Factors controlling the phytoplankton crops, taxonomic composition, and particulate organic carbon stocks in the Cosmonaut Sea, East Antarctica

The ecosystems in Southern Ocean (SO) are undergoing significant changes in the context of climate change. To identify environment-phytoplankton feedbacks in SO, seawater samples were collected in the Cosmonaut Sea (CS) during the 37 th China Antarctic Research Expedition (Jan. 2021) (CHINARE-37) and subjected to analysis of particulate organic carbon (POC) and phytoplankton pigments. The remote sensing data, CHEMTAX community compositional modeling analysis, and physicochemical measurements were combined to explore the spatial variation of phytoplankton crops, taxonomic composition, and their environmental drivers. Historical phytoplankton community data from the area were also compared against those of this study to investigate inter-annual community differences and their potential causes. The column-integrated POC and chlorophyll- a (Chl- a ) concentrations were 12.0±4.9 g/m 2 and 73.8±50.5 mg/m 2 , respectively. The two most dominant taxa were haptophyte that are adapted to high Fe availability (Hapt-HiFe, mainly Phaeocystis antarctica ) and Diatoms-A ( Phaeodactylum tricornutum ) that contributed to 33%±25% and 24%±14% to the total phytoplankton crops, respectively. Through cluster analysis, the study area was divided into two regions dominated by Hapt-HiFe and Diatoms-A, respectively. Spatially, Hapt-HiFe was mainly concentrated in the southwest coastal area that featured low temperatures, low salinity, and shallow euphotic zones. The coastal region southwest of the southern boundary of the Antarctic circumpolar current was experiencing a bloom of Hapt-HiFe during the study period that significantly contributed to the POC pool and Chl- a concentrations ( R =0.46, P