Antarctic Iceberg Distribution and Dissolution

Abstract

AbstractShipboard observations (in accordance with Norsk Polar-Institutt guidelines) from 6 years of Australian National Antarctic Research Expeditions (ANARE) voyages have provided data giving a detailed knowledge of iceberg sizes and concentrations in the Southern Ocean between long. 60° and 140° E. The resulting size–frequency distributions are examined in conjunction with a knowledge of water movement along known drift tracks in a selected study area (between lat. 59° and 64° S., and long. 90° and 120° E.) to determine iceberg-dissolution rates. The “median life” (before breaking) of icebergs less than 1000 m in horizontal dimension is estimated to be 0.2 a, which is significantly lower than was previously thought. The mean melt rate is estimated to be 0.12 m d–1, which agrees broadly with previous laboratory studies. The relative contributions of melt, calving, and breakage, plus the enhancement effect of roll-over, are examined in estimating the natural dissolution rate. Breakage appears to be the dominant mechanism for larger icebergs with melt and calving able to explain the disappearance of icebergs in the smallest categories only (within the mean “median-life” period). Examination of the historical records of Captain Cook indicates that iceberg concentrations, as well as the northerly extent in this region 200 years ago, were compatible with the present data.