Controls of Primary Production on Southern Ocean Mercury Cycling (COPPSOM)

汞（Hg）是一种有毒元素，从自然和人为来源向全球扩散。在全球汞生物地球化学循环中，大量的汞排放到大气中，通过大气沉积到达海洋，海洋沉积物被认为是最终的汞汇。海洋中的汞在海洋食物链中以有毒的甲基汞的形式被生物放大，甲基汞是通过微生物过程在水相或沉积物中形成的，而海洋鱼类的消费是汞进入人类的重要途径。陆地环境中汞的生物地球化学循环已被较好地了解，但对海洋中汞的命运，特别是海洋生物泵的作用知之甚少。以往的研究大多来自贫营养地区，表明汞在水柱中表现出类似营养物的行为，藻类对汞的清除是汞向沉积物输出的重要载体。然而，在高产地区，汞清除、汞物种转化和输出的影响只进行了很少的研究，尚未量化。本项目旨在研究海水、悬浮物、浮游植物和浮游动物以及沉积物岩心中总汞和甲基汞的含量。在“岛屿冲击”极地研究巡航期间（10月/ 11月），在南大西洋南乔治亚州附近的一个高产地区收集了样本。2022)在几个深加工站。对海水进行了最大限度的取样。深度为7000米，悬浮物和浮游生物的采样量最大。350米和600米分别使用网和大容量原位泵。沉积物岩心在采样水柱正下方取，最大深度为8000 m （Sandwich Trench）。汞和甲基汞浓度的数据将根据基本和扩展的水化学和物理参数进行解释，如叶绿素a、营养物、氧化还原指标、颗粒转化和通量，以及对悬浮物和沉积物的化学成分和生物来源（浮游植物、大型或中型浮游动物、粪便颗粒等）的分析，这些将由岛屿影响项目的其他参与者提供。利用这一综合数据集，我们旨在解决汞和甲基汞的生物地球化学循环，并量化高产地区的汞出口。我们假设浮游植物大量繁殖导致水柱中汞的消耗，并且是甲基汞形成和汞向沉积物出口的热点。此外，我们想要证明有机物在通过水柱的过程中分解是否会导致下沉颗粒中甲基汞的消耗和总汞的富集。我们将进一步解读浮游植物密集繁殖区浮游动物中的MeHg和THg是否比低营养区浮游动物的富集程度更高。

Mercury (Hg) is a toxic element that is globally dispersed from natural and anthropogenic sources. In the global biogeochemical Hg cycle, a substantial amount of Hg emitted to the atmosphere reaches the ocean through atmospheric deposition and ocean sediments are regarded as the ultimate Hg sink. Hg in the oceans biomagnifies in the marine food chain as toxic methyl-Hg which is formed in the water phase or sediment by microbial processes and consumption of marine fish is the crucial pathway of Hg to humans. The biogeochemical Hg cycle in the terrestrial environment is comparatively well understood, much less is known about the fate of Hg in the oceans, specifically about the role of the marine biological pump. Previous studies, most of them from oligotrophic areas, suggested that Hg shows a nutrient like behaviour in the water column and that Hg scavenging by algae is an important vector for the export of Hg to the sediments. However, the effect of Hg scavenging, Hg species transformation and export in highly productive areas has only been sparsely investigated and not yet been quantified. In this project we aim to investigate total Hg and methyl Hg in seawater, suspended matter, phyto- and zooplankton as well as in sediment cores. Samples were collected in a highly productive area in the South Atlantic around South Georgia during the “ISLAND IMPACT” Polarstern research cruise (Oct./Nov. 2022) at several Deep- and Process Stations. Seawater was sampled down to a max. depth of 7000 m while suspended matter and plankton was sampled to max. 350 and 600 m respectively using nets and large volume in-situ pumps. Sediment cores were taken directly below the sampled water column at a maximum depth of 8000 m (Sandwich Trench). The data of Hg and methyl Hg concentrations will be interpreted in context with basic and extended hydrochemical- and physical parameters such as chlorophyll a, nutrients, redox indicators, particle transformation and fluxes as well as analyses of the chemical composition and the biological origin (phytoplankton, macro or mesozooplankton, fecal pellets etc.) of suspended matter and sediments which will be provided by other participants of the ISLAND IMPACT project. With this comprehensive data set we aim resolve the biogeochemical cycling of Hg and methyl Hg and to quantify the Hg export in highly productive areas. We hypothesize that phytoplankton blooms cause depletion of Hg in the water column and are hot spots for methyl-Hg formation and Hg export to the sediment. Moreover, we want to prove if decomposition of organic seston on its way through the water column causes depletion of methyl Hg and enrichment of total Hg in sinking particles. We will further decipher if MeHg and THg in zooplankton of areas of intense phytoplankton blooms becomes higher enriched compared to zooplankton of oligotrophic zones.