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Author Topic: Discussion of the Antarctic Peninsula  (Read 30522 times)

AbruptSLR

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Re: Discussion of the Antarctic Peninsula
« Reply #50 on: May 26, 2015, 05:36:12 PM »
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/


Thanks for the update, but I am currently taking a hiatus from posting until after July 4 2015.
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AbruptSLR

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Re: Discussion of the Antarctic Peninsula
« Reply #51 on: July 07, 2015, 02:23:44 AM »
The linked reference (with an open access pdf) provides both field evidence and analysis that the Larsen C is at risk of imminent collapse by at least two different mechanisms:

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.: Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning, The Cryosphere, 9, 1005-1024, doi:10.5194/tc-9-1005-2015, 2015.

http://www.the-cryosphere.net/9/1005/2015/tc-9-1005-2015.html
http://www.the-cryosphere.net/9/1005/2015/tc-9-1005-2015.pdf

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). The ice loss is much larger than the air loss, but both contribute approximately equally to the lowering because the ice is floating. 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 the future. The most rapid pathways to collapse are offered by the ungrounding of LCIS from Bawden Ice Rise or ice-front retreat past a "compressive arch" in strain rates. Recent evidence suggests that either mechanism could pose an imminent risk."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Whit

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Re: Discussion of the Antarctic Peninsula
« Reply #53 on: January 10, 2016, 06:57:07 PM »
Larsen has the blues.

http://go.nasa.gov/1OIprQU
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AbruptSLR

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Re: Discussion of the Antarctic Peninsula
« Reply #54 on: January 11, 2016, 02:14:35 AM »
Larsen has the blues.

http://go.nasa.gov/1OIprQU


Does anyone know whether this blue indicates the presences of surface ice meltwater?
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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nukefix

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Re: Discussion of the Antarctic Peninsula
« Reply #55 on: January 11, 2016, 10:16:40 AM »
Larsen has the blues.

http://go.nasa.gov/1OIprQU


Does anyone know whether this blue indicates the presences of surface ice meltwater?

Those blue areas are on sea-ice, not on shelf-ice.

AbruptSLR

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Re: Discussion of the Antarctic Peninsula
« Reply #56 on: January 11, 2016, 04:12:09 PM »
Larsen has the blues.

http://go.nasa.gov/1OIprQU


Does anyone know whether this blue indicates the presences of surface ice meltwater?

Those blue areas are on sea-ice, not on shelf-ice.

nukefix,

Thanks.  Now that I look more closely, clearly your are correct.

Best,
ASLR
“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 the Antarctic Peninsula
« Reply #57 on: April 01, 2016, 07:01:33 PM »
The linked reference discusses the role of large-scale atmospheric oscillations (PDO, SOI & SAM) on the accumulation of snow in the Antarctic Peninsula:

Bradley P. Goodwin, Ellen Mosley-Thompson, Aaron B. Wilson, Stacy E. Porter and M. Roxana Sierra-Hernandez (2016), "Accumulation Variability in the Antarctic Peninsula: The Role of Large-Scale Atmospheric Oscillations and Their Interactions", Journal of Climate, DOI: http://dx.doi.org/10.1175/JCLI-D-15-0354.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0354.1

Abstract: "A new ice core drilled in 2010 to bedrock from the Bruce Plateau (BP) on the Antarctic Peninsula (AP) provides a high temporal resolution record of environmental conditions in this region. The extremely high annual accumulation rate at this site facilitates analysis of the relationships between annual net accumulation An on the BP and large-scale atmospheric oscillations. Over the last ~45 years, An on the BP has been positively correlated with both the southern annular mode (SAM) and Southern Oscillation index (SOI). Extending this analysis back to 1900 reveals that these relationships are not temporally stable, and they exhibit major shifts in the late-1940s and the mid-1970s that are contemporaneous with phase changes in the Pacific decadal oscillation (PDO). These varying multidecadal characteristics of the An–oscillation relationships are not apparent when only data from the post-1970s era are employed. Analysis of the longer ice core record reveals that the influence of the SAM on An depends not only on the phase of the SAM and SOI but also on the phase of the PDO. When the SAM’s influence on BP An is reduced, such as under negative PDO conditions, BP An is modulated by variability in the tropical and subtropical atmosphere through its impacts on the strength and position of the circumpolar westerlies in the AP region. These results demonstrate the importance of using longer-term ice core–derived proxy records to test conventional views of atmospheric circulation variability in the AP region."
“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 the Antarctic Peninsula
« Reply #58 on: April 08, 2016, 07:04:28 PM »
The first image from DeConto & Pollard (2016) indicates that ice mass loss contribution to SLR will peak first from the Antarctic Peninsula will peak first before other AIS sources.

The second image of the Larsen C South Cracks per Sentinel on April 7 2016, indicates just how wide these cracks are becoming.
“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 the Antarctic Peninsula
« Reply #59 on: June 15, 2016, 10:07:16 PM »
With a hat-tip to GeoffBeacon, the linked reference indicates that repeated drainage of surface meltwater likely formed a massive subsurface ice layer within the Larsen C Ice Shelf; which raises concerns not only about the fragility of the Larsen C Ice Shelf, but also of future fragility of other Antarctic ice shelves

Bryn Hubbard, Adrian Luckman, David W. Ashmore, Suzanne Bevan, Bernd Kulessa, Peter Kuipers Munneke, Morgane Philippe, Daniela Jansen, Adam Booth, Heidi Sevestre, Jean-Louis Tison, Martin O’Leary & Ian Rutt  (2016), "Massive subsurface ice formed by refreezing of ice-shelf melt ponds", Nature Communications, Volume: 7, Article number: 11897, doi:10.1038/ncomms11897


http://www.nature.com/ncomms/2016/160610/ncomms11897/full/ncomms11897.html

Abstract: "Surface melt ponds form intermittently on several Antarctic ice shelves. Although implicated in ice-shelf break up, the consequences of such ponding for ice formation and ice-shelf structure have not been evaluated. Here we report the discovery of a massive subsurface ice layer, at least 16 km across, several kilometres long and tens of metres deep, located in an area of intense melting and intermittent ponding on Larsen C Ice Shelf, Antarctica. We combine borehole optical televiewer logging and radar measurements with remote sensing and firn modelling to investigate the layer, found to be ~10 °C warmer and ~170 kg m−3 denser than anticipated in the absence of ponding and hitherto used in models of ice-shelf fracture and flow. Surface ponding and ice layers such as the one we report are likely to form on a wider range of Antarctic ice shelves in response to climatic warming in forthcoming decades."

See also (& the associated image):

http://www.carbonbrief.org/discovery-exposes-fragility-of-antarcticas-larsen-c-ice-shelf

Extract: "Meltponds tend to form in a line “like a string of sausages” and are thought to have contributed to the collapse of ice shelves in the past, including Larsen B.

...

Until now, scientists had suspected that meltponds exerted stress through the sheer weight of the water pushing down on the ice below it. But Hubbard and his team wondered if there was a different explanation. He tells Carbon Brief:

“The rationale for our project was to investigate whether the ponds had an influence on the internal structure of the underlying ice shelf.”

...

The team drilled a 100m-long borehole in a part of the Larsen-C ice shelf called Cabinet Inlet, where scientists first spotted meltponds 15 years ago.

Just a few metres below the surface, they struck upon a layer of solid ice about 100 metres thick, formed as water from the meltponds percolates through the ice and refreezes.

...

The vast icy layer below Larsen C is a concern, says Hubbard. It is warmer than the compacted snow it replaced because of the latent heat that is released as the percolating meltwater refreezes at depth. Thi, in turn affects how the ice moves, Hubbard explains:

“Similar to syrup, warm ice flows more readily than cold ice.”

Hubbard and his team installed a string of instruments to take measurements within the icy layer, returning to collect the data a year later. They found temperatures of between -5C and -10C, a full 10C above what they expected for this depth range. Hubbard says:

“This suggests that not only is the massive ice layer denser than that which would be present in the absence of surface ponds, but that it is also substantially warmer, both having implications for the movement and stability of the ice shelf.”"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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TerryM

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Re: Discussion of the Antarctic Peninsula
« Reply #60 on: June 15, 2016, 11:13:54 PM »
ASLR
If this region of increased mass is present in all Antarctic ice shelves I would expect that more water would be released when melt-out occurs than had otherwise been accounted for. Is there any indication that this only occurs on this particular shelf, or is it expected to be found in all ice shelves in the Antarctic? & Arctic? If this is more ubiquitous, is the increased mass large enough to alter sea level projections?
Terry

AbruptSLR

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Re: Discussion of the Antarctic Peninsula
« Reply #61 on: June 16, 2016, 12:02:31 AM »
ASLR
If this region of increased mass is present in all Antarctic ice shelves I would expect that more water would be released when melt-out occurs than had otherwise been accounted for. Is there any indication that this only occurs on this particular shelf, or is it expected to be found in all ice shelves in the Antarctic? & Arctic? If this is more ubiquitous, is the increased mass large enough to alter sea level projections?
Terry

Current this phenomena only occurs in ice shelves that have frequent meltpond formation, such as those in the Antarctic Peninsula; as more southerly ice shelves do not have frequent meltpond formation because it is currently too cold.  However, per DeConto & Pollard (2016) when the GMST departures exceed about 2.7C meltponds will frequently form in more southerly ice shelves like FRIS & RIS; which, might then induce both hydrofracturing and also this newly identified subsurface ice lense/layer formation mechanism.
“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 the Antarctic Peninsula
« Reply #62 on: July 15, 2016, 11:07:38 AM »
With a hat-tip to sidd, the linked reference indicates that ocean-induced (CDW-induced) glacial melt is the main factor inducing SLR contribution from the Antarctic Peninsula"


Cook, A. J., P. R. Holland, M. P. Meredith, T. Murray, A. Luckman & D. G. Vaughan (July 15 2016), "Ocean forcing of glacier retreat in the western Antarctic Peninsula", Science, doi:10.1126/science.aae0017

http://science.sciencemag.org/content/353/6296/283

Abstract: "In recent decades, hundreds of glaciers draining the Antarctic Peninsula (63° to 70°S) have undergone systematic and progressive change. These changes are widely attributed to rapid increases in regional surface air temperature, but it is now clear that this cannot be the sole driver. Here, we identify a strong correspondence between mid-depth ocean temperatures and glacier-front changes along the ~1000-kilometer western coastline. In the south, glaciers that terminate in warm Circumpolar Deep Water have undergone considerable retreat, whereas those in the far northwest, which terminate in cooler waters, have not. Furthermore, a mid-ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat. We conclude that changes in ocean-induced melting are the primary cause of retreat for glaciers in this region."


See also:

https://www.carbonbrief.org/warmer-oceans-driving-antarctic-peninsula-glacier-melt-study-says

Extract: "The Antarctic Peninsula is one of the largest current contributors to sea level rise, says Cook, so pinpointing the reasons why their glaciers are changing is important:

“The glaciers here are highly sensitive to changes in the environment and are key indicators of how the ice will respond to future changes.”
Knowing the impact that a warming ocean is having on the Peninsula’s glaciers will help scientists improve predictions of sea level rise for the century ahead, she concludes."

&

A. J. Cook, A. J. Fox, D. G. Vaughan & J. G. Ferrigno (22 Apr 2005), "Retreating Glacier Fronts on the Antarctic Peninsula over the Past Half-Century", Science, Vol. 308, Issue 5721, pp. 541-544, DOI: 10.1126/science.1104235

http://science.sciencemag.org/content/308/5721/541

Abstract: "The continued retreat of ice shelves on the Antarctic Peninsula has been widely attributed to recent atmospheric warming, but there is little published work describing changes in glacier margin positions. We present trends in 244 marine glacier fronts on the peninsula and associated islands over the past 61 years. Of these glaciers, 87% have retreated and a clear boundary between mean advance and retreat has migrated progressively southward. The pattern is broadly compatible with retreat driven by atmospheric warming, but the rapidity of the migration suggests that this may not be the sole driver of glacier retreat in this region."
“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 the Antarctic Peninsula
« Reply #63 on: July 21, 2016, 12:33:26 AM »
The linked reference provides information about the natural variability of temperatures on the Antarctic Peninsula:

John Turner, Hua Lu, Ian White, John C. King, Tony Phillips, J. Scott Hosking, Thomas J. Bracegirdle, Gareth J. Marshall, Robert Mulvaney & Pranab Deb (21 July 2016), "Absence of 21st century warming on Antarctic Peninsula consistent with natural variability", Nature, Volume: 535, Pages: 411–415; doi:10.1038/nature18645

http://www.nature.com/nature/journal/v535/n7612/full/nature18645.html

Abstract: "Since the 1950s, research stations on the Antarctic Peninsula have recorded some of the largest increases in near-surface air temperature in the Southern Hemisphere. This warming has contributed to the regional retreat of glaciers, disintegration of floating ice shelves and a ‘greening’ through the expansion in range of various flora. Several interlinked processes have been suggested as contributing to the warming, including stratospheric ozone depletion, local sea-ice loss, an increase in westerly winds, and changes in the strength and location of low–high-latitude atmospheric teleconnections. Here we use a stacked temperature record to show an absence of regional warming since the late 1990s. The annual mean temperature has decreased at a statistically significant rate, with the most rapid cooling during the Austral summer. Temperatures have decreased as a consequence of a greater frequency of cold, east-to-southeasterly winds, resulting from more cyclonic conditions in the northern Weddell Sea associated with a strengthening mid-latitude jet. These circulation changes have also increased the advection of sea ice towards the east coast of the peninsula, amplifying their effects. Our findings cover only 1% of the Antarctic continent and emphasize that decadal temperature changes in this region are not primarily associated with the drivers of global temperature change but, rather, reflect the extreme natural internal variability of the regional atmospheric circulation."

Also see:

https://www.carbonbrief.org/natural-forces-overpowering-antarctic-peninsula-warming

Extract: "In the latter half of the 20th century, the tip of the Antarctic Peninsula was among the fastest warming places on Earth. But since the late 1990s, this fast-paced warming has been tempered by extreme natural forces, according to new research. So much so, that some parts have switched to cooling.
In many ways, the results are unsurprising. Scientists know that natural variability superimposes temporary ups and downs on top of greenhouse gas-induced warming everywhere on Earth."

Edit: I agree with Gavin Schmidt's sentiment on this paper:
« Last Edit: July 24, 2016, 05:19:36 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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AbruptSLR

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Re: Discussion of the Antarctic Peninsula
« Reply #64 on: August 03, 2016, 08:18:17 PM »
The linked reference discusses the relative influence of ENSO & SAM on Antarctic Peninsula climate:

Kyle R. Clem, James A. Renwick, James McGregor & Ryan L. Fogt (1 August 2016), "The Relative Influence of ENSO and SAM on Antarctic Peninsula Climate", Journal of Geophysical Research Atmospheres, DOI: 10.1002/2016JD0253051 August 2016

http://onlinelibrary.wiley.com/doi/10.1002/2016JD025305/abstract

Abstract: "Recent warming of the Antarctic Peninsula during austral autumn, winter, and spring has been linked to sea surface temperature (SST) trends in the tropical Pacific and tropical Atlantic, while warming of the northeast Peninsula during summer has been linked to a strengthening of westerly winds traversing the Peninsula associated with a positive trend in the Southern Annular Mode (SAM). Here we demonstrate that circulation changes associated with the SAM dominate interannual temperature variability across the entire Antarctic Peninsula during both summer and autumn, while relationships with tropical Pacific SST variability associated with the El Niño-Southern Oscillation (ENSO) are strongest and statistically significant primarily during winter and spring only. We find the ENSO-Peninsula temperature relationship during autumn to be weak on interannual timescales, and regional circulation anomalies associated with the SAM more important for interannual temperature variability across the Peninsula during autumn. Consistent with previous studies, western Peninsula temperatures during autumn, winter, and spring are closely tied to changes in the Amundsen Sea Low (ASL) and associated meridional wind anomalies. The interannual variability of ASL depth is most strongly correlated with the SAM index during autumn, while the ENSO relationship is strongest during winter and spring. Investigation of western and northeast Peninsula temperatures separately reveals that interannual variability of northeast Peninsula temperatures is primarily sensitive to zonal wind anomalies crossing the Peninsula and resultant lee-side adiabatic warming rather than to meridional wind anomalies, which is closely tied to variability in the zonal portion of the SAM pattern."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

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Re: Discussion of the Antarctic Peninsula
« Reply #65 on: May 02, 2017, 08:41:46 PM »
doi: 10.1002/2016GL072110

Most of the usual suspects among the authors. Evidence for CDW intrusion below 300m. Open access. Read all about it.

sidd

AbruptSLR

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Re: Discussion of the Antarctic Peninsula
« Reply #66 on: July 17, 2017, 11:20:49 PM »
New research indicates that strong winds in East Antarctica generate oceanic Kelvin waves that promote ice melting along the western side of the Antarctic Peninsula:

Title: "Stronger winds heat up West Antarctic ice melt"

https://www.eurekalert.org/pub_releases/2017-07/uons-swh071417.php

Extract: "Strengthening winds in the East Antarctic generate Kelvin waves that lead to increasing melting along the West Antarctic Peninsula.

New research published today in Nature Climate Change has revealed how strengthening winds on the opposite side of Antarctica, up to 6000kms away, drive the high rate of ice melt along the West Antarctic Peninsula.

Researchers from the ARC Centre of Excellence for Climate System Science found that the winds in East Antarctica can generate sea-level disturbances that propagate around the continent at almost 700 kilometers per hour via a type of ocean wave known as a Kelvin wave.

When these waves encounter the steep underwater topography off the West Antarctic Peninsula they push warmer water towards the large ice shelves along the shoreline. The warm Antarctic Circumpolar Current passes quite close to the continental shelf in this region, providing a source for this warm water."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson