Testing the Silicic Acid Leakage Hypothesis: A Study of Opal in the Atlantic

智力优势：营养物质从深水和中层水向表层海洋的循环和供应在控制全球生物生产力方面发挥着关键作用。硅是硅藻必不可少的营养物质：光合作用的藻类负责向海底输出近一半的有机碳。因此，需要重建海洋中溶解硅分布的过去变化，以检验将生物碳减少与气候变化联系起来的假说。深海海绵的骨架(针状物)由无定形二氧化硅(或蛋白石)组成。我们以前已经证明，海绵针状硅同位素组成反映了它们生长所在的溶解硅的浓度，因此可以用来重建过去的海水硅酸浓度。结合地表硅藻的同位素和微量元素组成，可以限制过去表层和深层硅循环的耦合。地表硅藻在很大程度上受地表水生产力的控制。在这项提议中，我们的目标是重建上一次冰期和随后的冰川消融期间大西洋中硅的分布和生物地球化学循环。伴随着海洋生物生产力和物理环流以及大气二氧化碳含量变化的快速气候变化期，伴随着消冰期变暖。为了研究硅在这一动态期海洋中的作用，我们将从西大西洋现有的测年沉积物岩心中提取并分析生物蛋白石。这些骨骼遗骸的同位素和微量金属成分将被用来重建深层、中间和表面溶解硅的浓度和表面生产力。我们的结果将结合现有的代理数据进行解释，并在二氧化硅循环的框模型框架内进行解释。这一建议的直接成果将包括：1)记录自上一次冰川盛期以来南大西洋和北大西洋盆地中水和深水中海绵针状体的硅同位素组成；2)北大西洋硅藻的硅同位素组成和痕量金属组成；3)大西洋硅循环的盒子模型，以帮助解释实验结果。该项目的数据将形成对中纬度和北大西洋深水硅循环的第一个全面研究。广泛的影响：考虑到公众对气候变化的关注以及对地球工程和海洋的兴趣，了解营养物质供应和碳生物消耗之间的联系是重要的和及时的。我们建议开展新的研究，以促进我们对海水中主要营养物质之一硅在生物生产力中的作用的理解。尽管我们的工作将侧重于过去两万年的变化，但它可能会为考虑未来大西洋环流变化的影响时，对硅循环和相关碳排放之间的联系提供有用的见解。该项目将资助博士后研究员凯瑟琳·亨德利的研究，并将对她的科学事业发展起到重要作用。将通过与世卫组织科学家的个人互动以及在部门和机构范围内共同协调的活动向Hendry博士提供指导。例如，该系有一个指导委员会，每两年举行一次会议，向他们的博士后研究人员提供正式和非正式的反馈。两位PI都预计会参与许多外展活动，包括媒体访问、采访、纳入本科生和演示我们的研究。所有数据将以电子方式存档，并通过世界卫生组织提供给社区。教育和公众宣传活动将继续是我们正在进行的所有研究的一个组成部分，我们认为，我们过去的记录证明我们致力于继续这些活动。

Intellectual merit: The circulation and supply of nutrients from deep and intermediate waters to the surface ocean plays a key role in controlling global biological productivity. Silicon is an essential nutrient for diatoms: photosynthetic algae that are responsible for nearly half of the export of organic carbon to the seafloor. Reconstructing past changes in the distribution of dissolved silicon in the oceans is therefore needed for testing hypotheses that link biological drawdown of carbon and climate change.The skeletons (spicules) of deep-sea sponges are composed of amorphous silica (or opal). We have previously demonstrated that sponge-spicule silicon isotope compositions reflect the concentration of dissolved silicon in which they grew and can, therefore, be used to reconstruct past seawater silicic acidconcentrations. Combined with the isotopic and trace element composition of surface dwelling diatoms, which are largely controlled by surface water productivity, the coupling of surface and deep silicon cycles in the past can be constrained. In this proposal we aim to reconstruct the distribution and biogeochemical cycling of silicon in the Atlantic Ocean during the last ice age and the subsequent the deglaciation. Deglacial warming waspunctuated by periods of rapid climate change accompanied with shifts in ocean biological productivity and physical circulation and atmospheric pCO2. To investigate the role of silicon in the ocean during this dynamic period, we will extract and analyze biogenic opal from existing well-dated sediment cores from the western Atlantic. The isotopic and trace metal composition of these skeletal remains will be used to reconstruct deep, intermediate and surface dissolved silicon concentrations and surface productivity. Our results will be interpreted in conjunction with existing proxy data, and in the framework of box-modeling the silica cycle. The direct output of this proposal will include: 1) record of the silicon isotope composition of sponge spicules in intermediate and deep waters of both the South and North Atlantic basins since the last glacial maximum; 2) silicon isotope compositions and trace metal compositions of diatoms from the North Atlantic; 3) box-models of silicon cycling in the Atlantic, to aid interpretation of the experimental results. The data from this project will form the first comprehensive study of deep-water silicon cycling in the mid-latitudes and the North Atlantic.Broader impacts: An understanding of the link between nutrient supply and the biological drawdown of carbon is important and timely given the public concern with climate change and interest in geoengineering and ocean. We propose to carry out novel research to advance our understanding of the role in biological productivity of one of the major nutrients in seawater, silicon. Although our work will focus on past changes over the last twenty thousand years, it may provide useful insights into the linkages between silicon cycling and related carbon drawdown relevant when considering the impact of future changes in Atlantic Ocean circulation. The project will fund the research of postdoctoral investigator Katharine Hendry, and will be instrumental in the development of her scientific career. Mentoring will be provided to Dr Hendry through personal interaction with WHOI Scientists, and through activities co-coordinated at Departmental and Institutionwide levels. For example, the department has a mentoring committee that meets biannually to provide formal and informal feedback to their postdoctoral researchers. Both PIs foresee participation in many outreach activities, including media calls, interviews, inclusion of undergraduate students anddemonstrations of our research. All data will be archived electronically and made available to the community through WHOI. Education and public outreach activities will continue to be an integral part of all our ongoing studies and we believe that our past records attest to our commitment to continue theseactivities.