Ice with everything - Antarctica: Global Science from a Frozen Continent - page 78

Figure 3.11 Schematic view of the

interplay between an ice sheet and the global
water cycle. (Credit: NASA)

be caused if all the continental ice was to melt. Altogether, the Antarctic ice
sheet represents an equivalent of around 57m of sea level, out of which 90% is
for the continental East Antarctic ice sheet and about 10% for the maritime
and more reactive West Antarctic ice sheet. Collapse of the marine unstable
portions of the West Antarctic ice sheet would cause a 3.3m global sea
level rise.
The Antarctic ice sheet is fed by snowfall. The modern snowfall amounts
vary strongly between the coastal areas which intercept cyclonic activity and
intense snowfall (reaching sometimes several metres of water equivalent per year,
in places such as Law Dome), and the inland dry deserts, with an annual mean
snowfall amount less than 2 cm of water equivalent per year in places such as
Dome A. On average, the snowfall on the Antarctic grounded ice sheet is estimated
to reach 18 cm of water equivalent per year: each year, about 6mm of global
sea level are deposited as snow on the surface of the Antarctic continent. If the
ice sheet was in equilibrium, then the amount of water returned to the ocean
would be similar. Estimating changes in this balance of water in and water out is
crucial to predicting the future contribution that the Antarctic could make to
changes in world sea level but is very dif cult to do accurately over such a

huge area.
Day after day, year after year, snowfall accumulates as successive
layers in the interior of the continent. Progressively, the ancient precipitation
is buried in the ice sheet, writing silently the history topic of the Earth s

climate. The shape of the ice sheet results from the interplay between the
inland accumulation of ice, the coastal melting, and the dynamics of ice

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ow
initiated by gravity. Although it seems as hard as rock, ice needs to be imagined as a
very viscous flow systems redistribute the

ice within Antarctica, from inland to coastal locations. Unlike glaciers from other
latitudes or Greenland, the major loss of mass from the Antarctic ice sheet is
not caused by melt but results from the drainage of ice into the sea. Indeed, 90% of

fluid that can flow downhill. Gigantic ice