基于五条太平洋海沟研究浊流对深渊沉积有机质来源，含量和活性的影响

深渊区（水深>6000米）是地球上最不被人类了解的生境之一。近年来的研究发现，深渊区具有远高于深海平原的底栖生物丰度和微生物活动，而这与深渊沉积有机质的高含量和高活性密切相关。浊流可能是导致活泼有机质在海洋最深处富集的重要机制，然而目前关于浊流影响深渊碳循环的报道还非常罕见（仅限日本海沟）。本项目拟以马里亚纳、玛索、新不列颠、克马德克、阿塔卡玛五条具有不同生物地球化学特征的太平洋海沟为研究对象，通过分析沉积柱状样的粒度、元素含量（碳、氮等）、放射性核素活度（210Pb、137Cs、14C）、同位素（δ13C、δ15N）和生物标志物（如脂类、色素、氨基酸、糖类）等参数，鉴定五条海沟的浊流沉积，评估海沟内外以及不同海沟之间浊流和非浊流有机质在来源、含量和活性方面的差异，从全球尺度揭示浊流活动-深渊有机质埋藏-深渊底栖微生物活动的关联。本项目的开展将拓展我们对深渊极端环境生物地球化学过程的认识。

Hadal zone (water depth > 6,000 meters) is one of the least explored habitats on Earth. Recent studies have revealed that the benthic biomass and microbial activity in the hadal zone are substantially higher than that in surrounding abyssal plains. These characters are closely related to higher concentration and higher bioavailability of sediment organic matter in the hadal trenches compared to surrounding areas. Turbidity current is hypothesized to be one of important mechanisms responsible for the accumulation of labile organic matter in the deepest ocean, but the effect of turbidity current on hadal carbon cycle was rarely reported. To the best of the applicants' knowledge, there are only two studies reporting the effect of turbidity current on organic carbon burial, both for Japan Trench, which is apparently unable to represent the entire hadal zone. In this project, the applicants will choose Mariana Trench, Mussau Trench, New Britain Trench, Kermadec Trench and Atacama Trench as the study area. These five Pacific hadal trenches are distinctly different by biogeochemical properties. By analyzing grain size, element concentrations (e.g., organic carbon, nitrogen), radionuclide activity (210Pb, 137Cs, 14C), stable isotopic compositions (δ13C, δ15N) as well as biomarkers (e.g., lipids, pigments, amino acids and carbohydrates) in multiple sediment cores, the applicants will determine the turbidite deposit and background deposit, assess the intra- and inter-trench variabilities in the source, concentration and bioavailability of sediment organic matter between turbidite and background deposits，and disentangle the relationship among turbidity current activity, organic matter burial and benthic microbial activity in the deepest ocean realm at the global scale. This project will be helpful for expanding our knowledge on hadal biogeochemical processes.