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Highlights
Glaciology
Ted Scambos

A growing recognition of climate change effects on every aspect of ice on Earth marked the past year in glaciology. The conclusion no longer comes solely from forecasts or model results, but increasingly from observations of active, ongoing changes in the ice-ocean-atmosphere system.

The year 2003 began with the launch of glaciology's first satellite, ICESat (Ice, Cloud, and land Elevation Satellite) on Jan. 12. ICESat contains a two-color laser altimeter instrument, GLAS (Geoscience Laser Altimeter System), that can measure decimeter-precision elevations below it's orbit track — and can use the scattered light from the atmosphere en route to determine aerosol concentrations and cloud structure. Designed to map the changing surface of the major ice sheets and glaciers, the instrument can yield a precise estimate of their contribution to sea level rise and identify regions of rapid elevation change. In its first year, the instrument collected several global grids of tracks .

In September, for the second time in as many years, sea-ice extent and area in the Arctic Ocean reached record minimum levels for the satellite observation era. Mark Serreze and others at National Snow and Ice Data Center, and Joey Comiso of NASA, reported that the 2002 and 2003 summers showed remarkably similar patterns, characterized by an ice edge far to the north of normal in the Beaufort Sea, and unusually open pack near the North Pole. An analysis by Matt Sturm,Don Perovich and Serreze fingered surface-air warming, circulation changes and thinning of ice in a broad region extending north of the Alaskan coast to the North Pole as the underlying causes of the downward sea ice trends. The amount of Arctic sea ice that survives one season of summer, so-called multi-year ice, is rapidly declining.

Glaciers in Greenland, Antarctica and Patagonia also showed dramatic responses to warming and melt. Speed-up and thinning of the world's fastest glacier, Jacobshavn in Greenland, was noted beginning in 1997 as bits of its floating ice front began to break away. There and in Antarctica, evidence is growing that these floating ice masses, or ice shelves, provide an important resistive force to the glaciers that feed them. Papers presented at the 2003 Fall Meeting of the American Geophysical Union, by Waleed Abdalati, William Krabill, Robert Thomas and others showed that Jacobhavn's speed increased from 7 kilometers per year to over 10 kilometers per year. Similar work by Eric Rignot and others showed that glacier speeds in the Antarctic Peninsula also jumped in areas where former shelves were removed by climate warming. The studies are significant because of the known high sensitivity of ice shelves to climate warming and surface melt. Moreover, the recently recognized accelerating effect of melt percolation — in which surface meltwater can drain through crevasses to the bed of the glacier, even though the intervening ice may be far below freezing — has further upped the ante for climate warming effects on glaciers. Studies of Patagoinian glaciers by Gino Cassasa of Chile, and of cold-cored glaciers in the Canadian Arctic by Luke Copeland and others, drove home this point in 2003.

Ultimately, the objective of these glacial change studies is to determine the mass balance, or net flux, of the ice sheets. An outstanding review of the current state of knowledge for Antarctic mass balance was presented at an international forum in Milan by Massimo Frezzotti of Italy's Antarctic research program. In addition to the points discussed above, Frezzotti highlighted an emerging recognition of the importance of snow redistribution by surface winds. Katabatic (gravity-driven) wind flow greatly alters the simple "layer cake" accumulation pattern that most models use when investigating ice sheet flow and climate history from ice cores. In some areas, accumulation may vary by 50 percent or more over just a few kilometers. In the most extreme cases, the redistribution can cause accumulation "striping" on the ice sheets, resulting in wide, gently-sloped "megadunes" in plateau regions of Antarctica. Both Frezzotti and Mary Albert of the U.S. Army Cold Regions Research Laboratory reported intense snow diagenesis and chemistry changes in the interspersed accumulation-free areas. Their results could impact climate interpretations from ice-core chemistry and physics.

Two major ship-based expeditions to the Antarctic were conducted with the intent of calibrating a host of satellite-borne sensors used for measuring sea ice and snow cover. The Nathaniel B. Palmer surveyed ice near Antarctica's rapidly changing Peninsula area, and the Australian ship Aurora Australis toured the opposite side of the continent south of Australia. Both cruises focused on comparing real sea-ice variability with maps from orbiting microwave-emission sensors, seeking to understand details of the interaction between waves, ice, salt and snow. Testing of airborne sensors using electromagnetic induction as a means of measuring sea-ice thickness proved very successful. Sea-ice thickness measurement has been a "holy grail" of glaciological remote sensing. The expeditions also included studies on the interactions between ice and algae (Jean-Louise Tison), and the effect of ultraviolet light on sub-ice biota (Jane Higgins and Robert Massom).

U.S. activity in ice core drilling will accelerate in the next few years as a new site in the central West Antarctic is drilled to provide a record of global climate for the past 200,000 years. The site is intended to provide a southern hemisphere counterpart to the landmark Greenland ice cores of the early 1990s. In preparation for the drilling, site surveys using airborne and ground profiling by radio-echo-sounders were conducted, led by Howard Conway and Ed Waddington of University of Washington, and David Morse of University of Texas.

On the horizon for the community is the proposed International Polar Year, scheduled for 2007-2008. The program's goal is to renew and stimulate innovation in the scientific exploration of the poles on the 50th anniversary of the International Geophysical Year (IGY). Interest swelled during 2003, and the global glaciological community enthusiastically welcomed calls for new ideas and program concepts.

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Scambos is a glaciologist at the National Snow and Ice Data Center at the University of Colorado. He specializes in the application of satellite remote sensing to glaciological problems and the effects of climate change on the world's ice.

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