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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.”
― Leon C. Megginson

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."
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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.
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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.”
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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 »
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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."
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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."
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AbruptSLR

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Re: Discussion of the Antarctic Peninsula
« Reply #67 on: February 06, 2018, 08:54:51 PM »
The linked reference looks a SLR contributions resulting from potential collapses of the Larsen C and George VI ice shelves:

Schannwell, C., Cornford, S., Pollard, D., and Barrand, N. E.: Dynamic response of Antarctic Peninsula Ice Sheet to collapse of Larsen C and George VI ice shelves, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-21, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-21/

Abstract. Ice shelf break-up and disintegration events over the past several decades have led to speed-up, thinning, and retreat of upstream tributary glaciers and increases to rates of global sea-level rise. The southward progression of these episodes indicates a climatic cause, and in turn suggests that the larger Larsen C and George VI ice shelves may undergo similar collapse in future. However, the extent to which removal of Larsen C and George VI ice shelves will affect upstream tributary glaciers and add to global sea levels is unknown. Here we apply numerical ice-sheet models of varying complexity to show that the centennial sea-level commitment of Larsen C embayment glaciers following immediate shelf collapse is low (< 2.5 mm to 2100, < 4.3 mm to 2300). Despite its large size, Larsen C does not provide strong buttressing forces to upstream basins and its collapse does not result in large additional discharge from its tributary glaciers in any of our model scenarios. In contrast, the response of inland glaciers to collapse of George VI Ice Shelf may add up to 8 mm to global sea levels by 2100 and 22 mm by 2300 due in part to the mechanism of marine ice sheet instability. Our results demonstrate the varying and relative importance to sea level of the large Antarctic Peninsula ice shelves considered to present a risk of collapse.
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Tealight

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Re: Discussion of the Antarctic Peninsula
« Reply #68 on: February 18, 2018, 09:56:36 PM »
Just for fun I created a gif to watch the snow melting on Anvers island (Palmer Station).

I downloaded the webcam image every day at 16:00UTC which should be 13:00 local time. Apart from the snow melting it's also possible to see the tide going up and down. The gif is a whole month from 18 January until 18 February.

Animation needs a click to start

All images from: https://www.usap.gov/videoclipsandmaps/palWebCam.cfm

AbruptSLR

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Re: Discussion of the Antarctic Peninsula
« Reply #69 on: May 08, 2018, 12:00:32 AM »
The linked reference discusses new findings w.r.t. Antarctic Peninsula Ice Shelves:

Susheel Adusumilli et al. (31 March 2018), "Variable Basal Melt Rates of Antarctic Peninsula Ice Shelves, 1994–2016", Geophysical Research Letters, https://doi.org/10.1002/2017GL076652

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076652

Abstract: "We have constructed 23‐year (1994–2016) time series of Antarctic Peninsula (AP) ice‐shelf height change using data from four satellite radar altimeters (ERS‐1, ERS‐2, Envisat, and CryoSat‐2). Combining these time series with output from atmospheric and firn models, we partitioned the total height‐change signal into contributions from varying surface mass balance, firn state, ice dynamics, and basal mass balance. On the Bellingshausen coast of the AP, ice shelves lost 84 ± 34 Gt a−1 to basal melting, compared to contributions of 50 ± 7 Gt a−1 from surface mass balance and ice dynamics. Net basal melting on the Weddell coast was 51 ± 71 Gt a−1. Recent changes in ice‐shelf height include increases over major AP ice shelves driven by changes in firn state. Basal melt rates near Bawden Ice Rise, a major pinning point of Larsen C Ice Shelf, showed large increases, potentially leading to substantial loss of buttressing if sustained."
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AbruptSLR

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Re: Discussion of the Antarctic Peninsula
« Reply #70 on: May 25, 2018, 04:01:23 PM »
The linked open access reference evaluates critical factors that contribute to the probability that the Larsen C Ice Shelf might collapse suddenly (as was the case for the Larsen B Ice Shelf in 2002):

Buzzard, S., Feltham, D., and Flocco, D.: Modelling the fate of surface melt on the Larsen C Ice Shelf, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-84, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-84/

Abstract. Surface melt lakes lower the albedo of ice shelves leading to additional surface melting. This can substantially alter the surface energy balance and internal temperature and density profiles of the ice shelf. Evidence suggests that melt lakes also played a pivotal role in the sudden collapse of the Larsen B Ice Shelf in 2002.

Here a recently developed, high physical fidelity model accounting for the development cycle of melt lakes is applied to the Larsen C Ice Shelf, Antarctica’s most northern ice shelf and one where melt lakes have been observed. We simulate current conditions on the ice shelf using weather station and reanalysis data, and investigate the impacts of potential future increases in precipitation and air temperature on melt lake formation, where concurrent increases lead to an increase in lake depth.

Finally, we assess the viability of future crevasse propagation through the ice shelf due to surface meltwater accumulation.
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Tor Bejnar

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Re: Discussion of the Antarctic Peninsula
« Reply #71 on: January 09, 2019, 05:04:33 PM »
Muller Ice Shelf, Antarctica 2018 Calving Event
This article in From a Glacier's Perspective describes see-sawing growth and shrinking of the Müller Ice Shelf (on the west coast of the Antarctic Peninsula) over the last seven decades, with Landsat images from 2016, '17 and '18.
Quote
This [2018 calving] is small by Antarctic standards, but large for the Muller Ice Shelf. The decreased connection to Humphreys Island and the expanding rift area indicates that the Muller Ice Shelf is poised for disintegration like what occurred on nearby Jones Ice Shelf and what is poised to occur on Verdi Ice Shelf.
[Wikipedia image has Verdi Ice Shelf reference added - there are named ice shelves in many of the inlets, e.g., see here]
« Last Edit: January 09, 2019, 05:11:22 PM by Tor Bejnar »
Arctic ice is healthy for children and other living things.

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Re: Discussion of the Antarctic Peninsula
« Reply #72 on: June 21, 2019, 02:27:19 PM »
Role of the South Pacific Convergence Zone in West Antarctic Decadal Climate Variability

First published: 23 May 2019 https://doi.org/10.1029/2019GL082108

Abstract
Regional atmospheric circulation along coastal West Antarctica associated with the Amundsen Sea Low (ASL) mediates ice shelf melt that governs Antarctica's contribution to global sea level rise. In this study, the South Pacific Convergence Zone (SPCZ) is identified as a significant driver of ASL variability on decadal time scales. Using the Community Earth System Model, we impose a positive sea surface temperature anomaly in the SPCZ that reproduces an increase in convective rainfall in the southwest SPCZ that has been observed in recent decades, consistent with the negative phase of the Interdecadal Pacific Oscillation (IPO). Many of the major climate shifts across West Antarctica during the 2000‐2014 period when the IPO was negative can be explained via a teleconnection over the ASL emanating from the SPCZ. Knowledge of these relationships significantly enhances our understanding and interpretation of past and future West Antarctic climate variability.

Plain Language Summary
Heavy convective rainfall in the South Pacific Convergence Zone (SPCZ) alters the regional atmospheric circulation along coastal West Antarctica, impacting the regional climate and potentially driving warm ocean water upwelling that melts ice shelves. Increases in SPCZ rainfall cause cooling on the Antarctic Peninsula and warming across the Ross Ice Shelf and portions of East Antarctica. Such conditions were observed during the 2000‐2014 period in which the phase of the Interdecadal Pacific Oscillation, a naturally occurring mode of tropical Pacific decadal variability, was negative. The influence of the SPCZ on West Antarctic climate is consistent with observed shifts in West Antarctic climate over the period 2000‐2014. Therefore, the SPCZ, though a tropical climate feature, is found to be an important driver of West Antarctic climate on decadal time scales governed by the Interdecadal Pacific Oscillation.

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL082108

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bligh8

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Re: Discussion of the Antarctic Peninsula
« Reply #73 on: June 25, 2019, 03:46:01 PM »
http://www-odp.tamu.edu/publications/178_SR/VOLUME/CHAPTERS/SR178_23.PDF

This is an older paper but nonetheless a fascinating read.

This paper is in a pdf format and discusses Ocean regional and Global circulation and how Antarctica sea ice effects the productivity in the Bellingshausen sea & changes in global climate effects productivity.

 

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Re: Discussion of the Antarctic Peninsula
« Reply #74 on: June 26, 2019, 04:28:31 PM »
Erosion and deposition beneath the Subantarctic Front since the Early Oligocene
https://www.nature.com/articles/s41598-019-45815-7

Published: 26 June 2019....open access

Abstract
The Antarctic Circumpolar Current (ACC) spills across the Falkland Plateau into the South Atlantic as a series of high-velocity jets. These currents are a driving force for global overturning circulation, and affect climate by modulating CO2 exchange between the atmosphere and ocean, but their timing of onset remains controversial. We present new evidence of strong currents associated with the Subantarctic Front (SAF) jet since the earliest Oligocene (~34 Ma) based on a widespread erosional surface on the Falkland Plateau, preserved below a 30,000 km2 contourite sand deposit. This is the largest such feature ever to be recognized, and provides the most robust constraint of the initiation of the SAF to date. By contrast, the South Falkland Slope Drift is dominated by contourite mud of Pleistocene-Recent age, substantially younger than previous estimates, indicating a significant decrease in long-term current strength at that time. As ACC strength is primarily a function of the position of the South-Westerly Winds, our data indicates that associated currents are likely to increase substantially in a warming world. Likely implications include increased upwelling and associated carbon flux from the deep ocean to the atmosphere, a positive feedback loop not included in most future projections of atmospheric CO2.

Kraken breath?

I attached two Figures....more within the document 

Figure 1

(A) Topographic features, plate tectonic and oceanographic setting of the Falkland Plateau (FP; outline in black dashed line), showing locations of main fronts of the Antarctic Circumpolar Current, including the Subantarctic Front (SAF), Polar Front (PF) and Southern Antarctic Circumpolar Current Front (SACCF)15. The yellow star shows the location of the 54–54 passage, where the SAF crosses the North Scotia Ridge between Burdwood Bank and Davis Bank. Image created using GeoMapApp. (B) Salinity and velocity data across the Falkland Plateau from the World Ocean Atlas, created using Ocean Data View software48. Blue dashed line shows the pycnoclines between water masses, including Subantarctic Mode Water (SAMW), Antarctic Intermediate Water (AAIW), Upper Circumpolar Deep Water (UCDW), and Lower Circumpolar Deep Water (LCDW). White dashed lines are velocity contours (in cm/s), measured using acoustic doppler current profilers on a parallel transect17, and show the location of the SAF and the PF. FT is the Falkland Terrace (C) Location map of the western Falkland Plateau showing depth contours (in metres), seismic and well data, and main sedimentary/geomorphological features associated with the SAF, including the main contourite drifts and the Falkland Terrace and the individual sand deposits that make up the Falkland Sand Sheet, based on the presence of high impedance seismic packages with distinct geomorphological features at the seafloor. SFSD – South Falkland Slope Drift; LFSD – Lower Falkland Slope Drift.

Figure 3
Seismic attributes from 3D data across the Falkland Terrace and Falkland Sand Sheet. Locations of the FINA (A) and FISA (B) survey are shown in Fig. 1. Attributes include depth, dip angle and absolute amplitude for both surveys, as well as an isopach (sediment thickness) map of the sand sheet for the FINA survey. ‘Warm’ colours (green-red) on the amplitude maps represent sand, which has a higher acoustic impedance than shale near the seafloor. The main geomorphological features annotated on the maps include individual sand sheets (ss), sand ribbons (sr), circular-elliptical scours (cs), erosional remnants (er) and escarpments (es), all of which are produced by bottom currents associated with the Subantarctic Front.




sidd

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Re: Discussion of the Antarctic Peninsula
« Reply #75 on: June 26, 2019, 07:53:51 PM »
Nice paper. They mention there are two shallow wells by BHP through that shallow  region, i wonder  if accurate dating of the opening of the Drake passage is possible with deeper cores ?

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Re: Discussion of the Antarctic Peninsula
« Reply #76 on: June 28, 2019, 12:22:36 AM »
I dunno Mr sidd.....thnks for your always observant question.  you sir have been reading the results & related science from these boreholes since.. God left Chicago, yes?  They do mention the widening & deepening of the Drake some 25 Ma in this paper & their BHP 200meter deep boreholes. They used what?..the Toroa#1 for this study, again 200meters deep...  Anyway, I do enjoy reading bout this stuff

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Re: Discussion of the Antarctic Peninsula
« Reply #77 on: July 13, 2019, 04:32:24 PM »
Zooplankton and micronekton respond to climate fluctuations in the Amundsen Sea polynya, Antarctica

https://www.nature.com/articles/s41598-019-46423-1

Abstract
The vertical migration of zooplankton and micronekton (hereafter ‘zooplankton’) has ramifications throughout the food web. Here, we present the first evidence that climate fluctuations affect the vertical migration of zooplankton in the Southern Ocean, based on multi-year acoustic backscatter data from one of the deep troughs in the Amundsen Sea, Antarctica. High net primary productivity (NPP) and the annual variation in seasonal ice cover make the Amundsen Sea coastal polynya an ideal site in which to examine how zooplankton behavior responds to climate fluctuations. Our observations show that the timing of the seasonal vertical migration and abundance of zooplankton in the seasonally varying sea ice is correlated with the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO). Zooplankton in this region migrate seasonally and overwinter at depth, returning to the surface in spring. During +SAM/La Niña periods, the at-depth overwintering period is shorter compared to −SAM/El Niño periods, and return to the surface layers starts earlier in the year. These differences may result from the higher sea ice cover and decreased NPP during +SAM/La Niña periods. This observation points to a new link between global climate fluctuations and the polar marine food web.

Introduction
Zooplankton are an essential link between primary producers and higher trophic levels. The vertical migration of zooplankton moves a massive biomass within the water column with impacts on trophic interactions and biogeochemical cycles1,2. Zooplankton feed on primary producers, repackaging organic matter into rapidly sinking fecal pellets, and their vertical migration can be an important mechanism for carbon export and sequestration to depth3. Active vertical migration of zooplankton could contribute up to a 14% increase in carbon sinking from the euphotic zone into deeper water4.

Rapid climate change has been shown to drive significant physical and ecological changes9,10,11,12. In the Southern Ocean, these changes include ocean warming13, glacial melt and retreat14, and sea ice loss15. These alterations of the marine environment impact phytoplankton16,17,18, zooplankton19,20,21,22, fish, and penguins23,24, although the relative roles of climate and overfishing have complicated the interpretation of higher predator responses. The region’s annual variability of phytoplankton biomass and sea ice concentration (SIC) is closely related to climate shifts25,26. ENSO and SAM are significant drivers of the trend of SIC and thereby help to control the conditions for phytoplankton growth. The Amundsen Sea is located in one of the most rapidly warming regions on Earth27. This region is presently undergoing a rapid reduction in sea ice16 and retreat and thinning of glaciers28,29 and harbors one of the most productive coastal polynyas (per unit area) in the Southern Ocean30.
Here, we present results obtained from satellite remote sensing (surface solar radiation (SSR), SIC and NPP) and subsurface moored instrumentation (acoustic backscatter and sediment traps) from 2010 to 2013 (see Methods for a detailed description of the measurements). These results represent the longest existing continuous record of acoustic backscatter from a highly productive polynya, coinciding with a period of cooling and heavy sea ice years.

During our study, the Amundsen Sea shelf area had a seasonal ice cover with an expanding polynya from January to March (Fig. 1 and Supplementary Fig. S1). Between 2010 and 2013, the mean NPP in the area peaked in January (Supplementary Fig. S2), co-varying with the SIC and SSR (Fig. 1a). The mean NPP (nearly all taking place during summer) decreased from 789 to 493 mg C m−2 d−1 between 2010 and 2013. During the same period, the mean SIC increased by 15%. The interannual variation in SIC was strongly correlated to the summertime NPP (r = −0.73, p < 0.05) and the annual NPP peak as expected31 coincided with the SIC minimum. This implies that the intense phytoplankton bloom is triggered by the increase in open water area (Supplementary Fig. S3).