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

OCE-0452692/0452743/0452654阿拉斯加湾是一个复杂的自然海洋系统，支持经济上重要的渔业和生态上重要的野生动植物区域。沿着东部陆架-斜坡边界向西北方向流动的阿拉斯加洋流和沿着西部陆架-斜坡边界向西南方向流动的阿拉斯加流，都支持着一种能量旺盛的大洋中尺度环流。这些平均流被认为主要是由风应力旋度强迫驱动的，而涡旋的发展是平均流的斜压不稳定、脉动风应力强迫和远程驱动的海岸波到达的结果。阿拉斯加海岸流沿着大陆架蜿蜒流过许多直道和岛屿，被认为是由海岸淡水排放和风应力共同驱动的。阿拉斯加湾大范围环流的一个有趣的方面是，开阔的海洋内陆通常是上升区，而沿海地区通常是下流区。即便如此，初级生产力在沿海地区是最高的，这些地区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很复杂，人们对此知之甚少。其中一些机制涉及跨陆架混合过程，在这种混合过程中，中尺度涡旋变率将公海营养丰富的公海水域与含有铁的陆架水域混合在一起。智力优势：将结合涡旋解析海洋模式、观测分析和海洋数据同化产品来研究阿拉斯加湾的海洋环流，以阐明控制阿拉斯加海流、阿拉斯加流和更广泛尺度的内部环流的平均、中尺度变率和年际至年代际气候变化的动力学。涡旋分辨模式(使用区域海洋模式系统)将把风应力、地表热通量、表层/沿海淡水通量和开阔海洋边界通量的影响以各种组合形式结合起来，以确定模式平均和中尺度场对这些强迫变化的敏感性，作为季节循环的一部分，作为气候变化的组成部分。对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涡旋解析模拟联系起来。物理海洋学分析的结果将在几个方面应用，以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，计算跨陆架颗粒传输，允许被动示踪剂横向和垂直平流和扩散，以及将简单的生态系统模型纳入物理模型运行。这些结果将有助于我们理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，以及影响较高营养层的生产力年际至年代际变化的原因，如中上层鱼类和海狮。更广泛的影响：本研究具有更广泛的影响，因为它与具有商业意义的渔业管理有关(必须处理鱼类种群的年代际变化)，它可能有助于解开海狮种群(一种受保护的海洋哺乳动物)数量下降背后的谜团，1990年代S的数量减少到1970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.