Southern coastal system of the San Jorge Gulf during spring

Abstract

The San Jorge Gulf was declared an area of national economic, commercial, conservation and diversity interest. To contribute to its study, the southern coastal sector of the gulf was characterised in physical and chemical parameters in spring campaigns (November 2016 and 2017). Samples were taken on board the oceanographic vessel Puerto Deseado in three perpendicular to the coast transects and another one to the southeast of the gulf, which crosses a thermohaline front. The perpendicular to the coast transects showed a similar pattern of distribution of physical and chemical properties in the water column. At nearshore stations, the water column was homogeneous and the nutrient concentrations between the surface and bottom layers were similar. At offshore stations, the water column was stratified and the nutrient concentrations were higher near the bottom than at surface. In 2016, a wind induced upwelling front was observed in the southwest of the gulf. Both sides of the thermohaline front did not show significant chemical differences. Throughout the study area, silicic acid and nitrate limited primary production. Satellite chlorophyll-a data and fluorescence profiles showed that the southern sector of the gulf has a high biomass of phytoplankton during November. We conclude that the southern sector of the SJG has different features depending on the external forcing caused by the front. The presence of fronts stimulates the growth of phytoplankton biomass through the injection of nutrients from the homogeneous part to the stratified sector. This would affect phytoplankton community and, thus, the productivity of the system.