Sources, cycling and biological impacts of trace metals in the Subarctic Pacific Ocean

海洋浮游植物（单细胞藻类）每年在海洋表面将约450亿公斤的二氧化碳（CO2）转化为有机碳，占地球光合作用总量的一半。这种有机碳支撑着绝大多数海洋生态系统（包括商业上重要的渔业，如鲱鱼、凤尾鱼和鲑鱼），并在海洋封存大气二氧化碳方面发挥着关键作用。因此，浮游植物生产力的变化对渔业和气候有很大的影响，并且已经进行了大量的研究，以了解对这种生产力的环境控制。海洋初级生产力是由光和营养的结合以及浮游动物的放牧控制的。传统上认为，大量营养物质，如氮，决定了浮游植物的生长。最近，微量元素铁已被证明限制了约30%的海洋浮游植物的生产力。东北太平洋亚北极地区是世界海洋中三个主要的缺铁地区之一。从沿海到远洋，该地区的铁浓度急剧下降，大气输入是近海水域铁的主要来源。这些输入的重要性在2008年的火山灰沉积事件中得到了证明，该事件引发了阿拉斯加湾大规模的浮游植物繁殖。虽然富含灰尘的大气气溶胶可能通过天然铁富集而潜在地刺激浮游植物生长，但气溶胶也可能来自人为来源，这些人为来源通常含有丰富的金属污染物，如铅和铜。因此，向亚北极太平洋地表水输入的气溶胶可以对浮游植物的生产力和群落组成产生重要的有益或有害的影响，并具有强烈的食物网影响。金属污染物可以抑制浮游植物的生长，也可能转移到更高的营养水平，包括人类食用的鱼类。东亚高度城市化和工业化地区日益成为有害污染物的来源，在穿越太平洋的远距离气溶胶运输过程中，这些有害污染物可能与来自沙漠的矿物粉尘一起携带。这些人为气溶胶在海水中高度可溶，增加了它们对东北太平洋生物的潜在毒性。拟议的研究将阐明沉积在亚北极东北太平洋的亚洲气溶胶中必需和潜在有毒微量元素的组成、通量和生物效应。通过补充实验室和实地研究，拟议的研究还将确定微量金属在食物网中的生物积累是否达到对人类健康构成威胁的水平。预期的结果将提高我们对海洋中微量金属循环的认识，以及微量元素在控制浮游植物生产力、渔业生产和海洋二氧化碳封存方面的作用。

Every year, marine phytoplankton (unicellular algae) convert ~45 billion kilograms of carbon dioxide (CO2) to organic carbon in the surface ocean, accounting for half of the total photosynthesis on Earth. This organic carbon supports the vast majority of marine ecosystems (including commercially important fisheries, such as herring, anchovy and salmon), and plays a key role in the oceanic sequestration of atmospheric CO2. Variations in phytoplankton productivity thus have a strong influence on fisheries and climate, and significant research has been directed towards understanding the environmental controls on this productivity.Marine primary productivity is controlled by a combination of light and nutrients, and grazing by zooplankton. Traditionally macronutrients, such as nitrogen, were thought to determine phytoplankton growth. More recently, the trace element iron has been shown to limit phytoplankton productivity in ~30% of the ocean. The Subarctic NE Pacific is one of three major iron-limited areas in the world's oceans. Iron concentrations in this region decrease dramatically from the coast to the open ocean, and atmospheric inputs are a dominant iron source in offshore waters. The importance of these inputs was demonstrated by a volcanic ash deposition event in 2008, which triggered a massive phytoplankton bloom in the Gulf of Alaska. While atmospheric aerosols rich in dust may potentially stimulate phytoplankton growth via natural iron enrichment, aerosols may also be derived from anthropogenic sources, which are often rich in metal contaminants, such as lead and copper. Aerosols inputs to surface waters of the Subarctic Pacific can thus exert important beneficial or detrimental effects on phytoplankton productivity and community composition, with strong food web implications.Metal pollutants can inhibit phytoplankton growth, and may also be transferred to higher trophic levels, including fish consumed by humans. Highly urbanized and industrialized areas of East Asia are increasing as a source of harmful pollutants that may be entrained with mineral dust from deserts during long-range aerosol transport across the Pacific. These anthropogenic aerosols are highly soluble in seawater, increasing their potential toxicity to organisms in the NE Pacific. The proposed research will elucidate the composition, flux and biological effects of trace elements, both essential and potentially toxic, in Asian-derived aerosols that are deposited in the Subarctic NE Pacific. Using complementary laboratory and field studies, the proposed research will also determine whether trace metals are bio-accumulating in the food web to levels that pose health risks to humans. Anticipated results will improve our understanding of trace metal cycling in the ocean, and the role of trace elements in controlling phytoplankton productivity, fisheries production and oceanic CO2 sequestration.