Antarctic Peninsula ice shelves | Ice shelf collapse on the Antarctic Peninsula | Rifting on Larsen C | Impact of calving the large iceberg | Sea level rise following ice-shelf collapse | References | Comments |
Antarctic Peninsula ice shelves
The Antarctic Peninsula is fringed by floating ice shelves. They are floating extensions of the glaciers on land, and receive mass by snowfall and marine freeze-on. They lose mass by melting at their base and by calving icebergs. Larsen C Ice Shelf, the largest ice shelf on the Antarctic Peninsula, is currently being closely watched. Following a series of high-profile ice-shelf collapse events on the Antarctic Peninsula over the last few decades, all eyes are watching Larsen C and wondering when, and if, it will collapse.
A growing rift on Larsen C Ice Shelf
Those concerns are growing more acute as a large rift on Larsen C Ice Shelf is growing rapidly, threatening to soon calve a huge iceberg, equivalent to losing 10% of the area of the ice shelf. This could destabilise the ice shelf, making it more susceptible to a total collapse.
The Antarctic Peninsula is warming very rapidly, about six times the global average[1-3]. There has been a 95% increase in positive degree day sums since 1948. Glaciers in the region are accelerating, in response to frontal thinning and recession. In addition, ice shelves are collapsing, glacier fronts are retreating. The causes for much of these changes has often been attributed to ocean forcing, with warm ocean waters melting these glaciers from below[8-11]. However, while ocean forcing may dominate further south, such as at Pine Island Glacier, a few recent papers have highlighted the importance of surface processes and surface melt induced by warmer surface air temperatures and longer melt seasons, specifically on the Antarctic Peninsula. Continue reading
The Antarctic continent
Antarctica: the enigmatic, romantic, remote white continent. Antarctica lies at the bottom of the world and all waters south of 60°S latitude are designated Antarctic, where no country owns the land and where only scientific and peaceful operations may take place. Military activity is banned in Antarctica, and it is a haven for wildlife.
Unlike the Arctic, where floating sea ice annual melts and refreezes, Antarctica is a solid ice sheet lying on a solid continent1. The Antarctic summer is during the northern Hemisphere winter. Antarctica may be remote and isolated, but the dynamics of Antarctic glaciers affect us all.
Antarctica is huge. The Earth’s southernmost continent is twice the size of Australia, and 98% of it is covered by ice. Antarctica is cold (the coldest recorded temperature is -89°C, from Vostok), but the peripheral islands and Antarctic Peninsula may have positive air temperatures in summer.
There is no permanent human population in Antarctica, but around 1000 people, mostly scientists and support staff, overwinter each year. Summer populations can be as high as 5000 (excluding the many hundreds of visitors who briefly visit on tourist ships). The British Antarctic Survey maintains eight research stations and operates many summer field camps each year.
You can use Google Earth to explore Antarctica for yourself. You can see how the great continent is surrounded by cold ocean waters. Note the Antarctic Peninsula, the thin spine of mountains pointing towards South America, the huge flat and floating ice shelves, and the large, high, East Antarctic Ice Sheet.
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The Antarctic continent lies on a large landmass. Underneath that smooth ice sheet there are mountains and valleys.
The surface of the Antarctic Ice Sheet is up to 4000 m high, and in places the ice is 4000 m deep, but the Gamburtsev Mountain range is up to 2,700 m high and lies underneath the East Antarctic Ice Sheet.
The Transantarctic Mountains divide East and West Antarctica. This mountain range is 3500 km long and 100-300 km wide. The summits of these mountains poke through the ice to form some of the only ice-free areas of Antarctica; these ‘nunataks’ are up to 4,500 m high.
The Transantarctic Mountains contain some of the oldest glacial sediments in Antarctica, and the Sirius Group, from Mount Sirius, indicates that there has been ice here for at least 15 million years. This webpage has beautiful photographs of the Transantarctic Mountains.
You can use the Google Map below to easily explore the Transantarctic Mountains. You can see how they go through the ice sheet. In this map, the Byrd and Shackleton glaciers are in the centre, and they flow into the giant, floating, flat Ross Ice Shelf. How does this compare with the BEDMAP2 figures above and below?
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The first ice in Antarctica grew on the Transantarctic Mountains and Gamburtsev Mountains around 34 million years ago2, when global air temperatures were around 4°C warmer than today. Since then, with on-going cooling, the ice sheets have fluctuated, growing and shrinking at different timescales.
During the Quaternary Period, the ice sheets fluctuated first at 41,000 year timescales, and after around 1 million years ago, they fluctuated at 100,000 year timescales. These huge ice sheets came to dominate and influence the Earth’s climate and global sea levels. The last glacial cycle ended around 11,000 years ago and the Last Glacial Maximum was around 18,000 years ago.
The Antarctic ocean
There is a strong circumpolar circulation around Antarctica. This results in a cooler continent, as heat exchange from the tropics is limited. The circulation in the Weddell Sea brings ice bergs and cold water north, up the Antarctic Peninsula, and is one of the reasons why the eastern Antarctic Peninsula is much warmer than the western Antarctic Peninsula.
Antarctica is globally important, and not just because melting Antarctic glaciers have the potential to raise global sea levels. Cold, salty water forms around Antarctica, which sinks to the sea floor and drives global ocean currents. The Global Thermohaline Circulation drives large currents around the world, and brings the warm Gulf Stream to Britain, moderating its climate.
The Antarctic Ice Sheets
East Antarctic Ice Sheet
There are three ice sheets in Antarctica; the East Antarctic Ice Sheet (EAIS), the West Antarctic Ice Sheet and the Antarctic Peninsula Ice Sheet. Each of these ice sheets has its own unique characteristics and behaviour. East Antarctica is grounded mostly above sea level and forms the bulk of the Antarctic Ice Sheet; if it melted, the East Antarctic Ice Sheet would raise global sea levels by 53 m3.
The EAIS holds the bulk of frozen fresh water on planet Earth, and it’s the highest, driest, coldest and windiest ice sheet in Antarctica by far.
In fact, the East Antarctic Ice Sheet is so cold and dry, it is the world’s most southerly desert. The Dry Valleys of East Antarctica receive around 10 mm of precipitation per year, and the mean annual air temperature is -19.8°C, making this one of the harshest places in the world.
West Antarctic Ice Sheet
The West Antarctic Ice Sheet is grounded largely below sea level. If it melted, it would raise global sea levels by a mere 3.3 m4, but unlike the East Antarctic Ice Sheet, rapid ice-sheet melt is a threat and a possibility.
The West Antarctic Ice Sheet is grounded well below sea level and the base of the ice sheet deepens landwards; it is therefore known as a “Marine Ice Sheet“.
The West Antarctic Ice Sheet is located in a region of rapid warming, and warm ocean waters threaten to melt the ice sheet at its base5.
During past interglacials, it is likely that the West Antarctic Ice Sheet almost entirely disappeared, and was left as a series of islands – as shown in the figure opposite. A future collapse of the West Antarctic Ice Sheet could rapidly raise global sea levels6. The likely hood of this happening, when it would happen and how long it would take is currently a topic of hot debate7.
Antarctic Peninsula Ice Sheet
The Antarctic Peninsula Ice Sheet is the smallest, holding only 0.24 m of sea level equivalent. However, this small ice sheet, situated on a mountain range, is perhaps the most vulnerable to climate change.
The glaciers of the Antarctic Peninsula are small and located in a region of rapid warming8. This has already resulted in numerous observable changes: collapsing ice shelves9, thinning and accelerating glaciers10-12, and widespread glacier recession13.
Ice streams, subglacial lakes and ice shelves in Antarctica
The Antarctic Ice Sheets are not just domes of ice spreading slowly out to their margins. The Antarctic Ice Sheets are drained by fast-flowing ice streams14. The Twaites Ice Stream and Pine Island Glacier, for example, together drain 30% of the West Antarctic Ice Sheet.
Pine Island Glacier moves at about 4000 metres per year, and the stability and dynamics of this ice stream is essential for the stability of the larger Antarctic Ice Sheet. Ice streams send dendritic fingers deep into the Antarctic continent, and you can see on the figure of ice velocities the slow-moving ice divides at the centre of the different ice sheets.
Recent data published by Rignot et al. 2011 shows the ice flow across the Antarctic continent. This image, made from data downloaded from the NSIDC is shown on alogarithmic scale. This emphasises the ice divides clearly. You can see, by comparing with the BEDMAP figure above, that these tend to follow the mountain ranges. Large ice streams drain into fast-flowing, floating ice shelves.
Subglacial LakesDespite being so cold, there is water at the base of the Antarctic Ice Sheet. The huge weight of the ice above melts ice at the base of the ice sheet, aided by geothermal heating. This water lubricates the base of the ice sheet, and helps the ice streams achieve their great speeds.
The water ponds in lows and hollows beneath the ice sheet, and it may exist at huge hydrostatic pressure, enabling water to flow uphill.
379 subglacial lakes have now been mapped across Antarctica15, and more are being found all the time. These subglacial lakes influence the behaviour of the ice streams of Antarctica, and drainage of lakes may add more water to the base of an ice stream – helping it to flow faster16.
Antarctica is fringed with ice shelves; in fact, 75% of the Antarctic continent is buttressed with ice shelves. Ice shelves are floating extensions of Antarctic glaciers, supplemented by snow fall directly onto the ice shelves and freezing of marine waters below5.
Ice shelves cover ~1.561 million km2, which is similar in area to the Greenland Ice Sheet. Ice shelves collect 20% of Antarctica’s snowfall and cover 11% of its area.
Ice shelves lose mass by melting from below and by calving ice bergs. In fact, basal melting from ice shelves accounts for most of the ice loss from Antarctica, and most of this ice loss comes from a few small ice shelves in West Antarctica and along the western Antarctic Peninsula5.
Sea ice is seasonal and consists of frozen sea water, together with icebergs calved from Antarctic glaciers and ice shelves. Winter sea ice around Antarctica is increasing, in contrast with winter sea ice in the Arctic, which is decreasing.
This seasonal increase in sea ice may be due to colder, fresher water, released from the melting ice shelves, which accumulates in a cool, fresh surface layer and shields surface waters from the warmer, deeper waters that are melting the ice shelves17.
Wildlife of Antarctica
Antarctica is a wild continent. It is also largely deserted; all the wildlife lives in the ocean. It may come ashore briefly, but all the food is in the ocean. Small mites and springtails are the only animals that actually live on the small land oases around Antarctica. Birdlife, however, is prevalent in Antarctica.
Flying birds include Albatross, terns, cormorants, gulls, skuas, petrels and fulmar.
Penguins are Antarctica’s poster child, and Antarctica has seven species: Adélie penguins, chinstrap penguins, emperor penguins, Gentoo penguins, king penguins, rockhopper penguins and royal penguins.
The warm upwelling ocean currents around Antarctica make it a haven for sea animals, and this accounts for the high numbers of Antarctic whales and seals. There are true (earless) seals and fur seals, which have ear flaps.
Whales are common in Antarctica and for decades were hunted, in some cases nearly to extinction. The Antarctic Treaty has allowed some species to recover, although some are still vulnerable.
Exploration of Antarctica
Antarctica was first explored in the 19th Century. Captain James Cook, in the ships HMS Resolution and HMS Adventure, crossed the Antarctic Circle for the first time on 17th January 1773, and was repeatedly beaten back by sea ice. Land was first sighted, probably around 1820. James Clark Ross sailed through the Ross Sea in 1841, and sailed near the Ross Ice Shelf.
Ernest Shackleton lead the Nimrod expedition in 1907 and reached the magnetic South Pole. An expedition led by Roald Amundsen reached the geographic South Pole on 14th December 1911.
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1. Siegert, M.J. Antarctic subglacial topography and ice-sheet evolution. Earth Surface Processes and Landforms 33, 646-660 (2008).
2. Siegert, M.J., Barrett, P., Decont, R., Dunbar, R., Cofaigh, C.O., Passchier, S. & Naish, T. Recent advances in understanding Antarctic climate evolution. Antarctic Science 20, 313-325 (2008).
3. Fretwell, L.O., H. D. Pritchard, D. G. Vaughan, J. L. Bamber, N. E. Barrand, R. Bell, C. Bianchi, R. G. Bingham, D. D. Blankenship, G. Casassa, G. Catania, D. Callens, H. Conway, A. J. Cook, H. F. J. Corr, D. Damaske, V. Damm, F. Ferraccioli, R. Forsberg, S. Fujita, P. Gogineni, J. A. Griggs, R. C. A. Hindmarsh, P. Holmlund, J. W. Holt, R. W. Jacobel, A. Jenkins, W. Jokat, T. Jordan, E. C. King, J. Kohler, W. Krabill, M. Riger-Kusk, K. A. Langley, G. Leitchenkov, C. Leuschen, B. P. Luyendyk, K. Matsuoka, Y. Nogi, O. A. Nost, S. V. Popov, E. Rignot, D. M. Rippin, A. Riviera, J. Roberts, N. Ross, M. J. Siegert, A. M. Smith, D. Steinhage, M. Studinger, B. Sun, B. K. Tinto, B. C. Welch, D. A. Young, C. Xiangbin & Zirizzotti, A. Bedmap2: improved ice bed, surface and thickness datasets for Antarctica. The Cryosphere 7, 375-393 (2013).
4. Bamber, J.L., Riva, R.E.M., Vermeersen, B.L.A. & Le Brocq, A.M. Reassessment of the potential sea-level rise from a collapse of the West Antarctic Ice Sheet. Science 324, 901-903 (2009).
5. Rignot, E., Jacobs, S., Mouginot, J. & Scheuchl, B. Ice Shelf Melting Around Antarctica. Science (2013).
6. Vaughan, D.G. West Antarctic Ice Sheet collapse – the fall and rise of a paradigm. Climatic Change 91, 65-79 (2008).
7. Bamber, J.L. & Aspinall, W.P. An expert judgement assessment of future sea level rise from the ice sheets. Nature Clim. Change 3, 424-427 (2013).
8. Turner, J., Colwell, S.R., Marshall, G.J., Lachlan-Cope, T.A., Carelton, A.M., Jones, P.D., Lagun, V., Reid, P.A. & Iagovkina, S. Antarctic climate change during the last 50 years. International Journal of Climatology 25, 279-294 (2005).
9. Cook, A.J. & Vaughan, D.G. Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere 4, 77-98 (2010).
10. Pritchard, H.D., Ligtenberg, S.R.M., Fricker, H.A., Vaughan, D.G., van den Broeke, M.R. & Padman, L. Antarctic ice-sheet loss driven by basal melting of ice shelves. Nature 484, 502-505 (2012).
11. Pritchard, H.D., Arthern, R.J., Vaughan, D.G. & Edwards, L.A. Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets. Nature 461, 971-975 (2009).
12. Pritchard, H.D. & Vaughan, D.G. Widespread acceleration of tidewater glaciers on the Antarctic Peninsula. Journal of Geophysical Research-Earth Surface 112, F03S29, 1-10 (2007).
13. Cook, A.J., Fox, A.J., Vaughan, D.G. & Ferrigno, J.G. Retreating glacier fronts on the Antarctic Peninsula over the past half-century. Science 308, 541-544 (2005).
14. Rignot, E., Mouginot, J. & Scheuchl, B. Ice Flow of the Antarctic Ice Sheet. Science (2011).
15. Wright, A. & Siegert, M. A fourth inventory of Antarctic subglacial lakes. Antarctic Science 24, 659-664 (2012).
16. Smith, B.E., Fricker, H.A., Joughin, I.R. & Tulaczyk, S. An inventory of active subglacial lakes in Antarctica detected by ICESat (2003-2008). Journal of Glaciology 55, 573-595 (2009).
17. Bintanja, R., van Oldenborgh, G.J., Drijfhout, S.S., Wouters, B. & Katsman, C.A. Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion. Nature Geosci advance online publication(2013).
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Prince Gustav Ice Shelf
Prince Gustav Ice Shelf was the most northerly ice shelf on the Antarctic Peninsula, and it was the first to collapse in 1995. It shrank progressively throughout the second half of the 20th Century, before collapsing to leave open water between James Ross Island and Trinity Peninsula1. Anecdotal evidence suggests that in the early 20th Century it was connected to an enlarged Larsen A Ice Shelf, and that it had been shrinking and thinning for many decades prior to collapse.
Following the collapse of Prince Gustav Ice Shelf, tributary glaciers were observed to accelerate, thin and recede back even 15 years after collapse2,3, directly contributing to eustatic sea level rise.
Larsen Ice Shelf
The Larsen Ice Shelf actually comprises four ice shelves; Larsen A, on the north-eastern Antarctic Peninsula, Larsen B, south of Seal Nunataks (Larsen A and B have both collapsed), Larsen D, the large currently remaining ice shelf, and Larsen D, the long, thin ice shelf fringing the south-eastern Antarctic Peninsula.
Larsen A, close to Prince Gustav Ice Shelf, used to extend from Cape Longing to Robertson Island, and merged with Larsen B at Seal Nunataks. Larsen A was relatively stable and around 4000 km2 from 1961 until the 1980s, when periodic large calving events resulted in stepwise recession1. Larsen B underwent rapid calving and disintegration in 2002, when most of the ice shelf was lost1. Their collapse follows thinning both from basal melting and surface summer meltwater formation4. This recession began in the 1980s. Larsen C is also currently thinning5. Larsen B has been thinning throughout the Holocene6, but its recent collapse was unprecedented during the Holocene.
Following the collapse of the Larsen ice shelves, their tributary glaciers were observed to accelerate, thin and recede, resulting in a direct contribution to global sea level7.
Larsen C has been stable over the last few decades, a but a large and growing rift across the ice front is threatening to extent all the way across the ice shelf. This would calve the largest iceberg ever recorded, and could destabilise the ice shelf.
Wordie Ice Shelf
Wordie Ice Shelf is made up of six major glacier units that flow into it, and there are around 20 ice rises and ice rumples8. Wordie Ice Shelf disintegrated in a series of calving events during the 1970s and 1980s, and by 1992 was little more than a few disconnected glacier tongues1. This dramatic collapse could have been caused by warm summer air temperatures, which increased summer surface ablation9. Ice rises on the ice shelf, where the ice shelf is pinned to bedrock lumps on the sea floor, may have aided the ice shelf’s stability between large calving events1.
Wilkins Ice Shelf
Wilkins Ice Shelf is the largest ice shelf in West Antarctica that is currently undergoing rapid shrinkage. Recession has occurred through a series of rapid calving events, where it calved a number of large, tabular icebergs 1. Significant break-ups occurred in 1998 and March and July 2008, and finally again in April 2009. The overall area was reduced to 5434 km2, which is around two thirds of its original size.
Wilkins Ice Shelf flows only slowly, at around 30-90 metres per year (the nearby Wordie flows at 200-2000 metres per year). It has a catchment area of 16,900 km2, which is a small area of grounded ice to nourish an ice shelf, and it is sustained largely by in situ accumulation1. Melting on the Wilkins Ice Shelf is largely by basal melting and some surface melting in the summer10. The Wilkins Ice Shelf is thinning at a rate of 0.8 metres per year (1992-2008), which is driven by a basal melt rate of 1.3 ± 0.4 metre per year11. On slow-moving, thin, near-stationary ice shelves like the Wilkins Ice Shelf, basal melting rapidly melts away the original glacier ice within a few kilometres of its grounding line12. According to Rignot et al. (2013), the Wilkins Ice Sheet loses 18.4 ± 17 gigatonnes of meltwater each year as a result of basal melting, and 0.7 ± 0.4 gigatonnes of ice per year following iceberg calving.
You can explore these ice shelves using the Google Map below. Note the mountains running down the length of Alexander Island. George VI Ice Shelf lies between Alexander Island and the mainland Antarctic Peninsula (Palmer Land). On the west of Alexander Island, you have the Wilkins Ice Shelf and several smaller ice shelves. Can you see where the ice shelf starts? Look for a break in slope to see where the glacier ice starts to float.
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George VI Ice Shelf
George VI Ice Shelf is an unusual ice shelf that is trapped between the mainland (Palmer Land) and Alexander Island. Ice flows from the mainland north and south to the marine termini at either end of Prince Gustav Channel. George VI Ice Shelf is located on the -9°C annual isotherm (mean annual air temperature is -9°C), which has been proposed as the theoretical limit for ice-shelf viability13.
George VI Ice Shelf measures 24,000 km2, and is the second-largest ice shelf on the Antarctic Peninsula14. It is a slow-moving ice shelf. George VI Ice Shelf is melting rapidly at its base12, and is largely sustained by snow accumulation. George VI Ice Shelf is currently receding at a rate of 1 to 1.1 kilometres per year, and it is thinning, and the grounding line is retreating14. Frontal recession generally occurs as series of large calving events following the development of rifting.
You can read more about George VI Ice Shelf in this blog post.
1. Cook, A.J. & Vaughan, D.G. Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere 4, 77-98 (2010).
2. Glasser, N.F., Scambos, T.A., Bohlander, J.A., Truffer, M., Pettit, E.C. & Davies, B.J. From ice-shelf tributary to tidewater glacier: continued rapid glacier recession, acceleration and thinning of Röhss Glacier following the 1995 collapse of the Prince Gustav Ice Shelf on the Antarctic Peninsula. Journal of Glaciology 57, 397-406 (2011).
3. Davies, B.J., Carrivick, J.L., Glasser, N.F., Hambrey, M.J. & Smellie, J.L. Variable glacier response to atmospheric warming, northern Antarctic Peninsula, 1988–2009. The Cryosphere 6, 1031-1048 (2012).
4. Shepherd, A., Wingham, D., Payne, T. & Skvarca, P. Larsen ice shelf has progressively thinned. Science 302, 856-859 (2003).
5. Fricker, H.A. & Padman, L. Thirty years of elevation change on Antarctic Peninsula ice shelves from multimission satellite radar altimetry. Journal of Geophysical Research: Oceans 117, C02026 (2012).
6. Domack, E., Duran, D., Leventer, A., Ishman, S., Doane, S., McCallum, S., Amblas, D., Ring, J., Gilbert, R. & Prentice, M. Stability of the Larsen B ice shelf on the Antarctic Peninsula during the Holocene epoch. Nature 436, 681-685 (2005).
7. De Angelis, H. & Skvarca, P. Glacier surge after ice shelf collapse. Science 299, 1560-1562 (2003).
8. Reynolds, J.M. The structure of Wordie Ice Shelf, Antarctic Peninsula. British Antarctic Survey Bulletin 80, 57-64 (1988).
9. Doake, C.S.M. & Vaughan, D.G. Rapid disintegration of the Wordie Ice Shelf in response to atmospheric warming. Nature 350, 328-330 (1991).
10. Braun, M., Humbert, A. & Moll, A. Changes of Wilkins Ice Shelf over the past 15 years and inferences on its stability. The Cryosphere 3, 41-56 (2009).
11. Padman, L., Costa, D.P., Dinniman, M.S., Fricker, H.A., Goebel, M.E., Huckstadt, L.A., Humbert, A., Joughin, I., Lenaerts, J.T.M., Ligtenberg, S.R.M., Scambos, T. & van den Broeke, M.R. Oceanic controls on the mass balance of Wilkins Ice Shelf, Antarctica. Journal of Geophysical Research: Oceans 117, C01010 (2012).
12. Rignot, E., Jacobs, S., Mouginot, J. & Scheuchl, B. Ice Shelf Melting Around Antarctica. Science (2013).
13. Morris, E.M. & Vaughan, A.P.M. Spatial and temporal variation of surface temperature on the Antarctic Peninsula and the limit of viability of ice shelves. in Antarctic Peninsula climate variability: historical and palaeoenvironmental perspectives, Vol. Volume 79 (eds. Domack, E.W., Leventer, A., Burnett, A., Bindschadler, R., Convey, P. & Kirby, M.) 61-68 (American Geophysical Union, Antarctic Research Series, Volume 79, Washington, D.C., 2003).
14. Holt, T.O., Glasser, N.F., Quincey, D. & Siegfried, M.R. Speedup and fracturing of George VI Ice Shelf, Antarctic Peninsula. The Cryosphere 7, 797-816 (2013).
Introduction | Temperatures are rising | Ice shelves are collapsing | Glaciers are shrinking | Glaciers are thinning | Glaciers are accelerating | Sea level is rising | Impact of climate on glaciers | References | Comments |
What is happening around the Antarctic Peninsula? This is a region of very rapid warming, and this has resulted in a whole suite of glaciological changes. What are the implications of this change for us? How do glaciers respond to climate change, how are they related and linked, and what is driving these changes? This article summarises glaciers and climate change around the Antarctic Peninsula.
Temperatures are rising
Climate change is strongly affecting Antarctica. Around the Antarctic Peninsula, temperatures are warming at a rate that is approximately six times the global average. Air temperatures increased by ~2.5°C from 1950-20001. Regional rapid warming here began in the 1930s2. The annual mean air temperature -9°C isotherm has moved southwards, resulting in ice-shelf collapse and glacier recession3. A recent ice core from James Ross Island shows that warming in this region began around 600 years ago and then accelerated over the last century. This rate of warming is unusual, but not unprecedented4. Warming over the Antarctic Peninsula is exacerbated by a strengthening of the Antarctic Oscillation, which is a periodic strengthening and weakening of the tropospheric westerlies that surround Antarctica5. Changing pressure patterns result in flow anomalies, with cooling over East Antarctica and warming over the Antarctic Peninsula.But how unusual is this warmth? Ice core records provide a longer-term perspective on climate over the past four glacial cycles or longer6. The ice-core record indicates that carbon dioxide and temperature co-varied over the last 400 thousand years, which suggests a close link between these ‘greenhouse gases’ and temperature. Ice core records show that methane and carbon dioxide atmospheric concentrations are higher than at any point in the last 650,000 years7. The IPCC states,
“The total radiative forcing of the Earth’s climate due to increases in the concentrations of the LLGHGs CO2, CH4 and N2O, and very likely the rate of increase in the total forcing due to these gases over the period since 1750, are unprecedented in more than 10,000 years”
Ice shelves are collapsing
What effect is this having on the glaciers of the Antarctic Peninsula? Ice shelves have disintegrated very rapidly over the last few decades8-13, which has destabilised on-shore glaciers, which rapidly thinned and receded following removal of a buttressing ice shelf11,14-21 (quick check – do you understand the difference between ice shelves, sea ice, ice bergs and marine-terminating glaciers?). Higher air temperatures around the Antarctic Peninsula contribute to ice shelf collapse by increasing the amount of meltwater ponding on the surface8,9,22. When combined with ice shelves that are thinning due to melting from below following the incursion of warm ocean currents onto the continental shelf10,23-25, you have a recipe for rapid ice shelf disintegration. With one particularly warm summer, a thinned ice shelf that is close to its threshold is liable to break up very quickly as meltwater ponding on its surface propagates downwards and initiates iceberg calving by hydrofracture. Some of these ice shelves have collapsed for the first time26.
Larsen Ice Shelf
The Larsen Ice Shelf collapsed dramatically and very rapidly in 2002, and glaciers that previously fed into the Larsen Ice Shelf have since accelerated, thinned and receded. The ice shelf disintegrated very rapidly, with the main event happening over just one warm summer. The Larsen B Ice Shelf, shown in Figure 5, has been stable throughout the Holocene and this is the first time it has collapsed in the last 10,000 years.
Pine Island Glacier
Ice shelves are warmed from below, and the ice shelves around Pine Island Glacier are thinning and receding. The thinning of these ice shelves may limit their ability to buttress the flow of ice from the interior of the ice sheet. Pritchard et al. (2012) say in their paper in Nature (Figure 6) that melting from the base of ice shelves is the primary driver of Antarctic Ice Sheet ice loss, by reducing the buttressing capability of the ice shelves. The rapid thinning of the Pine Island Glacier ice shelf is caused by warm oceanic water at depth that reaches the underside of ice shelves by travelling along troughs on the continental shelf.
Glaciers are shrinking
There is increasing evidence that glaciers around the Antarctic Peninsula are shrinking and receding. Alison Cook found that 87% of the glaciers around the Antarctic Peninsula are receding27,28. Other workers have found evidence of glacier recession and a measureable sea-level contribution29. There is evidence of widespread glacier recession around the northern Antarctic Peninsula21,30. Land-terminating glaciers in this region are shrinking particularly rapidly31, which is significant, as their mass balance is more directly controlled by temperature and precipitation, compared with marine-terminating glaciers, which respond non-linearly to climate forcing.
Glaciers are thinning
A paper published recently in Geophysical Research Letters32 showed that glaciers around the Antarctic Peninsula are thinning. 12 glaciers around the Antarctic Peninsula showed near-frontal surface lowering since the 1960s, with higher rates of thinning for glaciers on the north-western Antarctic Peninsula. Surface lowering ceases at about 400m in altitude across all the glaciers, which may be due to increased high-altitude accumulation32. These marine-terminating glaciers are affected by both oceanic and atmospheric warming. The thinning of these glaciers is bringing them nearer to floatation. Kunz et al (2012) conclude that the majority of the glaciers around the Antarctic Peninsula are likely have been thinning for decades, but that the pattern of surface change is not simple. Lowering is not caused by reduced mass input, as it is not observed at higher elevations (in fact, the amount of lowering has probably been reduced by this higher precipitation).
Glaciers are accelerating
Glaciers are accelerating across the Antarctic Peninsula33. This may be due to the thinning observed at the glacier snouts32,33, and combined with the thinning and recession observed across the Antarctic Peninsula, indicates that there is a climatically-driven rise in sea level from this region. Thinning glaciers are easier to float. Once warm ocean water can access the underside of a glacier, melting from below exacerbates thinning from above, resulting in increased and rapid glacier thinning34. Thinning glaciers accelerate as part of their dynamic response, as changes near the grounding line can impact glacier velocity some distance inland35. Pritchard and Vaughan (2007) argue that thinning as a result of a negative mass balance will reduce the effective stress of a glacier’s bed near the margin, reducing basal resistance and increasing sliding. This leads to further thinning, floatation, rapid calving and increased glacier recession33. The retreat rate will be controlled to a large extent by fjord depth and geometry, and over deepened basins resulting in particularly rapid glacier recession.
Sea level is rising
Global sea levels are currently rising at a rate of about 3 mm per year7. The contribution from the Antarctic Peninsula is −41.5 Gt yr−1 36, although a recent study refines this to -34 Gt yr-1 37. King et al. calculate that the Antarctic Ice Sheet as a whole currently contributes about 0.19 mm±0.05 mm per year to global sea level rise, which is largely from the Antarctic Peninsula, the Amundsen Sea sector (including Pine Island Glacier), and which is partly balanced by increased ice accumulation in East Antarctica.
Most modern sea level rise, and sea level rise predicted over the next 100 years, comes from ocean expansion and the melting of small glaciers and ice caps. However, the amount that the sea level will rise in the future depends not only on temperature, glacier recession and ocean warming and expansion, but also the dynamic behaviour of the West Antarctic Ice Sheet. Marine Ice Sheet Instability may result in rapid future sea level rise, contributed to by ice-shelf collapse and the dynamic behaviour of ice streams. How much will Antarctica contribute to sea level rise in the future? You can read more about that in this blog post.
Impact of climate on glaciers
The Antarctic Peninsula is particularly vulnerable to climate change due to its small size and northerly latitude2. It receives high snowfall but high melt, with a large number of days above 0°C in the summer months33. It interrupts the Circumpolar Westerlies and is liable to be affected by small changes in these winds. Increased numbers of positive degree days 32 coincide with increased rates of thinning on Antarctic Peninsula marine-terminating glaciers, and increased meltwater ponding and hydrofracture on ice shelves. Glaciers are thinning and receding in response to warmer temperatures, and thinning glaciers are easier to float. We know that basal melting of ice shelves drives ice sheet loss34, and we can observe the impacts of climate change around the Antarctic Peninsula today.
- Marine Ice Sheet instability
- Ice shelves
- Sea level rise
- Glacier recession in Patagonia
- Glacier recession on the Antarctic Peninsula
- Antarctica’s contribution to global sea level rise
- Antarctic Peninsula Ice Sheet evolution
- The Antarctic Peninsula Ice Sheet
- Antarctic Peninsula photographs
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2. Vaughan, D.G., Marshall, G.J., Connelly, W.M., Parkinson, C., Mulvaney, R., Hodgson, D.A., King, J.C., Pudsey, C.J. & Turner, J. Recent rapid regional climate warming on the Antarctic Peninsula. Climatic Change 60, 243-274 (2003).
3. Morris, E.M. & Vaughan, A.P.M. Spatial and temporal variation of surface temperature on the Antarctic Peninsula and the limit of viability of ice shelves. in Antarctic Peninsula climate variability: historical and palaeoenvironmental perspectives, Vol. Volume 79 (eds. Domack, E.W., Leventer, A., Burnett, A., Bindschadler, R., Convey, P. & Kirby, M.) 61-68 (American Geophysical Union, Antarctic Research Series, Volume 79, Washington, D.C., 2003).
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5. van den Broeke, M.R. & van Lipzig, N.P.M. Changes in Antarctic temperature, wind and precipitation in response to the Antarctic Oscillation. Annals of Glaciology 39, 119-126 (2004).
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7. Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M. & Miller, H.L. (eds.). Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, (Cambridge University Press, Cambridge, 2007).
8. Scambos, T., Fricker, H.A., Liu, C.-C., Bohlander, J., Fastook, J., Sargent, A., Massom, R. & Wu, A.-M. Ice shelf disintegration by plate bending and hydro-fracture: Satellite observations and model results of the 2008 Wilkins ice shelf break-ups. Earth and Planetary Science Letters 280, 51-60 (2009).
10. Vieli, A., Payne, A.J., Shepherd, A. & Du, Z. Causes of pre-collapse changes of the Larsen B ice shelf: Numerical modelling and assimilation of satellite observations. Earth and Planetary Science Letters 259, 297-306 (2007).
11. Rack, W. & Rott, H. Pattern of retreat and disintegration of the Larsen B ice shelf, Antarctic Peninsula. Annals of Glaciology 39, 505-510 (2004).
12. Scambos, T., Hulbe, C. & Fahnestock, M. Climate-induced ice shelf disintegration in the Antarctic Peninsula. in Antarctic Peninsula climate variability: historical and palaeoenvironmental perspectives, Vol. Volume 79 (eds. Domack, E.W., Leventer, A., Burnett, A., Bindschadler, R., Convey, P. & Kirby, M.) 79-92 (American Geophysical Union, Antarctic Research Series, Volume 79, Washington, D.C., 2003).
13. Cook, A.J. & Vaughan, D.G. Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere 4, 77-98 (2010).
14. Rott, H., Müller, F. & Floricioiu, D. The Imbalance of glaciers after disintegration of Larsen B ice shelf, Antarctic Peninsula. The Cryosphere 5, 125-134 (2011).
15. Glasser, N.F., Scambos, T.A., Bohlander, J.A., Truffer, M., Pettit, E.C. & Davies, B.J. From ice-shelf tributary to tidewater glacier: continued rapid glacier recession, acceleration and thinning of Röhss Glacier following the 1995 collapse of the Prince Gustav Ice Shelf on the Antarctic Peninsula. Journal of Glaciology 57, 397-406 (2011).
16. Hulbe, C.L., Scambos, T.A., Youngberg, T. & Lamb, A.K. Patterns of glacier response to disintegration of the Larsen B ice shelf, Antarctic Peninsula. Global and Planetary Change 63, 1-8 (2008).
17. Scambos, T.A., Bohlander, J.A., Shuman, C.A. & Skvarca, P. Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica. Geophysical Research Letters 31, L18402 (2004).
18. Rignot, E., Casassa, G., Gogineni, P., Krabill, W., Rivera, A. & Thomas, R. Accelerated ice discharge from the Antarctic Peninsula following the collapse of Larsen B ice shelf. Geophysical Research Letters 31, L18401 (2004).
19. De Angelis, H. & Skvarca, P. Glacier surge after ice shelf collapse. Science 299, 1560-1562 (2003).
20. Rott, H., Rack, W., Skvarca, P. & De Angelis, H. Northern Larsen Ice Shelf, Antarctica: further retreat after collapse. Annals of Glaciology 34, 277-282 (2002).
21. Davies, B.J., Carrivick, J.L., Glasser, N.F., Hambrey, M.J. & Smellie, J.L. Variable glacier response to atmospheric warming, northern Antarctic Peninsula, 1988–2009. The Cryosphere 6, 1031-1048 (2012).
22. Glasser, N.F., Kulessa, B., Luckman, A., Jansen, D., King, E.C., Sammonds, P.R., Scambos, T.A. & Jezek, K.C. Surface structure and stability of the Larsen C Ice Shelf, Antarctic Peninsula. Journal of Glaciology 55, 400-410 (2009).
23. Walker, R.T., Dupont, T.K., Holland, D.M., Parizek, B.R. & Alley, R.B. Initial effects of oceanic warming on a coupled ocean-ice shelf-ice stream system. Earth and Planetary Science Letters 287, 483-487 (2009).
24. Smith, J.A., Bentley, M.J., Hodgson, D.A., Roberts, S.J., Leng, M.J., Lloyd, J.M., Barrett, M.S., Bryant, C.L. & Sugden, D.E. Oceanic and atmospheric forcing of early Holocene ice shelf retreat, George VI Ice Shelf, Antarctic Peninsula. Quaternary Science Reviews 26, 500-516 (2007).
25. Shepherd, A., Wingham, D., Payne, T. & Skvarca, P. Larsen ice shelf has progressively thinned. Science 302, 856-859 (2003).
26. Domack, E., Duran, D., Leventer, A., Ishman, S., Doane, S., McCallum, S., Amblas, D., Ring, J., Gilbert, R. & Prentice, M. Stability of the Larsen B ice shelf on the Antarctic Peninsula during the Holocene epoch. Nature 436, 681-685 (2005).
27. Ferrigno, J.G., Cook, A.J., Foley, K.M., Williams, R.S., Swithinbank, C., Fox, A.J., Thomson, J.W. & Sievers, J. Coastal-Change and Glaciological Map of the Trinity Peninsula Area and South Shetland Islands, Antarctica: 1843-2001, 32 (USGS, Denver, 2006).
28. Cook, A.J., Fox, A.J., Vaughan, D.G. & Ferrigno, J.G. Retreating glacier fronts on the Antarctic Peninsula over the past half-century. Science 308, 541-544 (2005).
29. Hock, R., de Woul, M., Radic, V. & Dyurgerov, M. Mountain glaciers and ice caps around Antarctica make a large sea-level rise contribution. Geophysical Research Letters 36, L07501 (2009).
30. Rau, F., Mauz, F., de Angelis, H., Jana, R., Neto, J.A., Skvarca, P., Vogt, S., Saurer, H. & Gossmann, H. Variations of glacier frontal positions on the northern Antarctic Peninsula. Annals of Glaciology 39, 525-530 (2004).
31. Carrivick, J.L., Davies, B.J., Glasser, N.F. & Nývlt, D. Late Holocene changes in character and behaviour of land-terminating glaciers on James Ross Island, Antarctica. Journal of Glaciology 58(2012).
32. Kunz, M., King, M.A., Mills, J.P., Miller, P.E., Fox, A.J., Vaughan, D.G. & Marsh, S.H. Multi-decadal glacier surface lowering in the Antarctic Peninsula. Geophys. Res. Lett. 39, L19502 (2012).
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35. Payne, A.J., Vieli, A., Shepherd, A.P., Wingham, D.J. & Rignot, E. Recent dramatic thinning of largest West Antarctic ice stream triggered by oceans. Geophysical Research Letters 31, L23401 (2004).
36. Ivins, E.R., Watkins, M.M., Yuan, D.-N., Dietrich, R., Casassa, G. & Rülke, A. On-land ice loss and glacial isostatic adjustment at the Drake Passage: 2003-2009. J. Geophys. Res. 116, B02403 (2011).
37. King, M.A., Bingham, R.J., Moore, P., Whitehouse, P.L., Bentley, M.J. & Milne, G.A. Lower satellite-gravimetry estimates of Antarctic sea-level contribution. Nature advance online publication(2012).
The Antarctic Peninsula Ice Sheet (sometimes written as APIS) is widely regarded as sensitive to climate change due to its small size and northerly location, and because this region is one of the most rapidly warming places in the world[2-5].
This sensitivity has been manifest through the collapse of numerous ice shelves, increased ice velocities, and the retreat and thinning of glaciers and ice caps[6-10].
The Antarctic Peninsula is a relatively long, thin spine Alpine-style mountain chain. These mountains extend north towards the Drake Passage, reaching 63°S. The Antarctic Peninsula is 70 km wide, with an average height of ~1500 m. It is 522,000 km2 in area and 80% ice-covered.
You can explore the Antarctic Peninsula Ice Sheet through the Google Map below. Note the flat ice shelves, the islands on the western and eastern Peninsula, and the flowline structures of the glaciers as they flow into the sea. You can also see the rifts in the Larsen Ice Shelf and the few mountain summits that poke through the ice.
View Larger Map
Oceanography and climate
These mountains form a significant barrier to the persistent westerly, moisture-laden winds. The climatic regime either side of the Antarctic Peninsula is therefore quite different.
In the Bellingshausen Sea, there is a polar maritime climate, and in the Weddell Sea, a cold, dry, polar continental climate[1, 3, 11, 13, 14].
The Weddell Sea is further cooled by the Weddell Sea Gyre, which circulates sea ice, icebergs and cold water clockwise towards the northern Antarctic Peninsula. Sea ice also modulates sea surface temperatures in the Weddell Sea[3, 16].
The modern Antarctic Peninsula Ice Sheet is approximately 500 m thick, with outlet glaciers flowing out east and west. Summer air temperatures are greater than 0°C at sea level, and the mass balance of Antarctic Peninsula glaciers is largely controlled by surface melting and glacier calving.
Many of these tidewater glaciers are grounded, particularly on the north-western Peninsula. However , there are large ice shelves fringing the Antarctic Peninsula south of 68°S in the east and 70°S in the west[1, 8].
The Antarctic Peninsula Ice Sheet contains enough water to raise sea level by 0.24m on full melting, and currently contributes 0.22 ± 0.16 mm per year to sea level rise.
The Antarctic Peninsula is particularly important because several large ice free areas, for example, on James Ross Island, Alexander Island and South Shetland Islands preserve important palaeoenvironmental archives [e.g., 20, 21-29].
In addition to these, the Bransfield Strait (and its topographic expression, Bransfield Basin) is an 1800 m deep marginal basin separating the South Shetland Islands from the Antarctic Peninsula. It is infilled with thick sequences of marine and glaciomarine sediments, which provide detailed information on Antarctic Peninsula Ice Sheet fluctuations throughout the Quaternary [30-35].
The Palmer Deep, south of Anvers Island, is 1000 m deep and 200 km2 in area, and also contains a long record of glacial activity and Holocene environmental variability [36, 37].
The Antarctic Peninsula was once part of the now fragmented Gondwana continent, that extended from South America through the Antarctic Peninsula and New Zealand until the Late Cretaceous.
Arc magnetism (resulting in volcanoes around the Antarctic Peninsula) was active throughout the Cenozoic, formed in response to subduction of the proto-Pacific ocean floor along the western margin of the Antarctic Peninsula. The Antarctic Peninsula basement rocks are the Trinity Peninsula Group; these intermediate grade rocks were metamorphosed during this subduction.
The Antarctic Peninsula is bordered to the east (for example, James Ross Island) by a back-arc basin stratigraphy of thick Jurassic and Cretaceous marine shales and siltstone. Deposits began to accumulate in James Ross Basin, providing evidence of the earliest glaciation.
The Drake Passage between South America and the Antarctic Peninsula began to open following fragmentation and brittle response of the crust from compressive to extensional forces. During this time (Palaeogene and Neogene; cf. Table 1), the Mesozoic rocks that now form the Antarctic Peninsula mountains were uplifted.
This uplift aided the accumulation of ice masses across the Peninsula and resulted in glacial and glacially-related erosion and deposition on the continental shelf. During this period, the Antarctic landmass also moved southwards, towards its present position. See Past Behaviour for information on the earliest glacierisation of the Antarctic Peninsula.
- Antarctic Peninsula photographs
- Evolution of the Antarctic Peninsula Ice Sheet
- West Antarctic Ice Sheet
- East Antarctic Ice Sheet
- Antarctic Peninsula glacier recession
1. Davies, B.J., et al., Antarctic Peninsula Ice Sheet evolution during the Cenozoic Era. Quaternary Science Reviews, 2012. 31(0): p. 30-66.
2. Vaughan, D.G., et al., Devil in the detail. Science, 2001. 293(5536): p. 1777-1779.
3. Vaughan, D.G., et al., Recent rapid regional climate warming on the Antarctic Peninsula. Climatic Change, 2003. 60: p. 243-274.
4. Smith, T.R. and J.B. Anderson, Ice-sheet evolution in James Ross Basin, Weddell Sea margin of the Antarctic Peninsula: The seismic stratigraphic record. GSA Bulletin, 2010. 122(5/6): p. 830-842.
5. Turner, J., et al., Antarctic climate change during the last 50 years. International Journal of Climatology, 2005. 25: p. 279-294.
6. De Angelis, H. and P. Skvarca, Glacier surge after ice shelf collapse. Science, 2003. 299: p. 1560-1562.
7. Scambos, T.A., et al., Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica. Geophysical Research Letters, 2004. 31: p. L18402.
8. Cook, A.J. and D.G. Vaughan, Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere, 2010. 4(1): p. 77-98.
9. Pritchard, H.D. and D.G. Vaughan, Widespread acceleration of tidewater glaciers on the Antarctic Peninsula. Journal of Geophysical Research-Earth Surface, 2007. 112(F3): p. F03S29, 1-10.
10. Cook, A.J., et al., Retreating glacier fronts on the Antarctic Peninsula over the past half-century. Science, 2005. 308(5721): p. 541-544.
11. Summerhayes, C.P., et al., The Antarctic Environment in the Global System, in Antarctic Climate Change and the Environment, J. Turner, et al., Editors. 2009, Scientific Committee on Antarctic Research: Cambridge. p. 1-32.
12. Bindschadler, R., The environment and evolution of the West Antarctic ice sheet: setting the stage. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2006. 364(1844): p. 1583-1605.
13. Reynolds, J.M., The distribution of mean annual temperatures in the Antarctic Peninsula. British Antarctic Survey Bulletin, 1981. 54: p. 123-133.
14. Morris, E.M. and A.P.M. Vaughan, Spatial and temporal variation of surface temperature on the Antarctic Peninsula and the limit of viability of ice shelves, in Antarctic Peninsula climate variability: historical and palaeoenvironmental perspectives, E.W. Domack, et al., Editors. 2003, American Geophysical Union, Antarctic Research Series, Volume 79: Washington, D.C. p. 61-68.
15. Barker, P.F., The history of Antarctic Peninsula glaciation. USGS Short Research Paper, 2002. 42: p. 1-5.
16. King, J.C., Recent climate variability in the vicinity of the Antarctic Peninsula. International Journal of Climatology, 1994. 14: p. 357-369.
17. Turner, J., et al., Antarctic Climate Change and the Environment. 2009, Cambridge: Scientific Committee on Antarctic Research. 555.
18. Heroy, D.C. and J.B. Anderson, Ice-sheet extent of the Antarctic Peninsula region during the Last Glacial Maximum (LGM) – Insights from glacial geomorphology. GSA Bulletin, 2005. 117(11/12): p. 1497-1512.
19. Hock, R., et al., Mountain glaciers and ice caps around Antarctica make a large sea-level rise contribution. Geophysical Research Letters, 2009. 36: p. L07501.
20. Björck, S., et al., Late Holocene palaeoclimatic records from lake sediments on James Ross Island, Antarctica. Palaeogeography, Palaeoclimatology, Palaeoecology, 1996. 121(3-4): p. 195-220.
21. Ingólfsson, Ó., et al., Late Pleistocene and Holocene glacial history of James Ross Island, Antarctic Peninsula. Boreas, 1992. 21(3): p. 209-222.
22. Clapperton, C.M. and D.E. Sugden, Late Quaternary glacial history of George VI Sound area, West Antarctica. Quaternary Research, 1982. 18(3): p. 243-267.
23. Clapperton, C.M. and D.E. Sugden, Geomorphology of the Ablation Point massif, Alexander Island, Antarctica. Boreas, 1983. 12(2): p. 125-135.
24. Sugden, D.E. and C.M. Clapperton, West Antarctic Ice Sheet fluctuations in the Antarctic Peninsula area. Nature, 1980. 286: p. 378-381.
25. Sugden, D.E. and C.M. Clapperton, An ice-shelf moraine, George VI Sound, Antarctica. Annals of Glaciology, 1981. 2(1): p. 135-141.
26. Troedson, A.L. and J.B. Riding, Upper Oligocene to lowermost Miocene strata of King George Island, South Shetland Islands, Antarctica: Stratigraphy, facies analysis, and implications for the glacial history of the Antarctic Peninsula. Journal of Sedimentary Research, 2002. 72(4): p. 510-523.
27. Nelson, A.E., et al., Neogene glacigenic debris flows on James Ross Island, northern Antarctic Peninsula, and their implications for regional climate history. Quaternary Science Reviews, 2009. 28(27-28): p. 3138-3160.
28. Smellie, J.L., et al., Six million years of glacial history recorded in volcanic lithofacies of the James Ross Island Volcanic Group, Antarctic Peninsula. Palaeogeography, Palaeoclimatology, Palaeoecology, 2008. 260(1-2): p. 122-148.
29. Smellie, J.L., et al., Late Neogene interglacial events in the James Ross Island region, northern Antarctic Peninsula, dated by Ar/Ar and Sr-isotope stratigraphy. Palaeogeography, Palaeoclimatology, Palaeoecology, 2006. 242(3-4): p. 169-187.
30. Heroy, D.C., C. Sjunneskog, and J.B. Anderson, Holocene climate change in the Bransfield Basin, Antarctic Peninsula: evidence from sediment and diatom analysis. Antarctic Science, 2008. 20(1): p. 69-87.
31. Banfield, L.A. and J.B. Anderson, Seismic facies investigation of the Late Quaternary glacial history of Bransfield Basin, Antarctica. Anarctic Research Series, 1995. 68: p. 123-140.
32. Gracia, E., et al., Morphostructure and evolution of the central and eastern Bransfield Basins (NW Antarctic Peninsula). Marine Geophysical Researches, 1996. 18(2-4): p. 429-448.
33. Gracia, E., et al., Central and eastern Bransfield basins (Antarctica) from high-resolutian swath-bathymetry data. Antarctic Science, 1997. 9(2): p. 168-180.
34. Khim, B.K., et al., Unstable climate oscillations during the late Holocene in the eastern Bransfield Basin, Antarctic Peninsula. Quaternary Research, 2002. 58(3): p. 234-245.
35. Prieto, M.J., et al., Seismic stratigraphy of the Central Bransfield Basin (NW Antarctic Peninsula): interpretation of deposits and sedimentary processes in a glacio-marine environment. Marine Geology, 1999. 157(1-2): p. 47-68.
36. Domack, E.W., et al., Chronology of the Palmer Deep site, Antarctic Peninsula: A Holocene palaeoenvironmental reference for the circum-Antarctic. The Holocene, 2001. 11(1): p. 1-9.
37. Leventer, A., et al., Laminations from the Palmer Deep: A diatom-based interpretation. Paleoceanography, 2002. 17(2).
38. McCarron, J.J. and R.D. Larter, Late Cretaceous to early Tertiary subduction history of the Antarctic Peninsula. Journal of the Geological Society, 1998. 155: p. 255-268.
39. Domack, E.W., A. Burnett, and A. Leventer, Environmental setting of the Antarctic Peninsula, in Antarctic Peninsula Climate Variability: Historical and Paleoenvironmental Perspectives, E. Domack, et al., Editors. 2003. p. 1-13.
40. Siegert, M.J. and F. Florindo, Antarctic climate evolution, in Antarctic Climate Evolution, F. Florindo and M.J. Siegert, Editors. 2009, Elsevier: Rotterdam. p. 2-11.
This section is largely taken from Davies et al. 2012 (Quaternary Science Reviews), and summarises Antarctic Peninsula Ice Sheet evolution throughout the Cenozoic, Last Glacial Maximum and into the Holocene.
Pre-Quaternary Antarctic Peninsula Ice Sheet evolution
Palaeogene (65.5 to 23.03 Ma)
Evidence for pre-Quaternary (see Table 1) glaciations of the Antarctic Peninsula mostly come from offshore seismic and drilling campaigns. There are some terrestrial records from King George Island, South Shetland Islands, and on James Ross Island.
The continental shelf and slope, extending beyond the reach of later Quaternary ice sheets, preserves thick sedimentary strata deposited during glacials and interglacials over the last 35-40 million years (Ma). Pre-Quaternary sediments have been dated using biostratigraphy (dinoflagellate cysts), isotopic dating of volcanic rocks[3-5] and strontium isotopes analysis on shells[6, 7].
The earliest ice sheets began to develop around the Palaeogene-Neogene boundary (see Table 1), circa 35 Ma. Mean global temperatures were around ~4°C higher than today[9, 10].
Mountain glaciation around the Antarctic Peninsula was initiated 37-34 Ma, coinciding with the opening of the Drake Passage, the separation of the Andes and the Antarctic Peninsula, and the development of the Antarctic Circumpolar Current. The Antarctic Circumpolar Current isolated Antarctica from other regimes, resulting in the development of a cooler polar climate.
These early ice sheets were thin and dynamic, fluctuating at 40,000 year cycles in response to variations in the earth’s orbit around the sun (Milankovitch cycles)[13, 14].
The longest terrestrial record of glaciation comes from King George Island, South Shetland Islands, with glaciers developing from the Miocene.
Neogene (23.03 to 2.54 Ma)
Sediments from the Pacific continental margin, ~9 Ma in age, have yielded a high-resolution history of multiple ice advances and erosional episodes, indicating a persistent Antarctic Peninsula Ice Sheet[1, 15, 16].
Sedimentary evidence suggests that Pliocene ice (<3 Ma) was probably relatively thin and did not inundate the topography.
During this period, the West Antarctic Ice Sheet and Antarctic Peninsula Ice Sheets together grew successively larger, with periodic collapses during interglacials.
During periods of West Antarctic Ice Sheet absence, the Antarctic Peninsula Ice Sheet remained as a series of island ice caps, and was also a refuge for plants and animals[2, 18, 19]. The East Antarctic Ice Sheet remained relatively stable during this time.
James Ross Island has yielded an excellent record of Neogene glaciations, preserved in glaciovolcanic sediments. The volcanic rocks are dateable, and the sequence provides an excellent record of glacial activity. The volcanic sequences were formed by repeated volcanic eruptions (>50) beneath glacier ice from 9.9 to 2.6 Ma, forming pillow lavas and hyaloclastites[4, 5, 20].
They form the Hobbs Glacier Formation, which lies between Cretaceous marine sediments and the younger James Ross Island Volcanic Group. See Subglacial Volcanoes for more information on this.
These sediments indicate that Antarctic Peninsula ice expanded as far as James Ross and Seymour islands, with a polythermal regime[4, 20, 21]. Sedimentary facies indicate a climatic regime similar to that in Svalbard today.
Ice thickness data can be deduced from these glaciovolcanic rocks. Maximum ice thicknesses are now well known for the Antarctic Peninsula since 7.5 Ma[4, 5, 20, 24].
Ice thicknesses were generally around 250-300 m around James Ross Island, but occasionally reached 850 m. Ice thicknesses were increasing towards the end of the Pliocene. This is covered in more detail under Subglacial Volcanoes.
Quaternary glaciation of the Antarctic Peninsula
Early Pleistocene (2.54 to 1 Ma)
Excepting a few glaciovolcanic sequences on James Ross Island, there is little terrestrial evidence of Early Pleistocene glaciation. Most of the data is from seismic profiling and coring of sediment drifts on the continental rise.
These sediments are dated by magnetic stratigraphy, tuned to the marine isotope record. These continental rise sediments indicate an ice-sheet dominated environment developing through the Pliocene into the Pleistocene, with increasing grounding on the continental shelf.
Middle Pleistocene (1Ma to 200 ka)
After the Mid-Pleistocene Transition at 1 Ma, ice streams began to develop on the continental shelf during this period, leading to the development of trough-mouth fans at their termini.
After 1 Ma, lower global sea levels encouraged grounding line advance well into the Bellingshausen Sea continental shelf. A positive feedback loop was established, with cooling leading to ice sheet growth and sea level lowering, which encouraged further ice sheet growth and cooling[26, 27].
During the Middle Pleistocene, ice sheets were reaching the continental shelf for longer, with more distinct glacial-interglacial cyclicity. Marine sediments from the continental slope have less ice-rafted debris, which suggests that the ice sheet was bound by sea ice and ice shelves, which inhibited iceberg transport of glacial debris.
The tuff cone Terrapin Hill on James Ross Island has been dated to 0.66 Ma, with a base resting on glacial material. The tuff cone morphology and sedimentology, however, indicates open marine, interglacial conditions[4, 21].
Late Pleistocene (200 ka to Last Glacial Maximum)
Late Pleistocene interglacials were characterised by ice shelves in the Larsen embayment. During the last interglacial, a smaller-than-present or absent West Antarctic Ice Sheet may explain globally higher sea levels[29-31].
Ice-rafted debris occurs in greater abundances on the continental slope and rise during interglacial periods during the Late Pleistocene, with more varied stone lithologies[32-34]. This is because warmer conditions during interglacials encouraged the collapse of ice shelves.
Combined with reduced sea ice, this allowed icebergs to transport debris to the continental shelf and slope. Warmer conditions would also have encouraged faster movement and increased bedrock erosion. This is therefore analogous to the situation during the Holocene.
During Late Pleistocene glacial periods, ice volumes increased markedly along the Antarctic Peninsula, possibly reaching 2350 m at Mount Jackson. Glacial cycles now had a dominant periodicity of 100,000 years, with around 120 m eustatic sea level change.
The Antarctic Polar Front was located further north than during earlier periods, with enhanced sea ice and reduced iceberg transport of debris[17, 34]. Thick ice streams were abundant on the continental shelf, with warm-based ice grounded on the continental shelf during glacials.
Last Glacial Maximum (~18,000 years ago)
There was a significant increase in ice volume during the Last Glacial Maximum[36, 37], which peaked prior to 18,000 years ago (18 ka BP). The Antarctic Peninsula Ice Sheet had an increased volume relative to today of 1.7 m eustatic sea level equivalent.
Geomorphological landforms on the continental shelf are typified by irregular, short erosional forms on the inner shelf, drumlins on the middle shelf, and elongate forms on the outer shelf[38-43].
These elongated “Mega Scale Glacial Lineations” are formed in thick off lapping sequences of deformable sedimentary strata, which were deposited on the continental shelf from the Miocene onwards.
These landforms indicate that, at the Last Glacial Maximum, ice streams occupied bathymetric troughs and flowed out across the continental shelf around the entire Antarctic continent.
These topographically-controlled ice streams scoured out their bathymetric troughs throughout Pleistocene glacials, each time leaving a record of their occurrence in the trough-mouth fans on the continental rise. These ice streams drained the Antarctic Peninsula Ice Sheet and confined its thickness to less than 400 m.
The figure above, from Davies et al. (2012), is a schematic map with the likely extent, disposition and behaviour of the ice sheet around 18 ka BP.
Antarctic Peninsula ice streams
Reconstructing past (palaeo) ice streams provides an important context for understanding their recent behaviour, controls on this behaviour, and how ice streams might behave in the future.
Studying the basal characteristics of Antarctic palaeo ice streams means that the role of basal topography, bedrock geology and sediment erosion, transportation and deposition can be better understood.
The diagnostic sediment-landform assemblages left behind by ice streams has meant that a large number of ice streams have been identified around the Antarctic continent, from both marine and terrestrial settings.
At the Last Glacial Maximum, palaeo-ice streams extended to the shelf edge in West Antarctica and in the Antarctic Peninsula, but in East Antarctica they usually were restricted to the mid-outer shelf.
These palaeo-ice streams occupied bathymetric troughs, and are identified by the glacial bedforms (such as mega-scale glacial lineations) in these troughs, and trough-mouth fans at their termini.
The outer-shelf zones of these cross-shelf troughs are characterised by soft, unconsolidated sediments, in which mega-scale glacial lineations and grounding zone wedges are preserved. The inner shelf, instead, is generally composed of crystalline bedrock and has a higher bed roughness. Drumlins, grooved bedrock and meltwater channels are often observed here.
Where there is detailed geomorphological data available, the retreat styles of various Antarctic ice streams can be better understood. Three styles of retreat have been identified around the Antarctic Peninsula.
Rapid retreat with floatation and calving results in well-preserved subglacial bedforms on the continental shelf. These include mega-scale glacial lineations. Marguerite Trough Ice stream is an example of an ice stream characterised by rapid recession.
Episodic retreat is recorded by mega-scale glacial lineations that are overprinted by transverse grounding-zone wedges, each recording a pause in ice stream retreat with a stationary grounding line. An example of this would be the ice stream that extended out of the Larsen A embayment on the Antarctic Peninsula.
Finally, slow and steady retreat is recorded by numerous closely-spaced moraines and intermittent grounding-zone wedges. In the Western Ross Sea, there are six bathymetric troughs on the continental shelf. The palaeo-ice stream was about 370 km long, with a zone of glacial deposition on the outer shelf, and erosional landforms on the inner shelf.
Transverse sedimentary ridges overprint mega-scale glacial lineations throughout. They are grounding zone wedges, and are 3-12 m high, 180 m to 8 km apart. There are also smaller moraines, 1-2 m high and 10-100 m apart[47, 48].
The geomorphological record therefore suggests that retreat varies strongly between different troughs, with three principle styles of retreat recognised. This suggests that individual ice streams respond differently to external forcings during deglaciation, and instead are regulated by local factors, such as drainage basin size, bathymetry and sediment supply.
The western sector of the Ross Sea is fed from two drainage basins in East Antarctica measuring 1.6 million km2 and 265,000 km2. This huge drainage basin may have meant that the outlet glaciers may have responded more slowly to external forcing.
The Marguerite Bay drainage basin, in contrast, would have been of the order of 10,000 to 100,000 km2 during the LGM, and the ice streams draining this basin would have responded more rapidly to changes in external forcing. Constraints such as these are important for numerical models that attempt to replicate and predict the past and future behaviour of the Antarctic Ice Sheet.
By analysing retreat styles and rates of retreat around Antarctica, we can put more recent variations into context and determine their significance. The individual characteristics of each ice stream modulates its recession. Even under the same changes in environmental conditions and external forcings, ice streams will retreat at individual rates. Ice-stream behaviour and grounding line retreat is therefore unique to every ice stream. In order to constrain future ice stream behaviour, a detailed understanding of subglacial bed properties and bed geometry is required.
Deglaciation and recession of the Antarctic Peninsula Ice Sheet
Around the Antarctic Peninsula, recession from the outer shelf began at about 17.5 ka BP, from the middle shelf around 14 ka BP and the inner shelf around 11 ka BP. Ice streams receded both rapidly and episodically, depositing grounding-line wedges during periods of stand-still.
Radiocarbon dates from marine sediment cores across the continental shelf provide an indication of ice marginal positions during recession.
- Mega Scale Glacial Lineations
- Antarctic Peninsula Ice Sheet
- Ice shelves
- Antarctic Peninsula photographs
- Glacier recession on the Antarctic Peninsula
- Glaciers and climate change
- Subglacial volcanoes
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Photographs from around the Antarctic Peninsula taken by Bethan Davies in 2011 and 2012 during cruises on RRV Ernest Shackleton, RRV James Clark Ross, and HMS Protector.
Article by Bethan Davies.