Ice Station Weddell

Program Description

The Weddell Gyre is the largest of the cyclonic flowing gyres occupying the region south of the antarctic circumpolar current. Its special environmental setting makes it a key constituent of the global climate system. Coupling of the Weddell waters with the atmosphere across a highly variable sea ice cover with the rather weakly stable water column (a condition forced by regional upwelling of deep water) results in vigorous vertical fluxes of heat, salinity, dissolved gases and nutrients that influence the atmosphere, the ice cover, the biology and ventilate the ocean with cold, oxygenated water. A central product of the ventilation process is the very cold antarctic bottom water, carried by the western boundary current of the Weddell Gyre into the circumpolar belt, from which it floods and chills the lower kilometer of the world ocean.

The importance of the Weddell Gyre has long been recognized, but observation has been hindered by its sea ice cover. The Weddell Gyre is nearly completely covered by sea ice in the winter, marking the greatest latitudinal range of the seasonal sea ice around Antarctica. During the 1980's a series of winter and spring expeditions (Somov-81; Polarstern-86, 89; Fedorov-89) provided a more precise view of the coupling of the deep water with the winter mixed layer and its significant impact on seasonal sea ice thickness. Along the western rim of the Weddell Gyre the high concentration of perennial sea ice has hindered even basic exploration of this important region.

Observations from ships are essentially non-existent in the western Weddell (west of 48°W; south of 65°S). A vast region stretching westward to Antarctic Peninsula is largely unexplored, except by satellite borne sensors, recent aircraft based geophysical observations and instrumented drifters placed on the ice. A range of very basic questions exist that can only be addressed with detailed in situ observations of the environmental conditions. Fundamental questions include: why is there an extensive all year ice cover in the western Weddell? how climatically stable is it? how do the ocean processes along the western rim of the Weddell Gyre contribute to the formation or further modification of antarctic bottom water? Even such a basic issue as the location of the continental slope was not resolved: LaBrecque and Ghidella, this issue, using satellite and aircraft data place the eastern continental margin of Antarctic Peninsula about 100 kilometers to the west of position shown on the GEBCO map.

An effective way to gather extensive observations in the ice cluttered western Weddell is to borrow a successful method from the Arctic: deployment of a scientific station on a drifting ice floe. In 1988 the concept for the US/USSR Ice Station Weddell (ISW), the first ice station of the Southern Ocean was initiated, with detailed planning in 1989-1991 and field deployment in 1992. The extensive experience of Russia and the United States in ice station operation formed a natural basis for a collaborative effort to meet the many challenges of establishing a scientific ice station in an unexplored part of the southern ocean.

In the spirit of basic exploration of an unknown region the science program spanned many disciplines. Included were measurements of full water column thermohaline and tracer fields; current measurements; estimations of turbulent fluxes within the oceanic and atmospheric planetary boundary layers; sea ice physical, chemical and biological characteristics; sea ice dynamics; and water column biology. US and Russian science programs complimented each other to yield a more complete picture of the environment. Observations were made at the ISW site, from remote instrumented drifters, from helicopters and from the ships associated with the various phases of the work (Fig. 1). The ISW drifted roughly along 53°W at a northward drift rate of 6.2 km/day between 71.4°S and 65.8°S, experiencing temperatures mostly about -25°C, but getting as low as -36°C.

The US-USSR Ice Station Weddell (ISW) may best be summarized by quoting the closing statement:

"Tuesday 9 June 1992 at 65.63 deg S and 52.41 deg W Aboard R/V Akademik Fedorov and R/V Nathaniel B. Palmer.
"The United States Antarctic Program of the National Science Foundation and the Soviet Antarctic Expedition state that on 9 June 1992 the experimental phase of the joint US-Russian project entitled Ice Station Weddell has been successfully completed.
"The difficult environmental conditions of the western Weddell Sea have previously prohibited data collection in this segment of the Southern Ocean. Only now in the closing decade of the 20-th century has this region been thoroughly observed through this joint effort (Fig. 1, 2). Ice Station Weddell , the first drift station of the Southern Ocean, becomes an important part of the history of Antarctic exploration, filling a large gap in our view of this remote part of the global ocean.
"Ice Station Weddell began operation on 11 February 1992 at 71°48'S; 51°43'W, with the support of the R/V Akademik Fedorov. 17 American and 15 Russian polar scientists successfully fulfilled the scientific program on the drifting ice floe. The scientific program consists of physical oceanography, meteorology, sea ice physics and marine biology. In March and April 1992 part of the US team were rotated with US aircraft (mid-March) and with the US icebreaker R/V Nathaniel B. Palmer (late April). In May and June 1992 Ice Station Weddell was recovered by cooperative cruise of the Aboard R/V Akademik Fedorov and R/V Nathaniel B. Palmer. The official closing ceremony was held on 9 June 1992 at 65.63 deg S and 52.41 deg W.
"The successful performance of this project was made possible by the significant polar experience both of the American and Russian teams. The success of Ice Station Weddell forms the basis for future collaboration between the US and Russia for both polar region.

Chairman of the
Soviet Antarctic Expedition Chief Scientist for
Ice Station Weddell
V. V. Lukin Arnold L. Gordon