Ocean, Ice, and Atmosphere: Interactions at the Antarctic Continental Margin

This volume is the seventy fifth in the Antarctic Research Series published since 1963 by the American Geophysical Union. This volume is a 380-page collection of twenty peer-reviewed papers focused mostly on currents and water masses on the continental margin around Antarctica. The Antarctic shelf is unique in its extent and impact on the global ocean. Relatively deep, typically 400 meters, this shelf has a sill at the shelf break in many places. Seaward, the continental slope averages three to six degrees down to abyssal depths at four to five kilometers. In most places, the bathymetry is unresolved at less than ten kilometer scales. Smaller scale features such as submarine canyons are in evidence and of likely import to offshelf transport. The volume includes a composite 1:3,000,000-scale bathymetric chart of the entire southern Weddell Sea synthesized from a number of different data sources by Hinze and Hoppman. Six 1:1,00,000-scale component charts are included in the GEBCO Digital Atlas. Depth accuracies range from 50 to 200 meters. Whitworth et al., in an analysis of 3544 historical hydrographic stations elucidates the subtleties of Modified Circumpolar Deep Water (MCDW) in its transit around the continent. Modifications occur at the Antarctic Slope Front, a ubiquitous feature near the shelf break associated with the Antarctic Circumpolar Current. Inshore of this Front, brine rejection from sea ice formation, particularly persistent in coastal polynyas, produces relatively dense High Salinity Shelf Water. MCDW mixes with saline Shelf Water to produce water found at the bottom of the shelf edge. Subsequent sinking of this water along the slope, entraining warmer, saltier CDW, produces Antarctic Bottom Water. This comprehensive analysis adds detail to and supports Gill's earlier (1973) hypothesis on the process of bottom water formation. Baines and Condie review both observational and modeling studies, and identify six possible mechanisms producing downslope transport of dense water. Evidence suggests the Weddell Sea as the site of the most active, persistent and largest downslope flows. In the western Weddell Sea, Gordon concludes that bottom water formed in recent decades is less saline than previously, consistent with an Increase in production of Ice Shelf Water, which in turn is a mixture of glacial meltwater and High Salinity Shelf Water. Chlorofluorocarbon and tritium data analyzed by Mensch et al. quantifies the production rate for Weddell Sea Deep and Bottom Waters at about five Sverdrups, and the mean residence time of contributing shelf waters at about six years. The tracer data clearly points to a large source area for bottom water in the western Weddell Sea. In contrast, on the west Antarctic peninsula continental shelf, Hofmann and Klinck find no evidence for the formation of dense shelf water in 1993-1994. Water properties on the outer shelf here are influenced most by meandering of the Antarctic Circumpolar Current, which is closer to the shelf break in this region than any other around the continent. Wind forcing is minimal, and water properties seem to be determined by horizontal mixing. In the Ross Sea, Jacobs and Giulivi synthesize a variety of data sources to describe interannual variability and trends over several decades in currents, water masses and sea ice extent. Regional air temperatures have Increased by 0.25°C and shelf water salinities have decreased by 0.03°C per decade since the late 1950s. An Antarctic version of the "Great Salinity Anomaly" appears to be in the making, with consequences on deep convection and high latitude ecology. In Prydz Bay, Wong et al. speculate on a high salinity type of Antarctic Bottom Water, similar to Ross Sea Bottom Water, that may be formed locally. Along the Adelie coast, Rintoul finds that deep water cooled and fresh-