Ross Ice Shelf - Composition and Movement

Composition and Movement

Ice shelves are thick plates of ice, formed continuously by glaciers, that float atop an ocean. The presence of the shelves acts as "brakes" for the glaciers. These shelves serve another important purpose -- "they moderate the amount of melting that occurs on the glaciers' surfaces. Once their ice shelves are removed, the glaciers increase in speed due to meltwater percolation and/or a reduction of braking forces, and they may begin to dump more ice into the ocean than they gather as snow in their catchments. Glacier ice speed increases are already observed in Peninsula areas where ice shelves disintegrated in prior years."

The Ross Ice Shelf is one of many such shelves. It is about the size of France, and reaches into Antarctica from the north. The ice mass is about 800 km (500 mi) wide and 970 km (600 miles) long. In some places, namely its southern areas, the ice shelf can be almost 750 m (2,450 ft) thick. The Ross Ice Shelf pushes out into the sea at the rate of between 1.5 and 3 m (5 and 10 ft) a day. There are other glaciers that gradually add bulk to it. At the same time, the freezing of seawater below the ice mass increases the thickness of the ice from 40 to 50 cm (16 to 20 in). Sometimes, fissures and cracks may cause part of the shelf to break off; the largest known is about 31,000 km2 (12,000 sq mi), that is, slightly larger than the size of Belgium. Iceberg B-15, the world's largest recorded iceberg, was calved from the Ross Ice Shelf during March 2000.

Scientists have long been intrigued by the shelf and its composition. In fact, most of the scientific teams have made camps on or adjacent to the Ross Ice Shelf. This includes McMurdo Station. One major effort was a series of studies conducted in 1957 and 1958, which were continued during the 1960–61 season. The efforts involved an international team of scientists. Some parties explored the glaciers and others the valleys on the ice shelf.

From 1967 to 1972 the Scott Polar Research Institute reported extensive observations using radio echo sounding. The technique allowed measurements to be taken from the air; allowing a criss cross track of 35,000 km to be covered; compared with a 3,000 km track from previous seismic sounding on the ground. More detailed surveys were executed between 1973 and 1978.

A significant scientific endeavor called the Ross Ice Shelf Project was launched with a plan of drilling into the shelf to sample the biomass in the area and make other determinations about the shelf and its relationship to the sea floor. The Project included surface glaciological observations as well as drilling, and the glaciological portion started during the planning phase of the drilling. The drilling portion of the project was to have begun during 1974, but the actual drilling was delayed until 1976. Finally, in 1977, the scientists were able to drill successfully through the ice, making a hole that could be sampled every few days for three weeks. The team was able to map the sea floor, study the tides, and assess the fish and various other forms of life in the waters. The team also examined the oceanographic and geological conditions as well as the temperature of the ice. They estimated that the base of the shelf was −2.16° Celsius (27.3°F). They also made other calculations about the fluctuations of the temperatures.

The results of these various projects are published in a series of reports in Science magazine, published 2 February 1979.

During the 1980s, a network of weather stations were installed to record temperatures on the shelf as well as throughout the more remote parts of the continent.

University of Colorado's National Snow and Ice Data Center has been studying ice shelves and, in 2002, announced that, based on several break ups of ice shelves, including Larsen B, has begun to reassess their stability. Their scientists stated that the temperature of the warmest portion of the shelf is "only a few degrees too cool in summer presently to undergo the same kind of retreat process. The Ross Ice Shelf is the main outlet for several major glaciers draining the West Antarctic Ice Sheet, which contains the equivalent of 5 m of sea level rise in its above-sea-level ice." The report added that observations of "iceberg calving" on the Ross Ice Shelf are, in their opinion, unrelated to its stability.

Continuing scientific exploration continues to uncover interesting information and the analyses have resulted in some interesting theories being posited and publicized. One such opinion, given in 2006 based on a geological survey, suggested that the ice shelf had collapsed previously, perhaps suddenly, which could well happen again.