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物理海洋学系统，支持经济上重要的渔业和生态上重要的野生动物区。阿拉斯加流，它运行西北沿着东部陆架-斜坡边界，和阿拉斯加流，它运行西南沿着西部陆架-斜坡边界，都支持一个充满活力的公海中尺度环流。这些平均流量被认为是主要由风应力旋度强迫驱动，而涡的发展作为斜压不稳定的平均流量，波动的风应力强迫，和远程驱动的海岸波的到来的结果。 阿拉斯加沿岸流沿着大陆架沿着流过许多海峡和岛屿，被认为是由沿岸淡水排放和风应力驱动的。 阿拉斯加湾大尺度环流的一个有趣的方面是，开阔的海洋内部通常是上升流区域，而沿海地区通常是下降流。 即便如此，沿海地区的初级生产力最高，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，人们对它的了解很少。其中一些机制涉及跨大陆架混合过程，在这种过程中，中尺度涡动变率将公海富营养沃茨与含铁的大陆架沃茨混合。阿拉斯加湾的海洋环流将使用涡流分辨海洋模式、观测分析和海洋数据同化产品的组合进行研究，以阐明控制平均值的动力学，中尺度变率和阿拉斯加海流、阿拉斯加海流以及更大尺度的内部环流的年际到年代际气候变化。涡旋分辨模式运行（使用区域海洋模拟系统）将以各种组合方式纳入风应力、表面热通量、表面/沿海淡水通量和公海边界通量的影响，以确定模式平均场和中尺度场对作为季节循环一部分和气候变化组成部分的这些强迫变化的敏感性。对海洋分析产品的研究将提供一个模型-数据兼容性基线，以帮助将非常有限的水文数据集与动态一致的涡流解析模拟联系起来。物理海洋学分析的结果将以几种方式应用于了解该区域复杂的生物海洋学。这将包括分析混合层的深度变化，计算跨大陆架的粒子运输，允许被动示踪剂平流和横向和垂直扩散，并在物理模型运行中纳入简单的生态系统模型。研究结果将帮助我们了解控制海湾生产力季节性变化的机制，维持大陆架高生产力的过程，以及生产力年际至年代际变化的原因，这些变化影响到更高的营养水平，如远洋鱼类种群和斯特勒海狮。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有关（必须处理鱼类种群的十年变化），这可能有助于解开斯特勒海狮数量下降背后的谜团（一种受保护的海洋哺乳动物），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了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产业）。研究生和博士后将接受培训是复杂的数值模拟和数据同化技术。

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.