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

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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