Antarctic icebergs distributions, 2002-2010

J. Tournadre (1) , F. Girard-Ardhuin , Benoît Legrésy (2)

1 LOS - Laboratoire d'Océanographie Spatiale
2 GLACIO LEGOS

Interest for icebergs and their possible impact on southern ocean circulation and biology has increased during the recent years. While large tabular icebergs are routinely tracked and monitored using scatterometer data, the distribution of smaller icebergs (less than some km) is still largely unknown as they are difficult to detect operationally using conventional satellite data. In a recent study, Tournadre et al. (2008) showed that small icebergs can be detected, at least in open water, using high resolution (20 Hz) altimeter waveforms. In the present paper, we present an improvement of their method that allows, assuming a constant iceberg freeboard elevation and constant ice backscatter coefficient, to estimate the top-down iceberg surface area and therefore the distribution of the volume of ice on a monthly basis. The complete Jason-1 reprocessed (version C) archive covering the 2002-2010 period has been processed using this method. The small iceberg data base for the southern ocean gives an unprecedented description of the small iceberg (100 m-2800 m) distribution at unprecedented time and space resolutions. The iceberg size, which follows a lognormal distribution with an overall mean length of 630 m, has a strong seasonal cycle reflecting the melting of icebergs during the austral summer estimated at 1.5 m/day. The total volume of ice in the southern ocean has an annual mean value of about 400 Gt, i.e., about 35% of the mean yearly volume of large tabular icebergs estimated from the National Ice Center database of 1979-2003 iceberg tracks and a model of iceberg thermodynamics. They can thus play a significant role in the injection of meltwater in the ocean. The distribution of ice volume which has strong seasonal cycle presents a very high spatial and temporal variability which is much contrasted in the three ocean basins (South Atlantic, Indian and Pacific oceans). The analysis of the relationship between small and large (>5 km) icebergs shows that a majority of small icebergs are directly associated with the large ones but that there are vast regions, such as the eastern branch of the Wedell Gyre, where the transport of ice is made only through the smaller ones.

Domaines: Océanographie

J. Tournadre, F. Girard-Ardhuin, Benoît Legrésy. Antarctic icebergs distributions, 2002-2010. Journal of Geophysical Research, 2012, 117, pp.1-15. ⟨10.1029/2011JC007441⟩. ⟨hal-00747264⟩