Collaborative Research: Coupling of physical and chemical processes in the shelf to basin transport of iron and iodine off Washington and Oregon

生产性沿海水域和相对非生产性近海水域之间的界限不是与海岸距离的简单函数，而是由生物、化学和海洋物理之间复杂的相互作用决定的。这种相互作用是控制海洋对食物供应和全球碳循环贡献的基本属性。在夏季的几个月里，海水变暖，含氧量低，海底附近的生物分解消耗了可用的氧气，并将沉积物中的铁释放到上面的海水中。在海洋深处，峡谷和其他崎岖不平的表面特征会影响洋流，并产生湍流，从而迅速将铁从离岸大陆架上移走。这些铁反过来又能提高几英里外的生物生产力。该项目将研究(1)大陆架海底的分解过程如何释放海洋生物所需的铁等元素；(2)洋流如何与大陆架和斜坡相互作用，使大陆架上的水向近海移动，以提高生产力。基于20多年来在加利福尼亚和俄勒冈海岸进行的模型模拟，表明铁通过羽流从大陆架运输到开阔的海洋，科学家将收集和分析铁和碘的样本，以证明模型的发现。碘被包括在这项研究中，因为它可以追踪从低氧沉积物到大陆架的输入。此外，研究结果将用于改进当前模型中使用的假设。该项目将支持四名研究生和几名本科生进行全部或部分研究。科学家们通过COOL项目（实验室外的化学海洋学）和冰上学生基金会参与了高中生指导。南加州大学和加州大学洛杉矶分校的科学家将沿着华盛顿和俄勒冈海岸研究铁（Fe）和碘(I)的地球化学，那里的有机物氧化率高，溶解氧浓度低，大陆架上的沉积铁通量高。这个项目假设一个大陆架到盆地的穿梭控制着从富铁大陆架到北太平洋内部的铁供应。区域海洋模拟系统（ROMS）与2007-2017年间运行的生物地球化学元素循环模型（BEC）的模拟表明，这条海岸线是海洋盆地铁的主要来源，显示出由极地潜流产生的地下漩涡产生的深层和浅层铁羽流。该模型的结果将用于预测铁的分布如何随季节变化，并在2021年到该地区的两次巡航中指导采样。根据ROMS-BEC模型，在夏末，底水氧最低时，铁库存量最高，冬季和早春库存量最低。模型产生的深层羽流类似于在纳米比亚、秘鲁和阿拉斯加湾报道的那些。这项工作将在深达4500米的深度取样，寻找这样的羽流。深羽流在全球铁收支中很重要，因为它们可能在高纬度水域露头，而这些水域的铁含量有限。碘也将被测量，因为像铁一样，它在沉积物水界面积聚，并在还原条件下释放。陆架沉积物中产生的碘羽状物将被用作侧向铁平流的半保守示踪剂。游船还将评估河流（特别是哥伦比亚河）的直接输入与减少沉积物的相对重要性，因为这些输入是季节性分离的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，认为值得支持。

The boundary between productive coastal waters and relatively non-productive offshore waters is not a simple function of distance from the coast, but is determined by a complex interplay between biology, chemistry, and ocean physics. This interplay is a fundamental property that controls the oceanic contribution to the food supply and the global carbon cycle. During summer months when waters are warmer with low oxygen, biological decomposition near the seafloor consumes available oxygen and releases iron from sediments into overlying seawater. In deeper parts of the ocean, canyons and other rugged surface features influence currents and create turbulence that rapidly moves iron from the shelf offshore. This iron in turn can enhance biological productivity miles away. This project will investigate (1) how decomposition processes on the continental shelf seafloor release elements like iron required for ocean life and (2) how ocean currents interact with the continental shelf and slope to move waters overlying the shelf offshore to enhance productivity. Based on model simulations from the California and Oregon coasts done over 20 years that show transport of iron via plumes from the shelf to the open ocean, scientists will collect and analyze samples for iron and iodine to prove the findings of the model. Iodine has been included in the study because it can track inputs from low oxygen sediments to the shelf. In addition, results from the study will be used to improve assumptions used in the current model. The project will support the research in whole or in part of four graduate students and several undergraduate students. The scientists are involved with High School student mentoring, through Project COOL (Chemical Oceanography Outside the Lab) and the Students on Ice Foundation. Scientists from the University of Southern California and the University of California, Los Angeles will study iron (Fe) and iodine (I) geochemistry along the Washington and Oregon Coasts, where high organic matter oxidation rates, low dissolved oxygen concentrations, and high sedimentary Fe fluxes on the continental shelf occur. This project hypothesizes that a shelf-to-basin shuttle controls the supply of Fe from the Fe-rich shelf into the interior of the North Pacific Ocean. Simulations of a Regional Oceanic Modeling System (ROMS) coupled with the Biogeochemical Elemental Cycling model (BEC) run between 2007-2017 showed that this coastline is a major source of Fe to the ocean basin, exhibiting both deep and shallow Fe plumes that arise from subsurface eddies generated by poleward undercurrents. Results from this model will be used to predict how the distribution of Fe evolves seasonally and guide sampling during two cruises in 2021 to the region. According to the ROMS-BEC model, the Fe inventory is highest in late summer, when bottom water oxygen is lowest, and the inventory is lowest in winter and early spring. Model-generated deep plumes resemble those reported off Namibia, Peru and the Gulf of Alaska. This work will sample depths up to 4500m and look for such plumes. Deep plumes are important in global Fe budgets and because they may outcrop in high latitude waters that are Fe limited. Iodine will also be measured because, like Fe, it accumulates at the sediment water interface and is released under reducing conditions. Plumes of iodine arising from shelf sediments will be used as a semi-conservative tracer for lateral Fe advection. The cruises will also assess the relative importance of direct inputs from rivers (especially the Columbia River) versus reducing sediments, since these inputs are decoupled seasonallyThis award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.