Spring distributions of density, nutrients, and phytoplankton biomass in the ice edge zone of the Weddell‐Scotia Sea

Abstract

We collected data on temperature, salinity, nutrient concentrations (nitrate, nitrite, phosphate, and silicic acid), and phytoplankton biomass (chlorophyll a, particulate carbon, nitrogen, and biogenic silica) in the upper 150 m in the marginal ice zone of the eastern Scotia Sea and northwestern Weddell Sea during November and early December of 1983. A distinct hydrographic front separating Drake Passage water from Weddell and Scotia sea surface waters was located at approximately 59°S and was the site of a consistent maximum in phytoplankton biomass. In addition, there was a pronounced phytoplankton biomass maximum associated with a surface salinity minimum near the northern limit of pack ice in the waters of the Weddell‐Scotia confluence that characterized the western portion of the study area. In the eastern half of the study area, characterized by largely unmodified Weddell Sea surface water, the phytoplankton biomass near the ice edge was 2–5 times lower than that in the Weddell‐Scotia confluence but was increasing with time. The water column structure, nutrient fields, and phytoplankton biomass distribution all suggest that the high phytoplankton biomass in the ice edge zone of the Weddell‐Scotia confluence and the lower but temporally increasing biomass near the ice edge in unmodified Weddell Sea water reflect ice edge phytoplankton blooms in different stages of their seasonal development. A bloom had become well established in the waters of the Weddell‐Scotia confluence by mid‐November, but the ice‐free, vertically stable near‐surface water column necessary for enhanced phytoplankton growth had apparently not been present long enough for high biomass levels to develop within the Weddell Sea proper.