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

每年，海洋浮游植物(单细胞藻类)在表层海洋中将约450亿公斤二氧化碳(CO2)转化为有机碳，占地球总光合作用的一半。这种有机碳支持绝大多数海洋生态系统(包括具有重要商业价值的渔业，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，为了了解环境对这种生产力的控制，人们进行了大量研究。海洋初级生产力受光照和营养物质的组合以及浮游动物的放牧控制。传统上，氮等常量营养素被认为决定了浮游植物的生长。最近，微量元素铁被证明限制了约30%海洋中的浮游植物生产力。亚北极东北太平洋是世界海洋中三个主要的铁限制区域之一。从沿海到公海，该区域的铁浓度急剧下降，大气输入是近海水域的主要铁源。这些投入的重要性在2008年的火山灰沉积事件中得到了证明，那次事件在阿拉斯加湾引发了大规模的浮游植物水华。虽然富含灰尘的大气气溶胶可能通过天然铁的浓缩而潜在地刺激浮游植物的生长，但气溶胶也可能来自人为来源，这些来源往往含有丰富的金属污染物，如铅和铜。因此，输入到亚北极太平洋表层水域的气溶胶可以对浮游植物生产力和群落组成产生重要的有利或不利影响，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，也可以转移到更高的营养水平，包括人类消费的鱼类。东亚高度城市化和工业化地区作为有害污染物的来源正在增加，在跨越太平洋的长距离气溶胶运输过程中，这些污染物可能夹带着来自沙漠的矿物粉尘。这些人为气溶胶在海水中高度溶解，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东北太平洋次北极圈的亚洲气溶胶中的微量元素的组成、通量和生物效应，这些元素既是必需的，也是潜在的毒性。通过补充实验室和实地研究，拟议的研究还将确定痕量金属是否在食物网中生物积累到对人类健康构成风险的水平。预期的结果将提高我们对海洋中痕量金属循环的理解，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.