Shape and size of Antarctic icebergs derived from ship observation data

Abstract

AbstractWe have examined information on the shape and size of Antarctic icebergs as derived from the ship data archive of Arctic and Antarctic Research Institute. The data in the archive cover the period from 1957–2009. For each of five major iceberg shapes we have established their relative frequency of occurrence in the Southern Ocean and the frequency distribution of the iceberg length and freeboard. Weathered and tabular icebergs were observed most often and comprised 66.9% and 22.6% of all reported icebergs respectively. Sloping, pinnacle, and dome icebergs represented correspondingly only 5.6%, 3.2% and 1.7% of the total number of icebergs observed. A distinct maximum was found in frequency distributions of the iceberg length and freeboard for all iceberg shapes. The most frequently observed iceberg lengths (modal length) ranged from 100–200 m for weathered and pinnacled icebergs to 400–600 m for tabular and dome-shaped iceberg. The modal freeboard of icebergs changed from 30–40 m for tabular and weathered icebergs to 50–60 m for domed, pinnacle and sloping icebergs. To calculate the overall mean size parameters of Antarctic icebergs we totalled corresponding mean values for each iceberg shape weighted by the frequency of occurrence of icebergs of each shape. The mean iceberg length and the standard deviation obtained within this approach were correspondingly 381 m and 349 m. The mean iceberg freeboard was equal to 41.2 m with a standard deviation of 12.1 m.