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

南大洋汞循环初级生产控制 (COPPSOM)

• 批准号: 528941462
• 负责人: Professor Dr. Harald Biester, Ph.D.
• 金额: --
• 依托单位: Department of Earth, Ocean and Atmospheric Sciences
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/528941462?language=en
• 关键词: Controls; Primary; Production; Southern; Ocean

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.

汞（Hg）是一种有毒元素，在全球范围内分布于自然和人为来源。在全球汞的地球化学循环中，大量排放到大气中的汞通过大气沉降到达海洋，海洋沉积物被认为是汞的最终汇。海洋中的汞在海洋食物链中以有毒甲基汞的形式进行生物放大，甲基汞通过微生物作用在水相或沉积物中形成，而食用海洋鱼类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相对来说已经得到了很好的了解，但对海洋中汞的归宿，特别是海洋生物泵的作用，了解得还少得多。以往的研究，其中大部分来自贫营养区，表明汞显示了营养的行为，在水柱和汞清除藻类是一个重要的载体出口汞的沉积物。然而，汞清除、汞形态转化和汞输出在高生产率地区的影响只得到了很少的调查，尚未量化。本项目旨在调查海水、悬浮物、浮游植物和浮游动物以及沉积物岩心中的总汞和甲基汞。在“岛屿影响”号北极星号研究巡航期间（2009年10月10日），在南格鲁吉亚南部周围的南大西洋高产地区采集了样本。2022年11月）在几个深加工站。海水被取样到最大值。水深7000 m，悬浮物和浮游生物采样最大。350和600米，分别使用网和大容量原位泵。在最大深度为8000米（三明治海沟）的采样水柱正下方采集沉积物芯样。汞和甲基汞浓度的数据将在基本和扩展的水化学和物理参数（例如叶绿素a、营养物质、氧化还原指标、颗粒转化和通量）以及化学成分和生物来源（浮游植物、大型或中型浮游动物、粪粒等）分析的背景下进行解释。悬浮物和沉积物的含量，将由ISLAND IMPACT项目的其他参与者提供。通过这套全面的数据，我们旨在解决汞和甲基汞的地球化学循环问题，并量化高产地区的汞出口。我们推测，浮游植物水华导致汞在水柱枯竭，是热点甲基汞的形成和汞出口到沉积物。此外，我们想证明，如果有机悬浮物的分解过程中通过水柱的原因消耗甲基汞和富集总汞在下沉颗粒。我们将进一步破译，如果甲基汞和THG在浮游动物的浮游植物密集区成为更高的富集相比，贫营养区的浮游动物。