Antarctic Iceberg Melt Rates Derived from Size Distributions and Movement Rates

Abstract

The melt rates of Antarctic icebergs derived by Morgan and Budd (1978) were based primarily on the distribution of iceberg concentrations, data on iceberg size distribution being limited. Recently, more detailed data have been obtained, especially north of lat. 60°S which allow more precise calculations of the changes in size during drifting. On Australian National Antarctic Research Expedition (ANARE) voyages each summer since 1977, observations of icebergs have included photographs, number per unit area from ship’s radar, widths, heights, and shapes. These data have allowed separate calculations to be made for tabular icebergs which give a clearer indication of the contribution to average size changes of melting, breakage, and rollover. New data from satellite transponders placed on icebergs have provided more definite estimates of the average northward and then eastward drift rates of icebergs near 90°E. Combined with the new data on size more accurate melt rates have been derived. Detailed measurements with expendable bathy-thermographs (XBT) along the shipping routes have provided more definite data on water temperature which allow the melt rates to be studied as a function of temperature. Historical data on iceberg locations have been used to estimate the melt and decay rates of the icebergs at higher temperatures.

Antarctic Iceberg Distribution and Dissolution

“…Close agreement is apparent (in Fig. 7) between our data and the frequency distribution of Budd and others (1980) (Orheim, 1985;between 1981 and. -*-*-* Tabular.…”

“…Figures I and 2 which were not apparent in the earlier profiles of Shilnikov (1969) or Budd and others (1980). In Figure 2, total iceberg concentrations increase from less than I per 12 n.m. radius at lat.…”

“…In general, however, the accuracy of these observations is indeterminate and obviously variable depending on the diligence of individual observers. Data presented in this paper represent observations from all ANARE voyages since 1979 covering a longitude range from approximately 60 ° to 140 o E. Budd and others (1980) used data to 1979 to determine the distribution of both concentration and size of icebergs to examine the process of iceberg dissolution. This paper therefore extends the work of Morgan and Budd (1978) and Budd and others (1980), and establishes new estimates of iceberg median life and dissolution rate based on the more extensive data now available.…”

“…7), which included the distributions of Romanov (1973). Note that the Budd and others (1980) compilation only considered icebergs above 50 m; therefore, to be consistent, the same cut-off is adopted. Close agreement is apparent (in Fig.…”

“…frequency distribution, since the data used by Budd and others (1980) came from earlier records of individual iceberg sightings and are not subject to categorization in variable size ranges. Figure 8 represents the iceberg concentration as a function of size for each of the longitude bands, 90-100 o E., 100-1I0 o E., and 1I0-120 o E. As was shown in Figure 6, the approximate doubling in concentration as the size factor halves (except for icebergs in the smallest category of 10-50 m) is evidence supporting, in principle, the breakage theory of Budd and others (1980), provided a volume loss from small fragments formed during breakage is taken into account.…”