These images show the Filchner Ice Shelf on the coast of Antarctica that faces the Atlantic Ocean. In the austral winter of 1986, the front edge of the Filchner Ice Shelf broke off into the sea, forming three large icebergs. This was a major, long-awaited calving.
Most images in Earthshots are in “false color”; they are red/green/blue composites, representing three bands of Landsat data. These images of the Filchner Ice Shelf, however, represent only one band of near-infrared reflection, so they are grayscale.
An ice shelf is a huge sheet of ice, connected to land but extending out into the ocean. Ice shelves develop mainly from glaciers flowing slowly downhill toward the ocean. “Upstream,” the ice shelf rests on land, but “downstream,” the ice shelf extends out onto and into the ocean, mostly below sea level.
The Filchner-Ronne Ice Shelf is by volume the largest ice shelf on Earth. It is really one ice shelf, nominally divided by Berkner Island.
Ice shelves are part of a cycle. Winds carry water (as clouds) to Antarctica, where it falls as snow, compacts into ice, flows slowly as glaciers into ice shelves, and then slowly progresses to the ocean, where chunks break off and are carried away by ocean and wind currents. These chunks are icebergs; the birth of icebergs (from glaciers, ice shelves, or larger icebergs) is called calving.
It is widely known that most of an iceberg lies under water; this is also true of ice shelves. When a large piece of ice shelf calves into the ocean, it does not drop and splash down into the water, because the front of the ice shelf was already floating on water. In fact, the ocean’s tides lift and drop the ice shelf every day; this is called hinging, and the place where the ice shelf connects to the “shoreline” bedrock is called the hinge-line, since the outer shelf swings up and down from it.
German scientists learned that the Filchner-Ronne Ice Shelf is two-layered. The top 150 m of ice came from snow and glaciers, but the bottom 80 m of ice came from the water below. This bottom layer is clear and bubble-free. The top layer is hard but snowy and bubbly. These bubbles (or “voids”) allow scientists to study atmospheric gasses trapped in the voids, by coring the ice.
Antarctica has 90% of the world’s ice. Scientists are very interested in the net gain/loss of this ice mass because of its implications for world climate and sea level.
Ferrigno, Jane G., and Gould, W.G., 1987, Substantial changes in the coastline of Antarctica revealed by satellite imagery: Polar Record, v. 23, no. 146, p. 577–583.
Korotkov, Andrey , Department of Ice Regime and Forecasts, Arctic and Antarctic Research Institute, personal commun.
Meier, Mark F., 1993, Ice, climate, and sea level—do we know what is happening? in Peltier, W.R., ed., Ice in the climate system: Berlin, Springer-Verlag, p. 141–160.
Oerter, H., 1992, Evidence for basal marine ice in the Filchner-Ronne ice shelf: Nature, v. 358, no. 6385, p. 399–401.
Stewart, John, 1990, Antarctica—an encyclopedia: Jefferson, N.C., McFarland, 1193 p.
Vaughan, David, 1993, Chasing the rogue icebergs: New Scientist, v. 137, no. 1855, p. 26.
Williams, Richard S., Jr., and Ferrigno, Jane G., 1988, Satellite image atlas of glaciers of the world—Antarctica: U.S. Geological Survey Professional Paper 1386-B, 278 p. (Also available online at http://pubs.usgs.gov/pp/p1386/.)