The Geophysics of Sea Ice: Overview

Abstract

Terrestrial temperatures happen to lie in a range where, in the course of a year, the sea surface at high latitudes becomes cold enough to freeze. According to paleoclimatic studies of the sea floor sediments, this has been the case for at least several million years. During that time, however, the extent of sea ice underwent large fluctuations. For instance, at the last glacial maximum 18,000 years ago, Atlantic sea ice extended as far south as the shores of France and northern Spain in Europe, and the eastern coastal states in North America. The heat of fusion released by the sea surface to form an ice layer of, say, one meter thickness is an order of magnitude smaller than the mean annual total of either short-wave or long-wave radiation at the surface. In a single year, these annual totals may easily deviate ten percent from their mean values. Thus it is not surprising that small changes in the climatic forcing are accompanied by large changes in the extent of the ice-covered area.