Antarctic Peninsula Ice Shelves

Prince Gustav Ice Shelf | Larsen Ice Shelf | Wordie Ice Shelf | Wilkins Ice Shelf | George VI Ice Shelf | References | Comments |

Prince Gustav Ice Shelf

Antarctic Peninsula Ice Shelves

Antarctic Peninsula Ice Shelves

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.

Prince Gustav Ice Shelf in 1988. It collapsed in 1995, and the glaciers which flowed into it subsequently accelerated and thinned, transmitting lots of ice into the ocean and resulting in measureable sea level rise.

Prince Gustav Ice Shelf in 1988. It collapsed in 1995, and the glaciers which flowed into it subsequently accelerated and thinned, transmitting lots of ice into the ocean and resulting in measureable 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 Ice Shelf in 2004

Larsen Ice Shelf in 2004

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.

Landsat images showing the collapse of the Larsen Ice Shelf. Note the blue mottled appearance in 2002, resulting from the exposure of deep blue ice.

Landsat images showing the collapse of the Larsen Ice Shelf. Note the blue mottled appearance in 2002, resulting from the exposure of deep blue ice.

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, Alexander Island

George VI Ice Shelf, Alexander Island

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.

Alexander Island and George VI Ice Shelf, from the Landsat Image Mosaic of Antarctica

Alexander Island and George VI Ice Shelf, from the Landsat Image Mosaic of Antarctica

References


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).

Antarctic ice shelves – the hidden villain

Sea ice and ice shelves

What is sea ice? Sea ice is frozen sea water; it perennially expands and contracts during each year’s winter and summer. Amongst the sea ice are icebergs calved from tidewater glaciers and ice shelves. Melting sea ice does not contribute directly to sea level rise (ice floats and displaces the same volume of water), but sea ice is important because it enhances climate warming. It changes the reflectivity of the sea water, reflecting lots of sunlight back (it has a high albedo), and is therefore an important component of the climate and cryospheric (icey) system.
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Antarctic Peninsula Ice Sheet

Introduction | Oceanography and climate | Modern Glaciology | Geological history | References | Comments |

Introduction

This section largely taken from Davies et al., 2012 (Quaternary Science Reviews)[1].

Map of the Antarctic Peninsula, after Davies et al., 2012 (Quaternary Science Reviews)

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[1]. 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[11]. It is 522,000 km2 in area and 80% ice-covered[12].

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

Sea ice in Antarctic Sound

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[15]. Sea ice also modulates sea surface temperatures in the Weddell Sea[3, 16].

Modern Glaciology

The modern Antarctic Peninsula Ice Sheet is approximately 500 m thick, with outlet glaciers flowing out east and west[17]. 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[18]. 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].

Whisky Glacier, James Ross Island; a tidewater glacier

The Antarctic Peninsula Ice Sheet contains enough water to raise sea level by 0.24m on full melting[9], and currently contributes 0.22 ± 0.16 mm per year to sea level rise[19].

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].

Bathymetry of the northern Antarctic Peninsula. Note the deep Bransfield Basin.

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].

Geological history

Table 1. Geological timescale

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[38].

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[39]. 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[39]. 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.

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Further reading

References


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.

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Antarctic Peninsula Ice Sheet evolution

Pre-Quaternary Antarctic Peninsula Ice Sheet evolution | Quaternary glaciation of the Antarctic Peninsula | Last Glacial Maximum | Antarctic Peninsula Ice streams | References | Comments |

This section is largely taken from Davies et al. 2012 (Quaternary Science Reviews)[1], 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)[2]. Pre-Quaternary sediments have been dated using biostratigraphy (dinoflagellate cysts)[2], isotopic dating of volcanic rocks[3-5] and strontium isotopes analysis on shells[6, 7].

Map of the Antarctic Peninsula, after Davies et al., 2012 (Quaternary Science Reviews)

The earliest ice sheets began to develop around the Palaeogene-Neogene boundary (see Table 1), circa 35 Ma[8]. 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[11]. The Antarctic Circumpolar Current isolated Antarctica from other regimes, resulting in the development of a cooler polar climate[12].

Westerly Winds and ocean fronts around Antarctica. The Antarctic Cirumpolar Current flows around the Antarctic Continent, driven by the Southern Hemisphere Westerly winds.

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 relatively high mountains of the Antarctic Peninsula probably acted as a nucleus for glaciation, with cooler temperatures at higher altitudes encouraging glacierisation[1, 11].

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[17].

During this period, the West Antarctic Ice Sheet and Antarctic Peninsula Ice Sheets together grew successively larger, with periodic collapses during interglacials.

Table 1. Timescale in the Antarctic Peninsula, showing glacial events from the Cenozoic to the present day. APIS – Antarctic Peninsula Ice Sheet. JRI – James Ross Island. WAIS – West Antarctic Ice Sheet. Small ice caps began to develop in the area about5 million years ago. Large continental wide ice sheets began to develop during the Quaternary, with oscillations at 100,000 year periodicities after about 400,000 years ago.

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[1]. 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.

Neogene glaciovolcanic outcrops on James Ross Island. From: Davies et al. 2012

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[22].

Ice thickness data can be deduced from these glaciovolcanic rocks[23].  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[17].

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[25].

Middle Pleistocene (1Ma to 200 ka)

Simplified cartoon of a tributary glacier feeding into an ice shelf, showing the grounding line (where the glacier begins to float).

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[17].

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[28]. 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[17].

Terrapin Hill, a tuff cone on James Ross Island

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[1], 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[35].

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.

Schematic figure of geomorphology on the continental shelf around the Antarctic Peninsula. From Davies et al., 2012.

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[17].

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[44].  

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[45].

Schematic reconstruction of the Antarctic Peninsula Ice Sheet during the Last Glacial Maximum. From: Davies et al., 2012

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[44].

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[46] has meant that a large number of ice streams have been identified around the Antarctic continent, from both marine and terrestrial settings.

Palaeo-ice streams around the Antarctic Peninsula during and after the LGM, showing isochrones of recession. From: Davies et al., 2012 (Quaternary Science Reviews).

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[44].

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[44]. 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[47]. 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[47].

Finally, slow and steady retreat is recorded by numerous closely-spaced moraines and intermittent grounding-zone wedges[47]. 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[47], 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[47]. 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[44].

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[40].

Radiocarbon dates from marine sediment cores across the continental shelf provide an indication of ice marginal positions during recession.

Schematic map showing isochrones of ice sheet and ice stream recession around the Antarctic Peninsula. From: Davies et al. 2012

Further reading

Go to top or jump to Subglacial Volcanoes.

References


1.            Davies, B.J., Hambrey, M.J., Smellie, J.L., Carrivick, J.L., and Glasser, N.F., 2012. Antarctic Peninsula Ice Sheet evolution during the Cenozoic Era. Quaternary Science Reviews, 2012. 31(0): p. 30-66.

2.            Anderson, J.B., Wamy, S., Askain, R.A., Wellner, J.S., Bohaty, S.M., Kirshner, A., Livsey, D.L., Simms, A.R., Smith, T.A., Ehrmann, W., Lawver, L.A., Barbeau, D.L., Wise, S.W., Kuhlhenek, D.K., Weaver, F.M., and Majewski, W., 2011. Progressive Cenozoic cooling and the demise of Antarctica’s last refugium. Proceedings of the National Academy of Sciences, 2011. 108: p. 11356-11360.

3.            Smellie, J.L., Hole, M.J., and Nell, P.A.R., 1993. Late Miocene valley-confined subglacial volcanism in northern Alexander Island, Antarctic Peninsula. Bulletin of Volcanology, 1993. 55: p. 273-288.

4.            Smellie, J.L., Johnson, J.S., McIntosh, W.C., Esser, R., Gudmundsson, M.T., Hambrey, M.J., and van Wyk de Vries, B., 2008. 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.

5.            Smellie, J.L., McArthur, J.M., McIntosh, W.C., and Esser, R., 2006. 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.

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10.          Mayewski, P.A., Meredith, M.P., Summerhayes, C.P., Turner, J., Worby, A., Barrett, P.J., Casassa, G., Bertler, N.A.N., Bracegirdle, T., Naveira Garabato, A.C., Bromwich, D., Campell, H., Hamilton, G.S., Lyons, W.B., Maasch, K.A., Aoki, S., Xiao, C., and van Ommen, T., 2009. State of the Antarctic and Southern Ocean climate system. Reviews of Geophysics, 2009. 47(RG1003): p. 1-38.

11.          Siegert, M.J., 2008. Antarctic subglacial topography and ice-sheet evolution. Earth Surface Processes and Landforms, 2008. 33: p. 646-660.

12.          Eagles, G. and Livermore, R.A., 2002. Opening history of Powell Basin, Antarctic Peninsula. Marine Geology, 2002. 185(3-4): p. 195-205.

13.          Naish, T., Powell, R., Levy, R., Wilson, G., Scherer, R., Talarico, F., Krissek, L., Niessen, F., Pompilio, M., Wilson, T., Carter, L., DeConto, R., Huybers, P., McKay, R., Pollard, D., Ross, J., Winter, D., Barrett, P., Browne, G., Cody, R., Cowan, E., Crampton, J., Dunbar, G., Dunbar, N., Florindo, F., Gebhardt, C., Graham, I., Hannah, M., Hansaraj, D., Harwood, D., Helling, D., Henrys, S., Hinnov, L., Kuhn, G., Kyle, P., Laufer, A., Maffioli, P., Magens, D., Mandernack, K., McIntosh, W., Millan, C., Morin, R., Ohneiser, C., Paulsen, T., Persico, D., Raine, I., Reed, J., Riesselman, C., Sagnotti, L., Schmitt, D., Sjunneskog, C., Strong, P., Taviani, M., Vogel, S., Wilch, T., and Williams, T., 2009. Obliquity-paced Pliocene West Antarctic ice sheet oscillations. Nature, 2009. 458(7236): p. 322-U84.

14.          Naish, T.R., Woolfe, K.J., Barrett, P.J., Wilson, G.S., Atkins, C., Bohaty, S.M., Bucker, C.J., Claps, M., Davey, F.J., Dunbar, G.B., Dunn, A.G., Fielding, C.R., Florindo, F., Hannah, M.J., Harwood, D.M., Henrys, S.A., Krissek, L.A., Lavelle, M., van der Meer, J., McIntosh, W.C., Niessen, F., Passchier, S., Powell, R.D., Roberts, A.P., Sagnotti, L., Scherer, R.P., Strong, C.P., Talarico, F., Verosub, K.L., Villa, G., Watkins, D.K., Webb, P.N., and Wonik, T., 2001. Orbitally induced oscillations in the East Antarctic ice sheet at the Oligocene/Miocene boundary. Nature, 2001. 413(6857): p. 719-723.

15.          Bart, P.J. and Anderson, J.B., 2000. Relative temporal stability of the Antarctic ice sheets during the late Neogene based on the minimum frequency of outer shelf grounding events. Earth and Planetary Science Letters, 2000. 182(3-4): p. 259-272.

16.          Pudsey, C.J., 2002. Neogene record of Antarctic Peninsula glaciation in continental rise sediments: ODP Leg 178, Site 1095, in Ocean Drilling Program Scientific Results, Vol. 178, P.F. Barker, et al., Editors. Texas A&M University: College Station, Texas. p. 1-25 (CD-ROM).

17.          Cowan, E.A., Hillenbrand, C.-D., Hassler, L.E., and Ake, M.T., 2008. Coarse-grained terrigenous sediment deposition on continental rise drifts: A record of Plio-Pleistocene glaciation on the Antarctic Peninsula. Palaeogeography, Palaeoclimatology, Palaeoecology, 2008. 265(3-4): p. 275-291.

18.          Convey, P., Gibson, J.A.E., Hillenbrand, C.-D., Hodgson, D.A., Pugh, P.J.A., Smellie, J.L., and Stevens, M.I., 2008. Antarctic terrestrial life – challenging the history of the frozen continent? Biological Reviews, 2008. 83(2): p. 103-117.

19.          Convey, P., Stevens, M.I., Hodgson, D.A., Smellie, J.L., Hillenbrand, C.-D., Barnes, D.K.A., Clarke, A., Pugh, P.J.A., Linse, K., and Cary, S.C., 2009. Exploring biological constraints on the glacial history of Antarctica. Quaternary Science Reviews, 2009. 28(27-28): p. 3035-3048.

20.          Smellie, J.L., Haywood, A.M., Hillenbrand, C.-D., Lunt, D.J., and Valdes, P.J., 2009. Nature of the Antarctic Peninsula Ice Sheet during the Pliocene: Geological evidence and modelling results compared. Earth-Science Reviews, 2009. 94(1-4): p. 79-94.

21.          Hambrey, M.J., Smellie, J.L., Nelson, A.E., and Johnson, J.S., 2008. Late Cenozoic glacier-volcano interaction on James Ross Island and adjacent areas, Antarctic Peninsula region. Geological Society of America Bulletin, 2008. 120(5-6): p. 709-731.

22.          Glasser, N.F. and Hambrey, M.J., 2001. Styles of sedimentation beneath Svalbard valley glaciers under changing dynamic and thermal regimes. Journal of the Geological Society, London, 2001. 158: p. 697-707.

23.          Smellie, J.L., Rocchi, S., and Armienti, P., 2011. Late Miocene volcanic sequences in northern Victoria Land, Antarctica: products of glaciovolcanic eruptions under different thermal regimes. Bulletin of Volcanology, 2011. 73(1): p. 1-25.

24.          Smellie, J.L., McIntosh, W.C., and Esser, R., 2006. Eruptive environment of volcanism on Brabant Island: Evidence for thin wet-based ice in northern Antarctic Peninsula during the Late Quaternary. Palaeogeography, Palaeoclimatology, Palaeoecology, 2006. 231(1-2): p. 233-252.

25.          Smith, T.R. and Anderson, J.B., 2010. 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.

26.          Huybrechts, P., 1990. A 3-D model for the Antarctic ice sheet: a sensitivity study on the glacial-interglacial contrast. Climate Dynamics, 1990. 5: p. 79-92.

27.          Barker, P.F., Barrett, P.J., Cooper, A.K., and Huybrechts, P., 1999. Antarctic glacial history from numerical models and continental margin sediments. Palaeogeography Palaeoclimatology Palaeoecology, 1999. 150(3-4): p. 247-267.

28.          Hillenbrand, C.-D. and Ehrmann, W., 2005. Late Neogene to Quaternary environmental changes in the Antarctic Peninsula region: evidence from drift sediments. Global and Planetary Change, 2005. 45(1-3): p. 165-191.

29.          Birkenmajer, K., 1982. Pliocene tillite-bearing sucession of King George Island (South Shetland Islands, Antarctica). Studia Geologica Polonica, 1982: p. 77-72.

30.          Mercer, J.H., 1978. West Antarctic Ice Sheet and CO2 Greenhouse effect – threat of disaster. Nature, 1978. 271(5643): p. 321-325.

31.          Overpeck, J.T., Otto-Bliesner, B., Miller, G.H., Muhs, D.R., Alley, R.B., and Kiehl, J.T., 2006. Palaeoclimatic evidence for future ice sheet instability and rapid sea level rise. Science, 2006. 311(no. 5768): p. 1747-1750.

32.          Pudsey, C.J., Barker, P.F., and Larter, R.D., 1994. Ice sheet retreat from the Antarctic Peninsula shelf. Continental Shelf Research, 1994. 14(15): p. 1647-1675.

33.          Pudsey, C.J., 2000. Sedimentation on the continental rise west of the Antarctic Peninsula over the last three glacial cycles. Marine Geology, 2000. 167: p. 313-338.

34.          Ó Cofaigh, C., Dowdeswell, J.A., and Pudsey, C.J., 2001. Late Quaternary Iceberg Rafting along the Antarctic Peninsula Continental Rise and in the Weddell and Scotia Seas. Quaternary Research, 2001. 56: p. 308-321.

35.          Reinardy, B.T.I., Pudsey, C.J., Hillenbrand, C.-D., Murray, T., and Evans, J., 2009. Contrasting sources for glacial and interglacial shelf sediments used to interpret changing ice flow directions in the Larsen Basin, Northern Antarctic Peninsula. Marine Geology, 2009. 266(1-4): p. 156-171.

36.          Huybrechts, P., 2009. GLOBAL CHANGE West-side story of Antarctic ice. Nature, 2009. 458(7236): p. 295-296.

37.          Huybrechts, P., 2002. Sea-level changes at the LGM from ice-dynamic reconstructions of the Greenland and Antarctic ice sheets during the glacial cycles. Quaternary Science Reviews, 2002. 21(1-3): p. 203-231.

38.          Wellner, J.S., Heroy, D.C., and Andersen, J.B., 2006. The death mask of the Antarctic ice sheet: comparison of glacial geomorphic features across the continental shelf. Geomorphology, 2006. 75: p. 157-171.

39.          Ó Cofaigh, C., Dowdeswell, J.A., Allen, C.S., Hiemstra, J.F., Pudsey, C.J., Evans, J., and Evans, D.J.A., 2005. Flow dynamics and till genesis associated with a marine-based Antarctic palaeo-ice stream. Quaternary Science Reviews, 2005. 24(5-6): p. 709-740.

40.          Ó Cofaigh, C., Dowdeswell, J.A., Evans, J., and Larter, R.D., 2008. Geological constraints on Antarctic palaeo-ice-stream retreat. Earth Surface Processes and Landforms, 2008. 33(4): p. 513-525.

41.          Ó Cofaigh, C., Justin, T., Julian A, D., and Carol J, P., 2003. Palaeo-ice streams, trough mouth fans and high-latitude continental slope sedimentation. Boreas, 2003. 32: p. 37-55.

42.          Ó Cofaigh, C., Larter, R.D., Dowdeswel, J.A., Hillenbrand, C.-D., Pudsey, C.J., Evans, J., and Morris, P., 2005. Flow of the West Antarctic Ice Sheet on the continental margin of the Bellingshausen Sea at the Last Glacial Maximum. Journal of Geophysical Research, 2005. 110: p. B11103.

43.          Ó Cofaigh, C., Pudsey, C.J., Dowdeswel, J.A., and Morris, P., 2002. Evolution of subglacial bedforms along a palaeo-ice stream, Antarctic Peninsula continental shelf. Geophysical Research Letters, 2002. 29: p. 41-1 – 41-4.

44.          Livingstone, S.J., O Cofaigh, C., Stokes, C.R., Hillenbrand, C.-D., Vieli, A., and Jamieson, S.S.R., 2012. Antarctic palaeo-ice streams. Earth-Science Reviews, 2012. 111(1-2): p. 90-128.

45.          Bindschadler, R., 2006. 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.

46            Stokes, C.R. and C.D. Clark, 1999. Geomorphological criteria for identifying Pleistocene ice streams. Annals of Glaciology, 28: 67-74.

47.           Ó Cofaigh, C., J.A. Dowdeswell, J. Evans, and R.D. Larter, 2008. Geological constraints on Antarctic palaeo-ice-stream retreat. Earth Surface Processes and Landforms, 33(4): 513-525.

48.          Shipp, S.S., J.S. Wellner, and J.B. Anderson, 2002. Retreat signature of a polar ice stream: subglacial geomorphic features and sediments from the Ross Sea, Antarctica. Geological Society of America Bulletin, 111: 1486-1516.

Ice shelf collapse

What is an ice shelf? | Ice shelf collapse | Mechanisms of ice shelf collapse | Ice shelf buttressing | References | Comments

What is an ice shelf?

Larsen Ice Shelf in 2004

Ice shelves are floating tongues of ice that extend from grounded glaciers on land. Snow falls on glaciers, which flow downstream under gravity. Ice shelves are common around Antarctica, and the largest ones are the Ronne-Filchner, Ross and McMurdo Ice Shelves.

Ice shelves surround 75% of Antarctica’s coastline, and cover an area of over 1.561 million square kilometres (a similar size to the Greenland Ice Sheet). Ice shelves gain mass from ice flowing into them from glaciers onland, from snow accumulation, and from the freezing of marine ice (sea water) to their undersides[1]. They lose mass by calving icebergs, and basal melting towards their outer margins, along with sublimation and wind drift on their surfaces. Ice shelves are important, because they play a role in the stability of the Antarctic Ice Sheet and the ice sheet’s mass balance, and are important for ocean stratification and bottom water formation; this helps drive the world’s thermohaline circulation. Melting from beneath ice shelves is one of the key ways in which the Antarctic Ice Sheet loses mass[1].

In the satellite image of Prince Gustav Ice Shelf below, you can see that the ice shelves have a very flat appearance. In fact, you can normally tell where the ice starts to float by a sharp break in slope at the grounding line. Ice shelves are therefore composed of ice derived from snowfall on land, but they also accrete marine ice from below[2]. Ice shelves are therefore distinct from sea ice, which form solely from freezing marine water. You can see an example from northern Antarctic Peninsula below. Prince Gustav Ice Shelf was situated between Trinity Peninsula and James Ross Island. It collapsed in 1995. You can see glaciological structures on the ice shelf, indicating that it flows out from its tributary glaciers. You can also see abundant melt ponds on the ice shelf.

Ice shelves around Antarctica are up to 50,000 km2 in size, and can be up to 2000 m thick. Their front terminus is often up to 100 m high. Ice shelves intermittently calve large icebergs, which is a normal part of their ablation. Around Antarctica, ice shelves form where mean annual temperatures are less than -9°C, with sequential break up of ice shelves as temperatures increase[3-5]. The geometry of the coastline is often important for determining where ice shelves will develop. The Larsen Ice Shelf, for example, is formed in an embayment.

Ice shelf collapse

Several of the ice shelves around Antarctica have recently collapsed dramatically, rather than retreating in a slow and steady manner.  Larsen A collapsed in 1995[6], and Larsen B Ice Shelf famously collapsed in 2002. It has shrunk from 12,000 km2 in 1963 to 2400 km2 in 2010[4]. During February 2002, 3250 km2 were lost through iceberg calving and fragmentation. In the figure below, you can see the blue, mottled appearance of the ice shelf in the 2002 image, caused by the exposure of deeper blue glacier ice.

Landsat images showing the collapse of the Larsen Ice Shelf. Note the blue mottled appearance in 2002, resulting from the exposure of deep blue ice.

Several ice shelves have now collapsed around the Antarctic Peninsula (Table 1). Their collapse has made it possible to core the sub-shelf sediments to investigate whether these collapses are part of normal ice-shelf behaviour. It appears that the more northerly ice shelves, such as Prince Gustav Ice Shelf, have indeed previously collapsed, resulting in open-marine organisms living in Prince Gustav Channel for a short period 5000 years ago[7]. However, the more southerly Larsen B Ice Shelf appears to have remained a fixture throughout the Holocene[8]. This suggests that certain thresholds have been passed, with environmental changes throughout the Antarctic Peninsula now surpassing any that have occurred before.

 

 

In the video below, you can see an animation of the Larsen Ice Shelf collapse from Modis imagery:

Table 1. Dates of ice shelf collapse

Ice shelf Largest area (km2) Previous behaviour Recent behaviour
Wordie 2000 ??? 1989 collapse
Larsen Inlet 400 Frequent removal throughout Holocene 1989 collapse
Prince Gustav 2100 Removal 5000 BP 1995 collapse
Larsen A 2500 Frequent removal throughout Holocene 1995 collapse
Larsen B 11,500 Stable throughout Holocene 2002 collapse
Jones 25 ??? 2003 collapse
Wilkins 16,577 Numerous large calving events 2008 collapse
Larsen C 60,000 Stable throughout Holocene Thinning & retreating
Müller 50 Advance during the Little Ice Age Gradual  recession (50 % left)
George VI 26,000 Brief absence (9000 BP) Still present & thinning. Confined, which may increase stability.

Mechanisms of ice shelf collapse

There are several reasons why ice shelves disintegrate rapidly rather than slowly and steadily shrinking. Ice shelves collapse in response to long term environmental changes, which cause on-going thinning and shrinking. When certain thresholds are passed, catastrophic ice shelf disintegration through iceberg calving is initiated. Before collapse, ice shelves first undergo a period of long-term thinning and basal melting, which makes them vulnerable. Meltwater ponding on the surface and tidal flexure and plate bending then all contribute to rapid calving events and ice shelf disintegration.

1. Long term thinning and basal melting

Antarctic ice shelf thickness changes. Note the rapid thinning of Pine Island Glacier ice shelf in West Antarctica. From Pritchard et al., 2012, Nature. Reprinted by permission from Macmillan Publishers Ltd: Nature (Pritchard et al. 2012), copyright (2012).

Antarctic ice shelf thickness changes. Note the rapid thinning of Pine Island Glacier ice shelf in West Antarctica. From Pritchard et al., 2012, Nature. Reprinted by permission from Macmillan Publishers Ltd: Nature
(Pritchard et al. 2012), copyright (2012).

Long-term thinning from surface and basal melting preconditions the ice shelf to collapse. Negative mass balances on tributary glaciers can lead to thinning of the glaciers and ice shelves. The highest rates of thinning are where relatively warm ocean currents can access the base of ice shelves through deep troughs[9,10]. Ice-shelf structure seems to be important, with sutures between tributary glaciers resulting in weaker areas of thinner ice, which are susceptible to rifting[11].

A recent analysis of ice shelves across Antarctica has shown that basal melt rates are around 1325 ± 235 gigatonnes per year, with an additional calving flux of 1089 ± 139 gigatonnes per year. Ice shelf melting is therefore one of the largest ablation processes in Antarctica[1]. However, this massive basal melting does not occur evenly distributed across all ice shelves; the massive Ronne, Filchner and Ross ice shelves cover two thirds of the total ice shelf area but account for only 15% of net melting. Instead, the highest melt rates occur around the Antarctic Peninsula and West Antarctica, from the northern end of George VI Ice Shelf to the western end of Getz Ice Shelf[1]. These ice shelves are also rapidly thinning rapidly[9]. On slow moving ice shelves (e.g., George VI, Abbot, Wilkins), almost all of the original land ice has melted away within a few kilometres of the grounding line. So, half of the meltwater produced comes from just ten small, warm-cavity ice shelves around the SE Pacific rim of Antarctica, and these ten ice shelves occupy just 8% of total ice shelf area. All this cold water being released into the ocean has a significant impact on the formation of sea ice, resulting in higher rates of sea ice concentration around Antarctica.

Melting of ice shelves around Pine Island Glacier in West Antarctica is concerning, because the West Antarctic Ice Sheet is grounded below sea level. A collapse of this ice shelf could lead to marine ice sheet instabilty and rapid global sea level rise.

Landsat Image Mosaic of Antarctica (LIMA) showing location of key ice shelves.

Landsat Image Mosaic of Antarctica (LIMA) showing location of key ice shelves.

2. Surface melting and ponding

Increased atmospheric temperatures lead to surface melting and ponding on the ice surface. Catastrophic ice-shelf collapsed tend to occur after a relatively warm summer season, with increased surface melting[12]. Based on the seasonality of ice shelf break up, and the geographic distribution of ice shelf collapse near the southerly-progressing -9°C isotherm, it appears that surface ponding is necessary for ice-shelf collapse[12]. This meltwater melts downwards into the ice shelf, causing fractures and leading to rapid ice-berg calving[5, 12]. Increased surface meltwater also leads to snow saturation, filling crevasses with water and increasing hydrostatic pressures. Brine infiltration can also cause crack over deepening.

3. Plate bending and tidal flexure

However, meltwater ponding alone does not explain rapid ice-shelf fragmentation. We need to invole a third process. Bending at the frontal margin of the ice shelf as a result of tidal flexure may cause small cracks to form parallel to the ice front. When subject to the above conditions (thinning with abundant surface water), a threshold may be passed, causing rapid ice shelf disintegration[12].

When icebergs are formed through the above mechanisms, long, thin icebergs are formed at the ice front. These icebergs will capsize as they are thinner than they are deep. Iceberg capsize releases gravitational potential energy and increases tensile stress on the ice shelf. This may lead to a cascade of fragmentation, capsize, and iceberg break up[13].

Ice shelf buttressing

Glacier-ice shelf interactions: In a stable glacier-ice shelf system, the glacier’s downhill movement is offset by the buoyant force of the water on the front of the shelf. Warmer temperatures destabilize this system by lubricating the glacier’s base and creating melt ponds that eventually carve through the shelf. Once the ice shelf retreats to the grounding line, the buoyant force that used to offset glacier flow becomes negligible, and the glacier picks up speed on its way to the sea. Original Image by Ted Scambos and Michon Scott, National Snow and Ice Data Center.

Collapsing ice shelves do not directly contribute to global sea level rise. This is because they are floating, and so their melting does not result in sea level rise. To check this, put a few ice cubes in a glass and check the water level. Does the water rise when the “icebergs” melt?

However, ice shelves play a very important role in “buttressing” their tributary glaciers. Glaciers that feed into ice shelves are held back by the ice shelf in front of them[14, 15]. Even small ice shelves play an important role in regulating flow from ice streams that feed into them[14]. This has been observed in several cases, most notably following the Larsen Ice Shelf [16-19] and Prince Gustav Ice Shelf collapses[20, 21]. In the Landsat image of Prince Gustav Ice Shelf above, you can see the rapid glacier recession from 1988 to 2009.

With glaciers thinning, accelerating and receding in response to ice shelf collapse[20, 21], more ice is directly transported into the oceans, making a direct contribution to sea level rise. Sea level rise due to ice shelf collapse is as yet limited, but large ice shelves surrounding some of the major Antarctic glaciers could be at risk, and their collapse would result in a significant sea level rise contribution[22]. See Marine Ice Sheet Instability for more information.

Further reading

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References


1.            Rignot, E., Jacobs, S., Mouginot, J., and Scheuchl, B. (2013). Ice Shelf Melting Around Antarctica. Science.

2.            Holland, P.R., Corr, H.F.J., Vaughan, D.G., Jenkins, A., and Skvarca, P., 2009. Marine ice in Larsen Ice Shelf. Geophysical Research Letters, 2009. 36: p. L11604.

3.            Morris, E.M. and Vaughan, A.P.M., 2003. 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. American Geophysical Union, Antarctic Research Series, Volume 79: Washington, D.C. p. 61-68.

4.            Cook, A.J. and Vaughan, D.G., 2010. 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.

5.            Scambos, T., Hulbe, C., and Fahnestock, M., 2003. Climate-induced ice shelf disintegration in the Antarctic Peninsula, in Antarctic Peninsula climate variability: historical and palaeoenvironmental perspectives, E.W. Domack, et al., Editors. American Geophysical Union, Antarctic Research Series, Volume 79: Washington, D.C. p. 79-92.

6.            Rott, H., Skvarca, P., and Nagler, T., 1996. Rapid collapse of northern Larsen Ice Shelf, Antarctica. Science, 1996. 271(5250): p. 788-792.

7.            Pudsey, C.J. and Evans, J., 2001. First survey of Antarctic sub-ice shelf sediments reveals Mid-Holocene ice shelf retreat. Geology, 2001. 29: p. 787-790.

8.            Domack, E., Duran, D., Leventer, A., Ishman, S., Doane, S., McCallum, S., Amblas, D., Ring, J., Gilbert, R., and Prentice, M., 2005. Stability of the Larsen B ice shelf on the Antarctic Peninsula during the Holocene epoch. Nature, 2005. 436(4): p. 681-685.

9.            Pritchard, H.D., Ligtenberg, S.R.M., Fricker, H.A., Vaughan, D.G., van den Broeke, M.R., and Padman, L., 2012. Antarctic ice-sheet loss driven by basal melting of ice shelves. Nature, 2012. 484(7395): p. 502-505.

10.            Shepherd, A., Wingham, D., and Rignot, E., 2004. Warm ocean is eroding West Antarctic Ice Sheet. Geophysical Research Letters, 2004. 31(23): p. L23402.

11.          Glasser, N.F. and Scambos, T.A., 2008. A structural glaciological analysis of the 2002 Larsen B ice shelf collapse. Journal of Glaciology, 2008. 54(184): p. 3-16.

12.          Scambos, T., Fricker, H.A., Liu, C.-C., Bohlander, J., Fastook, J., Sargent, A., Massom, R., and Wu, A.-M., 2009. 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, 2009. 280(1–4): p. 51-60.

13.          MacAyeal, D.R., Scambos, T.A., Hulbe, C.L., and Fahnestock, M.A., 2003. Catastrophic ice-shelf break-up by an ice-shelf-fragment-capsize mechanism. Journal of Glaciology, 2003. 49(164): p. 22-36.

14.          Dupont, T.K. and Alley, R.B., 2006. Role of small ice shelves in sea-level rise. Geophys. Res. Lett., 2006. 33(9): p. L09503.

15.          Dupont, T.K. and Alley, R.B., 2005. Assessment of the importance of ice-shelf buttressing to ice-sheet flow. Geophys. Res. Lett., 2005. 32(4): p. L04503.

16.          Scambos, T.A., Bohlander, J.A., Shuman, C.A., and Skvarca, P., 2004. Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica. Geophysical Research Letters, 2004. 31: p. L18402.

17.          Rott, H., Müller, F., and Floricioiu, D., 2011. The Imbalance of glaciers after disintegration of Larsen B ice shelf, Antarctic Peninsula. The Cryosphere, 2011. 5: p. 125-134.

18.          Hulbe, C.L., Scambos, T.A., Youngberg, T., and Lamb, A.K., 2008. Patterns of glacier response to disintegration of the Larsen B ice shelf, Antarctic Peninsula. Global and Planetary Change, 2008. 63(1): p. 1-8.

19.          Rott, H., Rack, W., Nagler, T., and Ieee. 2007. Increased export of grounded ice after the collapse of northern Larsen Ice Shelf, Antarctic Peninsula, observed by Envisat ASAR, in Igarss: 2007 Ieee International Geoscience and Remote Sensing Symposium, Vols 1-12 – Sensing and Understanding Our Planet. p. 1174-1176.

20.          Glasser, N.F., Scambos, T.A., Bohlander, J., Truffer, M., Pettit, E., & Davies, B.J., 2011. From ice-shelf tributary to tidewater glacier: continued glacier recession, acceleration and thinning following the 1995 collapse of the Prince Gustav Ice Shelf on the Antarctic Peninsula. Journal of Glaciology 57, 397-406.

21.          Davies, B.J., Carrivick, J.L., Glasser, N.F., Hambrey, M.J., & Smellie, J.S., 2012. Variable glacier response to atmospheric warming, northern Antarctic Peninsula, 1988–2009. The Cryosphere 6, 1031-1048. doi:10.5194/tc-6-1031-2012

22.          Joughin, I. and Alley, R.B., 2011. Stability of the West Antarctic ice sheet in a warming world. Nature Geosci, 2011. 4(8): p. 506-513.

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