Understanding biological carbon pump in the central Arabian Sea using phytoplankton biomarkers and diatom frustules from surface sediments.

The Central Arabian Sea, a tropical ocean basin, is impacted by monsoon winds that lead to high biological productivity in surface waters and form an oxygen minimum zone (OMZ) at intermediate depth. The present study aimed to understand the pattern of biological carbon pump driven by different phytoplankton groups along the central Arabians Sea, an area strongly impacted by monsoon wind forcings. The surface sediment samples from 5 locations along the central Arabian Sea were collected from 21 ° N to 11 ° N (at 2 ° intervals) along 64 ° E. These sediments accumulate materials originating from surface waters and can be used to understand the surface processes including the contributions of various phytoplankton groups in sinking materials. Bulk sediment parameters (total organic carbon, inorganic carbon, total nitrogen) were analyzed along with plankton biomarkers (sterols and alkenone) and sea surface temperature (SST) proxy using alkenone. Additionally, the frustules of diatoms that are siliceous phytoplankton shells, were also measured from the same sediments. We noticed a north-south gradient in all parameters and the biological proxies showed more organic matter preservation from larger diatoms in the north. Whereas, lower organic matter contributed by smaller phytoplankton and zooplankton were found in the south. These trends were attributed to ocean-atmospheric processes and oxygen availability in the water column.

阿拉伯海中部作为热带海洋盆地，受季风环流影响，表层水体生物生产力旺盛，并在中层水深形成了低氧区（oxygen minimum zone, OMZ）。本研究旨在探究受季风强迫作用显著的阿拉伯海中部海域中，不同浮游植物类群驱动的生物碳泵分布模式。研究团队沿64°E经线，在北纬21°至11°区间（间隔2°）采集了阿拉伯海中部5个站位的表层沉积物样品。此类沉积物富集了表层水体来源的物质，可用于解析表层海洋过程，包括不同浮游植物类群在沉降颗粒物中的贡献占比。本研究分析了沉积物总体参数（总有机碳、无机碳、总氮），同时检测了浮游植物生物标志物（甾醇与烯酮（alkenone）），并利用烯酮构建了海表温度（sea surface temperature, SST）代用指标。此外，本研究还对同批沉积物中的硅质浮游植物——硅藻的硅质壳体进行了检测。研究发现所有参数均呈现南北向梯度分布：北部区域的生物代用指标显示，大型硅藻来源的有机质保存程度更高；而南部海域中，小型浮游植物与浮游动物贡献的有机质含量相对偏低。上述分布趋势可归因于海-气相互作用过程与水体中的氧含量状况。