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

智力优点：营养物从深海和中层沃茨向海洋表层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。硅是硅藻的一种必需营养素：光合藻类负责向海底输出近一半的有机碳。因此，需要重建过去海洋中溶解硅分布的变化，以检验将生物碳减少与气候变化联系起来的假设。深海海绵的骨架（骨针）由无定形二氧化硅（或蛋白石）组成。我们以前已经证明，海绵骨针硅同位素组成反映了溶解硅的浓度，它们的生长，因此，可以用来重建过去的海水中的硫酸浓度。结合地表硅藻的同位素和微量元素组成，这在很大程度上是由地表水生产力控制的，可以约束过去的地表和深部硅循环的耦合。在这个建议中，我们的目标是重建在最后一个冰河时代和随后的冰消期在大西洋中的硅的分布和地球化学循环。冰川期变暖是由快速气候变化时期伴随着海洋生物生产力和物理循环和大气pCO 2的变化所引起的。为了研究硅在海洋中的作用，在这一动态时期，我们将提取和分析生物蛋白石从现有的良好的沉积物芯从西大西洋。这些骨骼遗骸的同位素和微量金属组成将用于重建深层、中层和表层溶解硅浓度和表层生产力。我们的研究结果将结合现有的代理数据进行解释，并在框建模的二氧化硅循环的框架。这一建议的直接产出将包括：1）自末次盛冰期以来南大西洋和北大西洋盆地中层和深层沃茨中海绵骨针的硅同位素组成记录; 2）北大西洋硅藻的硅同位素组成和微量金属组成; 3）大西洋硅循环的箱型模型，以帮助解释实验结果。更广泛的影响：鉴于公众对气候变化的关注以及对地球工程和海洋的兴趣，了解营养供应和生物碳减少之间的联系是重要和及时的。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。虽然我们的工作将集中在过去的变化在过去的两万年，它可能会提供有用的见解硅循环和相关的碳下降之间的联系时，考虑到未来的影响在大西洋环流的变化。该项目将资助博士后研究员凯瑟琳·亨德利的研究，并将有助于她的科学生涯的发展。将通过与WHOI科学家的个人互动以及通过在部门和机构层面协调的活动向Hendry博士提供指导。例如，该部门有一个指导委员会，每半年举行一次会议，为博士后研究人员提供正式和非正式的反馈。两个PI都预见到了许多外展活动的参与，包括媒体电话，采访，包括本科生和我们的研究演示。所有数据将以电子方式存档，并通过WHOI提供给社区。教育和公众宣传活动将继续是我们所有正在进行的研究的一个组成部分，我们认为，我们过去的记录证明了我们继续这些活动的承诺。

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.