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

智力价值：营养物质从深海和中层水到海洋表层的循环和供应在控制全球生物生产力方面起着关键作用。硅是硅藻必不可少的营养物质，硅藻是一种光合藻类，它负责向海底输出的有机碳的近一半。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（针状体）是由无定形的二氧化硅（或蛋白石）组成的。我们之前已经证明，海绵状针状硅同位素组成反映了它们生长的溶解硅的浓度，因此可以用来重建过去的海水硅酸浓度。结合地表居住硅藻的同位素和微量元素组成（主要受地表水生产力控制），可以限制过去地表和深层硅循环的耦合。在这一建议中，我们的目标是重建硅的分布和生物地球化学循环在大西洋的最后一个冰川期和随后的冰消期。随着海洋生物生产力、物理循环和大气二氧化碳分压的变化，快速气候变化的时期中断了冰川消融变暖。为了研究硅在这一动态时期在海洋中的作用，我们将从西大西洋现有的年代确定的沉积物岩心中提取和分析生物蛋白石。这些骨骼残骸的同位素和痕量金属组成将用于重建深层、中间和表面溶解硅浓度和表面生产力。我们的结果将与现有的代理数据结合起来进行解释，并在硅循环的盒建模框架内进行解释。本提案的直接成果将包括：1)记录末次盛冰期以来南、北大西洋盆地中深水海绵针状体硅同位素组成；2)北大西洋硅藻硅同位素组成和微量金属组成；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中纬度和北大西洋深水硅循环的第一个综合研究。更广泛的影响：考虑到公众对气候变化的关注和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。虽然我们的工作将侧重于过去两万年的变化，但在考虑大西洋环流未来变化的影响时，它可能会为硅循环与相关碳减少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通过在部门和机构各级协调的活动向Hendry博士提供指导。例如，该系有一个指导委员会，每两年召开一次会议，为博士后研究人员提供正式和非正式的反馈。两位pi都预计将参与许多外联活动，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成为我们所有正在进行的研究的一个组成部分，我们相信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.