the WAIS
« Reply #512 on: April 03, 2018, 11:43:07 PM »
FNORD

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #513 on: May 10, 2018, 05:55:47 PM »
The linked article indicates that the ocean has been the main driver of Antarctic ice sheet retreat throughout the Holocene which has had an atypically warm plateau as compare to earlier interglacial periods (see also the Early Anthropocene thread, in the Science folder).  This implies that the WAIS is more susceptible to abrupt collapse than consensus climate science likes to admit:

Xavier Crosta et al. (2018), "Ocean as the main driver of Antarctic ice sheet retreat during the Holocene", Global and Planetary Change, https://doi.org/10.1016/j.gloplacha.2018.04.007

https://www.sciencedirect.com/science/article/pii/S0921818118300249

Abstract: "Ocean-driven basal melting has been shown to be the main ablation process responsible for the recession of many Antarctic ice shelves and marine-terminating glaciers over the last decades. However, much less is known about the drivers of ice shelf melt prior to the short instrumental era. Based on diatom oxygen isotope (δ18Odiatom; a proxy for glacial ice discharge in solid or liquid form) records from western Antarctic Peninsula (West Antarctica) and Adélie Land (East Antarctica), higher ocean temperatures were suggested to have been the main driver of enhanced ice melt during the Early-to-Mid Holocene while atmosphere temperatures were proposed to have been the main driver during the Late Holocene. Here, we present a new Holocene δ18Odiatom record from Prydz Bay, East Antarctica, also suggesting an increase in glacial ice discharge since ~4500 years before present (~4.5 kyr BP) as previously observed in Antarctic Peninsula and Adélie Land. Similar results from three different regions around Antarctica thus suggest common driving mechanisms. Combining marine and ice core records along with new transient accelerated simulations from the IPSL-CM5A-LR climate model, we rule out changes in air temperatures during the last ~4.5 kyr as the main driver of enhanced glacial ice discharge. Conversely, our simulations evidence the potential for significant warmer subsurface waters in the Southern Ocean during the last 6 kyr in response to enhanced summer insolation south of 60°S and enhanced upwelling of Circumpolar Deep Water towards the Antarctic shelf. We conclude that ice front and basal melting may have played a dominant role in glacial discharge during the Late Holocene."
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #514 on: May 24, 2018, 09:29:01 PM »
While the reported implications of the three newly identified bed troughs at the bottleneck between East & West Antarctica (i.e. a projection of greater ice mass loss from the interior of Antarctica with continued global warming) are bad enough; I note that the fact that these troughs exist is a clear indication that such higher ice mass loss from the interior of Antarctica has occurred in the past.  This consideration increases the likelihood of such events occurring later this century:

Kate Winter et al. (2018), "Topographic Steering of Enhanced Ice Flow at the Bottleneck Between East and West Antarctica", Geophysical Research Letters, doi:10.1029/2018GL077504

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018GL077504

Abstract: "Hypothesized drawdown of the East Antarctic Ice Sheet through the “bottleneck” zone between East and West Antarctica would have significant impacts for a large proportion of the Antarctic Ice Sheet. Earth observation satellite orbits and a sparseness of radio echo sounding data have restricted investigations of basal boundary controls on ice flow in this region until now. New airborne radio echo sounding surveys reveal complex topography of high relief beneath the southernmost Weddell/Ross ice divide, with three subglacial troughs connecting interior Antarctica to the Foundation and Patuxent Ice Streams and Siple Coast ice streams. These troughs route enhanced ice flow through the interior of Antarctica but limit potential drawdown of the East Antarctic Ice Sheet through the bottleneck zone. In a thinning or retreating scenario, these topographically controlled corridors of enhanced flow could however drive ice divide migration and increase mass discharge from interior West Antarctica to the Southern Ocean."

Plain Language Summary: "The East and West Antarctic Ice Sheets meet at the inland termination of the Transantarctic Mountains. The ice sheets coalesce at a major ice divide, which could migrate and impact ice flow across large parts of Antarctica. A lack of satellite observations of ice flow and ice thickness has previously restricted characterization of this region, its glaciology, and its subglacial landscape. Our ice-penetrating radar surveys reveal three deep subglacial valleys and mountainous subglacial topography beneath the ice divide. New measurements of ice flow evidence faster ice flow within these troughs than in the surrounding thinner ice. Were the ice sheet to shrink in size, an increase in the speed at which ice flows through these troughs could lead to the ice divide moving and increase the rate at which ice flows out from the center of Antarctica to its edges."

See also:

Title: "Giant canyons discovered in Antarctica"

http://www.bbc.com/news/science-environment-44245893

Extract: "Scientists have discovered three vast canyons in one of the last places to be explored on Earth - under the ice at the South Pole.

And if Antarctica thins in a warming climate, as scientists suspect it will, then these channels could accelerate mass towards the ocean, further raising sea-levels.

"These troughs channelise ice from the centre of the continent, taking it towards the coast," explained Dr Winter.

"Therefore, if climate conditions change in Antarctica, we might expect the ice in these troughs to flow a lot faster towards the sea. That makes them really important, and we simply didn't know they existed before now," she told BBC News.
“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: Potential Collapse Scenario for the WAIS
« Reply #515 on: June 04, 2018, 06:22:57 PM »
Hopefully, governments will provide sufficient funding to support the recommended drilling program to test for past WAIS collapse. This could help to improve our understanding of the risks that we face in the coming decades:

Spector, P., Stone, J., Pollard, D., Hillebrand, T., Lewis, C., and Gombiner, J.: West Antarctic sites for subglacial drilling to test for past ice-sheet collapse, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-88, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-88/

Abstract. Mass loss from the West Antarctic Ice Sheet (WAIS) is increasing, and there is concern that an incipient large-scale deglaciation of the marine basins may already be underway. Measurements of cosmogenic nuclides in subglacial bedrock surfaces have the potential to establish whether and when the marine-based portions of the WAIS deglaciated in the past. However, because most of the bedrock revealed by ice-sheet collapse would remain below sea level, shielded from the cosmic-ray flux, drill sites for subglacial sampling must be located in areas where thinning of the residual ice sheet would expose presently subglacial bedrock surfaces. In this paper we discuss the criteria and considerations for choosing drill sites where subglacial samples will provide maximum information about WAIS extent during past interglacial periods. We evaluate candidate sites in West Antarctica and find that sites located adjacent to the large marine basins of West Antarctica will be most diagnostic of past ice-sheet collapse. There are important considerations for drill-site selection on the kilometer scale that can only be assessed by field reconnaissance. As a case study of these considerations, we describe reconnaissance at sites in West Antarctica, focusing on the Pirrit Hills, where in the summer of 2016–2017, an 8 m bedrock core was retrieved from below 150 m of ice.
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #516 on: June 14, 2018, 12:33:25 AM »
Ice sheet models will need to more sophisticated fast, if we are going understand the risks of the WAIS collapsing this century:

Title: "New study suggests surprising wrinkle in history of West Antarctic Ice Sheet"

https://phys.org/news/2018-06-wrinkle-history-west-antarctic-ice.html

Extract: "Scientists generally have believed that since the end of the last Ice Age, about 15,000 years ago, the West Antarctic Ice Sheet (WAIS) has been getting smaller and smaller, with its retreat triggered by a warming world and sea-level rise from collapse of Northern Hemisphere ice sheets.

A study published online June 13, 2018 in the journal Nature shows a more complicated history.
Surprising new data and ice-sheet modeling suggest that between roughly 14,500 and 9,000 years ago, the ice sheet below sea level partially melted and shrunk to a size even smaller than today—but it did not collapse. Over the subsequent millennia, the loss of the massive amount of ice that was previously weighing down the seabed spurred uplift in the sea floor—a process known as isostatic rebound. Then the ice sheet began to regrow toward today's configuration.
"The WAIS today is again retreating, but there was a time since the last Ice Age when the ice sheet was even smaller than it is now, yet it didn't collapse," said Northern Illinois University geology professor Reed Scherer, a lead author on the study. "That's important information to have as we try to figure out how the ice sheet will behave in the future."

Don't count on isostatic rebound, however, to be a panacea for modern-day rising sea level, he added.

"What happened roughly 10,000 years ago might not dictate where we're going in our carbon dioxide-enhanced world, where the oceans are rapidly warming in the polar regions. If the ice sheet were to dramatically retreat now, triggered by anthropogenic warming, the uplift process won't help regrow the ice sheet until long after coastal cities have felt the effects of the sea level rise."

Finally, Albrecht and a colleague conducted sophisticated numerical ice-sheet modeling driven by the warming climate and rising sea levels after the last glacial maximum. Those simulations show ice sheet retreat before reaching a turning point, with the grounding line up to 200 kilometers inland of its present day location in the Weddell Sea region and up to 400 kilometers in the Ross Sea region.

"The warming after the last Ice Age made the ice masses of West Antarctica dwindle rather rapidly," Albrecht said. "It retreated inland by more than 1,000 kilometers in a period of 1,000 years in this region—on geological time-scales, this is really high-speed. But now we detected that this process at some point got partially reversed. Instead of total collapse, the ice-sheet grew again by up to 400 kilometers. This is an amazing self-induced stabilization. However, it took a whopping 10,000 years, up until now. Given the speed of current climate-change from burning fossil fuels, the mechanism we detected unfortunately does not work fast enough to save today's ice sheets from melting and causing seas to rise."

Curiously, the ice modeling did not find grounding-line retreat and rebound-driven re-advance in the Amundsen Sea region, where present-day grounding-line retreat is causing concern about future runaway collapse.

"The model of the past doesn't show retreat of Amundsen Sea glaciers much beyond the present-day grounding line," Scherer said. "So what's happening today in that sector is troublesome and could be a wildcard in all this.""

See also:

J. Kingslake et al, Extensive retreat and re-advance of the West Antarctic Ice Sheet during the Holocene, Nature (2018). DOI: 10.1038/s41586-018-0208-x
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #517 on: August 10, 2018, 12:24:38 AM »
We should remember that each new generation of conventional model of Thwaites Glacier retreat projections this century indicates more and more retreat; and such conventional glacial models do not include the influence of cliff-hydrofracturing mechanisms:

Hongju Yu et al. (2018), "Retreat of Thwaites Glacier, West Antarctica, over the next 100 years using various ice flow models, ice shelf melt scenarios and basal friction laws", The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-104

https://www.the-cryosphere-discuss.net/tc-2018-104/

Abstract. Thwaites Glacier (TG), West Antarctica, experiences rapid, potentially irreversible grounding line retreat and mass loss in response to enhanced ice shelf melting. Several numerical models of TG have been developed recently, showing a large spread in the evolution of the glacier in the coming decades to a century. It is, however, not clear how different parameterizations of basal friction and ice shelf melt or different approximations in ice stress balance affect projections. Here, we simulate the evolution of TG using different ice shelf melt, basal friction laws and ice sheet models of varying levels of complexity to quantify the effect of these model configurations on the results. We find that the grounding line retreat and its sensitivity to ocean forcing is enhanced when a full-Stokes model is used, ice shelf melt is applied on partially floating elements, and a Budd friction is used. Initial conditions also impact the model results. Yet, all simulations suggest a rapid, sustained retreat along the same preferred pathway. The highest retreat rate occurs on the eastern side of the glacier and the lowest rate on a subglacial ridge on the western side. All the simulations indicate that TG will undergo an accelerated retreat once it retreats past the western ridge. Combining the results, we find the uncertainty is small in the first 30 years, with a cumulative contribution to sea level rise of 5mm, similar to the current rate. After 30 years, the mass loss depends on the model configurations, with a 300% difference over the next 100 years, ranging from 14 to 42mm.
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #518 on: August 13, 2018, 11:02:59 PM »
The ENSO cycle has repeatedly been demonstrated to generate decadal oceanic pulses of relatively warm CDW (circumpolar deep water) and relative cooler surface water into the Amundsen Sea Embayment, ASE.  The linked reference provides both field and model results that help to better delineate the influence of these ENSO driven oceanic pulses on ice mass loss from key marine glaciers in the ASE.  Furthermore, research indicates that as climate change increases the frequency of strong El Nino events, the frequency of warm CDW pulses into the ASE should increase, resulting in increased ice mass loss from this key region:

Jenkins et al. (2018), "West Antarctic Ice Sheet retreat in the Amundsen Sea driven by decadal oceanic variability", Nature Geoscience, https://doi.org/10.1038/s41561-018-0207-4

http://www.nature.com/articles/s41561-018-0207-4.epdf?referrer_access_token=Bc93rPzj5mAIgFxIj7ONaNRgN0jAjWel9jnR3ZoTv0PHtUgk_ZOT39EqrANp0b8eqygnJyFYtkZtZrrvzpzzWFxFRxOjGyBuySjpDsnaRQh7XJnWxZ3ao5NgE_FXw2TbspGSBS1Ou39d7UURpwlPi_Pto2nRLEma6yWSJG3jZtjtHknyJEJlg9BIxSQMv28PGhskTGPjzqBOEvvM0U4N9vO_qHWkDtkY-E5jhH1DvWdJkNePrE5W2mXS98uEvX9LRJGTRyR_k2N9kxRVb0DlMnr7Jn6NgoQ-PnofJG67wP8%3D&tracking_referrer=www.carbonbrief.org

Abstract: "Mass loss from the Amundsen Sea sector of the West Antarctic Ice Sheet has increased in recent decades, suggestive of sustained ocean forcing or an ongoing, possibly unstable, response to a past climate anomaly. Lengthening satellite records appear to be incompatible with either process, however, revealing both periodic hiatuses in acceleration and intermittent episodes of thinning. Here we use ocean temperature, salinity, dissolved-oxygen and current measurements taken from 2000 to 2016 near the Dotson Ice Shelf to determine temporal changes in net basal melting. A decadal cycle dominates the ocean record, with melt changing by a factor of about four between cool and warm extremes via a nonlinear relationship with ocean temperature. A warm phase that peaked around 2009 coincided with ice-shelf thinning and retreat of the grounding line, which re-advanced during a post-2011 cool phase. These observations demonstrate how discontinuous ice retreat is linked with ocean variability, and that the strength and timing of decadal extremes is more influential than changes in the longer-term mean state. The non-linear response of melting to temperature change heightens the sensitivity of Amundsen Sea ice shelves to such variability, possibly explaining the vulnerability of the ice sheet in that sector, where subsurface ocean temperatures are relatively high."

See also:

Title: "Scientists find ‘natural pulses’ in recent melting of West Antarctic ice sheet"

https://www.carbonbrief.org/scientists-find-natural-pulses-in-recent-melting-of-west-antarctic-ice-sheet

Extract: "Natural ocean variability is heightening the rate of retreat of the West Antarctic ice sheet, a new study finds.

A 16-year study of ocean conditions in Antarctica suggests that the periodic arrival of warm currents as a result of natural variability is worsening the rate of ice mass loss from key glaciers in the region.

The natural pulses of warm water could be key to driving short-term changes in glacier ice mass loss, the lead author tells Carbon Brief. In the long term, this periodic ocean warming is likely to be exacerbated by climate change, he adds.

The new findings serve as a “smoking gun” by helping scientists to understand the mechanisms behind the ice sheet’s retreat, another scientist tells Carbon Brief.

The researchers believe that El Niño is altering the strength of these ocean currents, periodically pulling or pushing the CDW towards or away from the glaciers on Antarctica’s coast, driving the “warm” and “cool” ocean phases, respectively."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #519 on: August 14, 2018, 06:39:26 AM »
Thanx for that reference. I notice that Dutrieux is an author. Nice work, they used soundings from cruise ships among a lot of other things. I attach a section of fig 4 showing 80Gton melt coming off the thing when section mean potential temperature rises to 1.5-2 C above surface freezing point.

sidd

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Re: Potential Collapse Scenario for the WAIS
« Reply #520 on: August 15, 2018, 06:19:39 PM »
The linked reference indicates that the projected increase (with continued global warming) of more frequent strong El Nino events combined with the projected increase in positive SAM, will significantly increase ice mass loss from the ASE, which will increase the risk of a collapse of the WAIS:

Deb, P., A. Orr, D. H. Bromwich, J. P. Nicolas, J. Turner, and J. S. Hosking, 2018: Summer drivers of atmospheric variability affecting ice shelf thinning in the Amundsen Sea Embayment, West Antarctica. Geophy. Res. Lett., 45. doi: 10.1029/2018GL077092.

http://polarmet.osu.edu/PMG_publications/deb_bromwich_grl_2018.pdf

Abstract:  "Satellite data and a 35-year hindcast of the Amundsen Sea Embayment summer climate using the Weather Research and Forecasting model are used to understand how regional and large-scale atmospheric variability affects thinning of ice shelves in this sector of West Antarctica by melting from above and below (linked to intrusions of warm water caused by anomalous westerlies over the continental shelf edge). El Niño episodes are associated with an increase in surface melt but do not have a statistically significant impact on westerly winds over the continental shelf edge. The location of the Amundsen Sea Low and the polarity of the Southern Annular Mode (SAM) have negligible impact on surface melting, although a positive SAM and eastward shift of the Amundsen Sea Low cause anomalous westerlies over the continental shelf edge. The projected future increase in El Niño episodes and positive SAM could therefore increase the risk of disintegration of West Antarctic ice shelves."

Extract: "Our study suggests that ASE ice shelves could experience an intensification of melt in the future from both above and below as a result of both regional and large-scale atmospheric changes, potentially increasing the risk of their disintegration, which in turn could potentially trigger a collapse of the West Antarctic ice sheet (DeConto & Pollard, 2016). To better understand this threat will require further detailed investigation of the impacts of ENSO, the polarity of the SAM, and the depth/location of the ASL on ASE ice shelves. Also necessary is improving the reliability of future projections, such as ENSO and its teleconnections, as well as the response of the SAM to recovery of the Antarctic ozone hole and increased greenhouse gas emissions (Polvani, Waugh, et al., 2011)."
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bluesky

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Re: Potential Collapse Scenario for the WAIS
« Reply #521 on: August 20, 2018, 05:37:39 PM »
Dear AbruptSLR

All these links are very interesting and somewhat very worrying considering the complacency of our policymakers...
Would it be possible to get a physical explanation of how the teleconnection between a strong El Nino and a stronger pulse of relatively warm water in CDW ? Maybe it is already explained somewhere in the forum, but I, unfortunately, have not been able to find it
Is there any paper quantifying the increase of warm water pulse based on modelled projection of higher frequency and stronger El Nino event? And, sorry maybe it is a very basic question,  from which process global warming will increase the frequenwy of El Nino and SAM?

Is there any potential link between the slow down of AMOC and the Antarctica, or is it too far fetched as deep water takes quite some time to go back to the South hemisphere?

Thanks

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #522 on: August 20, 2018, 08:18:27 PM »
Dear AbruptSLR

All these links are very interesting and somewhat very worrying considering the complacency of our policymakers...
Would it be possible to get a physical explanation of how the teleconnection between a strong El Nino and a stronger pulse of relatively warm water in CDW ? Maybe it is already explained somewhere in the forum, but I, unfortunately, have not been able to find it
Is there any paper quantifying the increase of warm water pulse based on modelled projection of higher frequency and stronger El Nino event? And, sorry maybe it is a very basic question,  from which process global warming will increase the frequenwy of El Nino and SAM?

Is there any potential link between the slow down of AMOC and the Antarctica, or is it too far fetched as deep water takes quite some time to go back to the South hemisphere?

Thanks

bluesky,

Basically, the top elevation of the circumpolar deep water, CDW, is typically just below deep troughs in the continental shelf of the Amundsen Sea Embayment, ASE.  Further the Amundsen Bellingshausen Sea Low, ABSL (or ASL) & see the first image), is a frequent low pressure atmospheric system that moves east-west along the Amundsen – Bellingshausen Seas coastline, depending on numerous atmospheric conditions, but predominately by the combination of the ENSO & SAM (see the second & third images), due to the teleconnection of atmospheric energy by Rossby Waves from the Tropical Pacific Ocean.  When in the correct position, the ABSL blows wind into the ASE which drags the surface ocean water with it; which in turn causes upwelling of the CDW into the deep troughs which, all lead to the grounding lines of the various ASE marine glaciers.

The AMOC slowdown can impact the ENSO via atmospheric telecommunication from the Atlantic to the Pacific basins, depending on the season and other metocean conditions.

Also see:
The thread entitled: "Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Time Frame":
From Reply #75:
The following linked article supports the point that in a big El Nino year both PIIS and PIG will lose ice more rapidly than normal:

http://www.science20.com/news_articles/antarcticas_pine_island_glacier_melt_blame_el_nino-127129
From Reply #76:
To those who would like access to the source material for the information cited in my immediate past post, please see the following links, abstract, and related references:

http://www.sciencemag.org/content/early/2014/01/02/science.1244341.abstract

http://www.sciencemag.org/content/suppl/2014/01/02/science.1244341.DC1/Dutrieux.SM.pdf

Pierre Dutrieux, Jan De Rydt, Adrian Jenkins, Paul R. Holland, Ho Kyung Ha, Sang Hoon Lee, Eric J. Steig, Qinghua Ding, E. Povl Abrahamsen, and Michael Schröder, 2014, "Strong Sensitivity of Pine Island Ice-Shelf Melting to Climatic Variability", Science; Published online 2 January 2014 [DOI:10.1126/science.1244341]

Abstract:
"Pine Island Glacier has thinned and accelerated over recent decades, significantly contributing to global sea-level rise. Increased oceanic melting of its ice shelf is thought to have triggered those changes. Observations and numerical modeling reveal large fluctuations in the ocean heat available in the adjacent bay and enhanced sensitivity of ice shelf melting to water temperatures at intermediate depth, as a seabed ridge blocks the deepest and warmest waters from reaching the thickest ice. Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event. Both atmospheric variability and local ice shelf and seabed geometry play fundamental roles in determining the response of the Antarctic Ice Sheet to climate."

Supplemental references:

1. S. S. Jacobs, A. Jenkins, H. Hellmer, C. Giulivi, F. Nitsche, B. Huber, R. Guerrero, The
Amundsen Sea and the Antarctic Ice Sheet. Oceanography 25, 154–163 (2012).
doi:10.5670/oceanog.2012.90
2. S. S. Jacobs, A. Jenkins, C. F. Giulivi, P. Dutrieux, Stronger ocean circulation and increased
melting under Pine Island Glacier ice shelf. Nat. Geosci. 4, 519–523 (2011).
doi:10.1038/ngeo1188
3. S. S. Jacobs, H. H. Hellmer, A. Jenkins, Antarctic Ice Sheet melting in the southeast Pacific.
Geophys. Res. Lett. 23, 957–960 (1996). doi:10.1029/96GL00723
4. A. Jenkins, P. Dutrieux, S. S. Jacobs, S. D. McPhail, J. R. Perrett, A. T. Webb, D. White,
Observations beneath Pine Island Glacier in West Antarctica and implications for its
retreat. Nat. Geosci. 3, 468–472 (2010). doi:10.1038/ngeo890
5. D. J. Wingham, D. W. Wallis, A. Shepherd, Spatial and temporal evolution of Pine Island
Glacier thinning, 1995–2006. Geophys. Res. Lett. 36, L17501 (2009).
doi:10.1029/2009GL039126
6. A. Shepherd, E. R. Ivins, G. A, V. R. Barletta, M. J. Bentley, S. Bettadpur, K. H. Briggs, D. H.
Bromwich, R. Forsberg, N. Galin, M. Horwath, S. Jacobs, I. Joughin, M. A. King, J. T.
Lenaerts, J. Li, S. R. Ligtenberg, A. Luckman, S. B. Luthcke, M. McMillan, R. Meister,
G. Milne, J. Mouginot, A. Muir, J. P. Nicolas, J. Paden, A. J. Payne, H. Pritchard, E.
Rignot, H. Rott, L. S. Sørensen, T. A. Scambos, B. Scheuchl, E. J. Schrama, B. Smith, A.
V. Sundal, J. H. van Angelen, W. J. van de Berg, M. R. van den Broeke, D. G. Vaughan,
I. Velicogna, J. Wahr, P. L. Whitehouse, D. J. Wingham, D. Yi, D. Young, H. J. Zwally,
A reconciled estimate of ice-sheet mass balance. Science 338, 1183–1189 (2012).
Medline doi:10.1126/science.1228102
7. E. Rignot, Changes in West Antarctic ice stream dynamics observed with ALOS PALSAR
data. Geophys. Res. Lett. 35, L12505 (2008). doi:10.1029/2008GL033365
8. I. Joughin, E. Rignot, C. E. Rosanova, B. K. Lucchitta, J. Bolhander, Timing of Recent
Accelerations of Pine Island Glacier, Antarctica. Geophys. Res. Lett. 30, 1706 (2003).
doi:10.1029/2003GL017609
9. I. Joughin, B. E. Smith, D. M. Holland, Sensitivity of 21st century sea level to ocean-induced
thinning of Pine Island Glacier, Antarctica. Geophys. Res. Lett. 37, L20502 (2010).
doi:10.1029/2010GL044819
10. H. D. Pritchard, S. R. Ligtenberg, H. A. Fricker, D. G. Vaughan, M. R. van den Broeke, L.
Padman, Antarctic ice-sheet loss driven by basal melting of ice shelves. Nature 484, 502–
505 (2012). Medline doi:10.1038/nature10968
11. A. Shepherd, D. Wingham, D. Wallis, K. Giles, S. Laxon, A. V. Sundal, Recent loss of
floating ice and the consequent sea level contribution. Geophys. Res. Lett. 37, L13503
(2010). doi:10.1029/2010GL042496
12. A. Shepherd, D. Wingham, E. Rignot, Warm ocean is eroding West Antarctic Ice Sheet.; Geophys. Res. Lett. 31, L23402 (2004). doi:10.1029/2004GL021106
From Reply #131:
The linked reference (the second link has a free pdf) ties the warming of the Tropical Atlantic SST to a strengthening of both the Antarctic Circumpolar Winds and the Amundsen Bellingshausen Sea Low (ABSL/ASL) via atmospheric Rossby waves in all seasons except the austral summer.  The conclusions of this paper (see the extract below) recommends that efforts be made to inter-relate this Atlantic tropical-Antarctic teleconnection with other tropical teleconnections (such as those identified by Fogt et al 2011, see the first attached image relating El Nino events & negative Southern Annular Mode, SAM, conditions that promote teleconnection of Tropical Pacific energy towards the Amundsen Sea Embayment, via atmospheric Rossby wave-trains).  As we are now likely approaching very strong El Nino conditions by October 2015, it will be very interesting to see whether both the Tropical Atlantic and the Tropical Pacific soon teleconnect large amounts of atmospheric energy into Western Antarctica.

Additionally, the second attached image today from the Earth nullschool shows that the ABSL is relatively strong (i.e. has a relatively low central pressure) and is currently directing energy directly into the Amundsen Sea Embayment, ASE.

XICHEN LI, EDWIN P. GERBER, DAVID M. HOLLAND, AND CHANGHYUN YOO, (2015), "A Rossby Wave Bridge from the Tropical Atlantic to West Antarctica", J. Climate, 28, 2256–2273, doi: http://dx.doi.org/10.1175/JCLI-D-14-00450.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00450.1

http://polarmet.osu.edu/ACCIMA/li_gerber_jc_2015.pdf

Abstract: "Tropical Atlantic sea surface temperature changes have recently been linked to circulation anomalies around Antarctica during austral winter. Warming in the tropical Atlantic associated with the Atlantic multidecadal oscillation forces a positive response in the southern annular mode, strengthening the Amundsen–Bellingshausen Sea low in particular. In this study, observational and reanalysis datasets and a hierarchy of atmospheric models are used to assess the seasonality and dynamical mechanism of this teleconnection.  Both the reanalyses and models reveal a robust link between tropical Atlantic SSTs and the Amundsen–Bellingshausen Sea low in all seasons except austral summer. A Rossby wave mechanism is then shown to both explain the teleconnection and its seasonality. The mechanism involves both changes in the excitation of Rossby wave activity with season and the formation of a Rossby waveguide across the Pacific, which depends critically on the strength and extension of the subtropical jet over the west Pacific. Strong anticyclonic curvature on the poleward flank of the jet creates a reflecting surface, channeling quasi-stationary Rossby waves from the subtropical Atlantic to the Amundsen–Bellingshausen Sea region. In summer, however, the jet is weaker than in other seasons and no longer able to keep Rossby wave activity trapped in the Southern Hemisphere. The mechanism is supported by integrations with a comprehensive atmospheric model, initial-value calculations with a primitive equation model on the sphere, and Rossby wave ray tracing analysis."

Extract: "Antarctic climate is also influenced by other tropical–polar teleconnections (Fogt et al. 2011; Ding et al. 2012), and key questions remain concerning the relative importance of these effects. The time scales of tropical SST variability differs significantly from one region to another (e.g., ENSO and the east Pacific dominate on interannual time scales, while the AMO and Pacific decadal oscillation are more significant on longer time scales). Moreover, SSTs in different tropical ocean basins may interact with each other through tropical ocean interbasin teleconnections. It is thus important to further investigate the relative importance and the relationship between the teleconnections from different tropical ocean sectors as a function of time scale."

Also see the thread entitled: "Risks and Challenges for Regional Circulation Models of the Southern Ocean"

From Reply #51:
It has been a while since I posted the attached figure from Bertler et al 2006 (see reference at bottom of this post), which shows pictorially the relationship between the location of the Amundsen Sea Low (or Amundsen Bellingshausen Sea Low), ASL (or ABSL) and either a La Nina or an El Nino event.  Taken together with the information in my immediately preceding post (which stated that sea surface warming related to the Atlantic Multidecadal Oscillation, AMO, reduces the surface pressure in the Amundsen Sea), this implies that when the next El Nino event occurs (which may be the austral summer of 2014 to 2015) and shifts the location of the ASL to blow wind directly into the ASE, the winds will likely be stronger due to the lower Amundsen sea pressure associated with AMO effect; which will drive more warm CDW into the ASE resulting in higher than previously expected ice mass loss from the glaciers in this area.

Bertler, N.A., Naish, T.T., Mayewski, P.A. and Barrett, P.J., (2006), "Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica", Advances in Geosciences, 6, pp 83-88, SRef-ID: 1680-7359/adgeo/2006-6-83.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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solartim27

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Re: Potential Collapse Scenario for the WAIS
« Reply #523 on: August 21, 2018, 01:04:32 AM »
Here's a nice shot of PIG from todays Sentinel.  I am amazed at the continued degradation of the ice sheet between PIG and the Trib.  Some say a picture is worth a thousand words.  Zoom in, guaranteed to be an interesting summer.
https://www.polarview.aq/images/105_S1jpgfull/S1B_IW_GRDH_1SSH_20180820T043510_80AB_S_1.final.jpg (50 MB image)
FNORD

bluesky

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Re: Potential Collapse Scenario for the WAIS
« Reply #524 on: August 21, 2018, 12:41:38 PM »
Thank you AbruptSLR for taking the time to reexplain the relationship between ENSO and CDW and all the links, this is so useful, I am very grateful

AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #525 on: August 27, 2018, 05:50:24 PM »
Thank you AbruptSLR for taking the time to reexplain the relationship between ENSO and CDW and all the links, this is so useful, I am very grateful

bluesky,

As a follow-on to my Reply #522:

The first  image shows the deepwater changes across the Amundsen Sea continental shelf through which the warm CDW flows towards the grounding lines of key marine glaciers.

The second image shows a computer simulation of the pattern of warm CDW flow in the Amundsen Sea continental shelf area; which indicates how warm CDW can flow from the PIG to the Thwaites grounding line.

The third image shows that the submerged ridge seaward of Thwaites can help direct the warm CDW come from the PIG towards the 'trough' that crosses the Thwaites ice plug.

Bertler, N.A., Naish, T.T., Mayewski, P.A. and Barrett, P.J., (2006), "Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica", Advances in Geosciences, 6, pp 83-88, SRef-ID: 1680-7359/adgeo/2006-6-83.

Next, the second linked reference indicates that from January to June the ASL typically moves from about 110 degrees W (where it is in position to help direct warm CDW into the ASE) to about 150 degrees W (where it does not help to direct warm CDW into the ASE).  I note also that:

(a) As the SAM has become more positive, due to global warming, the ASL has become more intensity and has tended to drift more to the west than previously; and

(b) El Nino events do not typically occur in the January to June timeframe but rather in the October to Dec timeframe, which helps to explain way more warm CDW flows into the ASE during El Nino events

Turner, J., Phillips, T., Hosking, J. S., Marshall, G. J. and Orr, A. (2013), The Amundsen Sea low. Int. J. Climatol., 33: 1818–1829. doi: 10.1002/joc.3558

http://onlinelibrary.wiley.com/doi/10.1002/joc.3558/abstract

Abstract: "We develop a climatology of the Amundsen Sea low (ASL) covering the period 1979–2008 using ECMWF operational and reanalysis fields. The depth of the ASL is strongly influenced by the phase of the Southern annular mode (SAM) with positive (negative) mean sea level pressure anomalies when the SAM is negative (positive). The zonal location of the ASL is linked to the phase of the mid-tropospheric planetary waves and the low moves west from close to 110°W in January to near 150°W in June as planetary waves 1 to 3 amplify and their phases shift westwards. The ASL is deeper by a small, but significant amount, during the La Niña phase of El Niño-Southern Oscillation (ENSO) compared to El Niño. The difference in depth of the low between the two states of ENSO is greatest in winter. There is no statistically significant difference in the zonal location of the ASL between the different phases of ENSO. Over 1979–2008 the low has deepened in January by 1.7 hPa dec−1 as the SAM has become more positive. It has also deepened in spring and autumn as the semi-annual oscillation has increase in amplitude over the last 30 years. An increase in central pressure and eastward shift in March has occurred as a result of a cooling of tropical Pacific SSTs that altered the strength of the polar front jet."


Finally, the third linked 2017 reference confirms that the ENSO is directly associated with surface air temperatures across the interior of West Antarctica, and I note that the frequency of Super El Nino events is projected to double when the global mean surface temp. anom. gets to 1.5C:

Kyle R. Clem, James A. Renwick, and James McGregor (2017), "Large-Scale Forcing of the Amundsen Sea Low and its Influence on Sea Ice and West Antarctic Temperature", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0891.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0891.1?utm_content=buffer2e94d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Using empirical orthogonal function (EOF) analysis and atmospheric reanalyses, we examine the principal patterns of seasonal West Antarctic surface air temperature (SAT) and their connection to sea ice and the Amundsen Sea Low (ASL). During austral summer, the leading EOF (EOF1) explains 35% of West Antarctic SAT variability and consists of a widespread SAT anomaly over the continent linked to persistent sea ice concentration anomalies over the Ross and Amundsen Seas from the previous spring. Outside of summer, EOF1 (explaining ~40-50% of the variability) consists of an east-west dipole over the continent with SAT anomalies over the Antarctic Peninsula opposite those over western West Antarctica. The dipole is tied to variability in the Southern Annular Mode (SAM) and in-phase El Niño-Southern Oscillation (ENSO) / SAM combinations that influence the depth of the ASL over the central Amundsen Sea (near 105°W). The second EOF (EOF2) during autumn, winter, and spring (explaining ~15-20% of the variability) consists of a dipole shifted approximately 30 degrees west of EOF1 with a widespread SAT anomaly over the continent. During winter and spring, EOF2 is closely tied to variability in ENSO and a tropically-forced wavetrain that influences the ASL in the western Amundsen / eastern Ross Seas (near 135°W) with an opposite sign circulation anomaly over the Weddell Sea; the ENSO-related circulation brings anomalous thermal advection deep onto the continent. We conclude the ENSO-only circulation pattern is associated with SAT variability across interior West Antarctica, especially during winter and spring, while the SAM circulation pattern is associated with an SAT dipole over the continent."

Best,
ASLR
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #526 on: August 27, 2018, 08:13:25 PM »
The linked reference provides paleo evidence from about 11,500 year ago, that indicates that portions of the WAIS are very sensitivity to collapse, even under conditions that were cooler than today:

J. Kingslake et al. (2018), "Extensive retreat and re-advance of the West Antarctic Ice Sheet during the Holocene", Nature, https://doi.org/10.1038/s41586-018-0208-x

http://www.nature.com/articles/s41586-018-0208-x.epdf?referrer_access_token=lOkN7hgTt7KBVbuYuXMwc9RgN0jAjWel9jnR3ZoTv0PagDqQuHClF_KBoNEwt0qCDswVby5xisTUuro2GVqEdVyNRmUsMYB32-gwCy-WQGiOJuRHvpbmk3l6OEkAKwxOiPNDPRAKMIlDGFP4EHQgKD_G1qFJE2DhzFl3IkCeDuHh2Xln7I7LeJAB1tog4tIasE0yBRLzYo4hLBA3XhRCpg%3D%3D&tracking_referrer=news.nationalgeographic.com

Abstract: "To predict the future contributions of the Antarctic ice sheets to sea-level rise, numerical models use reconstructions of past ice-sheet retreat after the Last Glacial Maximum to tune model parameters. Reconstructions of the West Antarctic Ice Sheet have assumed that it retreated progressively throughout the Holocene epoch (the past 11,500 years or so). Here we show, however, that over this period the grounding line of the West Antarctic Ice Sheet (which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf) retreated several hundred kilometres inland of today’s grounding line, before isostatic rebound caused it to re-advance to its present position. Our evidence includes, first, radiocarbon dating of sediment cores recovered from beneath the ice streams of the Ross Sea sector, indicating widespread Holocene marine exposure; and second, ice-penetrating radar observations of englacial structure in the Weddell Sea sector, indicating ice-shelf grounding. We explore the implications of these findings with an ice-sheet model. Modelled re-advance of the grounding line in the Holocene requires ice-shelf grounding caused by isostatic rebound. Our findings overturn the assumption of progressive retreat of the grounding line during the Holocene in West Antarctica, and corroborate previous suggestions of ice-sheet re-advance. Rebound-driven stabilizing processes were apparently able to halt and reverse climate-initiated ice loss. Whether these processes can reverse present-day ice loss on millennial timescales will depend on bedrock topography and mantle viscosity—parameters that are difficult to measure and to incorporate into ice-sheet models."

See also:

Title: "The West Antarctic Ice Sheet Seems to Be Good at Collapsing"

https://news.nationalgeographic.com/2018/06/west-antarctic-ice-sheet-collapse-climate-change/

Extract: "SCIENTISTS HAVE DISCOVERED that the West Antarctic Ice Sheet underwent a major retreat between 10,000 and 12,000 years ago, at a time when the world was actually cooler than it is today. The collapse happened at the close of the last Ice Age, and it left the ice sheet 135,000 square miles smaller than it is today – a difference nearly as large as the state of Montana.

“That the ice sheet could retreat beyond where it is today, in a climate that was likely quite a bit colder than today, points to extraordinary sensitivity,” says Robert DeConto, a glaciologist at the University of Massachusetts Amherst, who was not involved in the research."
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AbruptSLR

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Re: Potential Collapse Scenario for the WAIS
« Reply #527 on: September 19, 2018, 06:14:19 PM »
The findings of the linked reference imply that current ice shelf models err on the side of least drama with regard to ice mass loss associated with relatively warm ocean water beneath such ice shelves, as illustrated by measurements from the Getz Ice Shelf in West Antarctica:

Rippin, D. M.: Significant submarine ice loss from the Getz Ice Shelf, Antarctica, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-163, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-163/

Abstract. We present the first direct measurements of changes taking place at the base of the Getz Ice Shelf (GzIS) in West Antarctica. Our analysis is based on repeated airborne radio-echo sounding (RES) survey lines gathered in 2010 and 2014. We reveal that while there is significant variability in ice shelf behaviour, the vast majority of the ice shelf (where data is available) is undergoing basal thinning at a mean rate of nearly 13ma−1, which is several times greater than recent modelling estimates. In regions of faster flowing ice close to where ice streams and outlet glaciers join the ice shelf, significantly greater rates of mass loss occurred. Since thinning is more pronounced close to faster-flowing ice, we propose that dynamic thinning processes may also contribute to mass loss here. Intricate sub-ice circulation patterns exist beneath the GzIS because of its complex sub-ice topography and the fact that it is fed by numerous ice streams and outlet glaciers. It is this complexity which we suggest is also responsible for the spatially variable patterns of ice-shelf change that we observe. The large changes observed here are also important when considering the likelihood and timing of any potential future collapse of the ice shelf, and the impact this would have on the flow rates of feeder ice streams and glaciers, that transmit ice from inland Antarctica to the coast. We propose that as the ice shelf continues to thin in response to warming ocean waters and climate, the response of the ice shelf will be spatially diverse. Given that these measurements represent changes that are significantly greater than modelling outputs, it is also clear that we still do not fully understand how ice shelves respond to warming ocean waters. As a result, ongoing direct measurements of ice shelf change are vital for understanding the future response of ice shelves under a warming climate.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson