Smith, Walker O., Jr.¹, Vernon Asper², Alessandra Accornero³, Jill Peloquin¹, Amy Shields¹ and Clara Manno³

¹Virginia Institute of Marine Sciences, College of William and Mary, Gloucester Pt, VA 23602, Tel: 804-684-7709, E-mail: wos@vims.edu, ²Department of Marine Science, University of Southern Mississippi, Stennis Space Center, MS 39529 and ³Ist. Meteorologia ed Oceanografia, Università degli Studi di Napoli Parthenope, 80133 – Naples, Italy

Interannual variations in biogeochemical variables in the southern Ross Sea

Interannual variations of a number of physical (e.g., ice cover) and biological (e.g, penguin abundance) variables have been documented within various regions of the Southern Ocean for a number of years, but assessment of the long-term variations in nutrient and phytoplankton concentrations is much more difficult. However, an understanding of this variability is essential in order to understand and predict any changes that occur in the future due to anthropogenic forcing. We have begun a study of the interannual variations in the nutrient concentrations and phytoplankton standing stocks in the southern Ross Sea. Three approaches are being used. The first analyzes data collected from a series of cruises conducted from 1970 to the present. These data are compiled to assess the spatial variations within a restricted time period, and also objectively analyzed to produce a biogeochemical climatology of the entire Ross Sea. The second uses moorings to continuously collect chemical and biological data from two locations in the southern Ross Sea, which then are used to estimate the short-term and seasonal net community production. The third collects data from a grid of stations to assess the spatial variations in net community production of the region, as well as the proximate causes for the variations. Initial results suggest that interannual variations in nutrient concentrations, phytoplankton biomass, vertical flux of organic matter and net community production are substantial and are similar in magnitude to those of ice cover and concentration. Annual variability also is confounded by differing seasonal temporal patterns. Assessing anthropogenic changes may be difficult given the substantial interannual variations observed in the past 30 years.