Summer Phytoplankton Growth at Maxwell Bay, West Antarctic Peninsula: Role of Physical Forcings

The coastal zone of the Antarctic Peninsula is considered an area of high biological richness, where a high primary productivity is key to sustain high biomasses of zooplankton and other trophic levels of the marine food web. The main goal of this work is to study coastal abiotic conditions affecting the euphotic layer (e.g. wind stress, light availability, water stratification) that influence phytoplankton growth in Maxwell Bay, South Shetland Islands. Specifically, we focused in surface ocean features that allow generation of high phytoplankton biomass during the austral summer. Field campaigns during austral summers 2017-2019 were carried out at Maxwell Bay, additionally a phytoplankton growth model was developed. During summers 2017 and 2019, high chlorophyll-a (up to 29.2 mg m^-3) and primary production (up to 5 gC m^-2 d^-1) were observed associated with a stratified water column, characterized by less saline and warmer water (~2°C) at the surface, and decrease in the concentration of nutrients was observed. Wind events of 2-3 days interrupted water column stratification. In contrast, in 2018, lower chlorophyll-a (<2 mg m^-3) and primary production (less than 1.8 gC m^-2 d^-1) were observed throughout the period, despite a high concentration of nutrients, associated with lower ocean temperatures throughout the euphotic zone (<1.5°C). Observational and modeling results showed that Maxwell Bay can act as an area of high biological production that would be modulated mainly, but not exclusively, by less intense wind events and greater stratification of the water column. In addition, our result suggested an interannual variability during summer condition, and highlights the importance of continuing with long-term studies to generate a database that allows a better diagnose of the system through modeling especially under the current climate scenario. This research is supported by FONDAP IDEAL 15150003 and MG_12_18 project from "Instituto Antártico Chileno (INACH)".