Pigment concentrations in surface sediments of the Arabian Sea

As part of the large-scale, interdisciplinary deep-sea study \"BIGSET\", the relationship between the monsoon-induced regional and temporal variability of POC deposition and the small-sized benthic community was investigated at several sites 2316-4420 m deep in the Arabian Sea during four cruises between 1995 and 1998. Vertical and horizontal distribution patterns of chloroplastic pigments (a measure of phytodetritus deposition), readily soluble protein and activity, and biomass parameters of the small-sized benthic community (Electron Transport System Activity (ETSA); bacterial ectoenzymatic activity (FDA turnover) and DNA concentrations) were measured concurrently with the vertical fluxes of POC and chloroplastic pigments. Sediment chlorophyll a (chl. a) profiles were used to calculate chl. a flux rates and to estimate POC flux across the sediment water interface using two different transport reaction models. These estimates were compared with corresponding flux rates determined in sediment traps. Regional variability of primary productivity and POC deposition at the deep-sea floor creates a trophic gradient in the Arabian Basin from the NW to the SE, which is primarily related to the activity of monsoon winds and processes associated with the topography of the Arabian Basin and the vicinity of land masses. Inventories of sediment chloroplastic pigments closely corresponded to this trophic gradient. For ETSA, FDA and DNA, however, no clear coupling was found, although stations WAST (western Arabian Sea) and NAST (northern Arabian Sea) were characterised by high concentrations and activities. These parameters exhibited high spatial and temporal variability, making it impossible to recognise clear mechanisms controlling temporal and spatial community patterns of the small-sized benthic biota. Nevertheless, the entire Arabian Basin was recognised as being affected by monsoonal activity. Comparison of two different transport reaction models indicates that labile chl. a buried in deeper sediment layers may escape rapid degradation in Arabian deep-sea sediments.

作为大型跨学科深海研究项目"BIGSET"的一部分，研究团队于1995至1998年间开展了4次科考航次，在阿拉伯海2316~4420米深的多个站位，探究了季风驱动的颗粒有机碳（Particulate Organic Carbon, POC）沉积的区域与时间变异与小型底栖生物群落之间的关联。本研究同步测量了叶绿素类色素（植物碎屑沉积的检测指标）、易溶性蛋白及其活性，以及小型底栖生物群落的生物量参数——包括电子传递系统活性（Electron Transport System Activity, ETSA）、细菌胞外酶活性（FDA turnover）与DNA浓度——并同步记录了POC与叶绿素类色素的垂直通量。研究采用沉积物叶绿素a（chl.a）剖面计算chl.a通量速率，并通过两种不同的输运反应模型估算沉积物-水界面的POC通量，随后将这些估算值与沉积物捕集器测得的对应通量速率进行对比。深海海底的初级生产力与POC沉积的区域变异，在阿拉伯海盆形成了从西北向东南延伸的营养梯度，该梯度主要与季风活动、阿拉伯海盆地形及邻近陆块相关过程有关。沉积物中叶绿素类色素的储库与该营养梯度高度吻合。不过针对ETSA、FDA及DNA参数，未发现明确的耦合关系，尽管阿拉伯海西部站位（Western Arabian Sea, WAST）与北部站位（Northern Arabian Sea, NAST）的相关浓度与活性均处于较高水平。上述参数表现出显著的空间与时间变异，使得难以明确识别调控小型底栖生物群落时空分布格局的核心机制。尽管如此，整个阿拉伯海盆均被证实受到季风活动的影响。对两种输运反应模型的对比分析表明，埋藏于深层沉积物中的不稳定叶绿素a（chl.a），可在阿拉伯海深海沉积物中避免快速降解。