Discussion of the Antarctic Peninsula

[AbruptSLR]

So far I have only discussed the Antarctic Peninsula in passing; however, as it has one of the fastest rates of surface warming of any location on Earth, it will likely see significant ice degradation even before the WAIS, and thus merits a closer examination.  I will begin by looking at the Antarctic Peninsula, AP, ice shelves, focused on the Larsen C ice shelf (which could collapse rapidly any year now).  The following three recent articles from the internet indicate that a combination of crevasses, subglacial melting and increased surface melting put these ice shelves (an particularly the Larsen C ice shelf) in increasingly worst shape:

The first article is from:
http://cires.colorado.edu/steffen/larsenC/

"Significant glaciological and ecological changes are occurring along the Antarctic Peninsula in response to climate warming that is proceeding at 6 times the global average rate (King et al., 1994; Vaughn et al., 2003). Floating ice shelves, the extension of outlet glaciers, are responding rapidly and have lost ~28,000 km2 in the last 50 years, including the catastrophic collapse of Larsen A in 1995, Larsen B in 2002 and the Wilkins ice shelf in 2008-09 (Cook and Vaughn, 2009). Following ice shelf collapse, the outlet glaciers that nourished the ice shelves have accelerated and thinned in response to the removal of the backstress that the ice shelf provided. In the case of Larsen B, an additional -27 km3 yr-1 of ice was discharged due to the removal of this backstress (Rignot et al., 2004).
The significance of ice shelf collapse and subsequent acceleration of outlet glaciers is amplified by the fact that 40% of the Antarctic continent is ringed in ice shelves and that 80% of ice flux from the continent passes through these gates (Drewy, 1982; Jacobs et al., 1992). The climatic regime of the Antarctic Peninsula and the latitudinal changes in ice shelf stability provide a unique opportunity to study the full spectrum of ice shelf stability—from recently collapsed to fully stable—in order to gain a broader understanding of the climatic conditions and physical processes that result in ice shelf stability and instability. This understanding is essential to future estimates of ice sheet contributions to global sea level rise.
This project focuses on Larsen C, the largest remaining ice shelf on the Antarctic Peninsula. Larsen C has a surface area of ~55,000 km2 and is composed of 12 major flow units fed by outlet glaciers (Glasser et al., 2009). Average ice thickness is ~300 m but ranges from ~500 m near the grounding line to ~250 m near the ice edge (Griggs and Bamber, 2009). "


The second abstract is from:
Basal crevasses on the Larsen C Ice Shelf, Antarctica: Implications for meltwater ponding and hydrofracture, By McGrath et al 2012, GEOPHYSICAL RESEARCH LETTERS, doi:10.1029/2012GL052413
"A key mechanism for the rapid collapse of both the Larsen A and B Ice Shelves was meltwater-driven crevasse propagation. Basal crevasses, large-scale structural features within ice shelves, may have contributed to this mechanism in three important ways: i) the shelf surface deforms due to modified buoyancy and gravitational forces above the basal crevasse, creating >10 m deep compressional surface depressions where meltwater can collect, ii) bending stresses from the modified shape drive surface crevassing, with crevasses reaching 40 m in width, on the flanks of the basal-crevasse-induced trough and iii) the ice thickness is substantially reduced, thereby minimizing the propagation distance before a full-thickness rift is created. We examine a basal crevasse (4.5 km in length, ~230 m in height), and the corresponding surface features, in the Cabinet Inlet sector of the Larsen C Ice Shelf using a combination of high-resolution (0.5 m) satellite imagery, kinematic GPS and in situ ground penetrating radar. We discuss how basal crevasses may have contributed to the break up of the Larsen B Ice Shelf by directly controlling the location of meltwater ponding and highlight the presence of similar features on the Amery and Getz Ice Shelves with high-resolution imagery."


The third abstract is from:
http://nora.nerc.ac.uk/501292/

Basal melt rates on Larsen-C Ice Shelf by Jenkins, Adrian; Shepherd, Andrew; Gourmelen, Noel. 2013
Abstract/Summary
During the past decade, the Larsen Ice Shelf has progressively thinned and two large sections have collapsed, catastrophically, leading to increased ice discharge into the oceans and a consequent rise in global sea level. If similar events are to occur at the remaining Larsen-C section, the fate of a tenfold greater ice reservoir hangs in the balance. Although the origin of the underlying instability has yet to be determined, only three processes can realistically be to blame; enhanced basal or surface melting, or accelerated flow. To quantify rates of basal ice melting, a phase sensitive radar was deployed on the Larsen-C Ice Shelf. The radar is a high-precision instrument that directly measures changes in thickness of the ice shelf, in contrast to indirect methods that infer basal melting from surface observation while assuming steady state. We established three radar sites on Larsen-C where time-series of satellite altimeter data are also available. The sites were revisited twice over the course of one year to measure the annual mean and summertime rates of basal melting. The annual mean measurements proved difficult to interpret because of a lack of reproducibility in the radar layer structure within the ice shelf over long periods of time. Measurements made within one summer field season proved more reliable, yielding melt rates of between 4 and 8 m yr-1 near the grounding line, near zero over the ice shelf interior and around 2 m yr-1 near the ice front. Such a spatial pattern of melting is consistent with models of the ocean circulation beneath the ice shelf, while the magnitude near the grounding line suggests that waters with temperatures above the surface freezing point reach the inner cavity at least intermittently. Temporal variability in the melt rate is a strong candidate for driving the observed thinning to the ice shelf, at least over its southern half."

[AbruptSLR]

The attached figure is from:
Antarctic ice-sheet loss driven by basal melting of ice shelves By Pritchard, et al 2012, Nature, 484,502–505; doi:10.1038/nature10968
This figure from 2012 indicates a basal melt rate of up to about 2m/yr at the northern end of the Larsen C ice shelf; while the 2013 information that I provided in my preceding post by Adrian et al states:
"Measurements made within one summer field season proved more reliable, yielding melt rates of between 4 and 8 m yr-1 near the grounding line …"

Adrian et al's more accurate 2013 data is important as the thickness of the ice shelf near the grounding line is the most important ice thickness if Larsen C follows the same collapse mechanism as the Larsen B ice shelf.

[AbruptSLR]

The two attached figures are from:

Speedup and fracturing of George VI Ice Shelf, Antarctic Peninsula, by T. O. Holt et al 2013, The Cryosphere, 7, 797–816, www.the-cryosphere.net/7/797/2013/, doi:10.5194/tc-7-797-2013

This article and these figures indicate that while the George VI Ice Shelf (George VIIS) is not at risk of a collapse such as the Larsen C is at risk of, nevertheless, the data indicates that the observed rates of calving on both the north and south faces are expected to continue into the future until the ice shelf is gone.

[AbruptSLR]

The attached image and the following quote are from:

Understanding the SAM influence on the South Pacific ENSO
Teleconnection, by Fogt et al 2010; Clim Dyn;DOI 10.1007/s00382-010-0905-0

"Given the recent dramatic climate changes along the Antarctic Peninsula and West Antarctica (Steig et al. 2009), understanding the regional atmospheric circulation variations linked to SAM and ENSO is paramount. However, much more work needs to be done. Modeling studies investigating the circulation response during various ENSO–SAM events are planned, in order to understand if models can adequately simulate the strong changes found in this study.  Future work is also needed to investigate how the position of tropical convection during various ENSO–
SAM influences the high latitude ENSO teleconnection. This is especially important as Lachlan-Cope and Connolley (2006) demonstrate that the position of the convection within the tropical Pacific is also important for a significant downstream response during El Nino events."

This information implies that the end of the current El Nino hiatus period could result in significant amounts of additional ice mass loss from both the Antarctic Peninsula and the WAIS. 

This is particularly true of the wind pattern crossing the Antarctic Peninsula (see the second attached image).

Finally, to save another post, the third image indicates the land based ice flows that would be activated if the George VI ice shelf were to disappear.

[AbruptSLR]

The following link can be used to see what the ESA is doing to monitor the Wilkins ice shelf (which partially collapsed in both 2008 and 2009):

http://www.esa.int/Our_Activities/Observing_the_Earth/Keeping_an_eye_on_Wilkins_Ice_Shelf

[AbruptSLR]

From The University Corporation for Atmospheric Research, UCAR, website, the caption for the attached figure is:

"When a strong El Niño develops across the tropical Pacific, it can influence weather and climate as far away as the southern polar region. This occurs via a “wave train” of areas with unusually high or low pressure in the upper atmosphere (H’s and L’s) that leads to warmer-than-normal temperatures in West Antarctica. Bright reds near the equator show the unusually warm sea-surface temperatures (SSTs) associated with an El Niño during 1940-41. There are no SST data for that period for the portions of the Southern Ocean shown here. Analysis of ice cores drilled in West Antarctica (red dots) reveals that air temperatures there warmed by as much as 10°F as this three-year-long El Niño unfolded, then dropped by as much as 13°F afterward. "

[Bruce Steele]

ASLR, first of all I'd like to say your posts are a challenge in so many ways. I  experienced the full  force of the 82' -83' and 97'-98' ENSO events. I am a commercial fisherman/ diver and the memory/severity of both of those events are seared into my memory. I have some understanding of the ENSO northern hemisphere western tropical pacific bulge which propagates a mass of hot water that moves eastward across the pacific. The western pool of hot water in the southern hemisphere that feeds into the Antarctic Circumpolar Current is the other half of ENSO I hadn't thought about . Both your last post and the reply #7 May 15 Antarctic Weather and Meteorology post ( Bertler et al 2006 ) show how warm waters are avected onto the shelf in the Amundsen Sea during El Nino or conversely how a gyre in the Ross forms during La Nina.   As I understand it the slowdown in Antarctic Bottom Water  formation is two to three decades old( or older) So if I am correct about the duration of the slowdown in Bottom Water formation processes I was wondering how El Nino or extended La Nina change the strength of bottom water formation processes? Do we have a year by year reading on formation processes or just a long term average?    If meltwater is somehow implicated in the bottom water slowdown do you think the depth of the fresh water lens changes in the El Nino -La Nina shifts? That is does the Amundsen collect more meltwater during the ENSO and the Ross during the La Nina?   

[AbruptSLR]

Bruce,

I have been traveling for a while (and I am still traveling) so I cannot give you a proper response, but I will say that:
(a) the ENSO changes telecommunication of energy from the Pacific to the Bellinghasuen, Amundsen and Ross Seas by a variety of mechanism including: (i) atmospheric Rossby Wave; (ii) oceanic Rossby Wave; and (c) temporary changes in ocean current patterns.
(b) Clearly, such periodic telecommunication of energy can periodically accelerate the ice mass loss from both grounded and floating (shelves) ice; which can then periodically slow the formation of AABW in for the Weddell, and Ross, Sea areas.

With regard to the Weddell Sea, note that:  As cited in one of my previous posts, there are indications that when the Larsen B Ice Shelf collapsed that the weather (wind) patterns in the Weddell Sea changed; which may have contributed (in part) to a shift in the local ocean currently sufficiently to direct some warm CDW (at least periodically) underneath the FRIS (Filchner Ronne Ice Shelf); which may have contributed to increase sub-ice shelf melting that may have resulted in a freshening of the ocean surface waters on the northwest edge of the FRIS, that may have contributed to the expansion of the sea ice growth during the Austral Fall of 2013.  Furthermore, as stated in a previous post in this thread the observed sub-ice shelf melting rate for the Larsen C Ice Shelf indicates that ocean currents there have also changed sufficient to introduce warmer deep ocean water under this shelf as well (as least periodically).

As it is almost inevitable that the Larsen C ice shelf will collapse within a few years of the end of the current El Nino hiatus period; it is clear that the solar absorption of the ocean exposed by the collapse of the Larsen C ice shelf would have a still larger impart on the weather (wind) and associated ocean current patterns than did the collapse of the Larsen B Ice Shelf; which is likely to accelerate the degradation of the FRIS and also of other Antarctic Peninsula ice shelves, such as the Wilkins, and George VI, Ice Shelves.

When I finish traveling, I will try to provide a more focused response; but remember that with time the volume of ice melt water in the Southern Ocean should increase non-linearly; which implies that the impact of the ENSO on the AABW production could be change with time.

Best,
ASLR

[AbruptSLR]

Bruce,

Some additional information on the questions that you raised can be found in the following quote from:
http://www.washington.edu/news/2013/04/14/recent-antarctic-climate-glacier-changes-at-the-upper-bound-of-normal/

"Previous work by Steig has shown that rapid thinning of Antarctic glaciers was accompanied by rapid warming and changes in atmospheric circulation near the coast. His research with Qinghua Ding, a UW research associate, showed that the majority of Antarctic warming came during the 1990s in response to El Niño conditions in the tropical Pacific Ocean.
Their new research suggests the ’90s were not greatly different from some other decades – such as the 1830s and 1940s – that also showed marked temperature spikes.
“If we could look back at this region of Antarctica in the 1940s and 1830s, we would find that the regional climate would look a lot like it does today, and I think we also would find the glaciers retreating much as they are today,” said Steig, lead author of a paper on the findings published online April 14 in Nature Geoscience.
The researchers’ results are based on their analysis of a new ice core from the West Antarctic Ice Sheet Divide that goes back 2,000 years, along with a number of other ice core records going back about 200 years. They found that during that time there were several decades that exhibited similar climate patterns as the 1990s.
The most prominent of these in the last 200 years – the 1940s and the 1830s – were also periods of unusual El Niño activity like the 1990s. The implication, Steig said, is that rapid ice loss from Antarctica observed in the last few decades, particularly the ’90s, “may not be all that unusual.”"

The following quote from Steig et al 2012 (see reference below) also provides insight on the correlation of ENSO (and strong El Nino events) with ice mass loss from the ASE:

STEIG, E.J.,  DING, Q., BATTISTI, D.S., JENKINS, A., 2012, "Tropical forcing of Circumpolar Deep Water Inflow and outlet glacier thinning in the Amundsen Sea Embayment, West Antarctica", Annals of Glaciology (53)60 2012 doi: 10.3189/2012AoG60A110

"Flow of warm CDW onto the continental shelf has played a critical role in the high melt rates and recent thinning and retreat of glaciers in the ASE region of West Antarctica.  Variability in CDW inflow is strongly influenced by the westerly wind stress over the continental slope, and tropical SST forcing has played an important, if not dominant, role in recent changes in the zonal wind regime in the ASE.  Continued changes in tropical SSTs can be expected in the future, due to increased global radiative forcing from anthropogenic greenhouse gases, and warming in the central tropics is particularly pronounced in most IPCC (Intergovernmental Panel on Climate Change) AR4 (Fourth Assessment Report) model runs (Ding and others, 2011), suggesting that the current wind-stress regime in the ASE is likely to persist.   We caution that the link from wind forcing to CD inflow changes to glacier retreat is not a simple linear process, and that once the PIG retreated past a subglacial ridge some decades ago, continued glacier thinning and retreat was probably inevitable even without the recent changes in wind forcing (Jenkins and others, 2010; Jacobs and others, 2011). In this context, it is interesting to note that significant warming in the central tropical Pacific last occurred in the 1940s, and ice-core evidence indicates that the impact on climate in the Amundsen Sea sector of Antarctica was comparable with what has been observed recently (Schneider and Steig, 2008). This suggests that tropical SST forcing during the 1940s is a viable candidate for the initiation of the current period of change in the Amundsen Sea ice shelves, which clearly was underway at least by the 1970s (Jenkins and others, 2010). Photographic evidence shows that in 1947 the PIG ice shelf was only slightly more advanced than in the early 1970s, but that a large area of icebergs and sea ice extended seaward of the ice front, which may be evidence of significant calving over the preceding decade (Rignot, 2002). There is also independent evidence from sediment cores that a larger ice shelf may have occupied the ASE at some time prior to this, possibly during the 20th century (Kellogg and Kellogg, 1987). We speculate that a more extensive ice shelf may have partially collapsed following the very large El Nino event of 1939–42."

Finally, oceanic Rossby waves are thought to communicate climatic changes due to variability in forcing, due to both the wind and buoyancy. Both barotropic and baroclinic waves cause variations of the sea surface height (see attached figure), although the length of the waves made them difficult to detect until the advent of satellite altimetry.  Baroclinic waves also generate significant displacements of the oceanic thermocline, often of tens of meters. Satellite observations have revealed the stately progression of Rossby waves across all the ocean basins, particularly at low- and mid-latitudes. These waves can take months or even years to cross a basin like the Pacific; however when they arrive at the West Antarctic they can contribute to the accelerated calving of ice shelves there.

[AbruptSLR]

Bruce,

The following are some related abstracts from the Nineteenth Annual WAIS Workshop, 2012:

1. Significance of exceptional recent climate and glacier changes in West Antarctica
Eric Steig, University of Washington

The West Antarctic Ice Sheet (WAIS) has warmed significantly in the last 50 years, and sea ice concentrations have declined in the adjacent Amundsen and Bellingshausen Seas for at least the last three decades. Contemporaneously, outlet glaciers that drain the WAIS into the ocean have accelerated, leading to overall mass loss and a significant contribution to sea level rise. The rising temperatures and declining sea ice are linked with the glacier accelerations by changes in atmospheric circulation, which have enhanced the flow of warm Circumpolar Deep Water (CDW) onto the Antarctic continental shelf, resulting in thinning of floating ice shelves. Data from an array of ice core records from the WAIS show that recent conditions are likely unprecedented in at least the last 200 years, but are dominated by decadal variability. Similar conditions occur with a frequency of about once per century over the last 2000 years. The unusual climate in West Antarctica in recent decades can be attributed primarily to similarly unusual conditions in the tropical Pacific. Future changes in the tropics will need to be taken into account in projections of the Antarctic ice sheet contribution to sea level rise."

2. "Perspective on the West Antarctic warming from the reconstructed Byrd temperature record (1957--‐2012)
Julien P. Nicolas, David H. Bromwich, Aaron B. Wilson, Andrew J. Monaghan, Matthew A. Lazzara, George A. Weidner, and Linda M. Keller

Large uncertainty remains in our knowledge of the temperature changes in West Antarctica since the mid-20th century. Existing Antarctic temperature datasets show significant disagreement about the sign, magnitude and seasonality of the temperature trends, largely a result of the paucity of long-term observations in the region. Only one instrumental record, Byrd Station, in central West Antarctica, provides near-surface temperature observations from 1957 onward, yet its numerous gaps have largely precluded its use for long-term climate change assessment. Here, we present the results from a reconstruction of the Byrd temperature record in which the missing observations have been filled in with 2-meter temperature estimates from global reanalyses. The 1957-2011 temperature trends derived from this reconstructed dataset confirm earlier evidence of significant warming annually as well as in austral winter and spring, but suggest larger temperature increases than previously thought. In addition, our analysis reveals for the first time some significant warming occurring in summer, which has important implications for the West Antarctic Ice Sheet given the increased possibility of surface melting that it entails. The consistency of these results with recent analyses of the West Antarctic spring- and wintertime warming will be discussed. We will also propose some mechanisms accounting for the summer warming."



3.  "Sea‐ice ocean interactions in a high‐resolution global climate model
Emily Newsom
University of Washington
The physical processes regulating the stratification of the Southern Ocean are poorly understood in nature and important to global climate: the production of Antarctic Bottom Water (AABW) is important in moderating the global meridional circulation and ocean heat uptake; the rate of transport of Circumpolar Deep Water (CDW) onto the continental shelf is important in regulating the mass balance of the Antarctic Ice Sheet. Here, we seek to understand how the explicit resolution of oceanic eddies affects simulation of the Southern Ocean. To do so, we compare water mass production and stratification between standard (1 degree) and high (1/10 degree) resolution of ocean and sea ice in 150‐year integrations of the Community Climate Model Version 3.5 (CCSM 3.5). The atmosphere and land components are at 0.5 degree resolution in both cases. High resolution generally improves the agreement in temperature and salinity between simulation and observations in the Southern Ocean, as several key features emerge in the eddy‐resolving integration that are not captured at coarser resolution. At high resolution, the water mass similar to AABW is colder and more saline, sinks along steeper isopycnals, and contributes to a more vigorous deep overturning. At mid‐depths, water comparable to CDW upwells at greater rates, and extends closer to the continent. We argue that resolving localized sea ice formation regions has improved the production of AABW, driving a more vigorous deep overturning circulation at high resolution. In addition to considering the effect of resolution on the unforced ocean mean state, preliminary results are presented from two perturbed experiments branching from the same control simulation. In one, integrations at peak
(1960’s) and minimal (2000) ozone levels are contrasted. In the other, CO2 is ramped by 1% per year until it doubles. Fine resolution alters how the ocean evolves when perturbed, especially at depth. Irrespective of resolution, however, ozone depletion and CO2 ramping cause an increase in surface westerlies, a warming of the surface waters and a decrease in sea ice."

[Bruce Steele]

ASLR, I have a hard copy of the Purkey 2013 paper, and I found another Doney et al 2001 paper(Antarctic Bottom Water Formation and Deep Water CFC distributions in a global ocean climate model)that shows CFC enhanced bottom water as far as 20 degrees south. Doney references a Orsi et al 1999 paper that was a good read. Orsi shows that the Ross Sea bottom water moves west into the Australian -Antarctic Basin and describes the flow of Bottom Water along the Western edge of the Southeast Pacific Basin also from the Ross Sea Formation processes. The Orsi paper is written well and is  easy to follow. The slowdown , freshening and warming are several decades old. It would be interesting to see how the reduction in ventilation is changing oxygen concentrations at depth as the bottom waters propagate northwards. I didn't find an answer to how the ENSO or the extended La Nina has affected the formation processes but the long trend line of the slowdown obviously points to other larger drivers. Thanks for the links.                                                                                            ftp://kakapo.ucsd.edu/pub/sio_220/d02%20-%20Formation%20of%20Antarctic%20Bottom%20Water/Orsi_et_al.po_99.pdf

[AbruptSLR]

Bruce,

Thanks for the input.  My general rule of thumb is that the reduction in AABW is related to the production of fresh meltwater from both ice sheets and ice shelves.  Thus the strengthening of the Antarctic circumpolar wind velocities and the associated CDW upwelling, would clearly dominate over any ENSO influence which would be periodic in nature.  Nevertheless, I am concerned that the next strong El Nino event could last long enough to push enough warm CDW into the Thwaites Gateway trough, that the grounding line (at least at the south end of the trough portion of the gateway) could be melted back over the ridge leading down into the Byrd Subglacial Basin.  If this were to happen the associate groundling line retreat for the Thwaites Glacier could continue to accelerate even after the El Nino event has passed.

[AbruptSLR]

Bruce,

As the accompanying information from the Eighteenth Annual WAIS Workshop (2011) is related to ice meltwater (currently dominated by sub-ice shelf melting), I thought that I would post the attached four images here (as I related meltwater in the Southern Ocean to the slow-down in AABW production that you are interested in):

[AbruptSLR]

The following article from the website below, highlights the high rate of basal ice mass loss from Antarctic Peninsula iceshelves:

http://blogs.smithsonianmag.com/science/2013/06/antarcticas-ice-shelves-dissolve-thanks-to-warm-water-below/

"In the past two decades, we’ve seen dramatic images of ice shelves and the floating tongues of glaciers crumble into the ocean. The summer of 2012 saw a huge chunk of ice–two times the size of Manhattan–snap off of Greenland’s Petermann Glacier. Two years earlier, a piece of ice twice as big as that one split from the glacier’s front. In early 2002, ice covering an area the greater than the size of Rhode Island sloughed into the ocean from a lobe of the Antarctic Peninsula’s Larsen Ice Shelf, releasing into the ocean three-quarters of a trillion tons of ice. Seven years before that, the northernmost sector of the same ice sheet completely collapsed and an area of ice roughly the size of Hawaii’s Oahu island dissolved into the sea.
Scientists have long thought that sudden and dramatic ice calving events like these, along with more moderate episodes of calving that occur daily, were the main mechanisms for how polar ice gets lost to the sea. New research, however, shows that calving icebergs is only the tip of the iceberg–seawater bathing the undersides of ice shelves contributes most to ice loss even before calving begins, at least in Antarctica.
The discovery, published in the journal Science, shows that interactions with the ocean underneath floating ice account for 55 percent ice lost from Antarctic ice shelves between 2003 and 2008. The researchers arrived at their findings by studying airborne measurements of ice thicknesses from radar sounders and the rates of change in ice thickness based off of satellite data. Combining these data allowed them to calculate the rates of bottom melting.
Given that thick platforms of floating ice surround nearly 75 percent of Earth’s southernmost continent, covering nearly 580 million square miles, ice melted in this fashion may well be the main contributor to sea level rise. “This has profound implications for our understanding of interactions between Antarctica and climate change.” said lead author Eric Rignot a researcher at UC Irvine and NASA’s Jet Propulsion Laboratory, in a statement. “It basically puts the Southern Ocean up front as the most significant control on the evolution of the polar ice sheet.”
Interestingly, the big ice shelves–Ross, Ronne and Filchner, which cover about 61 of Antarctica’s total ice shelf area–only contribute a small fraction meltwater through their bases. Instead, less than a dozen small ice shelves, particularly those on the Antarctic Peninsula, are responsible for most–nearly 85 percent–of the basal melting observed by the authors during their study period. These shelves not only float in warmer water, relatively, but their small sizes may mean that their interiors are less sheltered from already warmer ocean waters that creep underneath the ice.
The findings reveal a lot about the vulnerability of polar ice in a warming world. Ice sheets ooze through glaciers to the sea, where they interlace and form ice shelves. These shelves are akin to a cork that keeps the contents inside from spewing out–when ice sheets collapse, the glaciers that feed them thin and accelerate, helping to drain the interior ice sheet. Polar ice sheets already are losing at least three times as much ice each year as they were in the 1990s, and the findings released today may give a mechanism for this frantic pace.
In fact, the major ice calving events of the last two decades on the Petermann Glacier and Larsen Ice Shelf may have started with the fact that melting from underneath was weakening the ability of ice to coalesce into a solid mass.
“Ice shelf melt can be compensated by ice flow from the continent,” Rignot added. “But in a number of places around Antarctica, they are melting too fast, and as a consequence, glaciers and the entire continent are changing.”


You might also want to read the excellent article at the following website:

http://community.adn.com/node/163569

[AbruptSLR]

The following abstract and images are from:
"Transport of warm Upper Circumpolar DeepWater onto the western Antarctic Peninsula continental shelf
By: D. G. Martinson and D. C. McKee
Ocean Sci., 8, 433–442, 2012, www.ocean-sci.net/8/433/2012/, doi:10.5194/os-8-433-2012

Abstract. Five thermistor moorings were placed on the continental shelf of the western Antarctic Peninsula (between 2007 and 2010) in an effort to identify the mechanism(s) responsible for delivering warm Upper Circumpolar Deep Water (UCDW) onto the broad continental shelf from the Antarctic Circumpolar Current (ACC) flowing over the adjacent continental slope. Historically, four mechanisms have been suggested: (1) eddies shed from the ACC, (2) flow into the cross-shelf-cutting canyons with overflow onto the nominal shelf, (3) general upwelling, and (4) episodic advective diversions of the ACC onto the shelf. The mooring array showed that for the years of deployment, the dominant mechanism is eddies; upwelling may also contribute but to an unknown extent. Mechanism 2 played no role, though the canyons have been shown previously to channel UCDW across the shelf into Marguerite Bay.Mechanism 4 played no role independently, though eddies may be advected within a greater intrusion of the background flow."

The first image shows the location of the Palmer Long Term Ecological Research, LTER, project in Marguerite Bay, Antarctic Peninsula.

The second image shows the interaction of the Antarctic Circumpolar Current, ACC, (composed of Upper Circumpolar Deep Water, UCDW) which is relatively warm, and the entire Antarctic continent and particularly showing how the ACC (UCDW) crosses the continential slope-shelf break for the entire West Antarctic; and also the potential temperature of the water with depth in the LTER sampling area.

The third image shows the measured fluctuations of temperature with depth and time in 2007, 2008 and 2010 in the LTER study area; indicating the nature of the eddies controlling UCDW transport in this particular area.

The fourth image shows a table of the number and nature of the eddies in the 2007, 2008 and 2010 at measured in the LTER area.

This Palmer LTER study shows warm CDW transport behavior that is somewhat different than that observed in other areas of Antarctica; indicating the need to avoid generalisms whenever possible; and the importance of trying to understand the many complex interacting mechanism controlling the CDW interaction with iceshelves, glaciers and ice sheets (including: eddies; upwelling; current flow velocities and temperatures; current interactions with bottom bathymetry and ice features; eposidic advective events such as El Nino events/SAM/storms/winds; sea ice, positive and negative feedback mechanisms; etc.)

[sidd]

Martinson et al. (2012) is interesting. In this sector they rule out " ...flow into the cross-shelf-cutting canyons ... " as proposed, for example in St. Laurent et al. in the WAIS 2012 workshop

www.waisworkshop.org/abstracts/2012/st-laurent.pdf

I see also from fig 3 in Martinson an average yearly flow of around 4GJ/m^2, which for that 0.5Km depth is about a tenth of the 1Gwatt/Km of coast in St. Laurent, which assumes 1 "large" (?) trough per 1000Km of coastline.  Perhaps the reason is the large troughs are further south than the Martinson survey.

More interesting to me, is that the definition of Q on p.436 of Martinson has in the integrand, the difference of the water temperature and _surface_ freezing point as the heat available to melt ice. But as we see CDW is efficiently channelled to the grounding line at grounding depth, the appropriate temperature is the _pressure melting point at the grounding depth_ which is much lower, and might as much as double the Q values.

I would dearly love to see the full presentations at WAIS 2012, but i suppose i shall have to wait patiently for the papers.

sidd

[AbruptSLR]

Sidd,

I think that the Martinson et al (2012) findings can only be taken to apply to the specific location that they are examining (on the west side of the Antarctic Peninsula).  Clearly, St. Laurent focuses on locations further southward and he sub-divides these more southerly location into two different cases (1&2); but it is clear to me that each location around the Antarctic coastline has a unique case for ocean heat input to either ice shelf and/or ice sheet melting.  Certainly, inclusion of the influence eddies are important in any GCM/RCM/LCM numerical model, but they do not always dominate the local ocean heat content transport (e.g. for the PIG/TG CDW circulation system, seasonal variations result in more significant fluctuations superimposed on a year-round current flow through local seafloor troughs).

Best,
ASLR

[AbruptSLR]

I think that the glacial ice mass loss for Antarctica indicated in the attached image from the Ice2sea 2013 report is primarily from the Antarctic Peninsula; and I think that it gives a good idea of the accelerated ice mass loss to be expected from the Antarctic Peninsula in the future.

[AbruptSLR]

For those interested in the details of the major calving event of the Wilkins Ice Shelf in 2008-2009, I provide the following reference and abstract:

Padman, L, DP Costa, MS Dinniman, HA Fricker, ME Goebel, LA Huckstadt, A Humbert, I Joughin, JTM Lenaerts, SRM Ligtenberg, T Scambos and MR van den Broeke (2012), Oceanic controls on the mass balance of Wilkins Ice Shelf, Antarctica. J. Geophys. Res.-Oceans 117, Art. No. C01010, issn: 0148-0227, ids: 880FP, doi: 10.1029/2011JC007301, Published 20-Jan 2012

"Several Antarctic Peninsula (AP) ice shelves have lost significant fractions of their volume over the past decades, coincident with rapid regional climate change. Wilkins Ice Shelf (WIS), on the western side of the AP, is the most recent, experiencing a sequence of large calving events in 2008 and 2009. We analyze the mass balance for WIS for the period 1992−2008 and find that the averaged rate of ice-shelf thinning was ∼0.8 m a−1, driven by a mean basal melt rate of 〈wb〉 = 1.3 ± 0.4 m a−1. Interannual variability was large, associated with changes in both surface mass accumulation and 〈wb〉. Basal melt rate declined significantly around 2000 from 1.8 ± 0.4 m a−1 for 1992–2000 to ∼0.75 ± 0.55 m a−1for 2001–2008; the latter value corresponding to approximately steady-state ice-shelf mass. Observations of ocean temperatureT obtained during 2007–2009 by instrumented seals reveal a cold, deep halo of Winter Water (WW; T ≈ −1.6°C) surrounding WIS. The base of the WW in the halo is ∼170 m, approximately the mean ice draft for WIS. We hypothesize that the transition in 〈wb〉 in 2000 was caused by a small perturbation (∼10–20 m) in the relative depths of the ice base and the bottom of the WW layer in the halo. We conclude that basal melting of thin ice shelves like WIS is very sensitive to upper-ocean and coastal processes that act on shorter time and space scales than those affecting basal melting of thicker West Antarctic ice shelves such as George VI and Pine Island Glacier."

[AbruptSLR]

The following reference, and accompanying image, measures the temperature signal for Bruce Plateau, Antarctic Peninsula during the 20th century.  This signal is a clear combination of natural changes and anthropogenic forcing; indicating that the anthropogenic contribution is getting stronger; and that when the natural contribution swings from its current negative contribution; one can expect much accelerated ice mass loss from the Antarctic Peninsula within the next 1 to 5 years:

Borehole temperatures reveal details of 20th century warming at
Bruce Plateau, Antarctic Peninsula; by: V. Zagorodnov1, O. Nagornov2, T. A. Scambos3, A. Muto3,*, E. Mosley-Thompson1, E. C. Pettit4, and S. Tyuflin3
The Cryosphere, 6, 675–686, 2012; www.the-cryosphere.net/6/675/2012/; doi:10.5194/tc-6-675-2012/

[AbruptSLR]

The following weblink leads to an article that discusses how the Wilkins Ice Shelf is still shedding icebergs five years after the 2008 major calving of a 405 sq km iceberg:

http://antarcticsun.usap.gov/science/contenthandler.cfm?id=2857

Whether this continued calving is driven by anthropogenic forcing, or not, it is still reducing both the buttressing of the adjoining glaciers and is also reducing the local albedo.

[AbruptSLR]

The linked reference discusses a method to monitor the risk of the Larsen C Ice Shelf collapsing in the future.  The link provides a free pdf of the paper:

http://www.the-cryosphere-discuss.net/7/3567/2013/tcd-7-3567-2013.html

Borstad, C. P., Rignot, E., Mouginot, J., and Schodlok, M. P.: Creep deformation and buttressing capacity of damaged ice shelves: theory and application to Larsen C ice shelf, The Cryosphere Discuss., 7, 3567-3610, doi:10.5194/tcd-7-3567-2013, 2013.

"Abstract. Around the perimeter of Antarctica, much of the ice sheet discharges to the ocean through floating ice shelves. The buttressing provided by ice shelves is critical for modulating the flux of ice into the ocean, and the presently observed thinning of ice shelves is believed to be reducing their buttressing capacity and contributing to the acceleration and thinning of the grounded ice sheet. However, relatively little attention has been paid to the role that fractures play in the flow and stability of ice shelves and their capacity to buttress the flow of grounded ice. Here, we develop an analytical framework for describing the role that fractures play in the creep deformation and buttressing capacity of ice shelves. We apply principles of continuum damage mechanics to derive a new analytical relation for the creep of an ice shelf as a function of ice thickness, temperature, material properties, resistive backstress and damage. By combining this analytical theory with an inverse method solution for the spatial rheology of an ice shelf, both backstress and damage can be calculated. We demonstrate the applicability of this new theory using satellite remote sensing and Operation IceBridge data for the Larsen C ice shelf, finding damage associated with known crevasses and rifts. We find that increasing thickness of mélange between rift flanks correlates with decreasing damage, with some rifts deforming coherently with the ice shelf as if completely healed. We quantify the stabilizing backstress caused by ice rises and lateral confinement, finding high backstress associated with two ice rises that likely stabilize the ice front in its current configuration. Though overall the ice shelf appears stable at present, the ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could portend significant change for the shelf. Using this new approach, field and remote sensing data can be utilized to monitor the structural integrity of ice shelves, their ability to buttress the flow of ice at the grounding line, and thus their indirect contribution to ice sheet mass balance and global sea level."

[AbruptSLR]

The following two abstracts are taken from the proceedings of the following IGSOC sponsored symposia, and they are relevant to lessons learned from the break-up of the Larsen B Ice Shelf on the Antarctica Peninsula:

International Symposium on Changes in Glaciers and Ice Sheets: observations, modelling and environmental interactions; 28 July–2 August; Beijing, China; Contact: Secretary General, International Glaciological Society


http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm



The impact of surface lakes on the stress regime of the Larsen B Ice Shelf
Douglas MacAYEAL, Alison BANWELL, Olga SERGIENKO, Martamaria CABALLERO, Neil GLASSER
Corresponding author: Douglas MacAyeal
Corresponding author e-mail: drm7@uchicago.edu
"The most conspicuous change to the Larsen B Ice Shelf in the years prior to its explosive break-up in February/March 2002 was the build-up of thousands of supraglacial lakes in response to environmental warming. In the present contribution, we present a numerical model study of the stress regime these lakes were likely to have introduced as a result of ice-shelf flexure in response to water load. Our goal is to illustrate how lake-induced stress regime is capable of fragmenting the ice shelf to the extent necessary to produce the multitude of small ice-shelf fragments characteristic of the explosive break-up."

Supraglacial lakes on ice sheets and ice shelves: a comparison
Alison BANWELL, Marta CABALLERO, Mac CATHLES, Neil ARNOLD, Neil GLASSER, Douglas MacAYEAL
Corresponding author: Alison Banwell
Corresponding author e-mail: afb39@cam.ac.uk
"The development of supraglacial lakes in the surface ablation zones of Greenland and Antarctica (mostly on ice shelves) constitute a major impact of environmental warming in the polar regions. However, it remains to be fully explained how the increasing lake coverage will drive changes to the ice sheets. Current thinking suggests that lakes on grounded ice sheets are fundamentally different from lakes on ice shelves, because in the former case, lake location (and therefore maximum water depth and volume) is constrained by bedrock topography, and in the latter case, lakes respond to the flexure made possible by floating ice. Large surface melt rates in Greenland are necessary to produce large lake volumes, but persistent multi-year lakes on ice shelves in the Antarctic may develop equivalent water volumes despite lower surface melt rates. Through the analysis of satellite imagery, this study seeks to establish a quantitative comparison among the spatial patterns, shapes, sizes and volumes between surface lakes on the Larsen B Ice Shelf (before its break-up in 2002) and on the grounded ice of Paakitsoq, a land-terminating region of the Greenland ice sheet. We suggest that the generic differences between lakes in the two regions help explain why the rapid drainage of lakes on the Greenland ice sheet can contribute to summer speed-up and why Antarctic ice-shelf lakes can be devastating to ice-shelf stability. This intercomparison across the full spectrum of supraglacial lake phenomena also highlights the range of behaviors that these lakes display in response to differing rates of surface ablation."

[AbruptSLR]

The following abstracts come from the linked sources and are relevant to the Antarctic Peninsula:

www.igsoc.org/symposia/2013/kansas/proceedings/procsfiles/procabstracts_63.htm
Contact: Secretary General, International Glaciological Society

67A031
Material heterogeneity and rift termination along suture zones in the Larsen C Ice Shelf, Antarctica
Daniel McGRATH, Konrad STEFFEN, Ted SCAMBOS, Paul HOLLAND, Eric RIGNOT, Hari RAJARAM, Waleed ABDALATI
Corresponding author: Daniel McGrath
Corresponding author e-mail: daniel.mcgrath@colorado.edu
Rifts are consistently observed to terminate along the lateral edges of suture zones, locations of material heterogeneity that form the bounds of meteoric inflows in ice shelves. The heterogeneity can consist of marine ice, meteoric ice with modified rheological properties due to past shear, or the presence of fracture. Ground-penetrating radar observations on the Larsen C Ice Shelf, Antarctica, investigate (1) the termination of a 25 km long rift in the Churchill Peninsula suture zone, which was found to contain ~45 m of accreted marine ice, and (2) the along-flow evolution of a suture zone originating at Cole Peninsula, to examine the ice column structure near the calving front. Basal mass-balance values are determined using a steady-state mass conservation model and are applied to a flowline model to delineate the along-flow evolution of layers within the ice shelf. Near the calving front, the thickening surface wedge of locally accumulated meteoric ice, which likely has limited lateral variation in its mechanical properties, accounts for ~60% of the total ice thickness. Thus, it is likely the lower ~40% of the ice column, and the material heterogeneities present there, are responsible for delaying the propagation of rifts, and therefore tabular calving events, as demonstrated in the >40 year time series leading up to the 2004/05 calving event for Larsen C. This likely represents a highly sensitive aspect of ice shelves as changes in the oceanic forcing may lead to the erosion of these features.

[AbruptSLR]

Colorado Bob (in the ASIB) provided the following linked article about research indicating that:

"Antarctica's crumbling Larsen B Ice Shelf is poised to finally finish its collapse, a researcher said Tuesday (Dec. 10) here at the annual meeting of the American Geophysical Union.

The Scar Inlet Ice Shelf will likely fall apart during the next warm summer, said Ted Scambos, a glaciologist at the National Snow and Ice Data Center in Boulder, Colo. Scar Inlet's ice is the largest remnant of the vast Larsen B shelf still attached to the Antarctic Peninsula. (Another small fragment, the Seal Nunataks, clings on as well.) In the Southern Hemisphere's summer of 2002, about 1,250 square miles (3,250 square kilometers) of the enormous Larsen B Ice Shelf splintered into hundreds of icebergs. Scar Inlet is about two-thirds the size of the ice lost from Larsen B."

http://www.livescience.com/41916-antarctica-ice-shelf-future-collapse.html

[johnm33]

Thanks for everything you here AbruptSLR
I was looking at M Owens blog  http://www.fairfaxclimatewatch.com/blog/2013/11/the-rise-and-fall-of-the-westerlies.html  a few days ago and wondering how long till we get a persistent rainstorm on the peninsular. Looks like it's going to be far too interesting down there this year.

[AbruptSLR]

johnm33,

Thanks for the link to a very interesting article and associated paper by Mayeski et al 2013.  For those interested in studying Mayewski et al 2013's paper in more detail, I provide a link to a free access pdf, a citation, an abstract, and a key quote from the paper's conclusion citing that when the ozone hole over Antarctica begins to heal itself (by 2070) this will likely lead to an abrupt disruption of the atmospheric circulation system in mid to high latitudes of the Southern Hemisphere:

http://onlinelibrary.wiley.com/doi/10.1002/jqs.2593/pdf

Mayewski, P.A., Maasch, K.A., Dixon, D., Sneed, S.B., Oglesby, R., Korotkikh, E., Potocki, M., Grigholm, B., Kreutz, K., Kurbatov, A.V., Spaulding, N., Stagger, J.C., Taylor, K.C., Steig, E.J., White, J., Bertler, N.A.N., Goodwin, I., Simões, J.C., Jaña, R., Kraus, S. and Fastook, J. 2013. "West Antarctica’s Sensitivity to Natural and Human Forced Climate Change Over the Holocene", Journal of Quaternary Science 28(1), pp 40-48. DOI: 10.1002/jqs.2593.

"Abstract
The location and intensity of the austral westerlies strongly influence southern hemisphere precipitation and heat transport with consequences for human society and ecosystems. With future warming, global climate models project increased aridity in southern mid-latitudes related to continued poleward contraction of the austral westerlies. We utilize Antarctic ice cores to investigate past and to set the stage for the prediction of future behaviour of the westerlies. We show that Holocene West Antarctic ice core reconstructions of atmospheric circulation sensitively record naturally forced progressive as well as abrupt changes. We also show that recent poleward migration of the westerlies coincident with increased emission of greenhouse gases and the Antarctic ozone hole has led to unprecedented penetration, compared with >100,000 years ago, of air masses bringing warmth, extra-Antarctic source dust and anthropogenic pollutants into West Antarctica."

Extract from the conclusions:
"Based on our results we suggest that continued greenhouse warming coupled with future healing of the Antarctic ozone hole will probably weaken the thermal gradient across the polar vortex, resulting potentially in abrupt disruptions to atmospheric circulation over the mid to high latitudes of at least the southern hemisphere. The implications of such changes are serious."

Best,
ASLR

[AbruptSLR]

It is bad enough that more Magellanic penguin chicks are dying due to climate change; but the associated increase in rainstorms indicate that accelerating ice mass loss is also occurring in the nearby Antarctic Pennisula:

Boersma PD, Rebstock GA (2014) Climate Change Increases Reproductive Failure in Magellanic Penguins. PLoS ONE 9(1): e85602. doi:10.1371/journal.pone.0085602

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0085602

Abstract: "Climate change is causing more frequent and intense storms, and climate models predict this trend will continue, potentially affecting wildlife populations. Since 1960 the number of days with >20 mm of rain increased near Punta Tombo, Argentina. Between 1983 and 2010 we followed 3496 known-age Magellanic penguin (Spheniscus magellanicus) chicks at Punta Tombo to determine how weather impacted their survival. In two years, rain was the most common cause of death killing 50% and 43% of chicks. In 26 years starvation killed the most chicks. Starvation and predation were present in all years. Chicks died in storms in 13 of 28 years and in 16 of 233 storms. Storm mortality was additive; there was no relationship between the number of chicks killed in storms and the numbers that starved (P = 0.75) or that were eaten (P = 0.39). However, when more chicks died in storms, fewer chicks fledged (P = 0.05, R2 = 0.14). More chicks died when rainfall was higher and air temperature lower. Most chicks died from storms when they were 9–23 days old; the oldest chick killed in a storm was 41 days old. Storms with heavier rainfall killed older chicks as well as more chicks. Chicks up to 70 days old were killed by heat. Burrow nests mitigated storm mortality (N = 1063). The age span of chicks in the colony at any given time increased because the synchrony of egg laying decreased since 1983, lengthening the time when chicks are vulnerable to storms. Climate change that increases the frequency and intensity of storms results in more reproductive failure of Magellanic penguins, a pattern likely to apply to many species breeding in the region. Climate variability has already lowered reproductive success of Magellanic penguins and is likely undermining the resilience of many other species."

[AbruptSLR]

The linked reference (with a free access pdf) contains the following key sentences that are of concern: "The new data set resolves the rugged subglacial topography in great detail, indicates deeply incised troughs, and shows that 34% of the ice volume is grounded below sea level. The Antarctic Peninsula has the potential to raise global sea level by 71 ± 5 mm. In comparison to Bedmap2, covering all Antarctica on a 1 km grid, a significantly higher mean ice thickness (+48%) is found.":


Huss, M. and Farinotti, D.: A high-resolution bedrock map for the Antarctic Peninsula, The Cryosphere Discuss., 8, 1191-1225, doi:10.5194/tcd-8-1191-2014, 2014.

http://www.the-cryosphere-discuss.net/8/1191/2014/tcd-8-1191-2014.html


"Abstract. Assessing and projecting the dynamic response of glaciers on the Antarctic Peninsula to changed atmospheric and oceanic forcing requires high-resolution ice thickness data as an essential geometric constraint for ice flow models. Here, we derive a complete bedrock data set for the Antarctic Peninsula north of 70° S on a 100 m grid. We calculate distributed ice thickness based on surface topography and simple ice dynamic modelling. Our approach is constrained with all available thickness measurements from Operation IceBridge and gridded ice flow speeds for the entire study region. The new data set resolves the rugged subglacial topography in great detail, indicates deeply incised troughs, and shows that 34% of the ice volume is grounded below sea level. The Antarctic Peninsula has the potential to raise global sea level by 71 ± 5 mm. In comparison to Bedmap2, covering all Antarctica on a 1 km grid, a significantly higher mean ice thickness (+48%) is found."

[AbruptSLR]

I making this post in the Antarctic Peninsula folder because most of the Antarctic glaciers addressed in the linked reference (with a free access pdf) are located in the Antarctic Peninsula; however, the whole paper provides information that is key to evaluating SLR in the future:

W. Tad Pfeffer, Anthony A. Arendt, Andrew Bliss, Tobias Bolch, J. Graham Cogley, Alex S. Gardner, Jon-Ove Hagen, Regine Hock, Georg Kaser, Christian Kienholz, Evan S. Miles, Geir Moholdt, Nico Mölg, Frank Paul, Valentina Radic, Philipp Rastner, Bruce H. Raup, Justin Rich, and Martin J. Sharp, (2014) "The Randolph Glacier Inventory: a globally complete inventory of glaciers",  Journal of Glaciology; 60 (221): 537 DOI: 10.3189/2014JoG13J176

http://www.igsoc.org/journal/60/221/j13J176.pdf

Abstract: "The Randolph Glacier Inventory (RGI) is a globally complete collection of digital outlines of glaciers, excluding the ice sheets, developed to meet the needs of the Fifth Assessment of the Intergovernmental Panel on Climate Change for estimates of past and future mass balance. The RGI was created with limited resources in a short period. Priority was given to completeness of coverage, but a limited, uniform set of attributes is attached to each of the 198 000 glaciers in its latest version, 3.2. Satellite imagery from 1999–2010 provided most of the outlines. Their total extent is estimated as 726 800 +/- 34 000km2. The uncertainty, about 5%, is derived from careful single-glacier and basin-scale uncertainty estimates and comparisons with inventories that were not sources for the RGI. The main contributors to uncertainty are probably misinterpretation of seasonal snow cover and debris cover. These errors appear not to be normally distributed, and quantifying them reliably is an unsolved problem. Combined with digital elevation models, the RGI glacier outlines yield hypsometries that can be combined with atmospheric data or model outputs for analysis of the impacts of climatic change on glaciers. The RGI has already proved its value in the generation of significantly improved aggregate estimates of glacier mass changes and total volume, and thus actual and potential contributions to sea-level rise."

[Shared Humanity]

This article, just posted on ASIB, may serve to explain, in part, the dramatic effects we are seeing in the Antarctic with regard to weather, precipitation and ocean currents.

http://www.dailykos.com/story/2014/03/05/1281907/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-is-Collapsing

[AbruptSLR]

The linked reference, and image, indicates that the northern Antarctic Peninsula is still losing grounded ice mass at one of the highest rates per unit of glaciated area in the world:

Scambos, T. A., Berthier, E., Haran, T., Shuman, C. A., Cook, A. J., Ligtenberg, S. R. M., and Bohlander, J., (2014), "Detailed ice loss pattern in the northern Antarctic Peninsula: widespread decline driven by ice front retreats", The Cryosphere Discuss., 8, 3237-3261, doi:10.5194/tcd-8-3237-2014

http://www.the-cryosphere-discuss.net/8/3237/2014/tcd-8-3237-2014.pdf

Abstract: "The northern Antarctic Peninsula (nAP, < 66° S) is one of the most rapidly changing glaciated regions on Earth, yet the spatial patterns of its ice mass loss at the glacier basin scale has to date been poorly documented. We use satellite laser altimetry and satellite stereo-image topography spanning 2001–2010 to map ice elevation change and infer mass changes for 33 glacier basins. Rates of ice volume and ice mass change are 27.7 ± 8.6 km3 a−1 and 24.9 ± 7.8 Gt a−1. This mass loss is compatible with recent gravimetric assessments, but it implies that almost all the gravimetry-inferred loss lies in the nAP sector. Mass loss is highest for eastern glaciers affected by major ice shelf collapses in 1995 and 2002, where twelve glaciers account for 60% of the total imbalance. However, losses at smaller rates occur throughout the nAP, and at high and low elevation, despite increased snow accumulation along the western coast and at high elevations. We interpret the widespread mass loss to be driven by decades of ice front retreats on both sides of the nAP, and by the propagation of kinematic waves triggered at the fronts into the interior."

[AbruptSLR]

The linked reference provides evidence that the retreat of the Northern Prince Gustave ice stream and the deglaciation of northern James Ross Island (Antarctic Peninsula) occurred earlier (circa 12.9 ka) than previously believed.  This indicates that the glaciers in the Antarctic Peninsula may be more sensitive to regional warming than previously expected (which implies that we can expect more contributions to SLR from this area, sooner rather than later):

Daniel Nývlt , Régis Braucher, Zbyněk Engel, Bedřich Mlčoch, and ASTER Team, (2014), "Timing of the Northern Prince Gustav Ice Stream retreat and the deglaciation of northern James Ross Island, Antarctic Peninsula during the last glacial–interglacial transition", Quaternary Research, DOI: 10.1016/j.yqres.2014.05.003


http://www.sciencedirect.com/science/article/pii/S0033589414000672


Abstract: "The Northern Prince Gustav Ice Stream located in Prince Gustav Channel, drained the northeastern portion of the Antarctic Peninsula Ice Sheet during the last glacial maximum. Here we present a chronology of its retreat based on in situ produced cosmogenic ¹⁰Be from erratic boulders at Cape Lachman, northern James Ross Island. Schmidt hammer testing was adopted to assess the weathering state of erratic boulders in order to better interpret excess cosmogenic ¹⁰Be from cumulative periods of pre-exposure or earlier release from the glacier. The weighted mean exposure age of five boulders based on Schmidt hammer data is 12.9 ± 1.2 ka representing the beginning of the deglaciation of lower-lying areas (< 60 m a.s.l.) of the northern James Ross Island, when Northern Prince Gustav Ice Stream split from the remaining James Ross Island ice cover. This age represents the minimum age of the transition from grounded ice stream to floating ice shelf in the middle continental shelf areas of the northern Prince Gustav Channel. The remaining ice cover located at higher elevations of northern James Ross Island retreated during the early Holocene due to gradual decay of terrestrial ice and increase of equilibrium line altitude. Schmidt hammer R-values are inversely correlated with ¹⁰Be exposure ages and could be used as a proxy for exposure history of individual granite boulders in this region and favour the hypothesis of earlier release of boulders with excessive 10Be concentrations from glacier directly at this site. These data provide evidences for an earlier deglaciation of northern James Ross Island when compared with other recently presented cosmogenic nuclide based deglaciation chronologies, but this timing coincides with rapid increase of atmospheric temperature in this marginal part of Antarctica."

[AbruptSLR]

The following research supports the melt-pond (due to warm air) theory for the collapse of the Larsen-B Ice Shelf (and I have assumed that the melt-pond theory is correct in all of my estimates):

M. Rebesco, E. Domack, F. Zgur, C. Lavoie, A. Leventer, S. Brachfeld, V. Willmott, G. Halverson, M. Truffer, T. Scambos, J. Smith, E. Pettit, (2014), "Boundary condition of grounding lines prior to collapse, Larsen-B Ice Shelf, Antarctica", Science 12 September 2014; Vol. 345 no. 6202 pp. 1354-1358; DOI: 10.1126/science.1256697


http://www.sciencemag.org/content/345/6202/1354.abstract

Abstract: "Grounding zones, where ice sheets transition between resting on bedrock to full floatation, help regulate ice flow. Exposure of the sea floor by the 2002 Larsen-B Ice Shelf collapse allowed detailed morphologic mapping and sampling of the embayment sea floor. Marine geophysical data collected in 2006 reveal a large, arcuate, complex grounding zone sediment system at the front of Crane Fjord. Radiocarbon-constrained chronologies from marine sediment cores indicate loss of ice contact with the bed at this site about 12,000 years ago. Previous studies and morphologic mapping of the fjord suggest that the Crane Glacier grounding zone was well within the fjord before 2002 and did not retreat further until after the ice shelf collapse. This implies that the 2002 Larsen-B Ice Shelf collapse likely was a response to surface warming rather than to grounding zone instability, strengthening the idea that surface processes controlled the disintegration of the Larsen Ice Shelf."

[AbruptSLR]

The linked reference (with an open access pdf) discusses a high-resolution bedrock map for the Antarctic Peninsula, which indicates that the glacial ice in this area is about 48% thicker than previously indicated by Bedmap2; which, in-turn, indicates a greater potential contribution to sea level rise, SLR, from the Antarctic Peninsula (of about 70 mm):

Huss, M. and Farinotti, D. , (2014), "A high-resolution bedrock map for the Antarctic Peninsula", The Cryosphere, 8, 1261-1273, doi:10.5194/tc-8-1261-2014.

http://www.the-cryosphere.net/8/1261/2014/tc-8-1261-2014.html

Abstract: "Assessing and projecting the dynamic response of glaciers on the Antarctic Peninsula to changed atmospheric and oceanic forcing requires high-resolution ice thickness data as an essential geometric constraint for ice flow models. Here, we derive a complete bedrock data set for the Antarctic Peninsula north of 70° S on a 100 m grid. We calculate distributed ice thickness based on surface topography and simple ice dynamic modelling. Our approach is constrained with all available thickness measurements from Operation IceBridge and gridded ice flow speeds for the entire study region. The new data set resolves the rugged subglacial topography in great detail, indicates deeply incised troughs, and shows that 34% of the ice volume is grounded below sea level. The Antarctic Peninsula has the potential to raise global sea level by 69 ± 5 mm. In comparison to Bedmap2, covering all Antarctica on a 1 km grid, a significantly higher mean ice thickness (+48%) is found."

[AbruptSLR]

The linked reference has an open access pdf documenting the glacial ice loss pattern in the northern Antarctic Peninsula:

Scambos, T. A., Berthier, E., Haran, T., Shuman, C. A., Cook, A. J., Ligtenberg, S. R. M., and Bohlander, J., 2014, "Detailed ice loss pattern in the northern Antarctic Peninsula: widespread decline driven by ice front retreats", The Cryosphere, 8, 2135-2145, doi:10.5194/tc-8-2135-2014.

http://www.the-cryosphere.net/8/2135/2014/tc-8-2135-2014.html

Abstract: "The northern Antarctic Peninsula (nAP, < 66° S) is one of the most rapidly changing glaciated regions on earth, yet the spatial patterns of its ice mass loss at the glacier basin scale have to date been poorly documented. We use satellite laser altimetry and satellite stereo-image topography spanning 2001–2010, but primarily 2003–2008, to map ice elevation change and infer mass changes for 33 glacier basins covering the mainland and most large islands in the nAP. Rates of ice volume and ice mass change are 27.7± 8.6 km3 a−1 and 24.9± 7.8 Gt a−1, equal to −0.73 m a−1 w.e. for the study area. Mass loss is the highest for eastern glaciers affected by major ice shelf collapses in 1995 and 2002, where twelve glaciers account for 60% of the total imbalance. However, losses at smaller rates occur throughout the nAP, at both high and low elevation, despite increased snow accumulation along the western coast and ridge crest. We interpret the widespread mass loss to be driven by decades of ice front retreats on both sides of the nAP, and extended throughout the ice sheet due to the propagation of kinematic waves triggered at the fronts into the interior."

[AbruptSLR]

The linked article indicates that following its current rate of degradation it could take centuries for the Larsen C Ice Shelf, LCIS, to collapse.  On the other hand if future surface ice melting activates melt-pond failure mechanisms (ie hydrofracturing), then the collapse date could be brought forward considerably.

Holland, P. R., Brisbourne, A., Corr, H. F. J., McGrath, D., Purdon, K., Paden, J., Fricker, H. A., Paolo, F. S., and Fleming, A. H. , (2015) "Atmospheric and oceanic forcing of Larsen C Ice Shelf thinning", The Cryosphere Discuss., 9, 251-299, doi:10.5194/tcd-9-251-2015.

http://www.the-cryosphere-discuss.net/9/251/2015/tcd-9-251-2015.html

Abstract: "The catastrophic collapses of Larsen A and B ice shelves on the eastern Antarctic Peninsula have caused their tributary glaciers to accelerate, contributing to sea-level rise and freshening the Antarctic Bottom Water formed nearby. The surface of Larsen C Ice Shelf (LCIS), the largest ice shelf on the peninsula, is lowering. This could be caused by unbalanced ocean melting (ice loss) or enhanced firn melting and compaction (englacial air loss). Using a novel method to analyse eight radar surveys, this study derives separate estimates of ice and air thickness changes during a 15 year period. The uncertainties are considerable, but the primary estimate is that the surveyed lowering (0.066 ± 0.017 m yr−1) is caused by both ice loss (0.28 ± 0.18 m yr−1) and firn air loss (0.037 ± 0.026 m yr−1). Though the ice loss is much larger, ice and air loss contribute approximately equally to the lowering. The ice loss could be explained by high basal melting and/or ice divergence, and the air loss by low surface accumulation or high surface melting and/or compaction. The primary estimate therefore requires that at least two forcings caused the surveyed lowering. Mechanisms are discussed by which LCIS stability could be compromised in future, suggesting destabilisation timescales of a few centuries. The most rapid pathways to collapse are offered by a flow perturbation arising from the ungrounding of LCIS from Bawden Ice Rise, or ice-front retreat past a "compressive arch" in strain rates."

[AbruptSLR]

The following linked reference (with a free pdf) reports that recent extensions of rift in the Larsen C Ice Shelf could soon result in the largest calving event since the 1980's (see attached images):

Jansen, D., Luckman, A. J., Cook, A., Bevan, S., Kulessa, B., Hubbard, B., and Holland, P. R.: Brief Communication: Newly developing rift in Larsen C Ice Shelf presents significant risk to stability, The Cryosphere Discuss., 9, 861-872, doi:10.5194/tcd-9-861-2015, 2015.

http://www.the-cryosphere-discuss.net/9/861/2015/tcd-9-861-2015.pdf

Abstract. An established rift in the Larsen C Ice Shelf, formerly constrained by a suture zone containing marine ice, grew rapidly during 2014 and is likely in the near future to generate the largest calving event since the 1980s and result in a new minimum area for the ice shelf. Here we investigate the recent development of the rift, quantify the projected calving event and, using a numerical model, assess its likely impact on ice shelf stability. We find that the ice front is at risk of becoming unstable when the anticipated calving event occurs.

Edit: For those better set-up than me to handle large files, high-resolution images of the Larsen C Ice Shelf can be regularly downloaded from:

http://www.polarview.aq/antarctic

[AbruptSLR]

Attached is a Landsat8 image of the Larsen C rift on January 15, 2015

[Jester Fish]

Record high temp for Antarctica ....just another thing, nothing to see here.....move along folks... http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2944

[AbruptSLR]

Here is a Worldview image of Larsen C on March 27 2015, indicating essentially no change from January 2015.

[AbruptSLR]

The linked article (with an open access pdf) discusses the latest evidence documenting how much local ice mass loss has be accelerated due to the loss of the Larsen B Ice Shelf in 2002:

Wuite, J., Rott, H., Hetzenecker, M., Floricioiu, D., De Rydt, J., Gudmundsson, G. H., Nagler, T., and Kern, M.: Evolution of surface velocities and ice discharge of Larsen B outlet glaciers from 1995 to 2013, The Cryosphere, 9, 957-969, doi:10.5194/tc-9-957-2015, 2015.

http://www.the-cryosphere.net/9/957/2015/tc-9-957-2015.html

Abstract. We use repeat-pass SAR data to produce detailed maps of surface motion covering the glaciers draining into the former Larsen B Ice Shelf, Antarctic Peninsula, for different epochs between 1995 and 2013. We combine the velocity maps with estimates of ice thickness to analyze fluctuations of ice discharge. The collapse of the central and northern sections of the ice shelf in 2002 led to a near-immediate acceleration of tributary glaciers as well as of the remnant ice shelf in Scar Inlet. Velocities of most of the glaciers discharging directly into the ocean remain to date well above the velocities of the pre-collapse period. The response of individual glaciers differs and velocities show significant temporal fluctuations, implying major variations in ice discharge as well. Due to reduced velocity and ice thickness the ice discharge of Crane Glacier decreased from 5.02 Gt a−1 in 2007 to 1.72 Gt a−1 in 2013, whereas Hektoria and Green glaciers continue to show large temporal fluctuations in response to successive stages of frontal retreat. The velocity on Scar Inlet ice shelf increased 2–3-fold since 1995, with the largest increase in the first years after the break-up of the main section of Larsen B. Flask and Leppard glaciers, the largest tributaries to Scar Inlet ice shelf, accelerated. In 2013 their discharge was 38% and 46% higher than in 1995.

[AbruptSLR]

Climate Central's take on the threat to the stability of Larsen C Ice Shelf:

http://www.climatecentral.org/news/antarctic-ice-shelf-melting-18987

Extract: "The biggest threats to the ice shelf’s stability, Holland thinks, come from indications it could unpin itself from an island that helps slow its flow, as well as a rift that has formed across the ice. If that rift reaches more vulnerable parts of the ice sheet, it could seriously destabilize it."

[Jim Hunt]

A recent acceleration in ice loss in a previously stable region of Antarctica has been detected by ESA’s CryoSat-2 mission.

http://www.esa.int/Our_Activities/Observing_the_Earth/CryoSat/CryoSat_detects_sudden_ice_loss_in_Southern_Antarctic_Peninsula

The latest findings by a team of scientists from the UK’s University of Bristol show that with no sign of warning, multiple glaciers along the Southern Antarctic Peninsula suddenly started to shed ice into the ocean starting in 2009 at rate of about 60 cubic km each year.

The findings were published in Science yesterday.

http://www.sciencemag.org/content/348/6237/899.full

[Gray-Wolf]

I'd been following the progress of the 'warm bottom waters' as they pushed out from the peninsula ( after undercutting the strengthened circumpolar current by flowing through submarine canyons) as I hold concerns of their impacts on Ross ( esp. Roosevelt Island end of the shelf Which appears esp. disrupted by Crevasses).

 We were told that the waters arrived there back in 2012. The study appears to show us just what happens in the years after its arrival in a region?

[Rick Aster]

The story as covered by Jonathan Amos in BBC News:

Antarctic Peninsula in 'dramatic' ice loss
http://www.bbc.com/news/science-environment-32837201

[solartim27]

I took a look at PIG today on Polarview and noticed this nice crack over by the Bellingshausen Sea.  It appears to be an unnamed area between Abbott and Ferrigno from this UCI map
http://www.ess.uci.edu/news/brennan20110818

Original image is 38 MB
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20150522T033037_F2A5_S_1.final.jpg

Perhaps we need separate glacier threads like the Greenland pages have?

[Rick Aster]

The Washington Post story by Chris Mooney sheds some light on the instability of the southern Antarctic Peninsula.

To understand the problem here, it’s important to visualize what scientists call the ice shelf’s “grounding line” – the area where the ice mass simultaneously intersects with the bedrock below it and also the ocean in front of it. “The geometry of the bedrock … it’s below sea level and it dips inland” in this region, explains Bamber. “That geometry means that the grounding line is potentially unstable.”
“It only needs to change position slightly for it to move quite rapidly, and for a sustained period, further inland,” Bamber continues. “That’s the theory behind the instability of these sectors of West Antarctica and the peninsula.”

Yet another Antarctic ice mass is becoming destabilized, scientists report
http://www.washingtonpost.com/news/energy-environment/wp/2015/05/22/yet-another-antarctic-ice-mass-is-becoming-destabilized-scientists-report/

[J Cartmill]

Mauri Pelto has a post about another Antarctic ice shelf showing signs of instability.

http://blogs.agu.org/fromaglaciersperspective/2015/05/17/developing-instability-of-verdi-ice-shelf-antarctica-extensive-rift-formation/

[mspelto]

AbruptSLR:  The basal crevasses have been the focus of research for sometime by the British Antarctic Survey, and this is the threat for rift development.  These can develop without surface melting, of which there is little on Larsen C.  I do not think the breakup of this ice shelf is imminent, but it is beginning to develop instability features.  http://blogs.agu.org/fromaglaciersperspective/2012/12/01/jones-ice-shelf-loss-antarctica/