Oxygen flux measured in surface sediments of the Arabian Sea

During the large-scale deep-sea programme BIGSET in situ measurements of sediment community oxygen consumption (SCOC) were carried out during three cruises between 1995-1998 at five abyssal sites (3190-4450 m water depth) in the deep Arabian Sea in order to elucidate the regional and temporal variation of benthic carbon remineralisation. SCOC ranged from 0.9-6.3 mmol O2 m**-2 d**-1, with highest values in the western and northern Arabian Sea and lowest values in the southern Arabian Sea. For the central Arabian Sea intermediate oxygen uptake rates were detected. This regional pattern mirrors the overall regional pattern of primary productivity in surface waters and vertical particulate organic carbon (POC) flux at 1000 mab. Primary productivity in Arabian Sea surface waters and particulate flux into the deep-sea are controlled by the monsoon system and the flux maxima during the SW and NE monsoon are among the highest particle fluxes recorded in the deep open ocean. Highest flux rates were recorded in the western and northern Arabian Sea and decreased towards the central and southern Arabian Sea. SCOC at our western, northern and eastern Arabian Sea stations WAST, NAST and EAST were considerably higher than so far detected in other abyssal areas of the global oceans, and vertical POC flux can account for only 20-50% of benthic carbon remineralisation (BCR). Possible explanations for the high rates of BCR at these stations that are situated close to the continental margins are discussed: the accelerated deposition of very labile organic matter due to eolian dust particles, enhanced rain efficiencies, and lateral advection. A significant temporal variability in SCOC only could be detected at the eastern and western Arabian Sea stations WAST and EAST.

在1995-1998年的三次航次中，依托大型深海项目BIGSET，研究团队于阿拉伯海深海的5个深海站点（水深3190~4450米）开展了沉积物群落耗氧量（sediment community oxygen consumption, SCOC）的原位测量，以阐明底栖碳再矿化的区域与时间变化规律。SCOC取值范围为0.9~6.3毫摩尔氧气每平方米每天，其中阿拉伯海西部与北部的耗氧量最高，南部最低，中部海域的耗氧量处于中等水平。该区域分布特征与表层水体初级生产力及距海底1000米处的垂直颗粒有机碳（particulate organic carbon, POC）通量的整体区域模式高度吻合。阿拉伯海表层水体的初级生产力与深海颗粒物通量均受季风系统调控，西南（SW）季风与东北（NE）季风期间的通量峰值，属于深海开阔大洋中记录到的最高颗粒物通量之一。通量最高值出现在阿拉伯海西部与北部，并向中部及南部逐渐递减。本研究中阿拉伯海西部WAST站、北部NAST站与东部EAST站的SCOC显著高于目前全球其他深海区域已观测到的数值，且垂直POC通量仅能解释20%~50%的底栖碳再矿化（benthic carbon remineralisation, BCR）。针对这些位于大陆边缘附近站点的高BCR速率，本文探讨了多种潜在解释机制：风尘颗粒介导的高活性有机质快速沉降、增强的颗粒物沉降清除效率，以及侧向平流输送。仅在阿拉伯海东部EAST站与西部WAST站，观测到SCOC存在显著的时间变异。