Quantifying Antarctic icebergs and their melting in the ocean.

From the Antarctic Ice Sheet calves every year into the Southern Ocean, an
average of 2000 km3 of icebergs. The meltwater is spread over a large area in the
Southern Ocean but the large temporal variability in iceberg calving and the clustering
of iceberg distribution means that meltwater injection can be locally very high.
This study quantifies iceberg distribution, movement and melting using remote
sensing observations and modelling. Icebergs were detected and tracked on Synthetic
Aperture Radar images using a new computer-based iceberg detection method. The
method allows an efficient and systematic processing of large volumes of SAR images,
necessary to build a climatology of icebergs in the Southern Ocean. Tests were
conducted using ground data from a field campaign and against manual image
classification. The method was applied to several SAR image collections, namely the
RADARS AT RAMP mosaic for the totality of coastal Antarctica, providing the first
picture of iceberg distribution over such a large area.
Giant icebergs (icebergs above 100 km2 in area) were shown to carry over half
the total mass of the Antarctic iceberg population. Estimates of the spatial distribution
of giant iceberg melting over the ocean were made using observed tracks and
modelling the melting and spreading along its path. The modelling of basal melting
was tested using ICESat laser altimetry to measure the reduction in the freeboard of
three giant icebergs in the Ross.
The distribution of meltwater for giant icebergs was combined with an existing
simulation of meltwater distribution from smaller icebergs to produce the first map of
total iceberg meltwater for the Southern Ocean. The iceberg contribution to the
freshwater flux is shown to be relevant to both the Weddell Sea and the Southern
Ocean south of the Polar Front.