Role of phytoplankton in marine silicon cycling

海洋浮游植物是地球系统的关键组成部分。它们贡献了世界年度光合作用固定碳的一半，并在海洋的营养循环中发挥着基础性作用。在所有浮游植物中，硅藻占地球光合作用的20%，是硅、碳、氮和其他营养物质循环过程的主要生物驱动因素。表层水中硅藻产生二氧化硅细胞壁，这种生物成因二氧化硅通过水柱溶解，以及生物成因二氧化硅和相关碳从表层向深海输出，这些都是海洋硅和碳循环中最重要的通量。这项建议描述了一个集成的现场和实验室计划，将促进我们对这些关键的、但鲜为人知的硅循环过程的理解。在接下来的5年里，我的目标是量化： (A)地表水中硅藻硅的使用与亚北极水域和太平洋源头水中悬浮颗粒和下沉颗粒的天然硅同位素组成之间的联系， (B)亚北极和北极硅藻组合的结构对硅循环的影响，在自然条件和模拟温室情景下进行了评估， (C)海洋颗粒和溶解水池中的硅、氮、碳和磷之间的耦合，从远洋环境到底栖环境。 这些短期目标将有助于我的研究计划的长期目标，即更好地了解浮游植物生态生理学和海洋生物地球化学循环之间的联系。 实地工作将在高纬度海洋进行，目前对浮游植物和营养物质动态的描述很少。气候变化正在不成比例地影响这些地区，这些地区正在经历海冰覆盖、水团循环、温度和海水化学的戏剧性变化。因此，从实验上评估东北太平洋和北极西部亚北冰洋和北冰洋的浮游植物反应和生物地球化学过程至关重要。 实验工作将采用前沿方法，例如用于测量硅同位素丰度的高分辨率电感耦合等离子体质谱，以及用于测量二氧化硅产生和溶解的低水平放射性硅的贝塔计数和荧光成像技术。该提案中描述的项目将为接触跨学科科学的研究生和本科生提供极好的培训机会。 这项研究将填补我们目前在生物介导的硅循环过程中的关键空白，并将促进我们对海洋古生产力的变化、对生物地球化学循环的控制以及高纬度海洋中碳输出的大小的理解。

Marine phytoplankton are key components of the Earth system. They contribute half of the world's annual photosynthetic fixation of carbon and play a fundamental role in nutrient cycling in the ocean. Of all phytoplankton groups, diatoms account for 20% of Earth's photosynthesis and are the main biological drivers of processes involved in the cycling of silicon, carbon, nitrogen and other nutrients. Production of silica cell walls by diatoms in surface waters, dissolution of this biogenic silica through the water column, and export of biogenic silica and associated carbon from surface to deep waters are some of the most important fluxes in the oceanic silicon and carbon cycles. This proposal describes an integrated field and laboratory program that will advance our understanding of these critical, but poorly known, processes of the silicon cycle. During the next 5 years, my objectives are to quantify: (A) the linkage between diatom silicon use in surface waters and the natural silicon isotopic composition of suspended and sinking particles in Subarctic waters and in Pacific source waters into the Arctic, (B) the impact of the structure of Subarctic and Arctic diatom assemblages on the silicon cycle, evaluated under natural conditions and under simulated greenhouse scenarios, (C) the coupling between silicon, nitrogen, carbon and phosphorus in marine particulate and dissolved pools, from pelagic to benthic environments. These short-term objectives will contribute to the long-term goal of my research program, which is to better understand the links between phytoplankton eco-physiology and biogeochemical cycling in the ocean. Field work will be conducted in high-latitude oceans where phytoplankton and nutrient dynamics are currently poorly described. Climate variability is disproportionally affecting these regions, which are experiencing dramatic changes in sea-ice cover, water mass circulation, temperature and seawater chemistry. It is therefore critical to experimentally evaluate phytoplankton responses and biogeochemical processes in Subarctic and Arctic seas of the NE Pacific and western Arctic. Experimental work will employ leading-edge methodologies, such as high-resolution inductively coupled plasma mass spectrometry for measuring silicon isotopic abundance, and low-level beta counting of radioactive silicon and fluorescence imaging techniques for measuring silica production and dissolution. The projects described in this proposal will provide excellent training opportunities for graduate and undergraduate students who will be exposed to interdisciplinary science. This research will fill critical gaps in our current knowledge of biologically mediated processes of the silicon cycle, and will advance our understanding of variations in marine paleoproductivity, controls on biogeochemical cycles, and the magnitude of carbon export in high-latitude oceans.