Size-fractionated primary production studies in the vicinity of the Subtropical Front and an adjacent warm-core eddy south of Arica in austral winter.

Results are presented of size-fractionated primary production studies conducted in the vicinity of the Subtropical Front (STF), an adjacent warm-core eddy, and in Sub-antarctic waters during the third South African Antarctic Marine Ecosystem Study (SAAMES III) in austral winter (June/July) 1993. Throughout the investigation, total chlorophyll (Chl a) biomass and production were dominated by small nano- and picophytoplankton. No distinct patterns in total Chl a were evident. At stations (n=7) occupied in the vicinity of the STF, total integrated biomass at the eddy (n=2). At the station occupied in the Sub-antarctic waters, total integrated biomass was 43 mg Chl a m-2. Total daily integrated production was highest at stations occupied in the vicinity of the STF and at the eddy edge. Here, total integrated production ranged from 150 to 423 mg C m-2 day-1 nd from 244 to 326 mg C m-2 day-1, respectively. In the eddy centre, total integrated production varied between 134 and 156 mg C m-2 day-1. At the station occupied in the Sub-antarctic waters, the lowest integrated production (141 mg C m-2 day-1) during the entire survey was recorded. Availability of macronutrients did not appear to limit total production. However, the low silicate concentrations during the survey may account for the predominance of small nano- and picophytoplankton. Differences in production rates between the eddy edge and eddy core were related to water column stability. In contrast, at stations occupied in the vicinity of the STF, the control of phytoplankton production appears to be related to several processes, including water column stability and, possibly, iron availability. [ABSTRACT FROM PUBLISHER]