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Author Topic: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe  (Read 93109 times)

AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #200 on: July 28, 2016, 04:50:17 PM »
For Thwaites, I concur with the conclusion (of the linked open access reference) that: "… basal hydrological system may not be the most important feature of the ice sheet for models to capture…"

Smith, B. E., Gourmelen, N., Huth, A., and Joughin, I.: Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica, The Cryosphere Discuss., doi:10.5194/tc-2016-180, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-180/
http://www.the-cryosphere-discuss.net/tc-2016-180/tc-2016-180.pdf

Abstract: "We present conventional and swath altimetry data from Cryosat-2 revealing a system of subglacial lakes that drained between June 2013 and January 2014 under the central part of Thwaites Glacier, West Antarctica. Much of the drainage happened in less than six months, with an apparent connection between three lakes spanning more than 130 km. Hydropotential analysis of the glacier bed shows a large number of small closed basins that should trap water produced by subglacial melt, although the observed large-scale motion of water suggests that water can sometimes locally move against the apparent potential gradient, at least during lake-drainage events, suggesting that there are important limitations in the ability of hydropotential maps to predict subglacial water flow. An interpretation based on a map of the melt rate suggests that lake drainages of this type should take place every 20–80 years, depending on the connectivity of the water flow at the bed. Although we observed an acceleration in the downstream part of TWG immediately before the start of the lake drainage, there is no clear connection between the drainage and any speed change of the glacier."


Extract: "While our data suggest water is routed in ways not presently accounted for in most ice sheet models, it also indicates that the basal hydrological system may not matter much. The basal water system is able to sequester large volumes of water over years which it then releases rapidly with little or no apparent change in glacier speed. This insensitivity suggests that the details of the basal hydrological system may not be the most important feature of the ice sheet for models to capture, especially now that data assimilation techniques allow us to infer the dynamic properties of the bed (e.g., the coefficients in a sliding law) directly (Joughin et al., 2010; Morlighem et al., 2010)."
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #201 on: August 19, 2016, 06:35:11 PM »
The linked reference is entitled: "Grounding Line Variability and Subglacial Lake Drainage on Pine Island Glacier, Antarctica", & presents state-of-the art findings from the past 6 years on these topics:

Ian Joughin, David E. Shean, Ben E. Smith & P. Dutrieux (17 August 2016), "Grounding Line Variability and Subglacial Lake Drainage on Pine Island Glacier, Antarctica", Geophysical Research Letters, DOI: 10.1002/2016GL070259

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070259/abstract

Abstract: "We produced a 6-year time series of differential tidal displacement for Pine Island Ice Shelf, Antarctica, using speckle-tracking methods applied to fine-resolution TerraSAR-X data. These results reveal that the main grounding line has maintained a relatively steady position over the last 6 years, following the speedup that terminated in ~2009. In the middle of the shelf, there are grounded spots that migrate downstream over the 6-year record. Examination of high-resolution DEMs reveals that these grounded spots form where deep keels (thickness anomalies) advect over an approximately flow-parallel bathymetric high, maintaining intermittent contact with the bed. These datasets also reveal several subsidence and uplift events associated with subglacial lake drainages in the fast-flowing region above the grounding line. Although these drainages approximately double the rate of subglacial water flow over periods of a few weeks, they have no discernible effect on horizontal flow speed."
“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: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #202 on: August 26, 2016, 02:42:41 AM »
Nice present from Schoof and others, extending his model of marine ice sheet instability  to deformable beds. Loved it.

doi:10.5194/tc-10-1883-2016

Coulomb plastic till, with basal melt and freeze. Competent thermo (as always.) Binge and purge oscillation cycles. Stability regimes. Grounding line persistence on retrograde slopes. Implications for Antarctica.  " ... we step away from the limiting confines of the classical marine ice-sheet instability."

open access. read all about it.

sidd

Lennart van der Linde

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #203 on: August 26, 2016, 08:59:20 AM »
Thanks for the tip, sidd.
Here's the full paper:
http://www.the-cryosphere.net/10/1883/2016/tc-10-1883-2016.pdf

Would this imply that the MISI on a retrograde bed could be less severe, depending on the kind of bed, than thought based on the simpler model? Or rather that the behaviour of such a grounding line could be more variable, without really slowing down the overall collapse of the ice stream/sheet? Or too early to tell?

sidd

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #204 on: August 26, 2016, 07:20:16 PM »
"The grounding line of an ice stream retreating onto a section of retrograde slope may continue to retreat irreversibly or may pause for centuries during stagnation before re-advancing onto the prograde slope."

Plastic beds could slow down the retreat is my takeaway. That is what i suspected. But not something to count on.

sidd

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #205 on: August 26, 2016, 10:48:30 PM »
There is one important point I neglected to mention. In the Schoof treatment sea water at the ice front is at freezing temperature. But as we know, CDW is warmer. Whether this is sufficient to remove the stagnation regimes i dont know, perhaps write to Schoof or Rignot ?

AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #206 on: August 27, 2016, 06:26:13 PM »
There is one important point I neglected to mention. In the Schoof treatment sea water at the ice front is at freezing temperature. But as we know, CDW is warmer. Whether this is sufficient to remove the stagnation regimes i dont know, perhaps write to Schoof or Rignot ?

I note that the Schoof paper also does not address the influence of hydrofracturing on the destruction of ice shelves in the Weddell, Ross, Bellingshausen and Amundsen Sea Sectors when the GMST anom gets into the 2 to 2.7C range.  Once the ice shelves are degraded (or lost) the adjoining marine glacial ice flow will accelerate 4 to 7 times, which will effect the stability of the relevant grounding line retreat.
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #207 on: August 27, 2016, 08:11:28 PM »
There is one important point I neglected to mention. In the Schoof treatment sea water at the ice front is at freezing temperature. But as we know, CDW is warmer. Whether this is sufficient to remove the stagnation regimes i dont know, perhaps write to Schoof or Rignot ?


sidd,
Rignot's comments in the linked Washington Post article towards the end of this post, addresses the issue that you raise about the systemic impact of warmer CDW on both accelerating the melting of key Antarctic marine glaciers and the associated impact on the positive ice-climate feedback mechanism projected by Hansen et al (2016); which indicates that this process has already started.
Best,
ASLR

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.”
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sidd

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #208 on: August 27, 2016, 11:45:29 PM »
That Robel, Schoof, Tziperman paper does not put in iceshelves or surface melt, hence cannot simulate either ice shelf buttressing or hydrofracture. I do not think the regions explored include ice faces taller than the stability limit, judging from the parameters for ice divide height of 100m, retrograde sections of 80 km at slopes of 1e-4 to 1e-3

The surface temperature is prescribed, so in principle one could raise it above freezing to get surface melt. As for ice shelves, and warmer than freezing seawater at the face, that would be more complicated, since one  has to put in a realistic ocean, instead of  a deus ex oceana who makes the ice thru the grounding line magically go poof.

But I like everything with Schoof's name on it.

I think i posted something about the paper with seals in anoher thread perhaps. Apart from the nice oceanographic data, the movements of the seals are also fascinating.

sidd

AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #209 on: August 30, 2016, 10:43:55 PM »
The linked reference uses satellite radar interferometry data for the Amundsen Sea Embayment, ASE, into 2016 to determine that: .. ice shelf and glacier retreat in this sector remain unabated."

B. Scheuchl, J. Mouginot, E. Rignot, M. Morlighem & A. Khazendar (29 August 2016), "Grounding line retreat of Pope, Smith, and Kohler Glaciers, West Antarctica, measured with Sentinel-1a radar interferometry data", Geophysical Research Letters, DOI: 10.1002/2016GL069287

http://onlinelibrary.wiley.com/doi/10.1002/2016GL069287/abstract
&
http://onlinelibrary.wiley.com/store/10.1002/2016GL069287/asset/supinfo/grl54607-sup-0001-supplementary.pdf?v=1&s=b625b6d95964be55c06e73d53ca8aa72336c940c

Abstract: "We employ Sentinel-1a C band satellite radar interferometry data in Terrain Observation with Progressive Scans mode to map the grounding line and ice velocity of Pope, Smith, and Kohler glaciers, in West Antarctica, for the years 2014–2016 and compare the results with those obtained using Earth Remote Sensing Satellites (ERS-1/2) in 1992, 1996, and 2011. We observe an ongoing, rapid grounding line retreat of Smith at 2 km/yr (40 km since 1996), an 11 km retreat of Pope (0.5 km/yr), and a 2 km readvance of Kohler since 2011. The variability in glacier retreat is consistent with the distribution of basal slopes, i.e., fast along retrograde beds and slow along prograde beds. We find that several pinning points holding Dotson and Crosson ice shelves disappeared since 1996 due to ice shelf thinning, which signal the ongoing weakening of these ice shelves. Overall, the results indicate that ice shelf and glacier retreat in this sector remain unabated."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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FishOutofWater

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #210 on: September 01, 2016, 04:28:28 PM »
While the AABW formation is declining the heat content and sea surface heights are jumping up off of Florida and the southeastern U.S. The recent rate of sea level rise along the south Florida coast is shocking.

Local sea level rise effects from the rapid increase of oceanic heat discussed by Jim Hansen can happen far more suddenly that global SLR. Ultimately, the global effects are much larger but the local effects can combine with hurricanes and intense cold core storms to accelerate coastal damage. I'm watching Hermine closely.

Yes, Hansen's predictions are starting to verify.

Bruce Steele

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #211 on: September 01, 2016, 04:53:21 PM »
Fish, Any chance you might chime in over on the Hansen + 3 meter page ? Appreciate your opinion !

AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #212 on: October 14, 2016, 03:34:18 PM »
The linked reference provides additional background about the recent sensitivity of the PIG to ocean forcing:

Knut Christianson et. al., (12 October 2016), "Sensitivity of Pine Island Glacier to observed ocean forcing", Geophysical Research Letters, DOI: 10.1002/2016GL070500

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070500/abstract

Abstract: "We present subannual observations (2009–2014) of a major West Antarctic glacier (Pine Island Glacier) and the neighboring ocean. Ongoing glacier retreat and accelerated ice flow were likely triggered a few decades ago by increased ocean-induced thinning, which may have initiated marine ice-sheet instability. Following a subsequent 60% drop in ocean heat content from early 2012 to late 2013, ice flow slowed, but by < 4%, with flow recovering as the ocean warmed to prior temperatures. During this cold-ocean period, the evolving glacier-bed/ice-shelf system was also in a geometry favorable to stabilization. However, despite a minor, temporary decrease in ice discharge, the basin-wide thinning signal did not change. Thus, as predicted by theory, once marine ice-sheet instability is underway, a single transient high-amplitude ocean cooling has only a relatively minor effect on ice flow. The long-term effects of ocean-temperature variability on ice flow, however, are not yet known."
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #213 on: October 25, 2016, 07:56:04 PM »
While solartim27 has already posted this in the "Surge" thread, I figure the more the merrier, and if Pope accelerates this will reduce the stability of Thwaites.  Also, if it is not clear why ice mass loss from Pope's grounding line is occurring faster than for Thwaites, it may be because the grounding line for Pope is deeper than for Thwaites and the freezing temperature of seawater increases with depth, thus Pope's grounding line has more melting potential:

The linked NPR article is entitled: "Antarctica's Ice Sheets Are Melting Faster — And From Beneath".  I cites unbalanced/unstable basal melt rates for several ice shelves draining into the Amundsen Sea Embayment, at a rate that will likely lead to the eventual collapse of the associated ice shelves and a subsequent acceleration of the associated glaciers (Pope, Smith & Kohler, see the attached image).

http://www.npr.org/sections/thetwo-way/2016/10/25/499206005/antarcticas-ice-sheets-are-melting-faster-and-from-beneath

Extract: "A team from JPL has been studying that grounding line in several places along the edge of the West Antarctic ice sheet. They used radar to look beneath the ice. In particular, overflights have targeted ice shelves along the West Antarctic ice sheet known as the Amundsen Sea Embayment.

They've found that the ice is melting faster than they've ever seen. The researchers believe the cause is warm water circulating beneath the ice shelf. The melting was most pronounced from 2002 to 2009. (The influx of warmer water to the region stalled recently, and the rate of melting seems to have slowed somewhat.)

Khazendar says the more the bottom of the shelves melt, the more ice is exposed to warm water. "It becomes a runaway process," he explains, "which makes it unstable."
Where's the warmer water coming from? The team, whose findings appear in the journal Nature Communications, points to global warming that's heating up the oceans. There's been a spate of research lately showing that Antarctic ice is melting faster than previously thought — and raising global sea levels.

Khazendar says the melting process appears to be irreversible. Polar scientists fear that at some point, the shelves will collapse and Antarctica's glaciers will flow into the sea."


For the reference see:
Khazendar et. al. (Oct 25 2016), "Rapid submarine ice melting in the grounding zones of ice shelves in West Antarctica", Nature Communications 7, Article no. 13243, doi: 10.1038/ncomms13243

http://www.nature.com/articles/ncomms13243

« Last Edit: October 25, 2016, 08:20:23 PM by AbruptSLR »
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #214 on: October 26, 2016, 01:41:46 AM »
...  if Pope accelerates this will reduce the stability of Thwaites.  Also, if it is not clear why ice mass loss from Pope's grounding line is occurring faster than for Thwaites, it may be because the grounding line for Pope is deeper than for Thwaites and the freezing temperature of seawater increases with depth, thus Pope's grounding line has more melting potential:

For those who do not remember the relationship of the PSK glacial basin to the Thwaites glacial basin I re-post the three attached images.
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solartim27

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #215 on: October 28, 2016, 01:18:06 AM »
Here is a gif of the Thwaites area for 2014, 2015, and today.  After comparing it to the Larsen B gif I made I do not have a warm fuzzy feeling in my gut.  I am leaving it full size because the white on white detail is hard to pick up, so click to animate. 
FNORD

solartim27

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #216 on: October 28, 2016, 05:08:58 PM »
I found a sentinel from march, so here is a gif of the southern part of Thwaites, closest to PIG, versus today

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20161028T044353_32E1_S_1.final.jpg

and S1A_EW_GRDM_1SSH_20160331T045150_542F_S_1.final.jpg
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #217 on: November 07, 2016, 06:37:47 PM »
The linked reference is entitled: "A 125-year record of climate and chemistry variability at the Pine Island Glacier ice divide, Antarctica".  The reference find a distinct seasonality to the mineral dust & sea salt in the ice cores.  It will be interesting to see how this seasonal behavior interactions with the risks of hydrofracturing & cliff failure mechanisms if/when GMSTA approaches 2.7C (a threshold identified by DeConto 2016):

Schwanck, F., C. Simões, J., Handley, M., A. Mayewski, P., D. Auger, J., T. Bernardo, R., and E. Aquino, F.: A 125-year record of climate and chemistry variability at the Pine Island Glacier ice divide, Antarctica, The Cryosphere Discuss., doi:10.5194/tc-2016-242, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-242/


Abstract. The Mount Johns (MJ) ice core (79º55' S; 94º23' W) was drilled near the Pine Island Glacier ice divide on the West Antarctic Ice Sheet during the 2008–2009 austral summer, to a depth of 92.26 m. The upper 45 m of the record covers approximately 125 years (1883–2008) showing marked seasonal variability. Trace element concentrations in 2,137 samples were determined using inductively coupled plasma mass spectrometry. In this study, we reconstruct mineral dust and sea salt aerosol transport and investigate the influence of climate variables on the elemental concentrations to the MJ site. The ice core record reflects changes in emissions as well as atmospheric circulation and transport processes. Our trajectory analysis shows distinct seasonality, with strong westerly transport in the winter months and a secondary northeasterly transport in the summer. During summer months, the trajectories present slow-moving (short) transport and are more locally influenced than in other seasons. Finally, our reanalysis trace element correlations suggest that marine derived trace element concentrations are strongly influenced by sea ice concentration and sea surface temperature anomalies. The results show that seasonal elemental concentration maxima in sea-salt elements correlate well with the sea ice concentration winter maxima in the West Amundsen and Ross Seas. Lastly, we observed an increased concentration of marine aerosols when sea surface temperature decreased.
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #218 on: November 09, 2016, 05:15:17 PM »
The linked reference discusses progress being made in modeling iceberg calving from Thwaites:

Yu, H., Rignot, E., Morlighem, M., and Seroussi, H.: Iceberg calving of Thwaites Glacier, West Antarctica: Full-Stokes modeling combined with linear elastic fracture mechanics, The Cryosphere Discuss., doi:10.5194/tc-2016-249, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-249/
http://www.the-cryosphere-discuss.net/tc-2016-249/tc-2016-249.pdf

Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades. Here, we present a study of its calving dynamics combining a two-dimensional flowband Full Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model crevasse propagation and ice fracturing. We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom crevasses that match the distribution of crevasse depth and width observed from NASA's Operation IceBridge radar depth sounders, whereas HO/LEFM and SSA/LEFM do not generate crevasses that match observations. We attribute the difference to the non-hydrostatic condition of ice near the grounding line, which facilitates crevasse formation, and is accounted for by the FS model but not by the HO or SSA model. We also find that calving is enhanced when pre-existing surface crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the time scale of calving events. It is more prominent for glaciers with rapid calving rates than glaciers with slow calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line for constraining crevasse formation and iceberg calving.
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solartim27

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #219 on: November 25, 2016, 02:48:33 PM »
Here is a gif of a small calving at the northern end of Thwaites near Haynes glacier.  Oct 28 to Nov 23.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20161123T042739_CF1E_S_1.final.jpg

S1A_EW_GRDM_1SSH_20161028T044353_32E1_S_1.final.jpg
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #220 on: November 28, 2016, 06:51:21 PM »
The linked reference indicates that the PIIS is calving further upstream than in the past due to oceanic driven disintegration of the northern shear margin mélange and intensified melting with basal crevasses.  As the ocean in this area will remain relatively warm for a long time, this indicates that the PIIS will continue to calve more rapidly than in the past and will calve further and further upstream, with time.  This will cause the buttressing on the SW Tributary Glacier to be reduced, which will help to trigger the acceleration of ice velocities for Thwaites:

Seongsu Jeong, Ian M. Howat & Jeremy N. Bassis (28 November 2016), "Accelerated ice shelf rifting and retreat at Pine Island Glacier, West Antarctica", Geophysical Research Letters, DOI: 10.1002/2016GL071360

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071360/full

Abstract: "Pine Island Glacier has undergone several major iceberg calving events over the past decades. These typically occurred when a rift at the heavily fractured shear margin propagated across the width of the ice shelf. This type of calving is common on polar ice shelves, with no clear connection to ocean-ice dynamic forcing. In contrast, we report on the recent development of multiple rifts initiating from basal crevasses in the center of the ice shelf, resulted in calving further upglacier than previously observed. Coincident with rift formation was the sudden disintegration of the ice mélange that filled the northern shear margin, resulting in ice sheet detachment from this margin. Examination of ice velocity suggests that this internal rifting resulted from the combination of a change in ice shelf stress regime caused by disintegration of the mélange and intensified melting within basal crevasses, both of which may be linked to ocean forcing."

See also:

http://www.csmonitor.com/Environment/2016/1128/Why-this-Antarctic-ice-shelf-is-breaking-up-from-the-inside-out

Extract: "The evidence of a deep subsurface rift indicates that a warming ocean likely contributed to the breakup and will likely lead to more significant breaks in the near future."
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #221 on: December 01, 2016, 05:46:53 PM »
As a follow-on to my last post, the linked Climate Central article is entitled: "Odd Rifts in Antarctic Ice Could Mean ‘Sayonara, Glacier’", and it cites an ocean-ice interaction mechanism that could accelerate the loss of the PIIS and subsequently the loss of the PIG (beyond current consensus projections):

http://www.climatecentral.org/news/rifts-antarctic-ice-sayonara-glacier-20923

Extract: "The key question for the future of Pine Island Glacier is whether rifts will keep forming in these valleys further and further inland. If they do, more and more icebergs could calve off at a quicker pace than is typical, diminishing the ice shelf and speeding the retreat of the glacier.
The study shows “a new mechanism for potentially rapid collapse,” Mankoff said. “It’s a little bit scary.”
Or, as Howat put it, if this mechanism does continue like this, “then it’s going to be, ‘Sayonara, glacier.’”"
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #222 on: January 03, 2017, 06:23:13 PM »
The linked reference is entitled: "In-situ GPS records of surface mass balance and ocean-induced basal melt for Pine Island Glacier, Antarctica", and it provides field data (in the 2008 to 2014 timeframe) to help better understand ice mass loss trends for the PIG.

Shean, D. E., Christianson, K., Larson, K. M., Ligtenberg, S. R. M., Joughin, I. R., Smith, B. E., and Stevens, C. M.: In-situ GPS records of surface mass balance and ocean-induced basal melt for Pine Island Glacier, Antarctica, The Cryosphere Discuss., doi:10.5194/tc-2016-288, in review, 2017.


http://www.the-cryosphere-discuss.net/tc-2016-288/

Abstract. In the last two decades, Pine Island Glacier (PIG) experienced marked speedup, thinning, and grounding-line retreat, likely due to ice-shelf basal melt and marine ice-sheet instability. To better understand these processes, we analyzed 2008–2010 and 2012–2014 in-situ GPS records for PIG to constrain surface mass balance, firn compaction, and basal melt. We computed time series of horizontal velocity, strain rate, antenna height, surface elevation, and Lagrangian elevation change (Dh/Dt). The antenna height time series show a surface elevation increase of ~ 0.7–1.0 m/yr, which is consistent with model estimates for surface mass balance (SMB) of ~ 0.7–0.9 mwe/yr and ~ 0.7–0.8 m/yr downward velocity due to firn compaction. An abrupt ~ 0.2–0.3 m surface elevation decrease, likely due to surface melt, is observed during a period of warm atmospheric temperatures from December 2012 to January 2013. Observed Dh/Dt for all PIG shelf sites is highly linear, with trends of −1 to −4 m/yr and residuals of < 0.4 m. Corresponding basal melt rate estimates range from ~ 10 to 40 m/yr, in good agreement with those derived from ice-bottom acoustic ranging, phase-sensitive ice-penetrating radar, and high-resolution stereo DEM records. The GPS and DEM records document higher melt rates within and near features associated with longitudinal extension (transverse surface depressions, rifts). Basal melt rates for the 2012–2014 period show limited temporal variability, despite significant changes in ocean heat content, suggesting that sub-shelf melt rates may be less sensitive to ocean heat content than previously reported, at least for these locations and time periods.
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #223 on: January 06, 2017, 04:27:13 PM »
The linked reference indicates that the PIIS is calving further upstream than in the past due to oceanic driven disintegration of the northern shear margin mélange and intensified melting with basal crevasses.  As the ocean in this area will remain relatively warm for a long time, this indicates that the PIIS will continue to calve more rapidly than in the past and will calve further and further upstream, with time.  This will cause the buttressing on the SW Tributary Glacier to be reduced, which will help to trigger the acceleration of ice velocities for Thwaites:

Seongsu Jeong, Ian M. Howat & Jeremy N. Bassis (28 November 2016), "Accelerated ice shelf rifting and retreat at Pine Island Glacier, West Antarctica", Geophysical Research Letters, DOI: 10.1002/2016GL071360

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071360/full


Also see: Lipuma, L. (2017), West Antarctic ice shelf breaking up from the inside out, Eos, 98, doi:10.1029/2017EO064743. Published on 04 January 2017.

https://eos.org/research-spotlights/west-antarctic-ice-shelf-breaking-up-from-the-inside-out?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz010617

Extract: "Although this is the first time researchers have witnessed a deep subsurface rift opening within Antarctic ice, they have seen similar breakups in the Greenland Ice Sheet, in spots where ocean water has seeped inland along the bedrock and begun to melt the ice from underneath. The satellite images provide the first strong evidence that these large Antarctic ice shelves respond to changes at their ocean edge in a way similar to that observed in Greenland.

The researchers note that this kind of rifting behavior provides another mechanism for rapid retreat of these glaciers, adding to the probability that there may be a significant collapse of the West Antarctic Ice Sheet in the next century.  They point out that there are many similar valleys farther up the glacier. If these sites are prone to rifting, we could potentially see more accelerated ice loss in Antarctica."
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oren

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #224 on: January 06, 2017, 04:58:21 PM »
The linked reference is entitled: "In-situ GPS records of surface mass balance and ocean-induced basal melt for Pine Island Glacier, Antarctica"
Very interesting. Note the article relates to the PIG ice shelf, rather than the glacier itself.

sidd

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #225 on: January 21, 2017, 12:43:34 AM »
nice paper by Millain et al in GRL doi:10.1002/2016GL072071 on better bedmaps for PIG,Thwaites,Smith,Kohler. Fearsome holes down there. I attach panels from fig2, PIG, Thwaites and Smith-Kohler


solartim27

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #226 on: February 01, 2017, 05:37:27 PM »
Southern Thwaites shelf had a decent size calving.  the big chunk is around 10 km, around the same size as the last small PIG calving, overall about 20 km.  Jan 25 to Feb 1

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170201T044350_123E_S_1.final.jpg (30 MB)

S1A_EW_GRDM_1SSH_20170125T045155_2FA4_S_1.final.jpg (34 MB)
« Last Edit: February 01, 2017, 05:47:43 PM by solartim27 »
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solartim27

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #227 on: February 03, 2017, 04:19:44 PM »
Just a screen shot of the new bergs.  I suppose extent just got a bump up.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170203T042736_5EF7_S_1.final.jpg (27MB)
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DrTskoul

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #228 on: February 09, 2017, 12:02:38 AM »
"Hidden lakes drain below West Antarctica's Thwaites Glacier"

Researchers at the University of Washington and the University of Edinburgh used data from the European Space Agency's CryoSat-2 to identify a sudden drainage of large pools below Thwaites Glacier, one of two fast-moving glaciers at the edge of the ice sheet. The study published Feb. 8 in The Cryosphere finds four interconnected lakes drained in the eight months from June 2013 and January 2014. The glacier sped up by about 10 percent during that time, showing that the glacier's long-term movement is fairly oblivious to trickles at its underside.

"This was a big event, and it confirms that the long-term speed-up that we're observing for this glacier is probably driven by other factors, most likely in the ocean," said corresponding author Ben Smith, a glaciologist with the UW's Applied Physics Laboratory. "The water flow at the bed is probably not controlling the speed."
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #229 on: February 17, 2017, 09:00:09 PM »
The linked article is entitled: "A New Theory Explains What's Driving Antarctica's Fastest Melting Glacier".

http://www.seeker.com/a-new-theory-explains-whats-driving-antarcticas-fastest-melting-glacie-2268234317.html

Extract: "Researchers previously pinpointed continental winds as the force pushing warm ocean waters underneath West Antarctica's Pine Island Glacier, but now they say local weather patterns are to blame.

Researchers have described the Pine Island Glacier as the "plug" that holds back the expansive West Antarctic Ice Sheet, the melting of which contributes to sea-level rise."

Also see the associated reference entitled: "Mechanisms driving variability in the ocean forcing of Pine Island Glacier" (doi: 10.1038/ncomms14507).

http://www.nature.com/articles/ncomms14507
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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #230 on: May 21, 2017, 04:02:27 AM »
The linked reference studies a subglacial draining event beneath Thwaites Glacier from June 2013 to January 2014:

Smith et. al. (2017), "Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica", The Cryosphere, 11, 451–467, doi:10.5194/tc-11-451-2017

http://www.the-cryosphere.net/11/451/2017/tc-11-451-2017.pdf

Abstract. We present conventional and swath altimetry data from CryoSat-2, revealing a system of subglacial lakes that drained between June 2013 and January 2014 under the central part of Thwaites Glacier, West Antarctica (TWG). Much of the drainage happened in less than 6 months, with an apparent connection between three lakes spanning more than 130 km. Hydro-potential analysis of the glacier bed shows a large number of small closed basins that should trap water produced by subglacial melt, although the observed largescale motion of water suggests that water can sometimes locally move against the apparent potential gradient, at least during lake-drainage events. This shows that there are important limitations in the ability of hydro-potential maps to predict subglacial water flow. An interpretation based on a map of the melt rate suggests that lake drainages of this type should take place every 20–80 years, depending on the connectivity of the water flow at the bed. Although we observed an acceleration in the downstream part of TWG immediately before the start of the lake drainage, there is no clear connection between the drainage and any speed change of the glacier."
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sidd

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #231 on: May 21, 2017, 05:28:52 AM »
That Webber 2017 article, (open, read all about it)

http://www.nature.com/articles/ncomms14507

documents a cold spell just b4 the drainage. I wonder ...

I notice Dutrieux and Jenkins on the author list of Webber article. Keep on truckin.

sidd

P.S. More specifically, i wonder if the ocean cooling in 2011 decreased shelf bottom melt slowing discharge, thickening ice inland; thus clamping down on interior bottom melt water efflux until pressure build caused submarine jokulhaup as seen in 2013-14 in Smith et al.

Whew, that was a long sentence, even with the semi colon.

sidd
« Last Edit: May 21, 2017, 07:14:07 AM by sidd »

AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #232 on: May 23, 2017, 12:07:21 AM »
The linked reference studies a subglacial draining event beneath Thwaites Glacier from June 2013 to January 2014:

Smith et. al. (2017), "Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica", The Cryosphere, 11, 451–467, doi:10.5194/tc-11-451-2017

http://www.the-cryosphere.net/11/451/2017/tc-11-451-2017.pdf


Here is more information on the June 2013 to Jan 2014 drainage of four subglacial lakes beneath the Thwaites Glacier.  The article is entitled: "Hidden lakes drain below West Antarctica’s Thwaites Glacier".

http://www.washington.edu/news/2017/02/08/hidden-lakes-drained-under-west-antarcticas-thwaites-glacier/

Extract: "Researchers at the University of Washington and the University of Edinburgh used data from the European Space Agency’s CryoSat-2 to identify a sudden drainage of large pools below Thwaites Glacier, one of two fast-moving glaciers at the edge of the ice sheet. The study published Feb. 8 in The Cryosphere finds four interconnected lakes drained in the eight months from June 2013 and January 2014. The glacier sped up by about 10 percent during that time, showing that the glacier’s long-term movement is fairly oblivious to trickles at its underside.

Melting at the ice sheet base would refill the lakes in 20 to 80 years, Smith said. Over time meltwater gradually collects in depressions in the bedrock. When the water reaches a certain level it breaches a weak point, then flows through channels in the ice. As Thwaites Glacier thins near the coast, its surface will become steeper, Smith said, and the difference in ice pressure between inland regions and the coast may push water coastward and cause more lakes to drain."
“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: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #233 on: May 23, 2017, 12:11:48 AM »
See also the attached image from 2016 data (release Feb 8 2017):

http://www.esa.int/spaceinimages/Images/2017/02/Glacier_speed_West_Antarctica

Extract: "This image from Sentinel-1 and geographic base map shows the speed of ice flow in West Antarctica. Reaching speeds of over 3 km per year, Thwaites and Pine Island are two of the fastest receding glaciers on the Western Antarctic Ice Sheet. Applying interferometric synthetic aperture swath processing techniques to CryoSat data revealed that four lakes beneath Thwaites drained into the Amundsen Sea."
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solartim27

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #234 on: June 25, 2017, 08:22:39 PM »
More calving, with continued rift development and sea ice dispersal at Thwaites.  22 May to 25 Jun, Click to animate.  (1.7 Mb)
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SDH_20170625T044410_9CB6_S_1.final.jpg
S1A_EW_GRDM_1SSH_20170522T042748_981A_S_1.final.jpg
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solartim27

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #235 on: June 28, 2017, 02:41:25 AM »
Whoa!  Looks like there's more on the way!
S1A_EW_GRDM_1SDH_20170627T042750_486D_S_1.final.jpg
S1A_EW_GRDM_1SDH_20170622T041938_79D0_S_1.final.jpg
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solartim27

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #236 on: July 06, 2017, 05:40:05 PM »
The calving continues at Thwaites, 22 Jun to 4 July
S1A_EW_GRDM_1SDH_20170704T041939_6046_S_1.final.jpg
S1A_EW_GRDM_1SDH_20170622T041938_79D0_S_1.final.jpg

Great video from Sep 2016 to May here:
http://www.cesbio.ups-tlse.fr/multitemp/?p=10666&utm_source=rss&utm_medium=rss&utm_campaign=watching-ice-shelfs-break-up-with-sentinel-1-2
« Last Edit: July 06, 2017, 05:50:26 PM by solartim27 »
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #237 on: July 20, 2017, 08:03:53 PM »
I would just like to note that in my opinion the force required by the Pine Island Ice Shelf, PIIS, to change the ice flow direction of the Southwest (SW) Tributary Glacier by about 90 degrees will soon (before the boreal summer of 2018) cause a new splitting tension crack across the PIIS by the mechanism illustrated in the first attached image.  Furthermore, it is my opinion that the reaction to such a crack formation in the PIIS will cause a major calving of the SW Tributary Glacier's Ice Shelf as suggested by the growth of the major crack in the SW Tributary Ice Shelf illustrated in the second attachment of a gif sequence provided by solartim27.  If so, this should cause the ice flow velocities of the SW Tributary Glacier to accelerate; which should reduce the boundary shear restrain from the associate border with the Thwaites Glacier.
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #238 on: July 26, 2017, 01:53:42 PM »
The linked 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 extreme 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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson