Phytoplankton distribution and abundance as related to a frontal system north of Elephant Island, Antarctica

Abstract

During January-March, 1991, the distribution and floristic composition of the phytoplankton around Elephant Island, Clarence Island and the northern end of King George Island were determined in relation to physical oceanographic conditions and to proximity of the shelf-break and continental slope. The study area included 180 stations, and c. 5400 km of transects providing continuous measurements of salinity, temperature, beam attenuation, and chlorophyll a (chl a) concentrations in surface waters. The richest phytoplankton areas (2-4 μg chl a 1^-1) were generally found associated with a strong salinity front, extending north of King George Island to north of Elephant and Clarence Islands. Data on the phytoplankton community suggest that shelf waters were charaterized by low biomass and a nanoplankton population, while in and just north of the front the biomass increased and there was a shift to a diatom-dominated microplankton population. This is thought to be related to increased stability of the water column just north of the front. The salinity front ran more or less parallel to the continental shelf-break, but its exact position varied during the period of study. It was generally associated with transition water (Type II) or with Weddell-Scotia Confluence water (Type III).