Collaborative Research: Isotopic insights to mercury in marine food webs and how it varies with ocean biogeochemistry

汞是一种普遍存在的微量元素，存在于海洋环境中的几个状态中，包括一甲基汞(MmHg)，这是一种在海洋生物中生物积累并对人类健康构成威胁的神经毒素。要了解汞在海洋中的命运及其对海洋食物网的影响，需要了解控制汞化学转化发生深度的机制。对北太平洋九种海鱼的汞初步分析表明，中间水域是毫米汞进入公海食物网的重要入口点。为了阐明控制这一过程的过程，研究人员将检查垂直溶解氧剖面不同地区的汞动态，这应该会影响汞转化的深度。这项研究的结果将有助于更好地了解汞进入海洋食物链并最终影响人类的途径。该项目将为研究生和本科生提供培训，并通过公共宣传和非正式科学计划传播对海洋汞的认识。汞的同位素变化可以提供对各种环境过程的洞察。汞的同位素组成在大多数生物和非生物化学反应中表现为质量依赖分馏(MDF)，在光化学自由基对反应中表现为质量无关分馏(MIF)。MDF和MIF的不同寻常的组合可以提供有关汞的反应途径和生物地球化学历史的信息。初步研究结果提供了强有力的证据，表明净毫米汞的形成发生在跃层表层混合层以下，并表明低氧中水的毫米汞是汞进入远洋食物网的重要入口点。这些发现突出表明，迫切需要了解海洋生物群中的毫米汞水平将如何应对大气汞排放的变化、无机汞向表层海洋的沉积以及假想的未来氧最低限度区域的扩大。利用具有对比生物地球化学和汞同位素分馏实验的跨生态系统的野外采集，研究人员将填补汞生物地球化学方面的关键知识空白。拟议研究的结果将使科学家能够评估水柱中汞甲基化和去甲基化可能发生的生物地球化学控制。

Mercury is a pervasive trace element that exists in several states in the marine environment, including monomethylmercury (MMHg), a neurotoxin that bioaccumulates in marine organisms and poses a human health threat. Understanding the fate of mercury in the ocean and resulting impacts on ocean food webs requires understanding the mechanisms controlling the depths at which mercury chemical transformations occur. Preliminary mercury analyses on nine species of marine fish from the North Pacific Ocean indicated that intermediate waters are an important entry point for MMHg into open ocean food webs. To elucidate the process controlling this, researchers will examine mercury dynamics in regions with differing vertical dissolved oxygen profiles, which should influence depths of mercury transformation. Results of the study will aid in a better understanding of the pathways by which mercury enters the marine food chain and can ultimately impact humans. This project will provide training for graduate and undergraduate students, and spread awareness on oceanic mercury through public outreach and informal science programs. Mercury isotopic variations can provide insight into a wide variety of environmental processes. Isotopic compositions of mercury display mass-dependent fractionation (MDF) during most biotic and abiotic chemical reactions and mass-independent fractionation (MIF) during photochemical radical pair reactions. The unusual combination of MDF and MIF can provide information on reaction pathways and the biogeochemical history of mercury. Results from preliminary research provide strong evidence that net MMHg formation occurred below the surface mixed layer in the pycnocline and suggested that MMHg in low oxygen intermediate waters is an important entry point for mercury into open ocean food webs. These findings highlight the critical need to understand how MMHg levels in marine biota will respond to changes in atmospheric mercury emissions, deposition of inorganic mercury to the surface ocean, and hypothesized future expansion of oxygen minimum zones. Using field collections across ecosystems with contrasting biogeochemistry and mercury isotope fractionation experiments researchers will fill key knowledge gaps in mercury biogeochemistry. Results of the proposed research will enable scientists to assess the biogeochemical controls on where in the water column mercury methylation and demethylation likely occur.