Ice Sheets and Glaciers Technical University of Denmark Kees van der Veen Department of Geography University of Kansas
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
Living along coasts 3of 52
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
Antarctica 5of 52
Greenland 6of 52
Distribution of mountain glaciers 7of 52
The Last Glacial Maximum VOLUME (10 6 km 3 ) present LGM Antarctica 26 34 Greenland 2.9 3.5 North America -- 33.0 Eurasia -- 13.3 8of 52
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(From: Murck and Skinner, 1999) 10 of 52 Map of central North America during the last glacial maximum, about 18,000 years ago
Glacial cycles Ice volume Temperature 11 of 52
Ice sheet in Kansas ~450,000 years B.P. 12 of 52
13 of 52 Retreat of the North American ice sheets; carbon-dated ages are in thousands of years (From: Ruddiman, 2001)
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
Building an ice sheet 15 of 52
Continental ice sheet 16 of 52
Mountain glacier 17 of 52
Equilibrium line 18 of 52
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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
geothermal heat meltwater 25 of 52
meltwater 26 of 52
meltwater 27 of 52
meltwater 28 of 52
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
Ice flow 30 of 52
ice streams in Antarctica 31 of 52
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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Retreat of calving front of Jakobshavn Glacier 34 of 52
Greenland s mass loss doubled in the last decade: 0.23 ± 0.08 mm slr / yr in 1996 0.57 ± 0.1 mm slr / yr in 2005 2/3 of the loss is caused by ice dynamics 1/3 is due to enhanced runoff Jakobshavns discharge: 24 km 3 / yr in 1996 46 km 3 / yr in 2005 Rignot and Kanagaratnam, Science (2006) 35 of 52
September 13, 2007, Petermann Glacier, northwest Greenland. 36 of 52 Photo credit NASA/EG&G/ATM team/yungel
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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
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
Retreating mountain glaciers 1928 1979 2003 South Cascade Glacier, WA 40 of 52
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Impacts of glacier retreat Flooding on the short term Change in water availability throughout the year Contribution to sea-level rise 42 of 52
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
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
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
Available glacier mass-balance records Total: > 180,000 Total: > 681,000 km 2 46 of 52
All glaciers cover a surface area of ~680 10 3 km 2 In a typical year, the area covered by observations is ~6000 km 2 What does this mean???? 47 of 52
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
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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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
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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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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