The biologically productive Northern Gulf of Alaska (NGA) continental shelf receives large inputs of freshwater from surrounding glaciated and non-glaciated watersheds, and a better characterization of the regional salinity spatiotemporal variability is important for understanding its fate and ecological roles. We here assess synoptic to seasonal distributions of freshwater pathways of the Copper River discharge plume and the greater NGA continental shelf and slope using observations from ship-based and towed undulating conductivity-temperature-depth (CTD) instruments, satellite imagery, and satellite-tracked drifters. On the NGA continental shelf and slope we find low salinities not only nearshore but also 100–150 km from the coast (i.e. average 0–50 m salinities less than 31.9, 31.3, and 30.8 in spring, summer, and fall respectively) indicating recurring mid-shelf and shelf-break freshwater pathways. Close to the Copper River, the shelf bathymetry decouples the spreading river plume from the direct effects of seafloor-induced steering and mixing, allowing iron- and silicic acid-rich river outflow to propagate offshore within a surface-trapped plume. Self-organized mapping analysis applied to true color satellite imagery reveals common patterns of the turbid river plume. We show that the Copper River plume is sensitive to local wind forcing and exerts control over water column stratification up to ∼100 km from the river mouth. Upwelling-favorable wind stress modifies plume entrainment and density anomalies and plume width. Baroclinic transport of surface waters west of the river mouth closely follow the influence of alongshore wind stress, while baroclinic transport east of the river mouth is additionally modified by a recurring or persistent gyre. Our results provide context for considering the oceanic fate of terrestrial discharges in the Gulf of Alaska.

中文翻译：

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阿拉斯加湾北部盐度田结构、淡水途径及控制机制展望


生物生产力高的阿拉斯加北部海湾 （NGA） 大陆架从周围的冰川和非冰川流域接收了大量淡水输入，更好地描述区域盐度时空变化对于了解其命运和生态作用非常重要。我们在这里使用船载和拖曳起伏电导率-温度-深度 （CTD） 仪器、卫星图像和卫星跟踪漂流器的观测来评估铜河排放羽流和更大的 NGA 大陆架和斜坡的淡水路径的天气到季节性分布。在 NGA 大陆架和斜坡上，我们发现不仅近岸而且距离海岸 100-150 公里的盐度较低（即春季、夏季和秋季的平均 0-50 米盐度分别低于 31.9、31.3 和 30.8），表明反复出现的中大陆架和大陆架断裂淡水路径。在靠近铜河的地方，大陆架测深法将扩散的河流羽流与海底诱导的转向和混合的直接影响分离，允许富含铁和硅酸的河流流出在地表捕获的羽流中向近海传播。应用于真彩色卫星图像的自组织制图分析揭示了浑浊河流羽流的常见模式。我们表明，铜河羽流对局部风强迫很敏感，并对距离河口 ∼ 约 100 公里的水柱分层施加控制。有利于上升流的风应力改变了羽流夹带和密度异常以及羽流宽度。河口以西表层水的斜压输送紧跟沿岸风应力的影响，而河口以东的斜压输送则受到反复或持续的环流的改变。 我们的结果为考虑阿拉斯加湾陆地排放的海洋命运提供了背景。