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The Ross Sea

by Ricardo A. Locarnini

Antarctic shelf and bottom waters are cold, dense water masses which have relatively high concentrations of the gases that the ocean acquires from the atmos-phere, such as oxygen. They form close to the sea surface near Antarctica, then flow away from their source and sink, introducing water with near-surface characteristics into the deep ocean. This process, usually called ventilation, is associated with important fluxes of heat, salt, nutrients, and gases.

In the past, most research focused on shelf and bottom waters from the Weddell Sea. In the fall of 1991 I gave a seminar at Texas A&M University in which I discussed the circulation and importance of the Weddell Sea bottom waters. During the question session, Dr. David A. Brooks asked me about the bottom waters from the Ross Sea. I could not answer his question, and Dr. Thomas Whitworth III and Dr. Worth D. Nowlin, Jr. suggested it as the topic for my doctoral research. The result was a comprehensive study of the circulation and water masses of the Ross Sea and environs.

This work, based on analysis of historical hydrographic data, shows that the Ross Sea is important in determining the characteristics of the world ocean's deep waters. This should not be surprising, as the Ross Sea contains approximately 0.6 times the volume of shelf waters found in the Weddell Sea. Evenly spread, Ross Sea shelf waters would cover the state of Texas with water about one kilometer (0.6 miles) deep!

The cyclonic (clockwise) Ross Gyre dominates circulation in the Southeast Pacific Basin, between 160E and 140W. The Ross Gyre extends from the surface to the deep ocean, and is approximately one half to one third as strong as the Weddell Gyre. Circumpolar Deep Water (CDW) enters the Ross Gyre at its eastern end, and is ventilated by the shelf waters of the Ross Sea. Salinity and oxygen distributions show that the influence of shelf waters can be traced beyond the Ross Gyre into the mid-depth waters of the South Pacific Ocean.

[170K] Bathymetric chart of the Ross Sea and environs showing locatoins of stations used in this study. Shaded areas are less than three kilometers deep. The thick line indicates the location of the section below.

[17K] Diagram showing salinity in a cross-section of the water column. Salinities less than 34.70 along the continental slope show the narrow boundary flow of Low Salinity Bottom Water.

CDW participates in the formation of antarctic shelf waters. The salinity of the cold shelf waters of the Ross Sea increases westward. The salty CDW influence reaches the surface layer in the western Ross Sea, and I believe this influence is instrumental in the formation of high salinity shelf waters found there. Finally, the Ross Sea is the source of High Salinity Bottom Water and Low Salinity Bottom Water. The latter type of antarctic bottom water flows as a fresh, cold, and narrow boundary current along the continental slope of the eastern Ross Sea. This boundary current is a component of the global abyssal circulation not previously described. The volume of shelf waters suggests that one third of the total resevoir of antarctic bottom waters can derive from the Ross Sea in the present climate.

Editor's Note: Ricardo defended his disseratation on September 15, 1994, and is now a Senior Research Scientist at the University of East Anglia, Norwich, England. This year Ricardo and his wife, Sally Jo, will participate in a research cruise that will run from the southern Weddell Sea to the Brazil Basin.

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Oceanography, Texas A&M University



Updated July 24, 1995