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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #50 on: March 11, 2013, 11:11:53 PM »
To clarify my thinking on this 2012 "Surge" event:
(a) I believe than the 2010-2011 La Nina event that temporarily lowered sea levels by transferring water to land, should have cause the various WAIS ice streams/glaciers to set-down harder on their gateway seafloor sills (due to the low water levels) which allowed the various drainages systems to build-up both water volume and water pressure for the various basal meltwater drainage networks.
(b) I believe that by Spring of 2012 essentially all of the 2010-2011 "La Nina" event water had returned to the oceans, so that when the GIS had a high surface meltwater run-off event in early Summer of 2012, that this caused the Southern Ocean to raise about 2 to 3 mm above the SLR trend line.
(c) Then I postulated that the higher Southern Ocean sea level allowed the various high pressure meltwater systems to lift-up the "ice plugs" from the gateway sills thus allowing meltwater to leak/outburst depending on the particulars of the different subglacial/basal meltwater drainage networks (sometimes including subglacial lakes).   This would cause all WAIS drainage basins to leak/surge nearly at the same time, resulting in "Surge" ice mass loss (both ice and meltwater) to the ocean.
(d) As Thwaites has the largest drainage basal meltwater system (and I believe a subglacial lake right near the old gateway) this basin contributed the largest volume to the surge, followed by the Ferrigno Glacier (note the Bellingshausen Sea area typically contributes 40% of all ice mass loss from WAIS); then PIG and the Siple Coast ice streams (both probably mostly leaked basal meltwater) and the Weddell Sea Embayment ice sheet (again probably mostly leaked basal meltwater).
Note the attached image from NASA shows how the GRACE satellite can identify the ice mass loss from the various different drainage basins for the WAIS.

I also believe that when the basal drainage networks had lost sufficient pressure and when the South Ocean lost sufficient sea level (due to the finger print effect) that essentially all of the "ice plugs" were re-sealed by the end of 2012; and that if enough pressure is built back up in the basal drainage networks and if the GIS has another large ice mass loss this Summer, then this cycle could repeat itself in either 2013 or 2014.
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Lennart van der Linde

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Re: Surge of WAIS Ice Mass Loss
« Reply #51 on: March 12, 2013, 12:36:22 PM »
ASLR,

So far only Mauri Pelto has responded. He says:

"The MODIS and Landsat imagery I have used could be used to assess velocity, but I did not do so. I have not seen evidence of a surge here, nor are surges typical in this setting. A surge is a rapid short lived acceleration. Instead what I noted is considerable calving retreat that has continued during this melt season, that is likely due to ice thinning and enhanced rifting. I will update the post I did as the melt season comes to a close. Operation Ice Bridge will certainly have excellent imagery that can be used for elevation change mapping and velocity determination."

I then asked him and the others if they know who's maybe doing these analyses or when they will be published. I will let you know if they reply. If you email me directly, it's maybe easier to communicate.

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #52 on: March 12, 2013, 02:34:55 PM »
Lennart,

Thank you for Mauri Pelto's response (and I have now sent you two e-mails, one from yesterday and one today).  I am not surprised that researchers prefer to avoid dramatic statement about possible abrupt changes without considerable amounts of carefully reviewed data, compiled over years and decades.  Nevertheless, I believe that the evidence that I have presented does support (but does not prove) the proposition that both: (a) a surge of SLR occurred in the Summer and Fall of 2012 with about 3.3mm of eustatic contribution from ice mass loss from the WAIS; and that (b) the WAIS ice streams seem to be accelerating (perhaps in surges with quasi-equibrium states inbetween).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Lennart van der Linde

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Re: Surge of WAIS Ice Mass Loss
« Reply #53 on: March 12, 2013, 04:53:15 PM »
ASLR,

Your mails have not reached me, so maybe the address is not correct?

Could you try again at: lennart.vanderlinde@haagsmilieucentrum.nl

I also asked some Dutch climate researchers to respond, but no luck yet.

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #54 on: March 14, 2013, 04:38:40 AM »
A4R has updated his methane website at the following link:

https://sites.google.com/site/a4r2013metop2iasich4co2/home/2011-airs-ch4-359-hpa-vs-iasi-ch4-970-600-mb

Which contain images showing atmospheric methane concentrations up to about 1890 ppb over the Amundsen Sea; which may be either an indication that the CDW is warming over the continental shelf, and/or that grounding line retreat is reducing pressure on methane hydrates in the seafloor resulting in high methane emissions.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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sg_smith

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Re: Surge of WAIS Ice Mass Loss
« Reply #55 on: March 15, 2013, 01:54:51 AM »
If I am interpreting these images of methane release correctly they show high methane concentrations coming from Wilkes land Area of the Antarctica.  This lies west of Australia, specifically Tasmania.  Since the weather moves from West the East I wonder if this is an indication we will have a warm winter?  It will be interesting to see what happens, so far the far South of Tasmania  has been cooler than the north of Tasmania/Victoria which have been having record number of hot days/nights.  Although to be fair we did have the hottest day ever recorded in Hobart 40.9C (105.6F) on 4 January 2013.

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #56 on: March 15, 2013, 09:06:57 AM »
Susan,

I can see that I was mistaken when I stated that the methane emissions were coming from the Amundsen Sea.  Now I wonder if these emissions might be associated with the increase in temperature, and the decrease in volume of the AABW, as it now looks to me like these emissions could be coming from areas of the continental slope (where it is possible that slope instabilities could release enough methane at one time that the methane could reach the surface of the ocean without being re-absorbed).

Thanks for making this catch,
ASLR
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Bruce Steele

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Re: Surge of WAIS Ice Mass Loss
« Reply #57 on: March 16, 2013, 05:41:57 PM »
ASLR, I found some info on Wilkes land and George V Coast. There are meters deep deposits of siliceous ooze at appropriate (200-600)meter depths for clathrates to develop . There are also the strongest offshore winds recorded in the world so large upwellings of deep shelf waters may enhance transport of methane into surface waters(just speculating).It would be nice to know the water temperature at those 200-600meter depths and changes due to the reduction of AADW formation processes. 

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #58 on: March 16, 2013, 11:38:13 PM »
Bruce,

Your theory is as good as any other; but as the winds blow methane around, it may be difficult to know for sure where the methane emissions are coming from; but in any event, they are not a good sign.

ASLR
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #59 on: March 17, 2013, 08:34:28 PM »
A4R has updated the METOP 2 IASI CH4 imagery through March 15 12-24 hrs.

https://sites.google.com/site/a4r2013metop2iasich4co2/home/2011-airs-ch4-359-hpa-vs-iasi-ch4-970-600-mb

The Antarctic areas in the Southern Ocean across from Africa and Australia continue to have record amounts of methane at 586-600 mb.
“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: Surge of WAIS Ice Mass Loss
« Reply #60 on: March 26, 2013, 01:46:31 AM »
While I realize that the accompanying image from CNES,LEGOS,CLS (from the following link), does not prove a surge in SLR in late 2012, still the trend in this figure seems unusually high for the end of 2012 and the beginning of 2013 (which could indicate a surge in ice mass loss from WAIS in this timeframe):

http://www.aviso.oceanobs.com/en/news/ocean-indicators/mean-sea-level/


In this figure, a 2-month filter is applied to the blue points, while a 6-month filter is used on the red curve. By applying the postglacial rebound correction (-0.3 mm/year), the  rise in mean sea level has thus been estimated as 3.18 mm/year (mean slope of the plotted data).
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bert

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Re: Surge of WAIS Ice Mass Loss
« Reply #61 on: March 31, 2013, 06:03:13 PM »
AbruptSLR,

Here's a plot of the GRACE observations for West Antarctica up to Dec. 2012. I don't see evidence for a surge in mass loss in Summer/Fall 2012. I haven't done a quality check on the data yet, so the numbers aren't final, but a sea level rise of ~3.3 mm would require a mass loss of about 1000 Gt, which would definitely show up in the data.

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #62 on: March 31, 2013, 06:59:24 PM »
Bert,

I greatly appreciate this GRACE West Antarctic data, which clearly indicates that no more than about 150 Gt of ice mass loss occurred in 2012 (certainly not 1000 Gt even leaving allowance for fluctuations due to unusually heavy snowfall).  Therefore, I agree that it appears clear that no "surge" event has happened in the WAIS in 2012, and that the ice mass loss in WAIS is currently following its long-term trend pattern.  In this regard, it appears likely that the "surge" of the Thwaites Ice Tongue primarily involved floating ice, and it is conceivable that such an ice movement many have collapsed any subglacial cavity in the Thwaites Glacier gateway (which if so, would be seen in the Icebridge radar survey taken in October of 2012, and which would also serve to temporarily stabilize the Thwaites Glacier from accelerated advection).

I (we) will need to continuing monitoring the SLR data, so see whether the current peak in SLR is due to mass contributions from other sources, or whether it is merely a temporary fluctuation.

Again, thank you for providing this data even before you have had a chance to check your analysis; and if you ever get to the point in your analysis where you can breakdown the ice mass loss by individual drainage basins, I would be happy to see whatever information that you can provide.

Best, ASLR
« Last Edit: March 31, 2013, 08:40:36 PM by AbruptSLR »
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Lennart van der Linde

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Re: Surge of WAIS Ice Mass Loss
« Reply #63 on: March 31, 2013, 09:38:38 PM »
Bert,

Thank you for your answer to ALSR's interesting hypothesis. These preliminary GRACE-data seem to point to about 200 Gton of net mass loss from WAIS in 2011-2012? That would (again) be quite some more than the average over the past 10-20 years, probably indicating continued accelerating mass loss. Where GIS lost about 570 Gton in 2012, GIS and WAIS together seem to contribute over 2 mm/yr by now. If you would have recent data on EAIS and Antarctic Peninsula that would be very interesting to know as well.

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #64 on: April 01, 2013, 12:46:05 AM »
I am certainly pleased that my hypothesis about a 2012 "surge" of ice mass loss in the WAIS has been disproved by the data, and I hope that the acceleration of ice mass loss in the WAIS that Lennart notes does not further increase; but I image that it will be several years before we get sufficient data to see just how sensitive the WAIS is, or is not.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Lennart van der Linde

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Re: Surge of WAIS Ice Mass Loss
« Reply #65 on: April 01, 2013, 09:45:32 AM »
Skeptical Science tries to clarify what factors are most important in explaining the 20 mm of SLR over the past two years:
http://www.skepticalscience.com/Earth-Encounters-Giant-Speed-Bump-on-the-Road-to-Higher-Sea-Level.html

La Nina rebound seems most important, but accelerating ice sheet mass loss also contributes (over 2 mm in the past year?). How much exactly we'll hopefully hear soon when the data have been analysed.

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #66 on: April 01, 2013, 12:15:10 PM »
Lennart,

Thanks for the link to the article where the author Rob Painting makes the following quote:

"This suggests that we are likely, for a time, to observe larger La Niña potholes - when more intense rainfall and snow is dumped over the continents, and larger El Niño speed bumps - when more intense rainfall and snow is focused over the oceans, and the continents become drier."

As we have been in an ENSO neutral condition for a while now, I am surprised that Rob attributes our current bump in SLR to an El Nino event that tried to form, but never got going last year.  Maybe ice mass loss from mountain glaciers and ice caps (and/or the Antarctic Peninsula), have contributed to the current bump in SLR.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Lennart van der Linde

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Re: Surge of WAIS Ice Mass Loss
« Reply #67 on: April 01, 2013, 01:05:35 PM »
ASLR,
Yes, I agree that it's not at all clear yet where particularly these last 10 mm or so of SLR have come from. Maybe Bert (Vermeersen?) can shed some light...

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #68 on: April 01, 2013, 08:02:05 PM »
Lennart,

I am also curious about the condition of the Thwaites Glacier gateway as observed by the October 2012 radar survey.  I e-mailed NASA some time ago requesting the findings of this survey, when they are available; but I have not heard back from them.

If the subglacial cavity that I postulated was in the trough in the Thwaites Glacier gateway was displaced by the Thwaites Ice Tongue surge, then Thwaites Glacier may be more stable than before the ice tongue surge; however, if the survey shows that a subglacial cavity is still there then the rest of my postulated hazard analysis collapse scenario for the Thwaites Glacier could be largely unaffected.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #69 on: April 02, 2013, 11:36:28 PM »
I received a reply from NASA directing me to all of the relevant IceBridge data that is available; which does not yet include the Oct 2012 aerial survey of the Thwaites Gateway.  I will put myself on NASA notice list for updates for when the data eventually is posted.

In the meantime, for convenience, I am reposting four key figures related to question of whether the trough in the Thwaites Gateway still has at least a portion of a subglacial cavity following the Oct 2012 Thwaites Ice Tongue surge event.

The first image by Tinto & Bell 2011 shows the 1996 and 2009 grounding lines in the Thwaites Gateway area.  This figure clearly shows the entire trough having a subglacial cavity but by 2009 Tino & Bell show some uncertianty about the extent of the subglacial cavity in the trough area.  Given these old survey results together with the shape of the now fully melted Thwaites Iceberg Tongue (which indicated series of surges of the ice tongue have occurred periodically over the past decades and centuries); this implies that the subglacial cavity in the trough has probably periodically grown through advection and then receded during ice tongue surge events.

The second image also by Tinto & Bell 2011 shows a plan and cross-sectional views per Rignot et al 2011.  The grounding line cross-section along line X-X' shows a hollow (or subglacial cavity) in the groundling line at the entrance to the trough, which shows that the trough is narrow enough for the ice above the trough to arch across the trough so that it is both thin but technically not floating.  This view also that the bottom the trough is below El -1000m, so that to me it look like between the ice arching action and the depth of the trough that it would be difficult to image that the Oct 2012 Thwaites Ice Tongue surge event would have completely infilled the trough with ice.

The third image by Rignot shows the bathymetry for the Thwaites Gateway that shows that immediately to the east of the trough there is a submerged/buried seamount with a top elevation about El -600m; and as I previously stated I believe that these Thwaites Ice Tongue surge events will increase in frequency sufficiently to thin the ice around the seamount enough so that around 2020 the Thwaites Ice Shelf will float directly over the top of the seamount which will contribute to the rapid retreat of the grounding line down into the BSB about 100km by 2040.

The fourth image shows an image of the ice surface elevations for both the PIG and Thwaites drainage basins; which I provide because I believe that it shows the gradual slope of the ice at the PIG Gateway for which the subglacial cavity is stable (from infilling), and I believe that when the slope of the ice in the Thwaites Gateway thins sufficiently to achieve a comparable slope that then its subglacial cavity should also stop infilling periodically, which will allow a substantial ice shelf to forward in the Thwaites Gateway (extending over the top of the seamount); until the postulated "Thwaites Effect" occurs circa 2060 to transform the ice shelf into an ice melange.
« Last Edit: April 03, 2013, 12:28:42 AM by AbruptSLR »
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #70 on: April 04, 2013, 12:00:18 PM »
I just thought that I would repost the attached image from Envisat June 2012 of the changes in elevations for the Antarctic.  This figure shows that the ice stream along the eastern arc (in the orange transparent area) of the Thwaites drainage basin is becoming more activated as indicated by the drop in ice surface elevation along this arc (which is more than previously observed).
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #71 on: April 08, 2013, 12:35:42 AM »
I thought that I would post the following abstract which indicates that after GIA correction the Amundsen Sea sector is contributing more to SLR than previously projected:

An investigation of Glacial Isostatic Adjustment over the Amundsen Sea sector, West Antarctica
by: A. Groh; H. Ewert, M. Scheinert, M. Fritsche, A. Rülke, A. Richter, R. Rosenau, R. Dietrich
http://dx.doi.org/10.1016/j.gloplacha.2012.08.001

Abstract
The present study focuses on the Amundsen Sea sector which is the most dynamical region of the Antarctic Ice Sheet (AIS). Based on basin estimates of mass changes observed by the Gravity Recovery and Climate Experiment (GRACE) and volume changes observed by the Ice, Cloud and Land Elevation Satellite (ICESat), the mean mass change induced by Glacial Isostatic Adjustment (GIA) is derived. This mean GIA-induced mass change is found to be 34.1 ± 11.9 Gt/yr, which is significantly larger than the predictions of current GIA models. We show that the corresponding mean elevation change of 23.3 ± 7.7 mm/yr in the Amundsen Sea sector is in good agreement with the uplift rates obtained from observations at three GPS sites. Utilising ICESat observations, the observed uplift rates were corrected for elastic deformations due to present-day ice-mass changes. Based on the GRACE-derived mass change estimate and the inferred GIA correction, we inferred a present-day ice-mass loss of − 98.9 ± 13.7 Gt/yr for the Amundsen Sea sector. This is equivalent to a global eustatic sea-level rise of 0.27 ± 0.04 mm/yr. Compared to the results relying on GIA model predictions, this corresponds to an increase of the ice-mass loss or sea-level rise, respectively, of about 40%.

The first accompanying figure shows an overview of the Amundsen Sea sector, West Antarctica. The red line defines the generalised drainage basins of Pine Island Glacier, Thwaites Glacier and Smith Glacier (PITS). Locations of three GPS campaign sites are marked by red triangles.

The second figures shows the GRACE data from 2003 to 2009 which the papers says needs to be corrected to indicate about 40% more ice mass loss than previously reported
« Last Edit: July 18, 2013, 11:19:29 PM by AbruptSLR »
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #72 on: April 08, 2013, 12:55:51 AM »
I thought that I would post the following abstract that indicates that the authors have identified a mechanism by which subglacial hydrology could trigger a grounding line retreat for the Thwaites Glacier:

Evidence for Ice-Flow-Coupled Subglacial Water Systems Beneath WestAntarctica’s Potentially Unstable Thwaites Glacier

by: Dustin M. Schroeder1, Donald D. Blankenship1, Duncan A. Young1
1: The University of Texas Institute for Geophysics

"Subglacial water in various forms has been observed and theorized to accelerate the flow of overlying ice. The acceleration depends on the flux through the subglacial water system and whether the dynamic state is hydrologically “distributed” or “concentrated” . Marine ice sheets with landward-sloping beds are in an unstable configuration for which such accelerations can initiate or modulate grounding line retreat and ice loss. Thwaites Glacier (TG) is one the largest, most rapidly changing glaciers on earth and its landwardsloping bed reaches the interior of the marine West Antarctic Ice Sheet (WAIS) which impounds enough ice to yield meters of sea level rise. Despite the potential instability of this configuration, the subglacial water systems beneath TG and their control on ice flow have not been characterized by geophysical analysis. Although, the size of TG makes airborne radar sounding the only practical means of observation, previous radar analysis approaches have proven inadequate to characterize the dynamic state and geographic extent of its subglacial water systems. We use advanced processing to focus radarsounding data collected over TG and measure the angular distribution of energy returned from the bed. This allows us to characterize the meter-scale geometry and dynamic state of subglacial water systems across TG and validate our interpretations with meter-scale imaging.  Our results show substantial water volumes ponding in a system of “distributed” canals upstream of a bedrock ridge that is breached and bordered by a system of “concentrated” channels. The transition between the “distributed” and “concentrated” systems is both co-located and physically consistent with increasing basal shear stress, surface slope, and water flux, indicating a strong feedback between the subglacial water and overlying ice. This feedback raises the possibility that variations in subglacial water flow could trigger a grounding line retreat in TG capable of spreading to the rest of the WAIS."


Also, I thought that I would post four figures (self-explanatory) related to subglacial water flow and the WAIS, and also noting that more ice stream flow creates more internal friction that generates more subglacial meltwater that creates a positive feedback for accelerating ice stream flow.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #73 on: April 08, 2013, 05:41:38 AM »
As Dustin Schroeder's work appears to be the most recent of its kind regarding the Thwaites Glacier's subglacial hydrology, I provide the following information from his website:


The Role of Subglacial Hydrology in Ice Sheet Flow and Stability
By: Dustin M. Schroeder

"Thwaites Glacier is one of the largest, most rapidly changing glaciers on earth with a landward sloping bed that reaches the interior of West Antarctica. Although there are records of melt-water intensive ice-stream retreats on the continental shelf and observations of water driven acceleration in large outlet glaciers, research has focused on the role of ocean-driven melting for Thwaites Glacier. Using radar souding, I compare the configuration of contemporary subglacial bedforms with those of paleo-ice-streams, showing that although prior retreats across regions of crystalline bedrock progressed quickly, Thwaites Glacier is currently grounded in one such region and may be poised for a melt-water intensive retreat.

From an ice flow acceleration perspective, the effect of subglacial water depends on whether the dynamic state of these water bodies is hydrologically distributed or concentrated. The sensitivity of ice flow acceleration and grounding line stability of Thwaites Glacier will depend on the existence, locations, and interconnections of these systems beneath it. Using the specularity of radar echos, I provide the first attenuation-independent characterization of the Thwaites Glacier subglacial water system, which consists of a distributed network of canals feeding a system of concentrated channels. This transition occurs with increasing surface slope, water flux, and basal sheer stress indicating feedback between the ice and water systems.

Despite the high resolution of along-track focused radar data, the survey of Thwaites Glacier was collected on a 15 km grid and simple interpolation does not accurately represent the observational information and uncertainties in these gaps. Using surface and bed topography with a subglacial water model, I invert radar echo information for a physically consistent interpretation of the water system with more geologically realistic spatial patterns and quantified uncertainties. This approach also provides insight into water depths, conductivity, and geothermal heat flux beneath Thwaites Glacier.

Characterizing Subglacial Hydrology with Airborne Radar Sounding
Subglacial water networks are pervasive, dynamic systems that can exert strong control on ice flow. The large spatial extent and thick ice cover of these systems make airborne radar sounding the only practical means of observation, but limited resolution and uncertainties in attenuation losses make traditional ice penetrating analysis techniques insufficient for observing critical processes. By exploiting advances in ice penetrating radar technology and processing, I develop new analysis techniques that quantify the angular distribution of echo energy, constrain the sub-resolution configuration of the bed, and provide an attenuation-independent indicator of subglacial water."

The three panels of the first image support the first three paragraphes above, while the second image supports the fourth paragraph.  While Mr. Schroeder's dissertation on this topic is not expected until 2014; the information provided on his website indicates the high risk that the Thwaites Glacier could begin a basal meltwater triggered retreat soon.

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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #74 on: April 08, 2013, 06:04:57 AM »
While the 40% increase of ice mass loss from the WAIS above the GRACE data posted by Bert, is still below the levels that I feared when I started this thread; nevertheless, it may just be sufficient to push the CNES-LEGOS-CLS SLR six months moving average (the red line labelled Exp. MA) above the 95% confidence level, CL, range for the first time as indicated in the attached figure.  We will need to watch the CNES-LEGOS-CLS trend line closely, in the future.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #75 on: April 09, 2013, 02:30:03 AM »
The Antarctic Peninsula may also be making an accelerating contribution to SLR as indicated in the article below:

Summer melt season is getting longer on the Antarctic Peninsula, new research shows.

"New research from the Antarctic Peninsula shows that the summer melt season has been getting longer over the last 60 years -- Increased summer melting has been linked to the rapid break-up of ice shelves in the area and rising sea level
New research from the Antarctic Peninsula shows that the summer melt season has been getting longer over the last 60 years. Increased summer melting has been linked to the rapid break-up of ice shelves in the area and rising sea level.
The Antarctic Peninsula – a mountainous region extending northwards towards South America – is warming much faster than the rest of Antarctica. Temperatures have risen by up to 3 oC since the 1950s – three times more than the global average. This is a result of a strengthening of local westerly winds, causing warmer air from the sea to be pushed up and over the peninsula. In contrast to much of the rest of Antarctica, summer temperatures are high enough for snow to melt.
This summer melting may have important effects. Meltwater may enlarge cracks in floating ice shelves which can contribute to their retreat or collapse. As a result, the speed at which glaciers flow towards the sea will be increased. Also, melting and refreezing causes snow layers to become thinner and more dense, affecting the height of the snow surface above sea level. Scientists need to know this so they can interpret satellite data correctly.
Dr Nick Barrand, who carried out the research while working for the British Antarctic Survey, led an analysis of data from 30 weather stations on the peninsula. "We found a significant increase in the length of the melting season at most of the stations with the longest temperature records" he says. "At one station the average length of the melt season almost doubled between 1948 and 2011."
To build up a more complete picture across the whole peninsula, the team (funded by the European Union's ice2sea programme) also analysed satellite data collected by an instrument called a scatterometer. Using microwave reflections from the ice sheet surface, the scatterometer was able to detect the presence of meltwater. The team were able to produce maps of how the melt season varied from 1999 to 2009, and showed that several major ice shelf breakup events coincided with longer than usual melt seasons. This supports the theory that enlargement of cracks by meltwater is the main mechanism for ice shelf weakening and collapse.
The researchers also compared data from both the satellite and weather stations with the output of a state-of-the-art regional climate model.
Dr Barrand, who now works at the University of Birmingham, says, "We found that the model was very good at reproducing the pattern and timing of the melt, and changes in melting between years. This increases confidence in the use of climate models to predict future changes to snow and ice cover in the Antarctic Peninsula."

See the attached figure for a comparison of the relative ice mass loss contribution from the Antarctic Peninsula and the WAIS (per GRACE for the period from 2003 to 2010).
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Re: Surge of WAIS Ice Mass Loss
« Reply #76 on: April 10, 2013, 04:41:35 PM »
As mentioned previously, the Thwaites Glacier, TG, already has a well documented network of basal meltwater channels and subglacial lakes [For additional evidence of the subglacial water flow paths beneath TG, see: Carter, S. P., D. A. Young, and D. D. Blankenship. 2012. Subglacial water flow paths under Thwaites Glacier, West Antarctica. Boulder, Colorado USA: National Snow and Ice Data Center]; however, the ICESat (Ice, Cloud and Land Elevation Satellite) measurements of ice surface elevations for TG do not yet show a history of "active subglacial lakes" as indicated by the observation (by laser altimeters) of ice surface depressions/bumps.  Note the first accompanying image (credit: Ben Smith, University of Washington, and NASA) indicating "active subglacial lakes" with rapid drainage and measures ice surface depressions (or bumps) in the Ross Sea Embayment/Siple Coast ice streams (but not yet in the TG drainage basin).  The ICEsat satellite observations of "active subglacial lakes" has shown that the ice surface above subglacial lakes is constantly changing, suggesting that water is flowing between lakes. Out of the 280 lakes mapped, there were 124 active lakes under the Antarctic Ice Sheet. These lakes are rapidly changing in elevation, filling and draining on timescales of months to years.
The location of subglacial lakes is important, because the presence of meltwater facilitates rapid ice velocities; and changes in the subglacial hydraulic system can result in rapid changes in glacier velocities.  The surfaces of these glaciers change in height in response to subglacial water motion, with lake volumes changing on annual timescales or faster. The drainage of these lakes has been linked to accelerated ice flow rates, for example, in the Byrd Glacier system (ice flowed 10% faster for more than one year).  Lakes may exchange water with other lakes, or with the surrounding glacier environment, via englacial or subglacial conduits. This second drainage pattern may help induce faster ice flow via distributed ice drainage systems at the ice-bed interface, which lubricate ice flow.
The thickness of the ice in the TG gateway (about 1km thick within 100km of the current grounding line, see the second image) currently inhibits hydraulic outbursts through the TG gateway; which limits the activity of the subglacial lakes in this drainage basin.  However, as the ice thickness in the TG gateway thins, (accelerated thinning may occur due both to advective formation of a subglacial cavity in the gateway and due to an acceleration of the ice flow velocities); it will become increasingly difficult for the weight of ice to maintain an effective seal against hydraulic outbursts of basal meltwater from subglacial lakes beneath TG.  While the precise mechanisms by which ice stream velocities are accelerated by basal meltwater and active subglacial lakes is not well understood (note in the Siple Coast area the ice stream surface elevations are lower than in the TG gateway and the bed conditions include extensive areas of saturated subglacial sediments, while the TG gateway is relatively sediment starved), nevertheless Schroeder, D.M., Blankenship, D.D., Young, D.A (Feb 2, 2013) make the following statement:
"We also use the anisotropy of the radar echo specularity to identify flow-aligned sedimentary bedforms consistent with mega-scale glacial lineations underlying most of the glacier tributaries and a transition from sediment to crystalline bedrock in the trunk upstream of the grounding line. We compare the configuration of sedimentary bedforms beneath Thwaites Glacier with marine bathymetric observations of paleo-icestreams and conclude that its configuration is consistent with the large melt water volumes and outbursts associated with the collapses of those ice streams. Finally, we offer a mechanism by which the configuration of subglacial water and sediments beneath Thwaites Glacier could facilitate a basal-watertriggered grounding-line-retreat."

Thus it is likely that in the near future that the subglacial lakes in the TG basin will become "active", which should serve to further accelerate the ice flow velocities in the TG gateway (well before any "Thwaites Effect" is initiated).
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Re: Surge of WAIS Ice Mass Loss
« Reply #77 on: April 13, 2013, 04:19:32 AM »
Previously, I have mentioned that the acceleration of ice mass loss from WAIS should be observable in the sea level rise, SLR, trend-lines (as presented previously for the AVISO slr trend-line); however, the amounts of the various contributions required to SLR to match the observed SLR trend-line (the SLR budget) is not yet full understood, as when the currently measured contributions are summed they to not yet match the SLR budget.  While from a scientific reticience point of view it may be advisable to focus on the contributions that can be currently quantified; however, from a hazard analysis point of view the highest risk comes from the uncertain SLR contributions, and thus this and the following several posts will focus on better understanding the current uncertainties associated with the SLR budget, with the objective of better understanding the risks of accelerating SLR contribution from the WAIS.  Inparticular, I plan to focus on the question of: "Whether the acceleration of ice mass loss from the WAIS over the past couple of decades could be masked by a deceleration in other contributions to SLR."
Regarding this question, I have previously posted that:
(a) The GRACE data posted by Bert clearly demonstrates that an abrupt "surge" in ice mass loss did not occur from the WAIS in 2012; but this WAIS/GRACE data does not disprove that the recent ice mass loss from WAIS may be accelerating at a faster pace than recognized by most researchers including the IPCC AR5 authors;
(b) I have noted that the AVISO SLR trend-line shows a current rate of SLR that exceeds the 95% CL for the reported/observed data (which presents the possibility that WAIS could be currently losing ice mass faster than expect);
(c) Recent glacial isostatic adjustment, GIA, measurements from the WAIS, indicate that the GRACE mass loss data reported by Bert needs to be multiplied by a factor of about 1.4 in order to determine the correct GRACE/GIA-adjusted ice mass loss from the WAIS.
(d) I have noted that the ice mass loss from the Antarctic Peninsula is accelerating rapidly (see the first re-posted image of GRACE measurements for different regions of Antarctica), and that the Antarctic Peninsula could serve as an early indicator of the type of future ice mass loss that could occur for the WAIS with continued global warming.
However, still more insight can be gained by reviewing the finding of recent research on the topic of the SLR response over the satellite era (ie for the past two decades from 1993 to 2013) including:
The presentation: Why has an acceleration of sea level rise not been observed during the altimeter era? by Nerem, Chambers, Fasullo, Merrifield, Mitchum, Velicogna, and Willis, 2011 presents the following summary points:
-  The cryosphere has clearly seen an acceleration of mass loss during the altimeter era of (0.05 to 0.1 mm/yr2)
-  ENSO-related variability contributes an error to determing the acceleration of ~0.04 mm/yr2.
-  It is likely that a slowdown in thermosteric sea level rise over the last decade has masked some of the acceleration from the cryosphere.
-  There is still the possibility of errors in the altimeter data, especially Jason-2.  Calibrating the altimeter systems to detect such small accelerations is very difficult.

The fourth attached image (note that I could not post the images in order because of my difficulties with Typepad) from this presentation illustrates how during the satellite era the observed SLR as been relatively linear; which, raises the question as to why this is the case considering the non-linear SLR behavior projected by various GCM's for the future.  Furthermore, the second image compares the indicated deceleration in altimeter measured SLR from 1993 to mid-2011 to the GRACE measured acceleration of SLR ice mass loss contribution from both Greenland and Antartica; which, raises the question as to why this is the case.  Also, the third image presents the approximate relationship of radiative forcing to climate sensitivity and ocean heat uptake, together with the IPCC AR4 2007 estimates of the various contributions to heat uptake (thermal inertia) from: the ocean, atmosphere, continents and cryosphere; which raises the question of whether the IPCC AR4 2007 heat uptake (thermal inertia) estimates are correct when the Ocean Atmosphere, Arctic Sea Ice, the Permafrost, the Mountain Glaciers and Ice Caps, and the Ice Sheets are all uptaking heat faster than projected by all GCM (general circulation models), and when the thermalsteric expansion of the oceans are not matching that expected from the projected heat uptake of the oceans.  With such questions in mind; in my series of following posts I plan to examine in more detail why the traditional interpretations of SLR contributions are not adequate to fully address the risk of accelerating ice mass loss from the WAIS.
« Last Edit: April 13, 2013, 04:28:14 AM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #78 on: April 13, 2013, 06:29:32 PM »
I have raised many questions in my immediately preceeding post and I will begin addressing them with a brief discussion of the influence of ENSO on global mean sea level (GMSL), global water cycles and ocean mass changes (OMC) or ocean mass fluctuations, using figures and conclusions from the following presentation:

ENSO, Global Mean Sea Level, Global Water Cycle and North Pacific Ocean Mass
By Cazenave, Henry, Llovel, Munier, Meyssignac, Palanisamy and Becker 2011

Conclusions:
- Interannual variability of the global mean sea level directly related to ENSO-driven changes in the global water cycle.
- The positive anomaly of the global mean sea level seen during El Nino essentially due to (tropical) North Pacific Ocean mass increase.
- North Pacific ocean mass increase during El Nino is well explained by net precipitation (P-E, or precipitation less evaporation) increase in that region.  The positive (P-E) anomaly is asymmetrical wrt the equator during El Nino events.
- There is a dominant role for the tropical North Pacific, but the whole North Pacific is involved.
The third image illustrates the relationship between ENSO, the global water cycle, global land water storage and detrended fluctuations in sea level.
The fourth image illustrates the tight correlation between the Multivariate ENSO Index (MEI) and detrended fluctuations in sea level.
The first image illustrates the tight correlation between total land water storage and detrended fluctuations in sea level.
The second image illustrates the important role played by changes in North Pacific precipation - evaporation (P-E) patterns (associated with the ENSO) in ocean mass changes (OMC) or ocean mass fluctuations and detrended fluctuations in sea level.
One of the images in my immediately preceeding post indicates that using the 1993-2011 satellite altimetry data that it was possible to calculate a negative acceleration for SLR over this period, while logically over the long-term the SLR trend line should show a possible acceleration.  However, it is clear that any such short-term calculation of negative SLR acceleration is associated with temporary fluctuations of SLR associated with such events and the ENSO, as is demonstrated by the linear Alviso SLR trend line for the period from 1993 to 2013 (which shows no negative acceleration).  I will discuss other masking factors in following posts (note that I am having considerable problems posting to Typepad which may slow my rate of posting).
 [Note also that again due to my considerable difficulties with posting my images are once again out of order.]
« Last Edit: April 13, 2013, 06:42:17 PM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #79 on: April 13, 2013, 07:37:38 PM »
Next I would like to briefly examine the role of fluctuations of thermosteric contributions to SLR.  In this regard, I will like to show the first/second images and conclusion from:
Can a Combination of Altimetry, ARGO, and GRACE Detect Deep Ocean Warming?By Chambers and Willis 2011
"Conclusion: Altimeter-Argo-GRACE residuals show a trend south of 50oS consistent with the rate of warming observed below 1000m by Purkey and Johnson (2010)"
The first image indicates that most prior SLR budget calculations have assumed that the SLR contribution from the deep ocean was negligible over the 1993 to 2011 timeframe; while Chambers and Willis's 2011 conclusion, together with the second image, clearly indicates that at least for the Southern Ocean the rate of ocean warming below 1000 m is too significant to ignore (which as I have repeatly noted implies that the Circumpolar Deep Water, CDW, is warming faster than previously expected which directly contributes to WAIS ice mass loss).  Including this effect should result in a faster rate of calculated SLR when summing all known contributions.
However, as I have previously noted, the rate of ocean warming (ocean heat uptake) in upper levels of the ocean (above 700m) has slowed over the past decade; which is particularly clear for the sea surface temperature, SST, as illustrated for the top 1m of ocean water in the third attached image from the April 2013 issue of Scientific American; which is in sharp contrast to the increase in global atmospheric temperatue increase (as also illustrated in the same third image).  This sharp contrast between the increase in global lower atmosphere temperature and the relatively flat change in global SST; emphasizes that the sea surface is being kept relatively cool by a combination of cold ice melt water and upwelling of cool deep ocean water.  This temporary cooling of the ocean surface waters is temporarily suppressing/masking the long-term trend for accelerating the rate of SLR (until the current ENSO hiatus period ends and the rate of melting of floating Arctic Sea Ice and Antarctic Ice Shelves slows in the future).  The fourth attached image illustrates how it is possible to calculate that the trend line for rate of SLR the 2002 to 2011 period has slowed compared to the 1993 to 2002 period due to the masking influences of both ENSO driven total land water storage, and the temporary cooling of the ocean's surface waters.  When these masking factors reverse, or stop, the observed rate of SLR will likely increase.
(note that my trouble with posting is continuing)
« Last Edit: April 13, 2013, 07:44:11 PM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #80 on: April 14, 2013, 01:01:51 AM »
To reduce my chances of encountering difficulties when posting I am going to limit my attachments per post, so from: Nerem, Chambers, Fasullo, Merrifield, Mitchum, Velicogna, and Willis, 2011; I provide the attached image.  This image of ice mass loss from 2002 to 2011 for the Arctic region (without GIS) shows that this contribution to SLR is also increasing non-linearly; which implies that when the temporary masking factors (that have been hiding this accelerating contribution to SLR) stop, or swing the other way; that global mean sea level (GMSL) will increase.
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Re: Surge of WAIS Ice Mass Loss
« Reply #81 on: April 14, 2013, 01:14:20 AM »
Here is another abstract indicating that the masking tendency of impounding water behind dams will reverse by 2015 in order to result in increasing contributions to SLR through at least 2050:

Past and future contribution of global groundwater depletion to sea-level rise
by Yoshihide et al, 2012

"Recent studies suggest the increasing contribution of groundwater depletion to global sea-level rise. Groundwater depletion has more than doubled during the last decades, primarily due to increase in water demand, while the increase in water impoundments behind dams has been tapering off since the 1990s. As a result, the contribution of groundwater depletion to sea-level rise is likely to dominate over those of other terrestrial water sources in the coming decades. Yet, no projections into the 21st century are available. Here we present a reconstruction of past groundwater depletion and its contribution to global sea-level variation, as well as 21st century projections based on three combined socio-economic and climate scenarios (SRES) with transient climate forcing from three General Circulation Models (GCMs). We validate and correct estimated groundwater depletion with independent local and regional assessments, and place our results in context of other terrestrial water contributions to sea-level variation. Our results show that the contribution of groundwater depletion to sea-level increased from 0.035 (±0.009) mm yr−1 in 1900 to 0.57 (±0.09) mm yr−1 in 2000, and is projected to increase to 0.82 (±0.13) mm yr−1 by the year 2050. We estimate the net contribution of terrestrial sources to be negative of order −0.15 (±0.09) mm yr−1 over 1970–1990 as a result of dam impoundment. However, we estimate this to become positive of order +0.25 (±0.09) mm yr−1 over 1990–2000 due to increased groundwater depletion and decreased dam building. We project the net terrestrial contribution to increase to +0.87 (±0.14) mm yr−1 by 2050. As a result, the cumulative contribution will become positive by 2015, offsetting dam impoundment (maximum −31 ± 3.1 mm in 2010), and resulting in a total rise of +31 (±11) mm by 2050."
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Re: Surge of WAIS Ice Mass Loss
« Reply #82 on: April 14, 2013, 01:28:45 AM »
The following information is from: Snowfall-driven mass change on the East Antarctic ice sheet. Geophysical Research Letters 39: 10.1029/2012gL053316; by Boening, C., Lebsock, M., Landerer, F. and Stephens, G. 2012.

".... an improved understanding of processes dominating the sensitive balance between mass loss primarily due to glacial discharge and mass gain through precipitation is essential for determining the future behavior of the Antarctic ice sheet and its contribution to sea level rise." They also "... describe the causes and magnitude of recent extreme precipitation events along the East Antarctic coast that led to significant regional mass accumulations that partially compensate for some of the recent global ice mass losses that contribute to global sea level rise."
Furthermore, they note ".... an abrupt mass increase in East Antarctica along the coast of Dronning Maud Land in the GRACE satellite data in 2009-2011," which they were pointed to by their study of precipitation data derived from CloudSat and ERA Interim re-analysis products [Dee et al., 2011] that showed the mass increase to have been caused by "anomalously high precipitation events during the Southern Hemisphere winter." And this gain of "almost 350 Gt from 2009 to 2011," as they describe it, "is equivalent to a decrease in global mean sea level at a rate of 0.32 mm per year."
In further analyzing the precipitation data, Boening et al. found that "the mass gain primarily occurred during May of 2009 and June of 2011," and they said that "most of the accumulation in these months resulted from snowfall from only a few main events," while additionally noting that the primary drivers of the observed mass increase were "prolonged changes in pressure patterns and induced poleward wind in the two years."

Reference:
Dee, D.P., Uppala, S.M., Simmons, A.J., Berrisford, P., Poli, P., Kobayashi, S., Andrae, U., Balmaseda, M.A., Balsamo, G., Bauer, P., Bechtold, P., Beljaars, A.C.M., van de Berg, L., Bidlot, J., Bormann, N., Delsol, C., Dragani, R., Fuentes, M., Geer, A.J., Haimberger, L., Healy, S.B., Hersbach, H., Holm, E.V., Isaksen, L., Kallberg, P., Kohler, M., Matricardi, M., McNally, A.P., Monge-Sanz, B.M., Morcrette, J.-J., Park, B.-K., Peubey, C., de Rosnay, P., Tavolato, C., Thepaut, J.-N. and Vitart, F. 2011. The ERA-Interim reanalysis: Configuration and performance of the data assimilation system. Quarterly Journal of the Royal Meteorological Society 137: 553-597.

As such heavy snow falls in the East Antarctic (which mask SLR) are uncommon, and may not occur for a long time; it is possible that we may now, or may soon, be seeing an acceleration in observed SLR.
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Re: Surge of WAIS Ice Mass Loss
« Reply #83 on: April 14, 2013, 01:50:25 AM »
For those who have not accessed the AVISO global mean sea level data (by CNES,LEGOS,CLS), I post their data (in meters) for 2012 and the begining of 2013 below:

2012.015649 5.868832e-02
2012.042796 5.945260e-02
2012.069944 5.962766e-02
2012.097091 5.916928e-02
2012.124239 5.846041e-02
2012.151387 5.811652e-02
2012.178534 5.847519e-02
2012.205682 5.927141e-02
2012.232829 5.985773e-02
2012.259977 5.978680e-02
2012.287124 5.921357e-02
2012.314272 5.873872e-02
2012.341419 5.884290e-02
2012.368567 5.946833e-02
2012.395714 6.015732e-02
2012.422862 6.058372e-02
2012.450010 6.091462e-02
2012.477157 6.159501e-02
2012.504305 6.277363e-02
2012.531452 6.398081e-02
2012.558600 6.444038e-02
2012.585747 6.376650e-02
2012.612895 6.239698e-02
2012.640042 6.132902e-02
2012.667190 6.134983e-02
2012.694338 6.242594e-02
2012.721485 6.377672e-02
2012.748633 6.454621e-02
2012.775780 6.445450e-02
2012.802928 6.390404e-02
2012.830075 6.355250e-02
2012.857223 6.374685e-02
2012.884370 6.432721e-02
2012.911518 6.485605e-02
2012.938665 6.512404e-02
2012.965813 6.539335e-02
2012.992961 6.596685e-02
2013.020108 6.685818e-02
2013.047256 6.790903e-02
2013.074403 6.846996e-02

This data shows a rate of eustatic SLR of over 8 mm/yr for the period from the beginning of 2012 to the beginning of 2013.  While much of this GMSL rise maybe due to water temporarily stored on land; a significant portion of this rise could be due to non-linear SLR contributions (including that from the WAIS) being unmasked (possibly by West/East Antarctic snow being blown by stong winds into the ocean; or an end to the El Nino hiatus period). 
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Re: Surge of WAIS Ice Mass Loss
« Reply #84 on: April 14, 2013, 02:08:39 AM »
I post the attached figure from Nereem & Wahr, 2011 of GIA (glacial isostatic adjustment)-corrected J2 variations in SLR, together with the J2 for Greenland and Antartica from GRACE; in order to note that the GIA correction used by Nereem & Wahr (2011) could not have incorporated the 2012 findings from: An investigation of Glacial Isostatic Adjustment over the Amundsen Sea sector, West Antarctica by A. Groh; H. Ewert, M. Scheinert, M. Fritsche, A. Rülke, A. Richter, R. Rosenau, R. Dietrich; which indicates that GIA for the Amundsen Sea Sector is 40% higher than previously (eg 2011) thought. 

I note here that: J2 is the Earth's oblateness observed by satellite laser ranging (SLR).
« Last Edit: April 14, 2013, 03:03:15 AM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #85 on: April 14, 2013, 02:49:20 AM »
In the attached pdf written by Stefan Rahmstorf (January 2013), Stefan presents the case that:

"Progress has been made in recent years in understanding the observed past sea-level rise. As a result, process-based projections of future sea-level rise have become dramatically higher and are now closer to semi-empirical projections. However, process-based models still underestimate past sea-level rise, and they still project a smaller rise than semi-empirical models."

I note that the process-based models for SLR projections referred to by Stefan are the ones currently favored by the IPCC for AR5; and many of Stefan's arguements indicate that IPCC AR6 will have still higher SLR projections than even those likely to be included in AR5.

While I am not necessarily promoting semi-empirical models for SLR projections; nevertheless, Stefan makes many excellent points and the pdf is well worth reading; including noting his point that increased snow fall in Antarctica will increase the rate of ice discharge from the affected ice sheets (due to the increased driving force).
« Last Edit: April 14, 2013, 02:54:44 AM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #86 on: April 14, 2013, 04:13:50 PM »
When Bert posted his GRACE ice mass loss curve for the WAIS, I asked him if he could provide information related to the distribution of this mass loss around the WAIS.  To this end I have captured the attached image from the JPL website at:

http://sealevel.jpl.nasa.gov/

This image clearly shows that most ice mass loss from WAIS is coming from the Thwaites drainage basin, which supports my position that ice streams in the Thwaites Glacier are becoming activated, which via positive feedback can result in further acceleration of this ice mass loss.
« Last Edit: June 16, 2013, 12:58:02 AM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #87 on: April 14, 2013, 06:39:52 PM »
The JPL GRACE Antarctic Mass Trends shown in my immediately preceeding post (which I believe averages ice mass loss from 2003 to about December of 2012), which shows upto a 15cm/yr mass loss from the gateway area of Thwaites, to both (a) the figure by Wahr that I posted on April 9 @ 2:30am (of average ice mass loss from 2003 to the end of 2010), which shows upto a 14cm/yr mass loss from the Thwaites gateway; and (b) the figure by Luthcke that I posted on March 11 @ 11:11pm (with regional information from 2003 to Dec 2010); which indicates that ice mass loss from PIG may be slowing in recent years (possibly due to snow fall); while ice mass loss from Thwaites appears to be continuing in recent years (note that due to its already steep surface gradient) any snow fall in the Thwaites gateway area should service to accelerate ice flow velocities by increasing the driving force.  In addition to the increase in average ice mass loss from 14cm/yr to 15 cm/yr in the Thwaites gateway; what is particularly disturbing to me in the JPL (January 2013) figure is that the maximum ice mass loss appears to be coming from an area about 100km up ice stream from the Thwaites groundline in an area demonstrated by Schroeder et al 2013 (via radar) to contain a significant subglacial lake.  Thus if this is true then this may provide evidence that this subglacial lake is becoming activity (which is not good).

Furthermore, according to the GRACE data for the WAIS posted by Bert on March 31 @ 6:03pm since about 2006 the period of most rapid ice mass loss from WAIS has occurred during the period from roughly Dec/Jan to roughly June/July; which if true for 2013 would imply that the ice streams in the Thwaites Glacier may be becoming more active at this moment (note that the warm CDW that induces advection can flow below the sea ice present during this period).

Finally, for this post I attach the first image from NOAA's SLR website for the North Pacific Ocean (thru March 2013) showing strong SLR here at the beginning of 2013 (which could be occurring both due more rainfall during an El Nino hiatus period and additional due to the finger print effect of ice mass loss from the WAIS); and I attach the second image of the corresponding SLR data for the Southern Ocean, indicating no accelerated SLR at the beginning of 2013 (which might have indicated negative SLR from a finger print effect of ice mass loss from the WAIS except for the fact that warming of the deep ocean water in the Southern Ocean is regionally contributing about 1mm/yr to local SLR).
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Re: Surge of WAIS Ice Mass Loss
« Reply #88 on: April 14, 2013, 08:15:41 PM »
For readers not familar with the concept of the sea level budget I can recommend reading the following reference:

Leuliette, E. W., and J. K. Willis. "Balancing the Sea Level Budget." Oceanography 24, no. 2 (2011): 122-129

From the Aviso website I provide the following summary:
"The sea level can vary over long periods for several reasons:
- water mass variations:
water can be added to the ocean, either by increased rain over the ocean, or run-off from the rivers; glaciers melting can also add water. On the reverse, more artificial reservoirs leads to a run-off decrease, and thus to less water being brought to the ocean. Increased evaporation can also decrease the water mass (as well as glaciation, as it happened during last Ice age, when sea level was about 100 m below the nowadays level)
- temperature variations:
water dilates when it warms, which leads to higher sea level. Among other things, it leads to sea level seasonal variations, and also year-to-year variations linked to climate events (e.g. El Niño). Temperature changes over longer time scale (global warming) have, of course, also an impact.
- salinity variations:
the saltier the water, the denser it is; thus saltier water will have a lower level. Salinity variations can occur by fresh water addition (increased run-off, rain, or ice melting), which decreases salinity, or by increased evaporation, or by glaciation, which increase salinity.
- ocean circulation changes:
changes in sea level can be due to changes in the ocean circulation. Over periods of ten years or more, the currents can shift position,
The main factors causing current global mean sea level rise are thermal expansion of sea waters and land ice loss. These contributions vary in response to natural climate variability and to global climate change induced by anthropogenic greenhouse gas emissions.  Terrestrial waters contribute little to long-term sea level rise.

Sea level budget of the ~last two decades
Although none of the climate factors discussed above evolve linearly with time, on average over the 1993-2010 time span, ocean warming and glaciers melting have roughly contributed by ~30% each. The ice sheet contribution is slightly less (~20%). Over the altimetry era, the sea level budget is almost closed given the uncertainties of each contribution."

The following information applies to the first attached image (from the Aviso website):

Blue solid curve: Observed sea level from satellite altimetry over 1993-2011.
Blue dotted curve:Total climatic contribution (sum of thermal expansion and land ice).
Red curve: Thermal expansion, mean value based on temperature data from Levitus et al.; 2009; Ishii and Kimoto, 2009).
Green curve: Contribution from glaciers.
Black curve: Total land ice contribution
Cyan curves: Contribution from Greenland and Antarctica.
Credits from Legos/Meyssignac.

The second image (also from the Aviso website) summarizes the water cycle.

The third image is Church et al's 2011 effort to close the sea level budget.

While this discussion makes it seem like the sea level budget is currently resolved, it is possible that the non-linear ice mass loss contribution from the WAIS is being masked my noise from the signals of other other primarily linear SLR contributions; which could alter SLR projections based on our current understanding of the sea level budget.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #89 on: April 15, 2013, 12:48:35 AM »
The first two accompanying figures (from satellite altimetry data from 1993 to 2011) indicates that it if normal ENSO oscillation were the only driver then it could take some years worth of SLR data (see the first figure) in order to eliminate the negative acceleration of SLR induced by the El Nino hiatus period from 2002 to 2011 (see the second figure).  However, if accelerating ice mass loss is beginning to dominate SLR then the recovery of the SLR trend line should happen more quickly as is indeed indicated by the Aviso SLR rise data that I have posted (for convenience of comparison I post the third figure should the acceleration of ice mass contribution to SLR from Greenland and Antarctica).

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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #90 on: April 15, 2013, 06:22:30 PM »
I would like to note that a recent paper entitled: "Probabilistic framework for assessing the ice sheet contribution to sea level change,"  by Little et al was published February 26 in the Proceedings of the National Academy of Sciences.  Quotes from an interview with Little regarding this paper (see also attached figure) include:

"During the past 20 years, the Greenland and Antarctic ice sheets have lost an increasing amount of ice and now contribute roughly one-third of the rate of global mean sea-level rise. However, the standard tools used to project these ice sheets' contribution to future sea levels are limited by inadequate process understanding and sparse data. Ice sheets interact with the ocean on small spatial scales, and their motion is strongly governed by poorly understood properties of the ice as well as the sediment hidden several miles beneath it. Sea-level rise projections should reflect these uncertainties.
"Recently, several groups have used alternative techniques to forecast maximum possible sea levels—known as upper bounds—that do not explicitly model ice dynamics. Upper bound estimates by the year 2100 projected using these techniques are up to 6 feet (three times higher than future sea level estimates from the Intergovernmental Panel on Climate Change (IPCC)). However, the physical basis underlying these projections and their likelihood of occurrence remain unclear.
"In our group, we think we can more consistently assess disparate sources of information. In two recent papers, we introduce a novel framework for projecting the mass balance of the Antarctic ice sheet that allows for the conversion of current and future uncertainties of ice-sheet dynamics into probability distributions that may be supplemented by expert judgments. The power of this framework arises from its ability to improve and compare projections in a transparent manner.
"Like watersheds on land, ice sheets discharge precipitation that falls over a wide drainage basin through relatively narrow outlets. Although ice flow is linked across basins, each basin may remain relatively independent over time periods less than a century.
"The first paper, published in PNAS, introduces this 'basin-by-basin' framework and reveals that, even with limited information, a comprehensive probabilistic approach can provide insight that is missing from previous projections. We performed sensitivity analyses by changing the set of assumptions applied to each basin. For each set of assumptions, Monte Carlo simulations [computer algorithms based on random sampling] were used to generate 30,000 to 50,000 scenarios of mass changes originating from each basin and the continent as a whole.
"In previous scenario-based projections, the contribution of Antarctica to future sea-level rise is almost entirely derived from locations where present-day mass loss is concentrated. This is despite evidence that future discharge in other drainage basins—which comprise more than 96 percent of the ice sheet's area—remains uncertain.
"By incorporating the entire ice sheet, the PNAS study demonstrated that uncertainty in ice discharge outside regions where scientists 'expect' ice loss might result in additional sea-level rise that must be considered in projections. In addition, we quantitatively show that the likelihood of upper bounds must be taken into account when assessing their magnitude and appropriate uncertainty reduction efforts.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #91 on: April 16, 2013, 04:43:44 PM »
I just thought that I would point-out the obvious that all measurements contain errors and uncertainty; which from a retice point of view can make it difficult to identify a trend when there is a high noise to signal ratio; but from a risk point of vice a high noise to signal ratio can mean greater risk.  For example:

The first figure shows five different researcher's reduction of GRACE data for Antarctic ice mass loss; which while showing a generally good trend correlation, can show significant differences at any give point in time.
The second figure shows an estimate of uncertainty in satellite sea level measurement using Altimeter/Argo/GRACE data.
The third figure illustrates that model projections of sea level contain systematic errors.
The fourth figure compares the Altimeter/Argo/GRACE observed sea level to the modeled projections and indicates the estimated surface water height error.

This implies that there is a risk that actual sea level may be higher than reported.
“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: Surge of WAIS Ice Mass Loss
« Reply #92 on: April 16, 2013, 08:16:28 PM »
I thought that it would be helpful to provide the three attached figures from Shepherd et al 2012 "A Reconciled Estimate of Ice-Sheet Mass Balance".

The first figure compares GRACE vs GPA estimates of water height equivalent (WHE) ice mass loss from Antarctic from January 2003 to Dec 2011.  The GRACE data shows upto an average (over the 9 years) ice mass loss of 200 mm/yr from above the subglacial lake area about 100 km from the grounding line for the Thwaites Glacier, TG (which may support concern for the influence of subglacial meltwater below TG).

The second figure presents different modeled projections of ice mass loss from Antartica.

The third figure compares GRACE measured ice mass loss from Greenland and Antartica (by region); and this figure makes it clear that the WAIS has the highest rate of acceleration of ice mass loss (particularly considering that the ice mass loss from the ASE glaciers should be multipled by 1.4 in order to correct for the newly measured GIA effect).
“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: Surge of WAIS Ice Mass Loss
« Reply #93 on: May 01, 2013, 02:41:46 PM »
The attached figure is from: SSALTO/DUACS User Handbook: (M)SLA and (M)ADT Near-Real Time and Delayed Time Products
Reference : CLS-DOS-NT-06-034
Nomenclature : SALP-MU-P-EA-21065-CLS
Issue : 3rev 4
Date : 2013/01/29

This Handbook contains the following statements that are relevant to the figure:
"Since February 6th, 2012, Cryosat-2 mission has been integrated in the sytem. This mission is dedicated to the observation of the floating sea-ice as well as the continental ice sheets, but all data acquired over ocean are valuable for the observation of oceanic circulation and mesoscale variations. This major change is the result of the long-standing and fruitful partnership between ESA and CNES and a response to the request from scientific and operational oceanography users. The integration of Cryosat-2 impacts the delivering of Near real time and Delayed time Sea Level Anomalies (SLA) and maps of SLA (MSLA)."
"A Cryosat-2 Processing Prototype (C2P) (described in Boy et al, 2011) has been developed on CNES side to lay the ground for various SAR processing studies. The processing chains ingest Level-0 telemetry files distributed by ESA, and perform the following steps to generate Sea Level Anomalies (SLA) values for each altimeter measurements:
- Level-1: Decommutation, time-tagging and localization of measurements
- Level-1b: Calculation of instrumental corrections and geophysical/meteorological corrections
-  Level-2: MLE4 waveforms Retracking and calculation of SLA
The prototype processes data almost continuously over ocean, either in Low Resolution Mode (LRM) or in the Doppler/SAR mode processed as pseudo-LRM mode allowing to increase the coverage (figure 2)."

This figure clear shows the very high (up to positive 0.3 meters in the ASE) SLA, from 2011 to 2012, all along the coastline of West Antarctica; very possibly due to upwelling of warm CDW along these coastlines.  This very high SLA along the West Antarctic coasting can directly contribute to destabilizing the WAIS.
« Last Edit: May 01, 2013, 02:54:52 PM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #94 on: May 04, 2013, 01:40:18 AM »
I thought that I would post the attached image from the website:
 
http://sealevel.colorado.edu/

Which correlates the global mean sea level, GMSL, with the Multivariate ENSO Index, MEI.

A quote from this website regarding this image is: "The Multivariate ENSO Index (MEI) is the unrotated, first principal component of six observables measured over the tropical Pacific (see NOAA ESRL MEI, Wolter & Timlin, 1993,1998).  To compare the global mean sea level to the MEI time series, we removed the mean, linear trend, and seasonal signals from the 60-day smoothed global mean sea level estimates and normalized each time series by its standard deviation. The normalized values plotted above show a strong correlation between the global mean sea level and the MEI, with the global mean sea level often lagging changes in the MEI."

I note that as changes in the GMSL typically lag changes in the MEI, then if the typical pattern is to occur then one can expect the GMSL to fall within the next three to six months as the MEI has already been below the normalized GMSL for about the past six months.  However, if the future SLR trend is no longer linear, then it is possible that the normalized GMSL value will stay above the MEI value until the researchers decide to detrend the GMSL data with a non-linear trend line.
“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: Surge of WAIS Ice Mass Loss
« Reply #95 on: May 12, 2013, 01:30:30 AM »
In the abstract below, please note that that correction for GIA in the Antarctic GRACE data is a major source of potential error in ice mass loss estimates; and that as cited earlier in this thread, the limited experimental field data supports the higher ice mass loss estimates from the WAIS.

Time-variable gravity observations of ice sheet mass balance: precision and limitations of the GRACE satellite data, by I. Velicogna and J. Wahr
DOI: 10.1002/grl.50527
©2013 American Geophysical Union.
Geophysical Research Letters

Abstract
Time-variable gravity data from the Gravity Recovery And Climate Experiment (GRACE) mission have been available since 2002 to estimate the mass balance of the Greenland and Antarctic Ice Sheets. We analyze current progress and uncertainties in GRACE estimates of ice sheet mass balance. We discuss the impacts of errors associated with spherical harmonic truncation, spatial averaging, temporal sampling, and leakage from other time-dependent signals (e.g. Glacial Isostatic Adjustment (GIA)). The largest sources of error for Antarctica are the GIA correction, the omission of l = 1 terms, non-tidal changes in ocean mass, and measurement errors. For Greenland, the errors come mostly from the uncertainty in the scaling factor. Using Release 5.0 (RL05) GRACE fields for Jan 2003 through Nov 2012, we find a mass change of −258 ± 41 Gt/yr for Greenland, with an acceleration of −31 ± 6 Gt/yr2, and a loss that migrated clockwise around the ice sheet margin to progressively affect the entire periphery. For Antarctica, we report changes of −83 ± 49 and −147 ± 80 Gt/yr for two GIA models, with an acceleration of −12 ± 9 Gt/yr2 and a dominance from the southeast pacific sector of West Antarctica and the Antarctic Peninsula.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #96 on: May 14, 2013, 03:55:17 PM »
I am posting this abstract for a speech by Joe MacGregor to the Norwegian Polar Institute in this thread, because: (a) it is the first time that I have seen a hint that the radar survey (probably from the Fall 2012 IceBridge survey) indicates that the shear zone on the east side of the Thwaites Glacier, TG, gateway has not yet degraded to permit the "surge" in ice mass loss that I incorrectly postulated at the beginning of this thread; and (b) it correctly implies that once the east side (nearest to PIG) shear zone degrades (possibly due to advection, or other means) then the TG ice velocities may accelerate rapidly:

NPI seminar: What holds Thwaites Glacier back? Surveying the edges of a large Antarctic glacier
Speaker: Joe MacGregor, University of Texas
Time: 14 May 2013 11:30 AM – 12:30 PM
Venue: Norwegian Polar Institute

Abstract
"Thwaites Glacier is one the largest, fastest flowing and fastest thinning glaciers in Antarctica. This state of affairs motivates investigation of the controls upon and stability of its present ice-flow pattern.
In this talk I will survey the state of two key edges of Thwaites Glacier – its ice–ocean interface and its eastern shear margin – and explain what their states might mean for the glacier’s future.
Thwaites Glacier used to be buttressed by an extensive ice shelf, but in the last four decades that ice shelf progressively disintegrated into an ice tongue and it is now nearly a tidewater glacier. This pattern of retreat is similar to other nearby glaciers, and it will likely impact Thwaites Glacier’s future response to ocean forcing.
Farther upstream, most of Thwaites Glacier’s shear margins are associated with troughs in its bed topography and are unlikely to migrate, but that is not the case for its eastern shear margin, which is closest to Pine Island Glacier. Airborne radar sounding across this shear margin reveals no clear evidence of a change in either bed topography or lubrication that could explain the large change in ice flow there. Given the likelihood of continuing mass loss from Thwaites and Pine Island Glaciers, the apparently weak bed control of the eastern shear margin suggests that it could migrate outwards, but there is no evidence that it is migrating presently."
“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: Surge of WAIS Ice Mass Loss
« Reply #97 on: May 16, 2013, 12:03:01 AM »
The following internet summary is related to the new article in Nature entitled:
Rapid ice melting drives Earth’s pole to the east, by Chen et al 2013:

"The North Pole has shifted east because of ice sheet loss caused by rising temperatures, a new study published in Geophysical Research Letters has found, according to the scientific journal Nature.
The pole drifted southeast toward northern Labrador, Canada, at a rate of about 6 centimeters per year between 1982 and 2005. But since 2005, the direction and speed of the pole's journey changed. It started moving rapidly east towards Greenland at a rate of more than 21 centimeters per year.
There has been huge ice sheet loss in the polar regions due to global warming.
The study was carried out by scientists from the University of Texas, Austin, using data collected by NASA's Gravity Recovery and Climate Experiment (GRACE).
Earth's two geographic poles do not have a fixed location. As the distribution of snow, rain and humidity changes every year, the poles too wobble around, usually in a circular manner. Besides this seasonal drift, there is a long range movement which scientists believe is driven by continental drift - the movement of land plates relative to each other.
GRACE's twin probes measure changes in the Earth's gravity field, which can be used to track shifts in the distribution of water and ice, Nature said. The researchers led by Jianli Chen, a geophysicist, used GRACE data to model how melting icecaps affect Earth's mass distribution. They found that more than 90% of the post-2005 polar shift was because of increasing ice loss and sea-level rise.
The explanation for this is that when mass is lost in one part of a spinning sphere, its spin axis will tilt directly toward the position of the loss, according to Erik Ivins, a geophysicist at NASA's Jet Propulsion Laboratory in Pasadena, California quoted by Nature. This is exactly what was observed in the case of the North Pole.
These findings have opened the way to estimate long term ice loss by studying polar drift. Scientists can locate the north and south poles to within about 0.9 millimeters by using Global Positioning System measurements to determine the angle of the Earth's spin. Since polar shifts have been recorded for almost a century, Nature says, it is possible to study ice losses for that period. Direct records of ice loss in Polar regions do not go back that much in time."

This process could increase the accuracy of estimating ice mass loss from the AIS.
In the attached images from the article, 1 mas = ~3 cm of polar motion.
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Re: Surge of WAIS Ice Mass Loss
« Reply #98 on: May 16, 2013, 09:44:05 AM »
Hello Abruptslr,
Do you have a link for that article ?
Thank you !

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #99 on: May 16, 2013, 03:28:52 PM »
Laurent,

The following link is to the prime author's website at the University of Texas, where you can download a preprint (made available by the author):

http://www.csr.utexas.edu/personal/chen/publication.html

and here is a link directly to the preprint pdf:

ftp://ftp.csr.utexas.edu/pub/ggfc/papers/2013GL056164_preprint.pdf


Best,
ASLR
« Last Edit: December 14, 2013, 04:32:09 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson