Ice with everything - Antarctica: Global Science from a Frozen Continent - page 94

in the world to work, high up on the Antarctic Plateau with a mean annual
temperature of 58 C.

Indeed, palaeoceanographic data show a major climate reorganisation
probably took place from 1.3 to 0.8million years ago. Prior to the last million
years, ice ages were less intense but more frequent, occurring with a spacing of
around 40 000 years. Since 800 000 years ago, ice ages have been more intense,
and longer, reaching a duration of ~100 000 years. This major climate transition
remains essentially unexplained, and could be linked with a long-term decrease in
atmospheric carbon dioxide concentration and different climate responses to orbital
parameters. Ice core data could help to test these hypotheses, and to document
key feedbacks between continental dust, Southern Ocean and sea ice variations,
carbon cycle feedbacks and Antarctic climate. Field work conducted during
the International Polar Year has improved the current knowledge of Antarctic
accumulation rates, bedrock properties and ice thickness, key information to start
planning new deep drilling operations.
The Antarctic ice sheet is the slowest changing component of the climate
system due to the time constant involved in its growth and decay, and it has
persisted over successive glacial and interglacial climate fluctuations. During

glacialperiods,theglobalsealevelwasup to 120m below the present-day, due
to the storage of water inside the two ice sheets which were covering the continents
of the northern hemisphere, both in America (the Laurentide ice sheet) and in
Eurasia (the Fennoscandian ice sheet). At the Last Glacial Maximum, about
21 000 years ago, these two ancient ice sheets had a volume of 80million km 3 ,
more than twice the volume of the modern Antarctic and Greenland ice sheets
combined. At that time, Antarctica was about 10 C colder than nowadays.
Because the sea level was lower than at present, the position of the West
Antarctic grounding line was much further out to sea than at present, inducing
a thickening of the inland West Antarctic ice sheet. This theory is supported by
the discovery of submarine moraines and former grounding lines and streams on
the continental shelf, about 100m below modern sea level. By contrast with the
maritime West Antarctic ice sheet, which is controlled by the rate of loss of ice into
the sea, the continental East Antarctic ice sheet volume is driven by the in ow,

i.e. the accumulation rates on the Antarctic plateau. During glacial times, the
accumulation rate was strongly reduced on the Antarctic continent, restricting
the ice volume of East Antarctica. Altogether, it is estimated that the Antarctic
ice sheet contributed about 10 15m to the 120m of sea-level change between

the last glacial maximum and today.
How does this climate history affect the modern Antarctic ice sheet?
The present-day

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flow of ice within the Antarctic ice sheet is still responding to
the changes produced by the last deglaciation. For instance, the distribution of