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

生产性沿海沃茨水域和相对非生产性近海沃茨水域之间的边界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的贡献的一个基本特性。 在夏季的几个月里，沃茨温度较高，含氧量较低，海底附近的生物分解会消耗可用的氧气，并将沉积物中的铁释放到上层海水中。 在海洋的更深处，峡谷和其他崎岖的表面特征会影响水流并产生湍流，迅速将铁从大陆架转移到近海。这种铁反过来可以提高几英里外的生物生产力。该项目将调查（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，以及（2）洋流如何与大陆架和陆坡相互作用，将大陆架上的沃茨移向近海，以提高生产力。 根据20多年来对加州和俄勒冈州海岸的模型模拟，科学家们将收集和分析铁和碘的样本，以证明模型的发现。 研究中包括碘，因为它可以跟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的全部或部分研究。 科学家们参与高中学生辅导，通过项目COOL（实验室外的化学海洋学）和冰基金会的学生。来自南加州大学和加州大学洛杉矶分校的科学家将研究华盛顿和俄勒冈州海岸沿着的铁（Fe）和碘（I）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。该项目假设，一个货架到盆地穿梭控制铁从富铁大陆架到北太平洋内部的供应。 区域海洋模拟系统（ROMS）与2007年至2017年运行的生物地球化学元素循环模型（BEC）相结合的模拟表明，该海岸线是海洋盆地的主要铁源，表现出深和浅的铁羽流，这些羽流来自向极暗流产生的地下涡流。 该模型的结果将用于预测Fe的季节性分布，并指导2021年对该地区进行两次巡航时的采样。 根据ROMS-BEC模型，铁库存在夏末最高，此时底层水氧最低，冬季和早春库存最低。 模型生成的深羽流类似于纳米比亚、秘鲁和阿拉斯加湾报告的深羽流。这项工作将采样深度达4500米，并寻找这样的羽。深羽在全球铁收支中很重要，因为它们可能在铁有限的高纬度沃茨露头。 碘也将被测量，因为像铁一样，它积累在沉积物-水界面，并在还原条件下释放。 来自陆架沉积物的碘羽流将被用作横向Fe平流的半保守示踪剂。 巡航还将评估来自河流（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NSF的法定使命，并被认为值得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来支持。

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.