Antarctic Iceberg Distribution and Dissolution

Abstract

ABSTRACT. Shipboard observations (in accordance withNorsk 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 0 and 140 0 E. The resulting size-frequency distributions are examined in conjunction with a knowledge of water movement along known drift tracks in a selected stud), area (between lat. 59 0 and 64 oS., and long. 90 0 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.

Antarctic iceberg distribution and dissolution from ship-based observations

“…, 140-1508 E (see later for details of volume calculations). Figure 4a (plotted in reverse order on the longitude axis) can be compared with Hamley and Budd's (1986) figures 1 and 2, noting that Hamley and Budd's concentrations were observed over a 12 mi (int., naut.) (22.2 km) radius.…”

“…We now have a total of 7186 observations of 60 749 icebergs, covering a period of $20 years, and we can have greater confidence in these results than we did 20 years ago (cf. Hamley and Budd, 1986). The following data quality categories were checked:…”

“…We have also included the iceberg concentrations and volumes for the period 1978/79-1983/84, i.e. the data examined by Hamley and Budd (1986). Both iceberg concentration and volume in the study area for 1984/85-1988/89 are higher (on average by a factor >2) than in the following two periods.…”

“…The study area Hamley and Budd (1986) considered iceberg dissolution rates within the area bounded to the south by 648 S latitude and to the north by 598 S latitude. They made the assumption that all icebergs entering that latitudinal band between longitudes 90 and 1008 E move to the east in the Circumpolar Current, remaining within these latitudinal limits.…”

“…Using the Australian Antarctic Program (AAP) iceberg dataset, Hamley and Budd (1986) extended the work of Budd and others (1980). They examined the concentration and size distribution of icebergs in the Australian sector of the Southern Ocean to infer iceberg median life and dissolution rates.…”