Ice with everything - Antarctica: Global Science from a Frozen Continent - page 97

Figure 3.24 Sunset on Concordia station, East Antarctica.

(Credit: IPEV/J. Zaccharia)

temperature inside the central part of the ice
sheet still preserves a signal linked with the last
glacial climate. Similarly, the sub-Antarctic
bedrock is still responding to the change in ice
mass with time, a process called isostatic
rebound where as the weight of ice decreases the
bedrock gradually rises up. As a result, the West
Antarctic grounding line may still be retreating and the ice sheet thinning, a
multi-millennial process which could account for up to 0.5mm of sea-level rise
per year. The massive ice sheet reacts only slowly to climate perturbations by
changing

flow rates on timescales varying from a decade for fast ice streams to
millennia for the inland ice.

Is Antarctica reacting to climate change?

While East Antarctic temperature appears rather stable, multi-decadal warming
has been detected in the Southern Ocean waters as well as in West Antarctica,
reaching 2.5 C in the Antarctic Peninsula. Until recently, there were not enough
measurements to determine whether Antarctica was growing or shrinking. Different
methodologies have been deployed to assess the mass balance of the Antarctic ice
sheet. Over the past two decades, radar and laser altimeters on satellites have been
used to monitor the surface height of the ice sheet and therefore estimate its volume.
Over the past few years, new spatial instruments have begun to monitor the
gravitational attraction of the Antarctic ice sheet and offer the potential to assess
the interannual variability in its total mass. The mass balance change can also be
analysed by comparing the input (snowfall accumulation) versus the output
(water lost into the surrounding oceans). The input is estimated using ice core
layer counting, meteorological measurements or atmospheric model simulations.
These models can also be used to estimate the runoff caused by coastal melting.
The mass loss due to calving processes is estimated from measurements of coastal
ice

flow velocity and thinning.
The different methods suggest that the West Antarctic ice sheet has been
increasingly losing mass over the past years, at a rate of about 0.4 ± 0.2mm per year,
which represents 10

30% of the current global sea level rise (3.2mmyear 1 ). With
evidence that the overall Antarctic continent accumulation of snow has been stable
over the past 50 years, the accelerating net loss of Antarctic ice appears mostly
due to the out

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ow of ice from the Antarctic Peninsula and some West Antarctic