Tabular Iceberg Evolution and Break-up at Low Latitude: Imitating Ice Shelves
Abstract
Over the past five years, a series of large icebergs have calved from the Ronne Ice Shelf front and drifted northward, first along the Antarctic Peninsula east coast, and later across the Scotia Sea towards South Georgia Island. The bergs broke up or disintegrated within a year of reaching the island. Observations of the icebergs using MODIS, ICESat, and QuikScat have revealed details of their evolution and break-up patterns. ICESat elevation profiles of tabular iceberg margins and the Ronne Ice Shelf edge reveal shapes indicative of two types of bending forces. Icebergs and shelf fronts in sea-ice-covered areas have broad (~1000m wide), rounded, ~0.6m high `berms' and outer edges that slope down several meters toward the water. Bergs in warmer water have 2 to 5m `ramparts' with ~1500m wide edge-parallel `moats' inboard of the edge. This latter pattern was first revealed in images from International Space Station (ISS) showing edge-parallel melt ponds on one iceberg just prior to its disintegration. Model results indicate the patterns are caused by hydrostatic and lithostatic forces acting on the ice face. "Berm' profiles arise from differences between ice and water pressure along the face. `Rampart-moat' profiles result from waterline erosion, creating a submerged bench of ice that lifts the ice edge. In cold (sea-ice covered) water, icebergs evolve slowly, with infrequent calving of large blocks, usually along pre-existing fractures. In warmer water north of the ice edge, bergs show more frequent edge-parallel calvings ('edge-wasting') in which berg shape is little changed, but berg area gradually decreases. Scatterometry observations of the icebergs indicate the berg firn undergoes significant evolution during northward drift, due to melt and melt percolation. The pattern of winter backscatter change for icebergs (over time) is similar to the variations of ice shelf backscatter with melt frequency (over space, i.e. latitude). This supports the hypothesis that winter backscatter versus melt season length (or degree days) may be used as an indicator of ice shelf `pre-conditioning' for a Larsen A- or B- style disintegration. A field expedition to establish automated sensors for weather, ice thickness, melt, firn temperature, and a digital camera with uplink, is planned for February 2006.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.C13A..02S
- Keywords:
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- 0700 CRYOSPHERE (4540);
- 0728 Ice shelves;
- 0732 Icebergs