Ice with everything - Antarctica: Global Science from a Frozen Continent - page 93

tropical locations. Interestingly, methane concentrations show rapid variations
synchronous with the Greenland changes. The rapid variations in global
methane were used to construct common age scales for both Greenland and
Antarctic ice cores. Precise comparisons of Antarctic and Greenland temperature
reconstructions have now shown that cold Greenland phases (

) are
associated with Antarctic warming. By contrast, the abrupt Greenland warming
marks the end of the Antarctic warmth, followed by a slow decline. In this respect,
the abrupt events have a global signature, but are not globally synchronous. The
systematic bipolar see-saw behaviour con

' stadials '

rmed that these abrupt climate events are
associated with a redistribution of heat between the two hemispheres, caused by
reorganisations of the global ocean circulation. Marine sediment palaeoceanographic
records have clearly shown that the north Atlantic Ocean circulation has undergone
major historical changes. These ocean circulation reorganisations were linked
with massive freshwater discharges provided by the huge ice sheets which used
to cover North America and north Eurasia. The formation of north Atlantic deep
waters is indeed strongly sensitive to the density of surface waters, and a substantial
in ow of freshwater can modify the density gradients, the formation of deep waters,

and the ef ciency of heat redistribution by the global ocean circulation. Recently, the

long-term Antarctic methane and temperature record has revealed that these
instabilities are not restricted to the last climatic cycle, but are a characteristic of
climate change during all the glacial periods of the past 800 000 years. Past climates
therefore show that unstable ice sheets can induce major reorganisations in
global ocean circulation.
Doweneedmoreicecores?Weneedabetter high-resolution description of the
spatio-temporal climate and environmental changes in Antarctic. The recent
history of Antarctic climate, mass balance, atmospheric aerosol load and climate
forcing factors remains largely unknown, and the International Partnership for
Ice Core Science aims to obtain high-resolution ice cores spanning the past 2000
years with annual resolution from all around the Antarctic. The processes involved
intherapidclimatechangesofthelasticeageclearlyinvolveoceancirculation
changes, but also large-scale atmospheric circulation changes. This raises the
need for circum-Antarctic high-resolution ice core records spanning the past
40 000 years, which can provide precise records of the sequence of regional
climate changes, in relationship to local sea ice feedbacks both during the last rapid
events and during the last glacial interglacial transitions. Finally, while the 800 000

year long Dome C record has already brought a wealth of information and
questions regarding glacial

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interglacial cycles, it is a major challenge for the ice
core community to obtain deep ice cores reaching back to 1.3million years or more
which may be possible in several places close to Vostok, Dome C, or Dome
A where the ice is over 3000m deep. This is perhaps the most challenging place

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