Introduction

Ice visually dominates most of the surface of the globe south of the Antarctic Circle for all or part of the year. This ice is either glacial ice formed by accumulated and compacted snow or sea ice formed from the freezing of sea water.

Ice covers 97.6% of the continental land mass, mainly in the form of an immense ice sheet up to 4,500 km wide, and with an area of about 12 million km2. This ice mass extends north of 66°S latitude in Wilkes Land, Enderby Land and the Antarctic Peninsula. The ice sheet is fringed by glacial ice in the form of floating ice shelves and other glaciers over half of its perimeter. This adds another 1.6 million km2 of ice. Icebergs break off these glaciers to drift around the continent and north into the Southern Ocean as far as 30°S (Burrows, 1976).

During winter, the area of ice doubles with the formation of sea ice. At its maximum in late winter, sea ice forms a belt 400 to 2,000 km wide from the coast of Antarctica to as far north as 53°S (Jacka, 1983). The maximum extent of this ice, including areas of open water within it varies from 17.3 to 20.2 million km2 or 18.5 million km2 on average (U.S. Navy, 1985). During spring and summer, this ice recedes south to the coast in several places. The sea ice extent reaches a minimum in February and varies depending on the summer, between 2.4 and 5.1 million km2 or 3.6 million km2 on average. The area of ocean actually covered by sea ice at the February minimum averages only 2.8 million km2.

In contrast, the snow coverage of the Antarctic continent changes little with the snow line being at, or close to, sea level year-round. Summer melting is confined to narrow coastal zones, the snouts of glaciers which end on ice-free terrain and the margins of some ice-free areas. Probably less than 4% of Antarctica's surface is either ice-free land or snow-free ice (Drewry, 1983; Robin, 1986); some of this area may be covered by snow at any time of the year, although such snow-falls do not normally last for more than a few days or weeks. Beneath the surficial snow, the seaward margins of the floating glaciers change on time scales of years to decades while the ice sheet margins take hundreds or thousands of years to alter.

This chapter examines Antarctic ice, concentrating on that in the Antarctic Sector of the Pacific Ocean. The significance and characteristics of this ice are discussed with emphasis placed on ice shelves, icebergs and sea ice as these are the main features in the marine environment.

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