Geoscience Reference
In-Depth Information
Rate of mass
increase (billion tonnes/year)
100
6
0
4
2
5
1
-100
-200
7
3
-300
1992
1996
2000
2004
Observation period
Surface-elevation change (cm/year)
-50
-2
0
25
50
Figure 3.25
Rates of surface elevation change from 2002 to 2005 derived from satellite
radar-altimeter measurements. (Credit: UNED/Global Outlook for Snow and Ice)
ice shelves. Satellite measurements have shown a rapid thinning of West Antarctic
ice shelves, for instance in the Admundsen Sea sector, where the surface height has
decreased by several metres over the last decade. The thinning of the ice shelves
appears to be mostly caused by basal melting at the contact with relatively warm
ocean waters lying below the shelves, and induces an acceleration of the tributary
glaciers. The ice shelf reaction can be quite abrupt, as illustrated by the collapse
of the Larsen B ice shelf in 2002, in the north-eastern Antarctic Peninsula. The
analysis of ocean sediment cores from beneath the lost ice shelf has revealed that
this collapse had not happened since the last ice age, and that it was associated with
the acceleration of the tributary glaciers by factors of 2 to 8. Ice shelf retreat has also
been recently monitored on the western side of the Antarctic Peninsula, with the
collapse of the Wordie ice shelf in 2009 and the recent fracturing of the huge
Wilkins ice shelf.
Fast ice sheet
flow can be associated with positive, amplifying feedbacks.
Typically, in response to air or ocean temperature rise, ice shelf melting or
calving is expected to be associated with ice
flow acceleration and thinning of
inland ice. This thinning results in a lower elevation and a higher temperature,
whichinturnmayincreasethesurfacewarming and melting, amplifying the initial
decay. Recently, it has been shown that sedimentary processes are associated with
movements of grounding lines. Till (ground up rock at the base of the ice sheet)
delta deposited by ice streams may help to stabilise the position of the
grounding lines, thicken the ice sheets, and lessen their vulnerability to
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