Diatom distribution in the Enderby Basin, East Antarctica

Abstract The distribution of diatom taxa was studied in the Enderby Basin, East Antarctica during the austral summer of 2010. In this study, the influence of freshwater at east of the 55°E was observed due to the melting of sea-ice, resulting in stratified (shallow Mixed Layer Depth (MLD)) and low saline conditions. This decrease in sea-surface salinity was associated with an increase in pCO2 and decrease in total diatom abundance. Corethron criophilum was recognized as the most abundant diatom (absolute abundance up to 30 × 104 cells L−1; 35% contribution to total diatom taxa) and its elevated abundances recorded at west of the 55°E. Reduced C. criophilum and increased abundances of Fragilariopsis curta and Thallassiothrix antarctica were documented at east of the 55oE. This study shows that despite shallow MLD and macronutrient availability, the diatom abundance at east of 55oE was low. We suspect that, the factors such as micronutrient unavailability, freshening of the upper water column, transportation by water masses, and photoinhibition possibly affect the production of diatoms at east of the 55oE. This elevated abundance resulted in low pCO2 levels and high meso-zooplankton abundance. This study suggests the need of long term monitoring of phytoplankton community structure in the in the East Antarctic region and factors influencing their production. This is essential to better understand the projected effects in physico-chemical conditions (especially pCO2 and temperature) on Southern Ocean phytoplankton and thus biological carbon pump.