Collaborative Research: Dynamics Of Ocean Climate Changes in the Gulf of Alaska

阿拉斯加湾是一个复杂的自然海洋学系统，它支持着经济上重要的渔业和生态上重要的野生动物区。沿着东大陆架斜坡边界向西北方向流动的阿拉斯加流和沿着西大陆架斜坡边界向西南方向流动的阿拉斯加流，都支持一个充满活力的开放海洋中尺度环流。这些平均流被认为主要是由风应力旋度强迫驱动的，而漩涡的形成是平均流的斜压不稳定、波动的风应力强迫和远程驱动的海岸波的到来的结果。阿拉斯加海岸流沿着大陆架蜿蜒曲折地穿过许多直道和岛屿，被认为是由沿海淡水排放和风的压力共同驱动的。阿拉斯加湾大规模环流的一个有趣方面是，开阔的海洋内部通常是上升流区，而沿海地区通常是下升流区。即便如此，初级生产力在沿海地区是最高的，那里维持着丰富多样的生态系统。物理环境影响这一生物系统生产力的机制是复杂的，人们对其知之甚少。其中一些机制涉及跨大陆架混合过程，在该过程中，中尺度涡变率将富含营养物质的公海水域与含铁的大陆架水域混合在一起。学术价值：阿拉斯加湾的海洋环流将使用涡旋解析海洋模型、观测分析和海洋数据同化产品的组合来研究，以阐明控制阿拉斯加流、阿拉斯加流以及更大尺度内部环流的平均、中尺度变化和年际至年代际气候变化的动力学。涡旋解析模式运行（使用区域海洋模拟系统）将把风应力、地表热通量、地表/沿海淡水通量和公海边界通量的影响以各种组合方式纳入，以确定模式平均场和中尺度场对这些强迫变化的敏感性，这些强迫是季节循环的一部分，也是气候变化的组成部分。海洋分析产品的研究将提供模型数据兼容性的基线，以帮助将非常有限的水文数据集与动态一致的漩涡解析模拟联系起来。物理海洋学分析的结果将以多种方式应用于了解该地区复杂的生物海洋学。这将包括分析混合层深度变化，计算跨大陆架粒子传输，允许被动示踪剂横向和纵向平流和扩散，并在物理模型运行中纳入简单的生态系统模型。这些结果将帮助我们了解控制墨西哥湾生产力季节性变化的机制，维持大陆架高生产力的过程，以及影响更高营养水平的生产力年际至年代际变化的原因，如远洋鱼类种群和虎头海狮。更广泛的影响:这项研究具有更广泛的影响，因为它与商业上重要的渔业管理（必须处理鱼类种群的年代际变化）有关，它可能有助于解开虎头海狮（一种受保护的海洋哺乳动物）种群数量下降背后的谜团，在20世纪90年代减少到20世纪70年代的20%。它可能有助于更好地理解气候的可变性和可预测性（这可能会影响农业和能源生产等社会重要行业）。研究生和博士后将接受复杂的数值模拟和数据同化技术的培训。

OCE-0452692/0452743/0452654The Gulf of Alaska is a complicated physical oceanographic system that supports economically important fisheries and ecologically important wildlife areas. The Alaska Current, which runs northwestward along the eastern shelf-slope boundary, and the Alaskan Stream, which runs southwestward along the western shelf-slope boundary, both support an energetic open-ocean mesoscale circulation. These mean flows are thought to be driven mainly by wind-stress curl forcing, while the eddies develop as a consequence of baroclinic instability of the mean flows, fluctuating wind stress forcing, and the arrival of remotely driven coastal waves. The Alaska Coastal Current, which winds and meanders along the shelf through numerous straights and islands, is thought to be driven by both coastal fresh-water discharge and wind stresses. An interesting aspect of the large-scale circulation of the Gulf of Alaska is that the open ocean interior is generally an upwelling region, while the coastal regions are generally downwelling. Even so, primary productivity is highest in the coastal regions, which sustain a rich and diverse ecosystem. The mechanisms by which the physical environment affects the productivity of this biological system are complicated and poorly understood. Some of these mechanisms involve cross-shelf mixing processes in which mesoscale eddy variability mix open-ocean nutrient rich waters with shelf waters that contain iron.Intellectual Merit: The ocean circulation of the Gulf of Alaska will be studied using a combination of eddy resolving ocean models, observational analyses and ocean data assimilation products to elucidate the dynamics that control the mean, mesoscale variability and interannual to interdecadal climate variations of the Alaska Current, the Alaskan Stream, as well as the broader-scale interior gyre flows. The eddy-resolving model runs (using the Regional Ocean Modeling System) will incorporate the effects of wind stresses, surface heat fluxes, surface/coastal fresh-water fluxes, and open-ocean boundary fluxes in various combinations to establish the sensitivity of the model mean and mesoscale fields to changes in these forcings as part of the seasonal cycle and as components of climate variations. The study of the ocean analysis products will provide a baseline of model-data compatibility to help link the very limited hydrographic dataset to the dynamically consistent eddy-resolving simulations. The results of the physical oceanographic analysis will be applied in several ways to understand the complicated biological oceanography of the region. This will include analyzing mixed-layer depth variations, computing cross-shelf particle transports, allowing passive tracers to advect and diffuse laterally and vertically, and incorporating simple ecosystem models in the physical model runs. The results will help us to understand the mechanisms that control the seasonal variability of the productivity of the Gulf, the processes that maintain high productivity on the shelf, and the reasons for interannual to interdecadal variations in productivity that affect higher trophic levels, like pelagic fish populations and Steller sea lions.Broader Impact: This research has broader impacts in that it is relevant to commercially important fisheries management (which must deal with decadal variations in fish populations), it may help to untangle the mysteries behind the decline of Steller sea lion populations (a protected marine mammal), which in the 1990's were reduced to 20% of their numbers of the 1970's, and it may contribute to a better understanding of climate variability and predictability (which may influence socially important industries like agriculture and energy production). A graduate student and post-doc will receive training is sophisticated numerical modeling and data assimilation techniques.