Determining the distribution and physicochemical speciation of bioactive trace elements in the oceans under a changing climate

海洋中必需微量元素（如Cu、Fe和Zn）和潜在有毒微量元素（如Cu、Ag和Cd）的分布和生物利用度会影响海洋生产力、生态系统结构，从而影响气候活性气体的海气交换。因此，理解海洋生物地球化学循环对全球变化的响应必须包括对微量元素来源、汇和化学形态的研究。这是因为海洋微生物对微量元素营养物质和毒素有绝对的需求或敏感性，这有助于解释微生物群落结构的时空变异性，并设定海洋中碳和氮固定的上限。微量元素对海洋微生物的生物利用度不仅受其浓度的控制，还受金属在海水中吸收的形态或化学形式的控制。反过来，微生物可以通过生物介导的摄取/渗出、氧化还原反应和强有机配体的产生来影响微量元素的分布和形态，这些配体可以复杂地溶解水柱中的微量元素。我的研究计划的长期目标是了解控制微量金属的分布、化学形态和由此产生的生物可利用性的过程，以及如何改变物理和化学条件以响应气候变化可能影响海洋中金属的生物地球化学循环。最近，我的研究小组通过在现场和实验室中开发和应用强大的分析方法，朝着这些目标取得了重大进展。我们重点研究了控制初级生产和群落结构的金属（如铁、铜和锌），作为古海洋示踪剂，提供了关于海洋在过去气候变化中作用的重要信息（如Cd、Ag），或可能对生态系统健康和功能产生负面影响的潜在有毒重金属（如Cu、Ag和Cd）。在接下来的5年里，我的研究目标是：1)研究高纬度海洋表面水域温度、pH值和光照制度的变化将如何影响生物上重要金属的循环；2)揭示海洋边缘的微量金属通量是如何变化的，重点是大陆架的来源和汇；3)确定海洋中氧含量降低的长期趋势将如何影响生物活性金属的相对分布。这里提出的工作将有助于阐明微量金属在塑造代表海洋食物链基础的海洋微生物群落组成和生产力方面所起的作用。金属可以作为必需的营养物质和毒素，调节气候活性气体的生物生产和消耗。我们的数据将允许在耦合大气-海洋模型中更好地参数化生物地球化学速率过程，该模型旨在预测亚北极和北极海洋系统对区域变暖、海洋酸化、海冰和光照变化的响应。此外，更深入地了解是什么控制了盆地尺度上痕量金属的分布，以及它们与主要藻类营养物质的关系，将有助于验证现有的代用物和开发新的代用物，这些代用物对于重建海洋在过去气候变化中的作用至关重要。

The distribution and bioavailability of essential (e.g. Cu, Fe and Zn) and potentially toxic (e.g. Cu, Ag and Cd) trace elements in the ocean can impact marine productivity, ecosystem structure and therefore the air-sea exchange of climate active gases. An understanding of the response of marine biogeochemical cycles to global change must, therefore, include studies of trace element sources, sinks, and chemical speciation. This is because marine microbes have absolute requirements or sensitivities to trace element nutrients and toxins that can help explain temporal-spatial variability in microbial community structure and set upper limits on carbon and nitrogen fixation in the sea. The bioavailability of trace elements to marine microbes is controlled not only by the concentration but the speciation, or chemical form, that metals take in seawater. In turn, microorganisms can affect the distribution and speciation of trace elements through biologically mediated uptake/exudation, redox reactions and the production of strong organic ligands that complex dissolved trace elements in the water column. The long-term goals of my research program are to understand the processes that control the distribution, chemical speciation and resulting bioavailability of trace metals, and how altered physical and chemical conditions in response to climate change are likely to impact the biogeochemical cycling of metals in the ocean. Recently, my research group has made significant progress towards these goals through the development and application of powerful analytical methods in both the field and the laboratory. We have focused on metals that control primary production and community structure (e.g. Fe, Cu and Zn), serve as paleoceanographic tracers that provide important information regarding the oceans role in past climate change (e.g. Cd, Ag), or potentially toxic heavy metals that might negatively impact ecosystem health and function (Cu, Ag and Cd). Over the next 5 years my research objectives are to: 1) examine how changing temperature, pH and light regimes in high latitude ocean surface waters will impact the cycling of biologically important metals; 2) unravel how trace metal fluxes are modified at the ocean margins with an emphasis on sources and sinks at the continental shelves; and 3) determine how the secular trend of decreasing oxygen levels in the ocean will impact the relative distribution of bioactive metals.The work proposed here will help to elucidate the role that trace metals play in shaping community composition and productivity of marine microbes that represent the base of the ocean food chain. Metals can act as essential nutrients and toxins that can modulate the biological production and consumption of climate active gases. Our data will allow for better parameterization of biogeochemical rate processes in coupled atmosphere-ocean models designed to predict the response of marine systems in the subarctic and Arctic to regional warming, ocean acidification, and changing sea ice and light regimes. In addition, a more thorough understanding of what controls the basin scale distribution of trace metals and their relationships with the major algal nutrients will aide in efforts to verify existing and develop new paleoproxies that are essential for reconstructing the oceans role in past climate variability.