Geoscience Reference
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Figure 3.12
Iceberg observed at
64 S from the
Marion Dufresne II
oceanographic cruise ship. (Credit: CNRS
Photothèque 2003N00780/Xavier
Crosta)
Figure 3.13
Small fragments of
continental ice ranging from a few
centimetres to a few tens of centimetres
and transported by ocean currents off
shore Dumont d'Urville until they melt.
Heave and waves are very ef cient in
cracking icebergs and accelerating their
fragmentation and melt. (Credit: CNRS/
Xavier Crosta)
the ice is lost from just 10% of the coast, especially through rapid ice streams: Amery,
Ross and Ronne ice shelves, and those all around the Antarctic Peninsula. By
contrast with the slow
flowing interior (with a movement rate below 10m per year),
these streams can be rapid, with
flow rates reaching 500m per year, and their
drainage basins extend over hundreds of kilometres square into the interior. After
passing the so-called
floating ice further accelerates
and gets thinner. The base melts into the sea and the dislocation of the ice shelves
results in the calving of icebergs,
'
grounding line
'
at the coast, the
finally bringing back to the ocean the water
accumulated as ice in the interior.
When did the giant Antarctic ice sheet form? Three hundred million years ago,
Antarctica was located far to the north in the Gondwana supercontinent,
surrounded by a tropical ocean. Progressively, plate tectonics drove Antarctica
towards its modern south polar location, reached about 80million years ago. At the
geological scale, the changing distribution of the continents altered the global
carbon cycle which results from the interplay of carbon sinks (burial of organic
matter and chemical weathering of silicate rocks which deposits carbonates on the
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