Arctic Ice Shelves: An Introduction

Abstract

Ice shelves are relatively thick ice masses that are afloat but attached to coastal land rather than adrift. They form by the seaward extension of glaciers or ice sheets or by build up of multiyear landfast sea ice. They thicken further by surface accumulation of snow and superimposed ice and by accretion of ice from water beneath. Composite ice shelves are composed of sea ice and glacier ice. Glacier tongues are floating ice margins that are narrow relative to their length. Ice shelves comprise 55% or 18,000 km of the Antarctic coast. ‘Classical’ Antarctic ice shelves are fed from glaciers or ice streams and are dynamically part of the parent ice sheet; the largest, the Ross and Ronne, are 105 km2 and hundreds of metres thick. Where they ground on isolated bedrock peaks, ‘ice rises’ are formed. Arctic ice shelves are restricted to several archipelagos fringing the Arctic Ocean and to a few Greenland fjords. The Ward Hunt Ice Shelf is the largest at about 400 km2. Arctic and Antarctic ice shelves have expanded and contracted during the Holocene. The Ellesmere Ice Shelf developed about 5500 years ago in response to Holocene cooling. In the warmer Twentieth century, calving events have broken this continuous ice-shelf into several remnants. Floating glacier tongues of the Greenland Ice Sheet have also broken up recently. The entire Arctic Ocean may have been covered by a huge ice shelf during the coldest Late Cenozoic glacial periods. Large, often tabular icebergs calve from ice shelves. Ice islands are a form of tabular iceberg in the Arctic Ocean which have a characteristic undulating surface. Icebergs drift mainly under the influence of currents and Arctic Ocean ice islands have been used occasionally as research stations.