Organic matter composition in sediments recording sea surface phytoplankton community structure in Prydz Bay of Antarctica

The coastal zones in Antarctica play an important role in the polar carbon cycle through the efficiency of the biological pump. In this study, Prydz Bay in East Antarctica was selected to investigate factors controlling organic matter composition in sediments using source-dependent biomarkers. The results show that fatty acids are the most abundant biomarkers in sediments, followed by sterols, fatty alcohols, and alkanes. Although microalgae are well known to be the main source of sedimentary organic matter in Prydz Bay, the distribution of low molecular weight branched alkanes and alkenes with an even-odd predominance suggest the importance of bacteria during organic matter transformation, and its contribution to sedimentary organic matter. High concentrations of highly branched isoprenoid alkenes (HBIs) with a distinctive enriched 13C signature indicate substantial inputs of ice algae to sediments. Principal component analysis of source-dependent biomarkers reveals that the spatial heterogeneity of organic composition in sediments of Prydz Bay is mainly controlled by the distribution of sea surface phytoplankton community in different geographical zones. Redundancy analysis demonstrates that seasonal sea-ice cover is the main driver for blooms of distinctive algae in each geographical zone as a result of spatial succession of the phytoplankton community. The result clearly exhibits that, at least in Prydz Bay, spatial succession of the sea surface phytoplankton community in austral summer can be recorded in sediments, suggesting that a high-resolution sediment record of source-dependent biomarkers can be used to reconstruct the evolution of sea surface phytoplankton community structure during geological history in Antarctic coastal zones.