THERMAL-ENERGY CONSERVATION IN ICEBERGS AND TRACKING BY TEMPERATURE

Calculations using a two-dimensional numerical model which simulates the heat balance and temperature distribution of icebergs show that the temperature in the central region of an iceberg is almost unaffected by the thermal conditions imposed on its boundary. Hence the original temperature of the iceberg at the time of calving is retained in its core owing to the insulating quality of the ice. When correlated with glacioclimatic conditions, this temperature conservation may be used to backtrack an iceberg to its parent ice cliff. Nine different icebergs were manually temperature-profiled in the Barents Sea during late winter 1988-1990. A scenario is considered wherein one of these icebergs under the forces of winds and currents is assumed to set off from Franz Josef Land in late autumn 1987. The numerical heat balance model is used to compute the temperature distribution, heat balance, and ablation of this iceberg as it drifts through the Barents Sea. The calculations show that the heat balance of the part of the iceberg exposed to air has marginal influence on the ablation and thus on the expected lifetime of the iceberg. Ablation of the submerged body also occurs during winter, when the water temperature is well below the melting point of glacial ice. This is caused by freezing-point depression leading to an ablation of about 0.5 m per month of the underside and sidewalls of the submerged body. For water temperatures above 0.6-degrees-C the ablation results in a steep temperature gradient reaching the core temperature 3 m into the ice. With a tolerance of 0.4-degrees-C the temperature is virtually free of any thermal boundary influence 12 m into the ice. The simulated and measured temperature profiles of the iceberg are compared with measurements of the thermal regime of Austfonna, Nordaustlandet, and the Churlenis Ice Dome on Franz Josef Land. The model calculations indicate that the ice cliffs on Svalbard can be excluded as parent ice cliffs for these icebergs and that the core temperature of the bergs appears to be a conservative tracer.