West Antarctic Ice Sheet Stability and Global Sea Level

Block diagram showing a schematic cross-section of the West Antarctic ice sheet, which is drained by ice streams underlain by water saturated, unconsolidated sediment. The underlying lithosphere (bedrock) may play role in the presence of the ice streams.

The west Antarctic ice sheet is the world's only remaining marine ice sheet, an ice sheet anchored to bedrock below sea level and with margins that are floating. Other marine ice sheets existed in the Northern Hemisphere during the last glacial maximum but all disintegrated and melted away during the current warm period. Marine ice sheets are important because their existence and future behavior depend not only on atmospheric conditions and ice movement, but also on sea level changes. As the sea level rises, more of the ice at the edge of the sheet floats, and the forces that hold the ice sheet together are reduced, causing ice to flow more rapidly to the oceans. This positive feed-back loop (sea-level rise, leading to reduced forces holding the ice together, leading to increased ice flow into the ocean, leading to sea-level rise) could lead to rapid disintegration or collapse of a marine ice sheet. Scientists want to learn more about the west Antarctic marine ice sheet to understand how it operates and to determine if it is vulnerable to future disintegration or collapse, which would affect global sea level.

Scientists have long recognized that global sea levels were 5 to 6 meters higher during the last interglacial warm period, about 125,000 years ago, than they are today. It is also estimated that the west Antarctic ice sheet contains ice which, if it were incorporated into the oceans, would cause global sea levels to rise about 6 meters. It has been suggested that the West Antarctic ice sheet might be responsible for the higher sea level during the last interglacial period. Future global warming could result in the disappearance of the West Antarctic ice sheet and a substantial rise in global sea level.

The west Antarctic ice sheet is drained by surprisingly large, fast, river-like currents of ice flowing through the ice sheet. These ice streams, as they are called, are up to 100 kilometers wide and several hundred kilometers in length, moving at rates as fast as several hundred meters per year. Studies have shown that the ice streams are underlain by a water-saturated, unconsolidated sediment layer a few meters thick. This sediment acts to lubricate the ice streams so that they flow rapidly over their beds. The size and speed of the streams lead to the possibility of rapid collapse of the ice sheet.

The West Antarctic Ice Sheet Program is an interdisciplinary program to study this ice sheet, understand the processes important to its behavior, and develop models to predict its future behavior. Recent studies suggest a possible connection between the subglacial geology and the presence of the ice streams. In fact, measurements of ice thickness, magnetics, and gravity, made using a specially equipped aircraft, have shown that there is evidence for high heat flow and active volcanism near the ice streams. These elements could explain the high degree of subglacial melting and lubrication of the sediment under the ice streams. This work demonstrates the importance of subglacial geology for a complete understanding of the stability of the west Antarctic ice sheet, its ice streams, and its potential for raising global sea level.

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