Sources and distribution characteristics of chromophoric dissolved organic matter in the Cosmonaut Sea and the Cooperation Sea, Antarctica

Dissolved organic carbon (DOC) constitutes the largest organic carbon reservoir in the ocean and plays a vital role in the oceanic carbon cycle. However, research on DOC in Antarctica has been limited, largely due to difficulties in sample collection. In this study, we investigate chromophoric dissolved organic matter (CDOM) in the Cosmonaut Sea and Cooperation Sea, Antarctica. The relative abundances of CDOM, as indicated by the absorption coefficient at 254 nm (a254), exhibit significant variability, ranging from 1.29 m-1 to 8.37 m-1. The diatom species B is the primary contributor to CDOM in the region influenced by the Antarctic slope current. Using excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis (EEM-PARAFAC), we identify three fluorescent components: one protein-like component (C1) and two humic-like components (C2 and C3). Our findings indicate that strong microbial activity in the euphotic zones of the Cosmonaut Sea and Cooperation Sea serves as a primary pathway for the removal of protein-like substances while also acting as a significant source of humic-like substances. Microbial degradation likely accounts for the decoupling of the vertical distribution of DOC and phytoplankton. Furthermore, the intrusion of modified circumpolar deep water (mCDW) into the euphotic zones of open ocean areas influences the distribution of CDOM at depths shallower than 200 m. These results have important implications for enhancing our understanding of the dynamics of CDOM and DOC in east Antarctica, as well as for improving assessments of the carbon cycle.