Ice Sheets and Glaciers

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1 Ice Sheets and Glaciers Technical University of Denmark Kees van der Veen Department of Geography University of Kansas

2 Why are glaciers and ice sheets important? Large volume of fresh water stored in ice masses Change in ice volume affects global sea level Potential threat to coastal communities 2of 52

3 Living along coasts 3of 52

4 How much ice is on Earth? Antarctica ~70 m sea-level equivalent Greenland ~7 m sea-level equivalent Mountain glaciers and small ice caps ~0.5 m sea-level equivalent 4of 52

5 Antarctica 5of 52

6 Greenland 6of 52

7 Distribution of mountain glaciers 7of 52

8 The Last Glacial Maximum VOLUME (10 6 km 3 ) present LGM Antarctica Greenland North America Eurasia of 52

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10 (From: Murck and Skinner, 1999) 10 of 52 Map of central North America during the last glacial maximum, about 18,000 years ago

11 Glacial cycles Ice volume Temperature 11 of 52

12 Ice sheet in Kansas ~450,000 years B.P. 12 of 52

13 13 of 52 Retreat of the North American ice sheets; carbon-dated ages are in thousands of years (From: Ruddiman, 2001)

14 Characteristics of glacial cycles Slow growth of ice sheet (~80 kyr) results from variations in incoming solar radiation (Milankovitch cycles) climate feedbacks amplify this forcing Rapid disintegration (~10 kyr) feedbacks make ice sheet unstable retreat not continuous: alternating rapid retreat and readvance 14 of 52

15 Building an ice sheet 15 of 52

16 Continental ice sheet 16 of 52

17 Mountain glacier 17 of 52

18 Equilibrium line 18 of 52

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24 Ice-sheet disintegration Surface melting not fast enough to explain rapid disappearance of NH ice sheets Iceberg calving proglacial lakes form, increasing iceberg production Ice streams fast-moving rivers of ice drain interior rapidly 24 of 52

25 geothermal heat meltwater 25 of 52

26 meltwater 26 of 52

27 meltwater 27 of 52

28 meltwater 28 of 52

29 Internal deformation Ice flow ice spreading under its own weight slow: up to 10s of m/yr Basal sliding ice slipping over a lubricated bed fast: up to 10s of km/yr 29 of 52

30 Ice flow 30 of 52

31 ice streams in Antarctica 31 of 52

32 Why are we concerned? Ice-shelf break-up in the Antarctic Peninsula Rapid thinning of outlet glaciers in Greenland Increased velocities on outlet glaciers 32 of 52

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34 Retreat of calving front of Jakobshavn Glacier 34 of 52

35 Greenland s mass loss doubled in the last decade: 0.23 ± 0.08 mm slr / yr in ± 0.1 mm slr / yr in /3 of the loss is caused by ice dynamics 1/3 is due to enhanced runoff Jakobshavns discharge: 24 km 3 / yr in km 3 / yr in 2005 Rignot and Kanagaratnam, Science (2006) 35 of 52

36 September 13, 2007, Petermann Glacier, northwest Greenland. 36 of 52 Photo credit NASA/EG&G/ATM team/yungel

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38 Is there a threshold? Conventional theory predicts slow icesheet adjustments to changes in climate Recent observations indicate rapid changes are possible Can polar ice sheets become unstable? 38 of 52

39 Goals of glacier studies Measure what ice sheets are doing Understand the cause for ongoing changes Predict future changes Interdisciplinary approach needed 39 of 52

40 Retreating mountain glaciers South Cascade Glacier, WA 40 of 52

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42 Impacts of glacier retreat Flooding on the short term Change in water availability throughout the year Contribution to sea-level rise 42 of 52

43 Glaciers as indicators of climate change The elephant and the mouse... Greenland and Antarctica: long memory current behavior caused in part by past climates Mountain glaciers: short attention span jump around 43 of 52

44 What do glaciers tell us? Small problem. Total number of glaciers on Earth: 180,000 or more Number of glaciers inventorized: 71,558 (< 40%) And what do we know about these glaciers? 44 of 52

45 Since 1946, the mass balance of ~300 glaciers has been measured at one time or another Records > 20 years exist for 43 glaciers Measured glaciers may not be a representative sample of all glaciers.. 45 of 52

46 Available glacier mass-balance records Total: > 180,000 Total: > 681,000 km 2 46 of 52

47 All glaciers cover a surface area of ~ km 2 In a typical year, the area covered by observations is ~6000 km 2 What does this mean???? 47 of 52

48 Less than 1% of all glacier area is measured in any one year... Kinda like measuring rainfall in the US with a single rain gauge in Lawrence. 48 of 52

49 On the bright side.. Glaciers in comparable regions behave similarly Regional trends can be seen Trends can be correlated with temperature 49 of 52

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52 Questions? A thin polar bear named Onassis moaned why can t you get off your asses? It s clear: climate change is reducing my range, so you must make big cuts to bad gases! 52 of 52

53 Retreat of the North American ice sheet was marked by erratic behavior with alternating periods of retreat and advance; throughout the Northern Hemisphere, large fluctuations in climate occurred during the final stages of deglaciation 53 of 52

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55 Meltwater pulse 1A: ca 14,000 yr B.P. sea level rose ~ 20 m over 400 yr average rise 5 cm/yr 55 of 52

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