Antarctic iceberg distribution and dissolution from ship-based observations

Abstract

The Australian Antarctic Program’s iceberg dataset (from ship-based observations), including information from the austral summer seasons 1984/85 to 1999/2000, is examined and used to extend earlier studies. Using ‘snapshots’ of the iceberg population to provide an idea of the iceberg life cycle, the distribution of icebergs between 60 and 1508 E is discussed in terms of calving regions and ocean currents. Temporal changes are also examined. The discussion leads us to the point where we can define an area, bounded to the north by the maximum sea-ice limit and to the south by the Antarctic Divergence, in which icebergs are confined as they drift eastward. This allows estimation of total dissolution, in terms of iceberg numbers and volume, within 108 longitudinal sectors and, with knowledge of drift speeds, iceberg movement rates and freshwater input across the sector. Iceberg dissolution rates are found to be 0.03–0.05md–1 and the total mass contribution of fresh water to the ocean as the icebergs traverse our 308 of longitude study sector is 32 Gt. This amounts to a contribution equivalent to precipitation of 15.5cm a–1, accounting for 2% of the total iceberg discharge from the Antarctic ice sheet.