Antarctic icebergs distributions, 2002–2010

Abstract

[1] 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.

Antarctic icebergs: A significant natural ocean sound source in the Southern Hemisphere

“…The maximum concentration of icebergs is found in the South Atlantic followed by the Indian Ocean, and the least in the South Pacific [Tournadre et al, 2012]. Considering the distances to each hydrophone station (Table 1), the order of iceberg volumes correlates to the mean noise levels in each Ocean.…”

“…Scatter in the acoustically derived locations results from signal dispersion, uncertainty in the sound velocity model, and the array geometry. It is also likely that some of the iceberg sounds were generated within the many unnamed daughter icebergs sourced from C19a and B15a [Tournadre et al, 2012].…”

“…It is estimated that the calving of icebergs >18.5 km in length can account for nearly half of the annual ice loss from Antarctica (1089 1 300 Gt) [Silva et al, 2006]. Altimeter-based measurements report an additional mean annual volume of 400 Gt, with icebergs exhibiting a mean length of 750 m in the austral summer and 450 m in the winter [Tournadre et al, 2012], and an average half-life of 200 days [Jacka and Giles, 2007]. In comparison, in the Northern Hemisphere, the mean annual iceberg flux from Greenland is estimated to be only 170-270 Gt [Bigg, 1999].…”

Freshwater fluxes in the Weddell Gyre: results from δ 18 O

“…Similarly, export of both giant [91] and small [92] icebergs may contribute to lower local glacial contributions. The return flow of either melted snow advected northwards on sea-ice floes or iceberg melt will also influence the final ocean transport.…”

Monitoring deep‐ocean temperatures using acoustic ambient noise

“…This likely explains why the amplitudes of the arrivals exhibit a weaker peak-to-variance ratio for the Wake Island site than the amplitudes for the Ascension Island site (compare Figure 1c to Figure 1d). An additional factor driving this difference in the peak-to-variance ratios is that the concentration of icebergs is typically higher in the South Atlantic than in the South Pacific [Tournadre et al, 2012]: iceberg concentration directly influences the ice noise source density and therefore the amount of coherent noise traveling along the SOFAR channel up to the hydroacoustic stations [Matsumoto et al, 2014;Gavrilov and Li, 2009].…”