Fatty acid composition, and bacteria and meiofauna abundance in sediment cores PS71/013 and PS71/085 during POLARSTERN cruise ANT-XXIV/2

During the RV Polarstern ANT XXIV-2 cruise to the Southern Ocean and the Weddell Sea in 2007/2008, sediment samples were taken during and after a phytoplankton bloom at 52°S 0°E. The station, located at 2960 m water depth, was sampled for the first time at the beginning of December 2007 and revisited at the end of January 2008. Fresh phytodetritus originating from the phytoplankton bloom first observed in the water column had reached the sea floor by the time of the second visit. Absolute abundances of bacteria and most major meiofauna taxa did not change between the two sampling dates. In the copepods, the second most abundant meiofauna taxon after the nematodes, the enhanced input of organic material did not lead to an observable increase of reproductive effort. However, significantly higher relative abundances of meiofauna could be observed at the sediment surface after the remains of the phytoplankton bloom reached the sea floor. Vertical shifts in meiofauna distribution between December and January may be related to changing pore-water oxygen concentration, total sediment fatty acid content, and pigment profiles measured during our study. Higher oxygen consumption after the phytoplankton bloom may have resulted from an enhanced respiratory activity of the living benthic component, as neither meiofauna nor bacteria reacted with an increase in individual numbers to the food input from the water column. Based on our results, we infer that low temperatures and ecological strategies are the underlying factors for the delayed response of benthic deep-sea copepods, in terms of egg and larval production, to the modified environmental situation.

2007至2008年间，极星号科考船（RV Polarstern）执行ANT XXIV-2航次，奔赴南大洋与威德尔海开展科考作业。航次期间，研究人员于南纬52°、东经0°处的浮游植物水华（phytoplankton bloom）发生期间及发生后采集了沉积物样品。该站位水深2960米，首次采样于2007年12月初，后于2008年1月底对该站位进行了复采。首次在水柱中观测到的浮游植物水华所产生的新鲜浮游植物碎屑（phytodetritus），至第二次采样时已沉降至海底。两次采样时段内，细菌与多数主要小型底栖生物（meiofauna）类群的绝对丰度未发生显著变化。作为仅次于线虫类（nematodes）的第二大优势小型底栖生物类群，桡足类（copepods）的有机物质输入增加并未使其繁殖投入出现可观测的提升。不过，当浮游植物水华残骸沉降至海底后，沉积物表层的小型底栖生物相对丰度显著升高。2007年12月与2008年1月间，小型底栖生物分布的垂直迁移可能与本研究测得的孔隙水氧浓度（pore-water oxygen concentration）、沉积物总脂肪酸含量（total sediment fatty acid content）及色素图谱（pigment profiles）的变化相关。浮游植物水华发生后的耗氧量升高，可能源于活体底栖生物群落的呼吸活动增强——因为无论是小型底栖生物还是细菌，其个体数量均未因水柱输入的食物而出现增长。基于本研究结果，我们推断，就卵与幼虫生成而言，深海底栖桡足类对环境变化的响应存在延迟，其背后的驱动因素为低温环境与物种生态策略。