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AbruptSLR

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Discussion of WAIS Collapse Main Period from 2060 to 2100
« on: March 03, 2013, 02:55:49 AM »
Due to complexity of a hazard analysis for the potential abrupt collapse (either partial of full) of the WAIS, I have made many posts already, and for the sake of brevity I will try not to repeat the information/postulations presented in the "Potential Collapse" thread, nor the final SLR projections presented in the "Philosophical" thread.  While my hazard analysis for RCP 8.5 50% CL forcing is quite aggressive, projecting a eustatic SLR of about 0.5m for the period from 2000 to 2060 (and about 1m of SLR by 2060 for the 95% CL scenario); my SLR projections for my "collapse main period" are more aggressive still, estimating about 3m of eustatic SLR by 2100 for the RCP 8.5 50% CL case, and just over 5m of SLR by 2100 for the RCP 8.5 95% CL case.  Nevertheless, I hope that the supporting information presented in this thread clarifies the nature and probability of the "Collapse Main Period this Century" from 2060 to 2100.

I will start this "clarification" by providing the first accompanying figure (not previously posted in the "Collapse" thread) showing a plan view of the my RCP 8.5 50% CL scenario estimates of WAIS areas that may have experienced grounding line retreat by 2070.  This figure indicates several significant areas of proposed grounding line retreat including:
(a) the transparent orange area with Jakobshavn Effect acceleration and associated "ice melange" discussed extensively in the thread on the PIG/Thwaites system behavior up to 2060 show the two significant changes: (i) the Eastern trough ice stream has continued to exhibit "Jakobshavn Effect" acceleration behavior and the grounding line retreat for this ice stream has extended about an additional 200km in 10 years, while the grounding line retreat for the Western trough ice stream is proposed to slow dramatically as the seafloor becomes rough at the western end of this trough; and (ii) with the extension of the Western trough ice stream slowed, this allows for the extension of the grounding line retreat in the Southernly direction into several different branching troughs in this direction at a slower rate than for Eastern trough ice stream.
(b) the Ferrigno Subglacial cavity showed marked rate of extension driven largely by advection associate with relatively high CDW in the Bellingshausen Sea (with no Jakobshavn Effect), while the PIG subglacial cavity extension (ie groundling line retreat) remains slow due to rough seafloor conditions.
(c) The grounding line retreat for the Siple Coast ice stream accelerates as the Ross Ice Shelf is assumed to provide rapidly degrading buttressing support.
(d) The Weddell Sea Embayment, WSE, glaciers show a major surge of grounding line retreat due both to a projected re-direction of advective warm CDW into the WSE (below the Filchner-Ronne Ice Shelf), and due to ideal seafloor conditions (in the area of indicated grounding line retreat) to support the classic gravitationally driven marine ice sheet retreat behavior addressed in the second accompanying figure).  I will discuss the WSE proposed surge of grounding line retreat (by 2070) in the next post.
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AbruptSLR

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #1 on: March 03, 2013, 03:20:03 AM »
The surge in groundling line retreat in the Weddell Sea Embayment, WSE, ice sheet between 2060 and 2070 (see previous post) is supported by Hellmer et al 2012's projections including the first accompanying figure that shows by that time frame a warm current of CDW water (through the Filchner Trough) will be directed beneath the Filchner-Ronne Ice Shelf, FRIS.  The second figure shows a profile view of this warm CDW current interacting (advectively ice melting) the basal area of the ice shelf and  ice at the grounding line for the ice sheet.  The third figure shows newly identified (in 2012) subglacial basins with very smooth seafloors that can sustain rapid groundling line retreat once the warm CDW has melted the ice providing buttressing support at the lip of the basins.  Finally, the fourth figure shows the projections from a regional global circulation model, GCM of: (a) the reduction of sea ice volume with time resulting in more exposure to wind driven surface stress; (b) the area mean ocean (wind driven) surface stress increase with time, which redirects the warm CDW under the FRIS; and (c) the acceleration of Basal ice Mass Loss, BML, associated with melting due to the warm CDW.
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AbruptSLR

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #2 on: March 03, 2013, 04:01:58 AM »
I am concerned that the Hellmer et al 2012 projections may be too scientifically conservation (or too non-conservative from a hazard analysis point of view) as I suspect that warm CDW may already be flowing beneath the FRIS for reasons including:
(a) The first attached figure from the NSIDC for the Antarctic sea ice (on March 2, 2013) shows an unsual multi-month pattern for the sea ice in the Weddell Sea, where more sea ice is absent than normal for the Southeastern portion of the Weddell Sea, while more sea ice is present than normal for the Northwest portion of the Weddell Sea.  This pattern could reflect warm CDW (which would melt the sea ice) entiring the Filchner Trough at the Northest corner of the FRIS and cold fresh melt water existing the Northwest corner of the FRIS, where its cold temperature would reduce the rate of sea ice melting.
(b) The second attached figure shows the banded nature of the various currents in the Southern Ocean including the Weddell Gyre where a large portion of the Antarctic Bottom Water is produced (together with that produced from the Ross Gyre which also is showning an unusual sea ice pattern this austral summer); and as recently there has been a marked reduction in the production of Antarctic Bottom Water from the Weddell Sea I wonder whether basal sub-ice shelf melting beneath the FRIS (due to a warm CDW current inflow through the Filchner Trough) may be producing so much light fresh water that is mingling with the normally cold dense (salty) Bottom Water, that the amount of Bottom Water sinking to the bottom has dropped.
(c) As noted by A4R in the Antarctic Methane thread, significant releases of methane have been recently observed down wind from the Weddell Sea which might possible have come from the decomposition of methane hydrates from sediment exposed to warm CDW as the marine ice sheet grounding line retreats past the lip of the subglacial basins (A & B).
(d) the GRACE satellite "fringer print" ocean water mass distribution (see the December 2012 image in "surge" thread), seems to should a pattern that might indicate significant ice mass loss from the WSE marine ice sheet.
(e) Finally, after observing how scientifically conservative (non-conservative from a hazard analysis point of view) the regional GCM projections have been with regard to the timing of loss of Arctic Sea Ice volume loss (being scientifically too conservative by several decades); I wonder whether the regional GCM projections of warm CDW current flow below the FRIS through the Filchner Trough may also be scientifically too conservative by several decades.  If so not only would the Weddell Sea Ice pattern be unusal during the austral summer but there would also be more Weddell Sea Ice during the austral winter (as was the case during 2012 when the surge discussed in the "surge" thread occurred (as the warm CDW would flow beneath the FRIS year round which would produce a cold fresh melt water at the ocean surface to help promote sea ice formation in the Weddell Sea during the austral winter).
If these concerns prove to be true that my hazard assessment of the timing of ice mass loss from the Weddell Sea marine ice sheet's contribution SLR may be non-conservative from a safety point of view.
“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: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #3 on: March 03, 2013, 04:35:29 AM »
I shift my focus now to the Ross Sea area; where as indicated in the first accompanying figure I believe that before 2070 (for the RCP 8.5 50% CL case) both sub-ice shelf basal melting and calving of ice from the Ross Ice Shelf, RIS, face will have accelerated to the point that (a) tidally induced stresses in the RIS will accelerate grounding line retreats for the Siple Coast ice streams; and (b) sufficiently reduced the contraints/confinement on the RIS to the point that the melt pond mechanism could allow for the rapid collapse of the RIS by 2070. 

The second figure from Schneider et al 2012 shows how the sea ice area for the Amundsen Bellingshausen Seas ABS, directly induces the West Antarctic surface temperatures to follow their same extent during the critical Austral Spring time (when the inflow of warm CDW into the ABS accelerates indicating that this warm ocean water warms the air flowing over the West Antarctic during the austral spring. 

The third figure also from Schneider et al 2012 shows maps of (a & b) the surface temperature anomalies for the Antractic during the austral Spring and Winter respectively from 1979 to 2008, and for the same time period in maps (c & d) the correlation of the ABS sea ice extent with the surface temperature anomalies.  These maps indicate over a 1.1 C/decade rise in the austral spring surface temperatures over the RIS (which exceeds the 0.8 C/decade mean surface temperature rise for the Western Antarctic discussed in the "collapse" thread; which inturn increases the risk of early surface ice melt water accumulation in ponds on the surface of RIS during late austral spring and the immediately following austral summer circa 2070 due to the (9 x 1.1) 9.9 C warmer austral spring surface temperatures for RIS (and the rest of the WAIS) as compared to the corresponding 1979 temperatures.  This should significantly increase the risk of of the melt pond mechanism driven collapse of the RIS by 2070 as compared current GCM projections for the timing of the potential collapse of the RIS.
« Last Edit: June 02, 2013, 11:19:07 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #4 on: March 03, 2013, 05:08:03 AM »
I now take a look at the risk of activing volcanic action in the WAIS by 2090 due to the potentially large amounts of ice mass loss under RCP 8.5 (both for a 50% and more so for a 95% CL) scenario.  The first figure shows both the West Antarctic Rift (note that since the time of the shown LeMasurier & Thomson 1990 map, the Rift has been shown to extend all the way to the valley that the Ferrigno Glacier occupies), and the locations of active volcanic center, three of which are located in the critial PIG/Thwaite ice drainage basin areas. 

The second figure from Behrendt 2011 shows the different numbers of identified subaerially erupted edifices and subglacially erupted edifices for currently subglacial West Antarctic volcanic centers.  Any future subglacial eruptions before the end of the century would clearly destabilize any adjoining ice mass without ejecting volcanic ash into the atmosphere (which could otherwise contribute to global cooling); while any future subaerial eruptions in the WAIS before the end of the century would not only directly melt ice (and temporarily acceleration calving) but would also likely cover a significant adjoining surface of the WAIS with dark ash that would temporarily decrease surface albedo (until more snow fall buries the ash).
“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: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #5 on: March 03, 2013, 02:20:07 PM »
Following-up on my immediatly preceding post, I re-post a modified version of the following statement from the "critique" thread related to the volcanic/seismic consequences of large ice mass removal:

It is noted that the WAIS is already a highly seismically & vocanically active area, and the loss of such large amounts of projected ice mass loss by 2090 could result in significant seismic and vocanic activity as indicated by Behrendt 2011's conclusion that: "The present rapid changes in stability of the WAIS resulting from global warming, could be accelerated by subglacial volcanism."; which is also supported by the following quote from McGuire 2012 regarding the Iceland's response to the loss of a kilometer thick icesheet (as WAIS is considered here to have lost by 2090):

"Twenty thousand years ago, Iceland was entirely covered by a layer of ice that averaged close to a kilometer in thickness.  Around 15-16,000 year ago, planetary warming triggered rapid melting of the glaciers, reducing the load acting on the volcanoes beneath and on the underlying asthenosphere.  By 12,000 years ago unloading was sufficiently advanced to trigger a spectacular response.  Over a period of 1500 years or so, the volcanic eruption rate jumped by between 30 and 50 times, before falling back to today's level.  This volcanic rejuvenation was in part a reflection of the release of magma held ready and waiting, within and beneath the volcanoes themselves, but mainly testament to a huge increase in the supply of fresh magma from deeper within the Earth.  Such was the load reduction due to the rapid loss of ice mass, that the depressed lithosphere quickly bounced back by as much as half a kilometer, dramatically reducing the pressures in the asthenosphere and triggering a 30-fold jump in magma production." I note here that the WAIS is must more sensitive to magma migration than the Iceland case due both to the very thin crust beneath the WAIS and due to the very close proximity of the very significant mass of the EAIS.

- It is noted further that GIA in the Northern Hemisphere typically reduces actual sea level by moving magna from under to ocean to under places like Greenland (thus dropping the seafloor) but in the case of WAIS the GIA would raise the seafloor by multiple meters and the magna would likely come from beneath the EAIS thus lowering the elevation of the EAIS and promoting future (after 2100) ice mass loss from glaciers in the EAIS.
“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: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #6 on: March 03, 2013, 02:55:34 PM »
As Greenland is the topic of another folder on this forum, I will only touch lightly on the topic of potential ice mass loss from the GIS during the period from 2060 to 2100, because as discussed in the "collapse" thread due to the "Finger Print" effect the ice mass loss contribution from the GIS to SLR as a multiplier effect on destabilizing the WAIS to to buoyancy effects associated with sea level.  First I will note that in the "critique" thread on SLR guidance the current conventional guidance (such as from NRC 2012) is that GIS will contribute more to SLR by 2060 than will the WAIS (which I agree with) thus during the "Collapse Initiation Period" ice mass loss from the GIS should help to destabilize the WAIS.  Furthermore, after 2060 I believe that the conventional estimates of the risk of ice mass loss from the GIS are substantially too scientifically conservative (ie too non-conservative from a hazard assessment point of view) and that as some of the key GIS marine terminating glaciers (see the three attached figures: particularly with regard to the Petermann, Jakobshavn and quite possibly the 79 North, Glaciers) will interconnect the ocean to the GIS interior which will likely provide some significant ice mass loss from the GIS between 2060 and 2100; which was not consider by conventional SLR guidance but that which add to the risk of abrupt SLR and directly to the potential destabilization of the WAIS.
“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: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #7 on: March 03, 2013, 03:57:48 PM »
Just as I did not present a rigorous analysis of the potential ice mass loss from the GIS from 2060 to 2100, I will not present in this post a rigorous analysis of the parallel contribution from the EAIS.  However, I note that I believe that both of these (GIS and EAIS) contributions to abrupt SLR (ASLR) are not negliable, and that I have used my judgement to include an allowance for these contributions within the relative ASLR curves that I present for California in the "philosphical" thread.  In the way of supporting evidence/logic with regard to the contribution from ice mass loss from the EAIS I present the accompanying figure and make the following comments/observations:
(1) Unlike the non-linear SLR projections from Hansen (or even from semi-empirical models), which continue to accelerate non-linearly after (roughly speaking) 2100; I have projected that under the RCP 8.5 95% CL WAIS collapse scenario that the WAIS contribution to ASLR will have largely stopped and the slope of the RSLR curve that I present in the "philosophical" thread numerically quantifies my opinion of largely how much RSLR contribution will be coming from ice mass loss from both the GIS and the EAIS (after subtracting the steric contributions) from 2100 to 2200 (after which it is possible that contributions from the GIS and the EAIS may, or may not, accelerate, on which topic I do not speculate here).
(2) The topopgrahy (bathymetry) shown in the accompanying figure illustrates that while the seafloor is much deeper beneath the WAIS, there are meaningful portions of the ground below the EAIS that are at least 500m below current sea level; which implies that glacial ice in these marine terminating glaciers are subject accelerated ice mass loss due to ocean/ice interaction including possible advective formation of subglacial cavities possibly sometime between 2060 and 2100.  This particularly true for the glaciers labeled TOT (Totten), DAV (David), NIN (Ninnis) and LAM (Lambert) on the accompanying figure.
(3) In both the RCP 8.5 50% CL and the 95% CL collapse scenarios for the WAIS, meaningful amounts of lateral buttressing support from the WAIS to the EAIS will have been degraded to the extent that such glaciers as those labeled BYR (Byrd), SLE, REC, FOU and SUF will accelerate between 2060 and 2100.
(4) As noted in the "collapse" thread satellite altimetry estimates of changes in the surface elevations of almost all of the East Antarctic marine terminating glaciers from 2012 indicate that accelerated ice mass loss from these glaciers due to ocean water-ice interaction appears to already be occurring (which implies that such ice mass loss contribution will likelyfurther accelerate by the 2060 to 2100 period).
“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: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #8 on: March 03, 2013, 07:55:21 PM »
It goes without saying (as most of the posts in this folder are on this topic) that one of the most important considerations for ice mass loss during the Collapse Main Period is the interaction between the warm CDW, the grounded ice, the seafloor bathymetry (subglacial topology), and the atmosphere.  Present GCM projections do not adequately consider the interaction of grounded-ice/water/land/air due to the difficulties of modelling such complex non-linear interactions; nevertheless, I will provide the following two comments and four figures from a hazard analysis point of view in order to help appreciates the risks to abrupt SLR with regard to this matter:
(1) As much of the non-linear ice mass loss potential from the WAIS has been and will be triggered by changes in the heat content of the CDW contacting the ice, the sooner this CDW warms (eg: due to extended La Nina events advecting tropic heat more directly down to depths of 700 to 2000m)  and the more upwelling the occurs (due to strong Antartic winds and increasing storm intensity/activity) to bring it into contract with the ice and the sooner that the ocean currents change directions in order to travel through pre-exist troughs across the continental shelf (as may happen for RIS and FRIS due to changes in the Weddell and Ross Gyres); the more dramatic will be the ice mass loss during the collapse main period.  The first two figures support the contentions made in the "forcing" thread that: (a) globally more heat content was delivered to the 700 to 2000m water depth from 2000 to 2012 than most GCM projected; and (b) more of the global ocean heat content is delivered to the Southern Ocean than any other ocean in the world.  Both of these facts indicate that it is inevitable that more ocean heat content will be delivered earlier than previously expected to the WAIS ice.
(2)  The next to figures present tranparent reddish lines superimposed on the subglacial topology (seafloor bathymetry) below the WAIS for both the 2090 RCP 8.5 50% and 95% CL scenarios; indicating the general alignment of seaways and interconnected subglacial cavities that may allow for both tidal flushing through the passageways and the redirection of ocean currents through these passages that may interconnect the Weddell, Bellingshausen, Amundsen and Ross seas before 2100; which I postulate would trigger highly accelerated calving and ice melting possibly resulting in a "fleet" of icebergs floating around the West Antarctic and Antarctic (as also postulated by Hansen).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #9 on: March 04, 2013, 04:39:06 AM »
In regard to my March 3rd post that I am concerned that warm CDW is findings it way prematurely beneath the FRIS to melt the grounded ice in the Weddell Sea Embayment I present the following addition evidence in the attached paper:  "Global contraction of Antarctic Bottom Water between the 1980s and 2000s", by SARAH G. PURKEY and GREGORY C. JOHNSON in the Climate Journal which contains the following quote:
"The delta V profiles of the three southernmost basins (Fig. 1) all show a remarkably similar pattern (Fig. 4; orange curves). Each reveals a loss of volume, ranging from -1.6 to -3.6 Sv, within the coldest ~0.5 C of the water column and a recovery from the bottom water contraction within the θ classes of the Circumpolar Deep Water (CDW).  In the Weddell-Enderby Basin (WEB; Fig. 1) of the South Atlantic Ocean, a contraction of bottom water is found for θ < -0.55 C, with a maximum value of -3.6 (±2.0) Sv (Fig. 4a). This rate of change in volume is equivalent to a mean isotherm fall rate of ~15 m yr-1 (not shown). Within error bars, this maximum value of delta V aligns with the -0.7 C boundary between WSBW and WSDW (Carmack and Foster 1975; Orsi et al. 1993) and is found roughly 1000–2000 m above the bottom of the basin. Above the WSBW, we find no significant gain or loss of WSDW for -0.7 < θ < 0 C (Fig. 4a). The bottom water contraction is compensated higher in the water column by an increase in the volume of water with 0.25 < θ < 0.5 C. This water is found shallower than 1000 m,
where a tongue of lower CDW rises to the south in the ACC as it enters the basin from
the north. The delta V curve for the basin suggests a southward surge of CDW into the region."

As shown in the first accompanying figure 4a the warm CDW has surged from the north into the Weddell-Enderby Basin at depths shallower than 1000m (depths that can feed directly into the Filchner Trough leading beneath the FRIS.  While the second figure (including section S2) shows the prior condition in the Weddell-Enderby Basin before the surge of warm CDW into the south.  If I am correct then this is a serious new trend that could accelerate ice mass loss from the WAIS.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #10 on: March 04, 2013, 05:08:03 AM »
ASLR, I'm greatly enjoying your posts. I haven't looked much at the Antarctic, so I don't have anything intelligent or helpful to say on the subject. I just wanted you to know that your hard work is being read and appreciated...even if it does take me a couple of hours to (partially) digest one of your posts. :)

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #11 on: March 04, 2013, 12:34:17 PM »
Birthmark,

Thank you for the kind words of encouragement, and I hope that my message is getting out to the community as the current topic that I am posting about of changes in the Antarctic currents (especially in Antarctic Bottow Water, AABW, related currents) has me especially concerned.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #12 on: March 04, 2013, 12:41:09 PM »
Further to my earlier posts focused on how changes (declines in the volumes produced) to the Antarctic Bottom Water, AABW, in the Weddell Gyre is likely accelerating ice mass loss below the FRIS (Filchner-Ronne Ice Shelf) and the grounding line for the adjacent marine ice sheet; I provide the following article (one of many on the internet on this well documented trend) about the general declines in volumes (currently up to 60%) of AABW around the entire Southern Ocean:

From "Antarctic bottom water disappearing", published in the Australian Antarctic Magazine, Issue 23, December 2012 by NISHA HARRIS, Corporate Communications, Australian Antarctic Division

"New research by teams of Australian and US scientists has revealed a massive reduction in the amount of Antarctic Bottom Water found off the coast of Antarctica.
Comparing detailed measurements taken during the Australian Antarctic program’s 2012 Southern Ocean marine science voyage, to historical data dating back to 1970, scientists estimate there has been as much as a 60% reduction in the volume of Antarctic Bottom Water – the cold dense water that drives global ocean currents.
In an intensive 25-day observing program in January this year, temperature and salinity samples were collected at 77 sites between Antarctica and Fremantle (Western Australia).  Such ship transects provide the only means to detect changes in the deep ocean.
The new measurements suggest the densest waters in the world ocean are gradually disappearing and being replaced by less dense waters. These measurements concur with a recent study by US-based researchers which showed that Antarctic Bottom Water is contracting over much of the global ocean. The ocean profiles also show that the dense water formed around Antarctica has become less saline since 1970.
‘It’s a clear signal to us that the oceans are responding rapidly to variations in climate in polar regions,’ Voyage Leader and Chief Scientist, Dr Steve Rintoul, said.
‘The sinking of dense water around Antarctica is part of a global pattern of ocean currents that has a strong influence on climate, so evidence that these waters are changing is important.’
Dr Rintoul, an oceanographer with the CSIRO and the Antarctic Climate and Ecosystems Cooperative Research Centre, led the scientific voyage from Hobart, south to Commonwealth Bay, before turning west along the Antarctic coast and returning to Fremantle. The ship visited Commonwealth Bay as part of a celebration of the centenary of Sir Douglas Mawson’s Australasian Antarctic Expedition.  Dr Rintoul’s team had the opportunity to repeat oceanographic measurements made by Mawson’s team 100 years ago, obtaining one of the few century-long records  obtained anywhere in the ocean.
‘Our measurements collected in 2012 are quite different to those collected by Mawson in 1912,’ Dr Rintoul said.
‘The water is cooler now than it was then, indicating a change in ocean currents that may be related to a reduction in the amount of dense water formed near Antarctica – as less dense water is exported, less warm water flows into the region to replace it.
‘When we speak of global warming, we really mean ocean warming:  more than 90% of the extra heat energy stored by the earth over the last 50 years has gone into warming up the ocean.
‘The Southern Ocean is particularly important because it stores more heat and carbon dioxide released by human activities than any other region, and so helps to slow the rate of climate change. A key goal of our work is to determine if the Southern Ocean will continue to play this role in the future.’
The causes of the observed changes in the Southern Ocean are not yet fully understood.  Changes in winds, sea ice, precipitation, or melt of floating glacial ice around the edge of Antarctica, may be responsible.  Data collected on the latest voyage will help unravel this mystery.
A major challenge is the lack of observations at high latitude, where much of the ocean is covered by sea ice in winter.  During the voyage, scientists deployed nine drifting profilers, called Argo floats, which will transmit profiles of temperature and salinity every 10 days for the next five years.
‘The Argo floats have revolutionised our ability to measure the ocean, particularly in winter when ship observations are very rare,’ Dr Rintoul said.
‘On this voyage we deployed a new kind of float designed to survive encounters with the sea ice.  These floats will allow us to see how dense water forms in winter for the first time.’"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #13 on: March 04, 2013, 12:53:12 PM »
As mentioned elsewhere in my posts, I generally agree with, and greatly respect the work that Hansen and Sato are doing to convey the risks of abrupt SLR to the community of concerned parties; including the following exerpt from: "Update of Greenland Ice Sheet Mass Loss: Exponential?" 26 December 2012  by James Hansen and Makiko Sato:

"Iceberg cooling effect. Exponential change cannot continue indefinitely. The negative feedback terminating exponential growth of ice loss is probably regional cooling due to the thermal and fresh-water effects of melting icebergs. Temporary cooling occurs as icebergs and cold fresh glacial melt-water are added to the Southern Ocean and the North Atlantic Ocean.
As a concrete example, Fig. 9 shows the global temperature change in simulations with GISS modelE (Schmidt et al., 2006; Hansen et al., 2007c) with and without the melting iceberg effect. GHGs follow the A1B scenario, an intermediate business-as-usual scenario (IPCC, 2001, 2007; see also Figs. 2 and 3 of Hansen et al., 2007b). Ice melt rate is such that it contributes 1mm/year to sea level in 2010, increasing with a 10-year doubling time; this melt rate constitutes 0.034 Sv (1 Sverdrup = 1 million m3 per second) in 2065 and 0.1 Sv in 2080. Half of this melt-water is added in the North Atlantic and half in the Southern Ocean.
By 2065, when the sea level rise (from ice melt) is 60 cm relative to 2010, the cold fresh-water reduces global mean warming (relative to 1880) from 1.86°C to 1.47°C. By 2080, when sea level rise is 1.4 m, global warming is reduced from 2.19°C to 0.89°C. These experiments are described in a paper in preparation (Hansen, Ruedy and Sato, 2011), which includes other GHG scenarios, cases with ice melt in one hemisphere but not the other, and investigation of the individual effects of freshening and cooling by icebergs (the freshening is more responsible for the reduction of global warming). Note that the magnitude of the regional cooling is comparable to that in 'Heinrich' events in the paleoclimate record (Bond et al., 1992), these events involving massive iceberg discharge at a rate comparable to that in our simulations. Given that the possibility of sea level rise of the order of a meter is now widely accepted, it is important that simulations of climate for the 21st century and beyond include the iceberg cooling effect.
Detailed consideration of the climate effects of freshwater from ice sheet disintegration, which has a rich history (Broecker et al., 1990; Rahmstorf, 1996; Manabe and Stouffer, 1997), is beyond the scope of our present paper. However, we note that the temporary reduction of global warming provided by icebergs is not likely to be a blessing. Stronger storms driven by increased latitudinal temperature gradients, combined with sea level rise, likely will produce global havoc. It was the prospect of increased ferocity of continental-scale frontal storms, with hurricane-strength winds powered by the contrast between air masses cooled by ice melt and tropical air that is warmer and moister than today, which gave rise to the book title "Storms of My Grandchildren" (Hansen, 2009)."

I have attached Hansen & Sato (Dec 2012)'s Figure 9 showing the severity of the influence of temperature change from the polar ice mass loss the they are projecting (note my projected ice mass loss occurs faster for WAIS, and a little bit slower for GIS, than they project).  Not only will this cooling and freshening of the adjoining ocean water create storms, and alter ocean currents due to changes in the AABW, but there can also be a feedback effect on more ice mass loss as in the case that I am proposing for the Weddell Sea Embayment marine ice sheet.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #14 on: March 04, 2013, 12:57:52 PM »
Due to the importance (in my opinion) of current changes taking place to the AABW, I while post a couple of more new clips from the internet on this topic:

From: "Amount of Coldest Antarctic Water Near Ocean Floor Decreasing for Decades" Apr. 3, 2012:

"Scientists have found a large reduction in the amount of the coldest deep ocean water, called Antarctic Bottom Water, all around the Southern Ocean using data collected from 1980 to 2011. These findings, in a study now online, will likely stimulate new research on the causes of this change.
Two oceanographers from NOAA and the University of Washington find that Antarctic Bottom Water has been disappearing at an average rate of about eight million metric tons per second over the past few decades, equivalent to about fifty times the average flow of the Mississippi River or about a quarter of the flow of the Gulf Stream in the Florida Straits.
"Because of its high density, Antarctic Bottom Water fills most of the deep ocean basins around the world, but we found that the amount of this water has been decreasing at a surprisingly fast rate over the last few decades," said lead author Sarah Purkey, graduate student at the School of Oceanography at the University of Washington in Seattle, Wash. "In every oceanographic survey repeated around the Southern Ocean since about the 1980s, Antarctic Bottom Water has been shrinking at a similar mean rate, giving us confidence that this surprisingly large contraction is robust."
Antarctic Bottom Water is formed in a few distinct locations around Antarctica, where seawater is cooled by the overlying air and made saltier by ice formation. The dense water then sinks to the sea floor and spreads northward, filling most of the deep ocean around the world as it slowly mixes with warmer waters above it.
The world's deep ocean currents play a critical role in transporting heat and carbon around the planet, thus regulating our climate.
While previous studies have shown that the bottom water has been warming and freshening over the past few decades, these new results suggest that significantly less of this bottom water has been formed during that time than in previous decades.
"We are not sure if the rate of bottom water reduction we have found is part of a long-term trend or a cycle," said co-author Gregory C. Johnson, Ph.D., an oceanographer at NOAA's Pacific Marine Environmental Laboratory in Seattle. "We need to continue to measure the full depth of the oceans, including these deep ocean waters, to assess the role and significance that these reported changes and others like them play in the Earth's climate."
Changes in the temperature, salinity, dissolved oxygen, and dissolved carbon dioxide of this prominent water mass have important ramifications for Earth's climate, including contributions to sea level rise and the rate of Earth's heat uptake.
"People often focus on fluctuations of currents in the North Atlantic Ocean as an indicator of climate change, but the Southern Ocean has undergone some very large changes over the past few decades and also plays a large role in shaping our climate," said Johnson.
The data used in this study are highly accurate temperature data repeated at roughly 10-year intervals by an international program of repeated ship-based oceanographic surveys. Within the U.S., the collection of these data has been a collaborative effort of governmental laboratory and university scientists, funded primarily by NOAA and the National Science Foundation. However, much of the data used in this study were measured by international colleagues."
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #15 on: March 04, 2013, 03:36:13 PM »
Rather than posting more articles related to AABW volume declines I thought that I would just provide the following bullet points above some implications of this AABW trend:

•   Normally as the AABW spills over the edge of the continental shelf (to the continental slope) some of this cold AABW becomes entrained in the ACC (Antarctic Circumpolar Current) and thus normally partially cools the CDW.  However, with the observed reduction in AABW production (with this reduction believed to be related to the introduction of ice melt water from ice shelfs/ice sheets into the ocean which has be measured to reduce the salinity of the entire Southern Ocean), this entrainment of some of the AABW into the CDW is and will likely continue to decline which will (is) cause the temperature of the CDW to increase which will accelerate AIS ice mass loss and particularly WAIS ice mass loss (as the CDW upwelling is more pronounced for the Bellingshausen and Amundsen Sea areas).
•   Not only is the AABW volume production declining but its temperature is also increasing and as most SLR projections do not include steric SLR contributions for the AABW, this AABW warming trend will directly contribute to SLR via thermal expansion of the AABW (in coming years).
•   As indicated by Sarah G. Purkey and Gregory C. Johnson's Figure 4a (posted previously) the loss of AABW volume near the Weddell Gyre AABW production location, can draw in a tongue of warmer CDW water from the north (to fill the space previously occupied by the missing AABW volume); and due to the direction of the Weddell Gyre current flow, this tongue of warm AABW (above the depth of 1000m) appears to driven below the FRIS; and I postulate that within a few years the same process will occur at the Ross Gyre (another AABW production site); which would drive a warm CDW tongue below the Ross Ice Shelf (RIS).  If so this would transform both FRIS and RIS from cold ice shelves into warm ice shelves with a dramatic increase in both sub-iceshelf basal melting and also in the acceleration of the grounding line retreat of the adjoining ice sheets/ice streams.
•   The currently observed non-linear acceleration of ice mass loss from the Amundsen/Bellingshausen Sea areas appears to have been triggered in the late 1970's and 1980's by to formation of an Ozone hole over Antarctica, which apparently cooled the upper atmosphere over the South Pole which in turn accelerated the circumpolar wind velocities, which in turn promoted upwelling of the CDW, particularly in the Amundsen/Bellingshausen Sea areas (due to the ACC's interaction with the Antarctic Peninsula).  Furthermore, as the Antarctic's ozone hole appears to be healing itself, still the increase in GHG is projected to maintain the current relatively high circumpolar wind velocities; thus maintaining the trend for ice melt loss in the WAIS.  But at indicated by Hansen & Sato (Dec 2012)'s Figure 9, by at least 2065 the decrease in the Southern Ocean's surface temperature due to the relatively large amounts of ice melt water volumes being produced by then (with these ice mass losses likely accelerating through at least 2100), the thermal gradients between the cold Southern Ocean surface temperatures and the adjoining warming subtropical ocean current, should generate very large and powerful cyclones that should drive additional ice melt loss from the AIS due to such factors as: storm waves, storm surge, barometric pressure variations and increased CDW upwelling.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #16 on: March 04, 2013, 04:47:06 PM »
To provide further support for my belief that both the Weddell Gyre and the Ross Gyre are changing in a manner to as to now (for the Weddell Gyre), and soon (for the Ross Gyre), re-direct warm CDW currents below the FRIS and RIS, respectively, I provide the accompanying two images from the NSIDC.  The first image is for the Antarctic sea ice extent averaged for the month of February and it looks similar to the unusual ice pattern that I posted about earlier in this thread in that sea ice area is abnormally low in the northeast edge of the FRIS and very much abnormally high on the northwest edge of the FRIS (which I previously postulated may be due to a warm CDW current entering through the Filchner Trough beneath the northeast edge of FRIS and then melting ice and existing on the northeast edge of FRIS as an unusually cold current), and I previously noted that the sea ice area pattern adjoining RIS is similarly anomalous.  The second image from March 3rd, 2013 shows that the sea ice area pattern adjoining both FRIS and RIS have become even more anomalous, appearly as ocean currents (probably warm CDW currents) are pushing more sea ice from adjoing areas (from the east) into both the Weddell and the Ross Sea areas.  I believe that this pattern supports my postulation that the reduction in AABW production in both the Weddell Gyre and the Ross Gyre will (sooner for Weddell and somewhat later for Ross) change the local ocean currents so as to direct more warm CDW under the FRIS and the RIS, respectively.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #17 on: March 04, 2013, 07:53:03 PM »
I thought that this figure might help some people understand/visualize the relationships between the various Antarctic gyres that produce AABW, the ACC (that carries CDW) and the Deep Western Boundary Currents (that carry the AABW north).
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #18 on: March 04, 2013, 08:18:23 PM »
The accompanying figures from NOAA's daily (2/28/13) and monthly (1/27/13 tp 2/23/1 ), respectively, Sea Surface Temperature, SST, anomalies, which provides supporting evidence for two of my previously stated proposals that: (a) the Pacific system pumps tropical energy directly into the Bellingshausen/Amundsen Seas; and (b) warm CDW maybe entering below the northeast corner of the FRIS then melting large amounts of subiceshelf basal ice and much smaller amounts of ice near the grounding line of the adjoing marine ice sheet thus forming subglacial cavities causing initial grounding line retreat of the ice streams leading into subglacial basins A &B [see previous post in this thread showing their locations].
« Last Edit: March 04, 2013, 08:37:19 PM by AbruptSLR »
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #19 on: March 04, 2013, 08:39:47 PM »
Birthmark,

Thank you for the kind words of encouragement, and I hope that my message is getting out to the community as the current topic that I am posting about of changes in the Antarctic currents (especially in Antarctic Bottow Water, AABW, related currents) has me especially concerned.
There are just so very many aspects to AGW that's it's difficult for the average person to follow all of them at length. I had sort of thrown the Antarctic into the SEP (Somebody Else's Problem) bin since it didn't look likely to have much effect on what I would experience since I will be a Senior Citizen in a very few years. That's a bit self-centered, I admit, but one has to prioritize in some manner.

Now, after reading your posts it appears that I'll have to learn about the Antarctic as well. I estimate that if I'm diligent in my studies I'll have something substantive to contribute to the topic in about two years. What I've learned from your efforts leads me to believe that you have put your finger on one of the big possible problems --AABW and its effects on currents. Correct me if I'm wrong, but my understanding is that if the glaciers detach from the sea bottom, then they will increase in speed, possibly catastrophically?

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #20 on: March 05, 2013, 12:40:23 AM »
Birthmark,

The problem is a little be more complicated than you state, but in the simplest terms that I can state: "Any floating ice essentially has already made its contribute to the current sea level, so regarding SLR we only need to consider the portion of the ice whose weight is supported by the land.  When you look at Vaughen et al 2011's figures (including in several of my posts) he clearly shows the portion of ice mass that is supported by the ground, so that if these ice sheets were to thin sufficiently by any combination of: (a) flowing out by gravity like honey; (b) by bottom (sub as by advection inside a cavity) or top (by sunshine, warm air or rain) ice melting; (c) by the top snow being blown into the ocean by stronger than normal winds; or by (d) toppling over by instability (say calving or Jakobshavn Effect) then that portion of thin submerged ice will float-up.  But typically it is only a small region near the old grounding line that floats-up leaving the rest of the grounde upstream ice with less buttressing support so that it flows faster.  As to whether flowing faster is just a small amount faster or catastrophically faster depends on many details; however the most commonly thought of example of the upstream ice flowing much faster (say 5 to 10 times faster is that for the collapse of the Larsen B ice shelf in 2002 which lead to the glaciers that it buttressed to accelerate by a factor of over 5 times as discussed in the 2010 passage below by NASA:

"The retreat of West Antarctica's glaciers is being accelerated by ice shelf collapse. Ice shelves are the part of a glacier that extends past the grounding line towards the ocean they are the most vulnerable to warming seas. A longstanding theory in glaciology is that these ice shelves tend to buttress (support the end wall of) glaciers, with their mass slowing the ice movement towards the sea, and this was confirmed by the spectacular collapse of the Rhode Island-sized Larsen B shelf along the Eastern edge of the Antarctic Peninsula in 2002. The disintegration, which was caught on camera by NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) imaging instruments on board its Terra and Aqua satellites, was dramatic: it took just three weeks to crumble a 12,000-year old ice shelf. Over the next few years, satellite radar data showed that some of the ice streams flowing behind Larsen B had accelerated significantly, while others, still supported by smaller ice shelves, had not. This dynamic process of ice flowing downhill to the sea is what enables Antarctica to continue losing mass even as surface melting declines.
Michael Schodlok, a JPL scientist who models the way ice shelves and the ocean interact, says melting of the underside of the shelf is a pre-requisite to these collapses. Thinning of the ice shelf reduces its buttressing effect on the glacier behind it, allowing glacier flow to speed up. The thinner shelf is also more likely to crack. In the summer, meltwater ponds on the surface can drain into the cracks. Since liquid water is denser than solid ice, enough meltwater on the surface can open the cracks up deeper down into the ice, leading to disintegration of the shelf. The oceans surrounding Antarctica have been warming, so Schodlok doesn't doubt that the ice shelves are being undermined by warmer water being brought up from the depths. But he admits that it hasn't been proven rigorously, because satellites can’t measure underneath the ice."
Thus one of the main reasons that I am stating that the change in the AABW is very important is that up to now both the large Filchner-Ronne Ice Shelf, FRIS, and the even larger Ross Ice Shelf, RIS, only had cold water circulating under them, so scientists have previously assumed that their is no way for them to sustain sufficient thinning from basal ice melting before say 2500 for them to break apart rapid like the Larsen B ice shelf did in 2002. However, I am saying that with the introduction of warm CDW below these shelves (due to the changes in AABW production) that they could thin and calve sufficiently to break apart by around 2060 to 2070 (also by which time the surface of the FRIS and RIS could be subjected to sufficient surface melting as the WAIS warms to develop large surface melt ponds); which could then accelerate the ice velocity of the adjoining glaciers; which taken together with the scenario that I presented in the folder on the PIG/Thwaites glacial drainage basins, could then lead to a catastrophic collapse of the WAIS by 2100 due to: (a) the formation of sea passage ways through the glaciers remaining after about 2080 to 2090; (b) earthquakes and volcanic eruptions degrading the ice; and (c) increasingly violent storms (see Hansen and Sato 2012).
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #21 on: March 05, 2013, 01:29:33 AM »
Readers should also be aware that as I postulate that both FRIS and RIS will be substantial collapsed/degraded by about 2070, and that as the winds will likely be stronger (thus blowing the snow fall into the ocean) than more of the current snow fall (see the first attached image) will wind-up in the oceans; also more open water will decrease albedo for Western Antarctica.  Furthermore, the top elevation of the WAIS is already substantially lower than for the EAIS (see the seconded attached image); that after 2070 the rapid ice sheet thinning of the WAIS will top the top elevation of the ice sheet thus increasing the surface temperature due to change in elevation (ie proximity to the warm ocean), which will increase the chance of surface melt and of rainfall (instead of snowfall) on the top of the WAIS.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #22 on: March 05, 2013, 02:04:37 AM »
Just to change topics for a moment, accompanying please find an image of the proximity of the Circa 200 BC Hudson Mountain Eruption to the Pine Island Glacier, indicating possible current thermal contributions to basal ice melting, and to the risk of possible future volcanic action (possibly triggered by significant ice mass losses before 2080 to 2090) near the PIG.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #23 on: March 05, 2013, 02:42:18 AM »
Just to shake things up some more, the accompanying figure shows how the March 2011 earthquake in Honshu Japan induced significant ice calving of an ice shelf near the Ross Ice Shelf.  The possible effects of tsunamis generated by earthquakes within Western Antarctica itself after the postulated significant ice mass loss by 2070 to 2100 could have much more devastating effects on ice mass loss.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #24 on: March 05, 2013, 03:10:20 PM »
Some readers maybe still doubt that even if they concede that: (a) the ice mass loss for the Thwaites/PIG/Ferrigno systems could be accelerated by the processes discussed in both the "surge" and the "PIG/Thwaites 2012 to 2040-2060" threads; and the (b) the ice sheets adjoining Weddell and Ross Sea areas could become activated for ice mass loss by the present changes in AABW water production (and once the sea ice is seasonally gone [mid-century] the changes in wind shear stresses) changing the ocean current directions to turn FRIS and RIS into warm ice shelf subjected to rapid basal ice mass and melt pond collapse mechanisms sometime after 2060; still they do not see why the WAIS ice mass loss should continue to accelerate non-linearly after 2060 (even with the postulated sea passageways, the increased seismic/volcanic activity, the decreased glacial basal friction [due to geothermal ice melting due to the thin crust], the decrease in the internal viscosity of the glacial ice due to internal friction as the ice stream velocities increase; and the posulated temporary high gravity driving ice slope gradients particularly in the Thwaites basin [see Jakobshavn Effect discussion].  They may think that certainly, as in the case of mountain glaciers, the ice mass loss will begin to choke-off rather than accelerate once the main ice streams lose much of their ice mass, leaving the side slopes of ice mass (with less driving head) stabilized, particularly sense the "finger print effect" will lower the local sea level around WAIS once a meanful amount of ice mass has been lost between 2060 and 2080.  Nevertheless, in the plan views that I present in the "collapse" thread I indicate the risk of rapid loss of the ice mass in the side slopes after sea passageways have been formed, and in this and in my next few posts I hope to illustrate how the amplification of tides, storm surge and storm tides within many of these sea passageways will locally raise the sea level within the sea passageways by many meters thus on each tidal/storm event the ice mass on the side slopes (to the sea passageways that are postulated to follow the trough system in the subglacial topography [see previous posts in this thread] will be subject to accelerated calving due to the unbalancing effect of elevated hydraulic water pressure seeping many meters beneath the base of the section of ice slope mass subject to calving on that particular tidal/storm surge event.
First, in this post I note that by 2060 to 2070 much of the fast sea ice will be lost in the WAIS during the austral summer and that many of the warm ice shelves above the subglacial cavities [formed by advection through the ice stream troughs such as is the current condition for the PIG ice shelf] will have collapsed [due to thinning from basal melt and accelerated calving as can be seen to be occurring for the PIG ice shelf which is cracking up faster than previously expected] for much of the length of the postulated sea passageways.
Second, given the expected loss of landfast sea ice and many warm ice shelves (within passageways) one can expect tidal action (and storm surge/storm tide) to amplify several times as indicated by the Arctic research from Andrey Pnyushkov 2011 of the International Arctic Research Center for which a summary states:
"Sea ice in high-latitude regions is a complicating factor in tidal dynamics. The important influence of sea ice on tides in Arctic seas has been demonstrated in several studies (e.g., Sverdrup 1926; Zubov 1945; Murty 1985; Prinsenberg 1988; Bourke and Parsons 1993; Kowalik and Proshutinsky 1994; Pease et al. 1994, 1995). In this project, IARC researcher Andrey Pnyushkov and collaborators examined a year-long (2004–05) record of current observations from a mooring deployed at the continental slope of the Laptev Sea (78°26′N, 125°40′E). They found a strong negative correlation (-0.73±0.05) between the upper 50m tidal current amplitudes and local sea ice concentration. Under ice-free conditions, researchers observed a four-fold (from ~2.0 to 8.5 cm/s) amplification of tidal currents. Pnyushkov hypothesizes that a major reason for this amplification of tides in ice-free areas is a change of local resonance conditions for the semi-diurnal (twice daily) tidal current. Based on this finding, he further hypothesizes that sea ice may be an important regulator of tidal current strength in this region. This is potentially an important finding because a four-fold amplification of tidal currents under ice-free conditions leads to a 16-fold increase of kinetic energy, resulting in enhanced tidal energy dissipation and mixing rates in the upper ocean layer. It is possible that enhanced mixing contributes to increased heat flux.
Arctic summer sea ice has retreated dramatically in recent years (Comiso et al., 2008), and in consequence the Arctic Ocean slopes have become more and more exposed to seasonally ice-free conditions. Global climate models predict that the ice will retreat even more in the future. Therefore, the strong tidal amplification observed over the slopes under ice-free conditions may play an increasingly important role in the energy budget of the upper ocean layer for these areas."  See the attached figure for an illustration of how the previously dampened tidal (storm surge) action can amplify several times once the ice cover is eliminated.


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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #25 on: March 05, 2013, 03:29:15 PM »
Further to the immediately preceding post, I note that many of the worlds current convergent estuaries with high tidal amplification (and/or high tidal bores) occur within topography formed by glaciers [once the glaciers are gone].  Therefore, I believe that most of the WAIS sea passageways postulated to occur after 2060 to 2080, will be of a topology similar to that shown in the first figure from van Rijn 2011 [see attached pdf], with a meaningful amount of meltwater and floating ice/bergy bits flowing down side channels to the main interconnected passageways [note that rivers in Greenland were overflowing in the summer of 2012 due to a surface ice melt event and that such surges of meltwater within the confined side channels will also promote rapid calving of ice on the side slopes of the channels].  While the specific amount of tidal (or storm/tide surge) amplification is a function of geometry and damping effects (see second attached figure) and thus cannot be specifically determined in advance, still the combination of: increased frequency and magitude of confined melt water run-off, tidal (storm/tide surge) amplification and increase storm frequency/intensity after 2060-2080 should  promote continued acceleration of ice mass loss from the sides of the main and side channels of the passageway network posulated to be present in the WAIS during the "Collapse Main Period" until circa 2100.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #26 on: March 05, 2013, 03:41:54 PM »
As indicated in the following summary (from the internet), researchers (such as Jerry X. Mitrovica) acknowledge that if/when the WAIS collapses the earth's center of rotation would shift approximately 500 meters from its current position:

"The collapse of an ice sheet in West Antarctica would not only threaten coastal areas of North America and nations in the southern Indian Ocean, but would also cause a shift in the earth’s rotation axis, researchers report in Science.  If the entire West Antarctic Ice Sheet (WAIS) collapses and melts, as some scientists feel is likely due to global warming, the earth’s rotation would shift an approximate 500 meters from its current position. Rather than cause a uniform rise in sea level, this would result in a 30 percent greater increase in certain areas—about 21 feet for Washington, D.C., for example, compared with the uniform 16 to 17 feet already predicted. The researchers say the melting would change the balance of the globe in much the same way that tsunamis move huge amounts of water from one area to another.  Because the gravitational pull of an ice sheet on the ocean is reduced when it melts, water then moves away from it. The net effect is that the sea level actually falls within 2,000 km of a melting ice sheet, and rises progressively further away from it. If the West Antarctic Ice Sheet collapses, sea level will fall close to the Antarctic and will rise much more than the expected estimate in the northern hemisphere because of this gravitational effect. In addition the sheer weight of ice is forcing down the land underneath it and having an impact on the Earth’s spin. When the ice is removed up bounces the land and the Earth moves.  No need to panic about drowning next week, however. It’s a time scale of hundreds of years, said Jerry X. Mitrovica, one of the authors of the study."

As stated throughout this topic, I am far less sure than researchers like Jerry X. Mitrovica (or Tad Pfeffer) that it will take several hundred years for WAIS to collapse rather than approximately one hundred years (circa 2100).
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #27 on: March 05, 2013, 05:52:11 PM »
I would also like to note that the current well know trend of increase Antarctic sea ice extent (see NSIDC) may well serve to provide additional insulation to protect the heat of the upwelling warm CDW (particularly in the Bellingshausen/Amundsen Seas) from now through 2060; which (if so) should facilitate the advective melting of the grounding line ice for PIG/Thwaites/Ferrigno (and other) glaciers.  Furthermore, as the formation of AABW is dependent of the freezing of open seawater into sea ice (notably in the Weddell and Ross Sea areas), that if ice lingers in the Weddell and Ross Sea areas through the austral summer (as is happening now, see earlier posts) then there should be less open seas in these areas during the austral fall, which I believe should result in the formation of less AABW, which may likely drawing in more warm CDW water beneath the FRIS and RIS (which would produce more cold fresh meltwater from basal ice shelf melting which could help to protect the sea ice in these areas from melting during following austral summer).  Thus it is likely that the current trend to increase the extend of West Antarctic sea ice through 2060 will accelerate ice shelf thinning and degradation in these areas, that then when the Antarctic sea ice begins to break-up (& decrease in extent) after 2060, that this would assist the final collapse of both the FRIS and the RIS by 2070 to 2080.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #28 on: March 05, 2013, 08:18:30 PM »
While this not be very relvant; but I note here that according to the attached UN document, the temperature in the Himalaya mountains have been raising at a rate of 0.6 C per decade which has resulted in the creation of a number of glacial lakes behind ice dams (that are at risk of failure and water outburst).  While the WAIS surface temperature is currently below freezing essenstially year round; however, as the average WAIS surface temperature is currently increasing at a rate of 0.8 C per decade (and 1.1 C per decade for the austral WAIS spring season), it is possible that by 2080 to 2100 that many of the envisioned ice/water flow channels through the WAIS.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #29 on: March 06, 2013, 12:03:57 AM »
Getting back to my much more important belief that changes in the AABW production could already be introducing a tongue of warm CDW beneath FRIS, and I am concerned that this trend may accelerate (possibily due to the trend of grewing local sea ice, or more likely due to ice mass loss deluting the AABW so less of it is produced) for both FRIS and RIS.  IF this is the case then the basal ice shelf rate of melting for the cold FRIS and RIS (ranging from 0.03 to 0.2 m/yr) could increase by a factor of 100, 200 or 300 times if/when these ice shelves are changed to warm ice shelves such as is documented for the Pine Island Ice Shelf, PIIS, in the attached pdf and by the two attached images of the rate of melting for PIIS as related to CDW temperature, according to:

"Adjoint sensitivities of sub-ice-shelf melt rates to ocean circulation under the Pine Island Ice Shelf, West Antarctica" by Patrick HEIMBACH and Martin LOSCH, 2012

If this is the case then it is very likely that the buttressing action of FRIS and RIS could be largely degraded by 2060 to 2070.
« Last Edit: March 06, 2013, 12:19:48 AM by AbruptSLR »
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #30 on: March 06, 2013, 12:36:03 AM »
As indicated by Sarah G. Purkey and Gregory C. Johnson's Figure 4a (posted previously) the loss of AABW volume near the Weddell Gyre AABW production location, can draw in a tongue of warmer CDW water from the north; and due to the direction of the Weddell Gyre current flow, this tongue of warm AABW (above the depth of 1000m) appears to driven below the FRIS primarily through the Filchner Trough; which according to the attached bathymetric chart (pdf) and two associate images from the chart, the lip at the entrance to the Filchner Trough has a sill depth of about El-650m (which can accommodate a large volume of warm CDW).
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #31 on: March 06, 2013, 06:16:25 PM »
AbruptSLR, I have a concern about the decrease in Antarctic bottom water formation and the associated effects on the carbon cycle. Atlantic deep water formation is responsible for about 50% of the carbon transport to the depths and the other half is delivered by Antarctic deep water formation. The approximate lifespan of these waters is 1000 years before they are upwelled back to the surface in the eastern equatorial pacific. If the rate of Antarctic deep water formation has been reduced 60% then there must be an associated reduction in the carbon pump. Do you know of any papers which attempt to quantify effects of the ADW formation on the carbon cycle ?  It goes without saying that either a decrease in primary productivity or a slowdown in deep water formation would result in more Co2 accumulating in  surface waters and the atmosphere. This is a positive feedback which I haven't seen adequately described but the lifespan of these drivers would span tens of thousands of years. I have an interest in how AGW plays out in biological terms which means trying to understand bacterial remineralization, viruses, yeasts and carbonate chemistry. Thanks in advance for any insight you can lend. 

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #32 on: March 07, 2013, 01:35:11 AM »
Bruce,

I am not an expert on carbon dioxide absorption; however, from what I read, several different governments are sufficiently concerned about the decline in AABW that they are mounting multi-million dollar expeditions on research vessels to gather more data (include carbon dioxide absorption).  The best that I can suggest is that you read the article at the link below:

http://www.nature.com/scitable/knowledge/library/deep-atlantic-circulation-during-the-last-glacial-25858002

Best, ASLR
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #33 on: March 07, 2013, 06:45:44 AM »
ASLR, thanks for the link. I found this.         Although beyond the scope of this article, geologic data suggest that deep ocean circulation changes we describe above played an important role in raising atmospheric CO2 from glacial levels of ~ 200 parts per million to pre-industrial interglacial values of ~ 280 parts per million (e.g., Sigman et al. 2007).   So I have more to read.   

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #34 on: March 07, 2013, 12:05:01 PM »
Hello AbruptSLR,

Thank you for these fascinating posts.  I don't understand alot of the details but your explanations are very clear.  I have been concerned that a lot of effort has been going into researching what is happening in the Arctic but not nearly enough effort is going into looking at the Antarctic.

There are of course many reasons for this including geographical isolation but it is my understanding that much of the climate  and water currents etc is driven by what happens in the Antarctic.  We are in for interesting times ahead.

Cheers SG

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #35 on: March 07, 2013, 03:48:24 PM »
Bruce,

Thanks for the quote.  It seems undeniable that a reduction in AABW production will result in a reduction in CO2 absorption by the Southern Ocean, which will clearly result in a positive feedback for global warming; and I am afraid that the positive feedback that took thousands of years going from the last glacial maximum to the holocene peak, may only take a few decades as we race past radiative forcing conditions not seen since the Eemian peak.
Also, if you Google Andrex you can get to the website for the British expedition that will be gathering AABW data along the alignment (north of the Weddell Gyre) shown in the attached figure.

Susan,

I could not agree more with you that too much focus is put on the Arctic in comparision to the Antarctic; but to be fair: (a) the albedo flip that I expect from the seasonal loss of the Arctic Sea Ice in the next few years, will have a major positive feedback to global warming and thus the Arctic is like a canary in a coal mine; and (b) Antarctic research costs many times that compared to the Arctic research costs (due both the isolation and extreme conditions) and money is in fact in short supply for research everywhere.  Nevertheless, if even a few of my postulations come to pass in the next one to two decades, government offices will be forced to re-priorize research spending toward the Antarctic.
« Last Edit: March 07, 2013, 04:30:15 PM by AbruptSLR »
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #36 on: March 07, 2013, 04:26:28 PM »
I think that the issue of the changes (reductions) in the AABW production for both the Weddell and Ross Sea areas is so important that I would like to make a few more points on this topic:
- While the mechanism for the reduction in AABW production has not be fully modelled; there is a smoking gun connecting the reduction in AABW production to the entrainment of light/fresh (and relatively warm) ice shelf melt water, in that measurement of the ratio of oxygen isotopes in the AABW indicates an entrainment of glacial melt water (as the oxygen isotopes in glacial water is different than in other possible sources such as sea ice melt); and in the volumes of entrained glacial melt water could only come primarily from floating ice shelves because if that much water came came primarily from grounded ice sheets then the rate of SLR would have been higher than observed (over the past few decades).
- I believe that due a documented to ocean heat uptake in the past decade increasing the ocean heat content between 700 and 2000m (and possible due to some insolation from increasing sea ice cover in the Antarctic) that the temperature of the CDW (and likely the volume of CDW) is increasing faster than expected in models.
- I believe that the FRIS is more exposed to iceshelf basal melting as the local currents generated by the Weddell Gyre should direct the intrusion of warm CDW from the north (discussed earlier in this thread) directly into the Filchner Trough; however, as illustrated by the two attached figures, I believe that the Antarctic Slope Front Current that runs from east to west from the Bellingshausen Sea to the western end of the Amundsen Sea both: (a) helps to deliver iceshelf meltwater (and some glacial melt water) from the Bellingshausen and Amundsen Sea iceshelves and glaciers into the AABW production zone for the Ross Sea, which accounts for the loss in production of AABW in the Ross Sea; and (b) the Antarctic Slope Front Current restricts that volume of warm CDW that can flow on to the continental shelf on the eastern end of the Ross Gyre; which limits the amount of warm CDW that is currently delivered below the RIS; however, I note that the Antarctic Slope Front Current flucuates and divers working under the RIS have reported short-term pulses of warm water currents under the RIS (which could only be CDW that pulsed past a temporarily weakened Antarctic Slope Front Current).  Thus I believe that a slight change in the direction, extent and or magnitude of the Antarctic Slope Front Current in the next few years could make a profound impact on the stability of the RIS.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #37 on: March 07, 2013, 08:18:27 PM »
ASLR, I made a mistake in my earlier post. I read Sabine et al 2004 and it says anthropogenic Co2 leaves the surface in Antarctic Intermediate formation processes rather than Antarctic Deep Water. Not being a physical oceanographer I need to write out which water mass I am trying to describe and think hard about the sources of salinity + cold water that drive them. Only yesterday I read that evaporation of Atlantic surface water is transported across the isthmus of Panama as rain which increases salinity in the Atlantic and lowers it in the Pacific. Simple, logical ,but someone had to point it out first. The current freshening of polar waters both north and south can upset the drivers of deep water formation. There is a very long tail of climate responses to the failure of these systems. Deep time, Sv ( flow rates ), gigatonnes as a measure, and other metrics of large scale processes certainly make the whole subject a challenge.   

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #38 on: March 07, 2013, 08:57:29 PM »
Bruce,

Thanks for the clarification.  If I am right and a collapse of the WAIS freshens the entire Southern Ocean sometime after 2060, then the Antarctic Intermediate formation processes may be affected also.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #39 on: March 07, 2013, 10:52:47 PM »
For those not immediately familar with where the Antarctic Intermediate Water is I attach the three accompanying images that should help clarify this matter.  Inparticular note how the overturning of the upper CDW mixes with the Antarctic Intermediate Water which then carries the CO2 enriched water away from the Southern Ocean.  When you look at Hansen & Sato's image (in an earlier post in this thread) of how cold the Southern Ocean would get after a collapse of much of the WAIS, you can see how this freshening of the Southern Ocean from this meltwater would potentially distrupt this overturning process.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #40 on: March 08, 2013, 12:44:19 PM »
http://www.bbc.co.uk/news/science-environment-21692423

4.5% more ice and lower bedrock is not good news. At least it is mostly East Antarctica not West.

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #41 on: March 08, 2013, 03:26:54 PM »
Candles,

Thank you very much.  But I will point out that while realizing that the depth of the seafloor that the marine ice sheets/marine glaciers are resting on are deeper than perviously thought, does not contribute (meaningfully) to the potential total SLR if the AIS were to melt; still a deeper seafloor depth demonstrates that these ice sheets/glaciers are less stable, and more susceptible to abupt collapse,  than perviously realized as: (a) this means that the negative slope that the grounding line retreat along are either steeper, or longer, than previously realized; and (b) the ease with which subglacial cavities become interconnected is facilitated by the deeper depths and the greater will be the volume of seawater that will eventually flowing through these interconnected sea passageways (after 2070).  For those disinclined to look at the new Bedmap2 illustrations linked by Candles, I provide the following images that illustrate (among many other points): (a) how interconnected the seafloor troughs/trenches are in the West Antarctic; (b) how deep the Byrd Glacier trough is (the deepest in the Antarctic); which gives an idea of how much ice flow/export will occur here (from the EAIS) if the RIS turns from a cold ice shelf to a warm ice shelf which thins and then retreats (circa 2070) so as to stop buttressing the Byrd Glacier; (c) how the Ferrigno Glacier trough leads straight into the backside of the PIG trough; and (d) the sea passaway identified by Vaughen between the Weddell and Ross Seas.
« Last Edit: March 09, 2013, 12:49:44 AM by AbruptSLR »
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #42 on: March 11, 2013, 02:50:58 AM »
The following abstract states that in some locations the measured ice shelf basal melt rates at the grounding line of the Ronne Ice Shelf are already as high as 7m/yr; which fully supports my concern that the FRIS is already degrading relatively rapidly:

Ice shelf basal melting at the grounding line, measured from seismic observations
By A. M. Smith
Article first published online: 19 DEC 2012; DOI: 10.1029/96JC02173

"Analysis of seismic data provides a new technique to measure basal melting of an ice shelf close to the grounding line. Internal reflections have been observed within the ice on a seismic reflection profile at the grounding line of Ronne Ice Shelf. The changes in ice thickness above and below these reflections have been used in a steady state model to calculate the basal mass flux of the ice shelf soon after the ice begins to float. Strain rates within the ice, calculated during the modeling, agree with values from nearby survey data. The calculated melt rates range between 0 and 7 m yr−1 with an estimated standard error of ±2.4 m yr−1, in reasonable agreement with earlier estimates based on surface glaciological observations. Limitations in the method include the difficulties in determining reflector geometry from a single seismic section and also the limitations imposed by the assumption of steady state. Additional seismic data would greatly reduce these limitations."

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #43 on: March 11, 2013, 03:58:45 PM »
The attached pdf details a measurement program to document (the pdf documents until just before 2009) some of the changes of the CDW flow and the AABW flow in the Weddell Sea that, through various atmospheric/ocean/ice interaction, have progessively directed more and more warm CDW under the FRIS leading an acceleration of ice melting near the FRIS grounding line (such as areas as high as 7m/yr cited in the previous post).
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #44 on: March 17, 2013, 01:32:41 AM »
To provide additional supporting information for the hazard analysis (of the risk of WAIS collapse this centry), I provide the following quote from: Report of the  International Weddell Gyre Workshop  at the Hanse Wissenschaftskolleg (Hanse Institute for Advanced Study), Delmenhorst, Germany,  17 – 19 September 2012: "Circumpolar Deep Water from the Antarctic Circumpolar Current to the north is introduced into the Weddell Gyre mainly near its eastern edge, and constitutes the large intermediate water mass of the gyre at depths <1500 m. This water mass, locally known as Warm Deep Water (WDW) is characterized by a temperature maximum. Virtually all other water masses in the Weddell Gyre derive from the WDW. It mixes with shelf and surface waters to produce the densest waters in the world’s oceans, i.e., Weddell Sea Bottom Water. Such formation sequences at the shelves also generate Weddell Sea Deep Water, the latter of which is also formed from large-scale mixing within the gyre. The Weddell Sea Deep Water occupies a depth range which allows it to abandon the gyre circulation, thus it is the main ingredient of the Antarctic Bottom Water, which is found at abyssal depths of all world oceans, not only in the Southern Hemisphere. The processes that lead to the deep and bottom waters involve surface waters which in this way contribute to the ventilation of abyssal waters and through these of the world oceans. Besides ventilation (i.e., providing oxygen), these processes also sequester gases, like (anthropogenic and natural) CO2 and man-made gases, such as chlorofluorocarbons. …. The Weddell Gyre, as maybe the most prominent ocean region connecting the deep ocean with the surface and eventually the atmosphere, has a high potential to influence global climate by controlling gas exchange and direct heat flow, modulated through sea ice. …. The sensitivity of the heat balance in the Weddell Gyre, as well as the potentially global effects of relatively small changes in this area, make it a key area for understanding the implications of global change. Continuous observation of the Weddell Sea is mandatory if we want to ensure that we do not miss essential changes in the Earth system."
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AbruptSLR

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #45 on: May 04, 2013, 12:48:33 AM »
I would like to briefly address the belief held by many that as significant ice mass loss occurs in the WAIS (such as in the 2060 to 2100 period) that the gravitational "finger print" effect will act as a strong negative feedback, which will serve to stabilize the WAIS sufficiently to avoid abrupt sea level rise in this century; to which I offer the following points:

-  As noted in my May 1 post in the "Surge" thread, recent Cryosat 2 data (see Aviso handbook) shows that all along the coastline of the WAIS the sea level actually rose between 2011 and 2012 even as ice mass loss was occurring; presumably because the influences of upwelling (thermal, salinity and hydrostatic [such as stagnation pressure]) are presently dominating the finger print effect.

- Once the grounding line has retreated upstream of the lip of the subglacial basin, the increased gravitational thrust from a drop in sea level becomes less important for stabilizing the various glaciers, ice streams and ice sheets; while advection of warm CDW and the action of basal meltwater both become more dominant.

- The Southern Ocean is warming faster than most oceans in the world, and this ocean heat, combined with changes in ocean current paths (as subglacial passageways become interconnected); and increased basal meltwater (due both to increased internal friction within the ice masses and due to increased surface melting by 2060); will all serve to guarantee accelerating WAIS ice mass loss even as the finger print effect is increasing with increasing ice mass loss.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #46 on: June 21, 2013, 06:37:12 PM »
I am making this post to remind people reading my posts in the "Antarctic Atmospheric Methane" thread circa June 19 to 21, 2013; that this "WAIS Collapse" thread contains much of my prior discussions of the influence of the upwelling of warming CDW (the upwelling is influenced by atmospheric methane concentration over Antarctica).  I am also reminding readers that I recommend following the results of the ANDREX program (see attached image for the study area) at the following website:

http://projects.noc.ac.uk/andrex/results

The warming of the CDW in the ANDREX program area can contribute directly to the decomposition of methane hydrates along the Queen Maud coastline, which would represent a positive feedback for SLR from Antarctica.
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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #47 on: July 12, 2013, 05:26:22 PM »
I am concerned that some readers are not familiar with the excellent work of Purkey and Johnson focused on AABW but also very important to the trends in warm CDW (see reply #9 in this trend, and in the first attached figure see the Weddell-Enderby temperature curve indicating warm water that could be contributing now to basal ice melting for FRIS).  The following reference and abstract cites their continuing valuable work in 2013:
 
Antarctic Bottom Water warming and freshening: Contributions to sea level rise, ocean freshwater budgets, and global heat gain
by: Sarah G. Purkey, and Gregory C. Johnson; Journal of Climate 2013 ; doi: http://dx.doi.org/10.1175/JCLI-D-12-00834.1

Abstract: "Freshening and warming of Antarctic Bottom Water (AABW) between the 1980s and 2000s are quantified, assessing the relative contributions of water-mass changes and isotherm heave. The analysis uses highly accurate, full-depth, ship-based, conductivity-temperature-depth measurements taken along repeated oceanographic sections around the Southern Ocean. Fresher varieties of AABW are present within the South Pacific and South Indian oceans in 2000s compared to the 1990s, with the strongest freshening in the newest waters adjacent to the Antarctic continental slope and rise indicating a recent shift in the salinity of AABW produced in this region. Bottom waters in the Weddell Sea exhibit significantly less water-mass freshening than those in the other two southern basins. However, a decrease in the volume of the coldest, deepest waters is observed throughout the entire Southern Ocean. This isotherm heave causes a salinification and warming on isobaths from the bottom up to the shallow potential temperature maximum. The water-mass freshening of AABW in the Indian and Pacific sectors is equivalent to a freshwater flux of 73 ±26 Gt yr-1, roughly half of the estimated recent mass loss of the West Antarctic Ice Sheet. Isotherm heave integrated below 2000 m and south of 30 °S equates to a net heat uptake of 34 ±3 TW of excess energy entering the deep ocean from deep volume loss of AABW and 0.37 ±0.15 mm yr-1 of sea level rise from associated thermal expansion."
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AbruptSLR

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #48 on: August 04, 2013, 12:47:40 PM »
Given the amount of increased seismic activity (due to post-glacial rebound from ice mass loss) expected during the 2060 to 2100 period, the information in the following reference is of major concern not only for methane release from the Southern Ocean, but also in the Arctic Ocean:

Subduction zone earthquake as potential trigger of submarine hydrocarbon seepage
by: David Fischer, José M. Mogollón, Michael Strasser, Thomas Pape, Gerhard Bohrmann, Noemi Fekete, Volkhard Spiess & Sabine Kasten; Nature Geoscience;  6, pp. 647–651; (2013); doi:10.1038/ngeo1886

Abstract:
"Methane, a potent greenhouse gas, is abundant in marine sediments. Submarine seepage of methane-dominated hydrocarbons is heterogeneous in space and time, and mechanisms that can trigger episodic seep events are poorly understood. For example, critical gas pressures have been predicted to develop beneath impermeable sediments that bear gas hydrates, making them susceptible to mechanical failure and gas release. Gas hydrates often occur in seismically active regions, but the role of earthquakes as triggers of hydrocarbon seepage through gas-hydrate-bearing sediments has been only superficially addressed. Here we present geochemical analyses of sediment cores retrieved from the convergent margin off Pakistan. We find that a substantial increase in the upward flux of gas occurred within a few decades of a Mw 8.1 earthquake in 1945—the strongest earthquake reported for the Arabian Sea. Our seismic reflection data suggest that co-seismic shaking fractured gas-hydrate-bearing sediments, creating pathways for the free gas to migrate from a shallow reservoir within the gas hydrate stability zone into the water column. We conservatively estimate that 3.26×108 mol of methane have been discharged from the seep site since the earthquake. We therefore suggest that hydrocarbon seepage triggered by earthquakes needs to be considered in local and global carbon budgets at active continental margins."
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AbruptSLR

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Re: Discussion of WAIS Collapse Main Period from 2060 to 2100
« Reply #49 on: August 18, 2013, 11:00:22 PM »
The following weblink provides access to a 2013 thesis by Michael Hübner using the Max Planck Institute Earth System Model, that addresses both Arctic and Antarctic sea ice projections. 

Evaluation of Sea-ice in the Max Planck Institute Earth System Model; Michael Hübner; March 2013

http://www.pa.op.dlr.de/~VeronikaEyring/Publications/2013_Huebner_Bachelorthesis_FINAL.pdf

As my projections of ASLR by 2100 use a modification of the IPCC RCP 8.5 scenario; the following statement from the Hübner 2013 thesis supports my position that for a business as usual radiative forcing scenario there is a good possibility that the loss of austral summer Antarctic sea ice before the turn of the century (largely after 2060) will contribute to the risk of ASLR this century (largely those the collapse of the WAIS):

"The simulation of RCP 8.5 projects a further decrease during the 21st century and the possibility of an ice-free Antarctic summer by the end of the century."

Furthermore, the following website provides forecasts of Antarctic sea ice extent and concentrations for up to 4 years into the future using the Lamont-Doherty Earth Observatory (Columbia University) Antarctic sea ice Markov model.

http://www.ldeo.columbia.edu/res/div/ocp/projects/sea_ice.html
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson