The Northern Gulf of Alaska (NGA) shelf is a productive high-latitude environment where nutrient dynamics are greatly impacted by the seasonal variability in freshwater input. Iron is a key nutrient on the NGA shelf that directly modulates primary production, and freshwater is a major input of iron to the NGA shelf. However, variability in the input of dissolved iron from freshwater sources is obscured by high biological uptake and by the concentration of organic ligands, which bind iron and help maintain it in solution. Riverine inputs of other lithogenic elements such as aluminum and manganese are expected to behave quasi-conservatively on the NGA shelf and could help provide insight into the variability of iron input in this region.

Here we present the seasonal (spring, summer, and fall) distribution of dissolved aluminum (dAl) and manganese (dMn) observed during 2018 and 2019 in the NGA region. Data were obtained during the NGA Long Term Ecological Research (LTER) site cruises and include several surface transects from Kayak Island to Kodiak Island, vertical profiles at several locations sparsely distributed throughout the shelf, and surface information from a Copper River plume study. We find that seasonal patterns in the surface concentrations of dMn and dAl mirrored annual glacial melt cycles, with the lowest values observed in spring and higher values in summer and fall. Sharp cross-shelf gradients were observed for both metals particularly in summer and fall. Surface concentrations decreased (by 1–2 orders of magnitude) away from the outflow of the Copper River, the major point source of freshwater within the NGA LTER site. Extremely high concentrations in the Copper River plume (≤1395 nM dAl, ≤128 nM dMn) and strong correlations with salinity (p = 7.9E-14 for dAl, 1.4E-14 for dMn) highlight the quasi-conservative nature of these metals within the plume. Enhanced dAl and dMn concentrations within nepheloid layers in subsurface waters indicate regions where a sedimentary source of iron could also be important. Residence times for dAl and dMn in surface waters over the NGA shelf were estimated to be 31 days (dAl) and 42 days (dMn) on average based on summer and fall data from both years.

阿拉斯加湾北部 (NGA) 大陆架是一个多产的高纬度环境，其中的营养动态受到淡水输入的季节性变化的极大影响。铁是 NGA 架上的关键营养素，直接调节初级生产，淡水是 NGA 架上铁的主要输入。然而，来自淡水源的溶解铁输入的可变性被高生物吸收和有机配体的浓度所掩盖，有机配体与铁结合并有助于将其保持在溶液中。其他成岩元素（如铝和锰）的河流输入预计在 NGA 大陆架上表现出准保守性，并有助于深入了解该地区铁输入的变化。

在这里，我们展示了 2018 年和 2019 年在 NGA 地区观察到的溶解铝 (dAl) 和锰 (dMn) 的季节性（春季、夏季和秋季）分布。数据是在 NGA 长期生态研究 (LTER) 站点巡航期间获得的，包括从皮划艇岛到科迪亚克岛的几个地表横断面、在整个大陆架中稀疏分布的几个位置的垂直剖面，以及来自铜河羽流研究的地表信息。我们发现 dMn 和 dAl 表面浓度的季节性模式反映了每年的冰川融化周期，在春季观察到最低值，在夏季和秋季观察到更高值。两种金属都观察到了明显的跨货架梯度，特别是在夏季和秋季。远离铜河的外流，地表浓度降低（1-2 个数量级），NGA LTER 站点内淡水的主要点源。Copper River 羽流中的极高浓度（≤1395 nM dAl，≤128 nM dMn）以及与盐度的强相关性（dAl 的 p = 7.9E-14，dMn 的 p = 1.4E-14）突出了这些金属的准保守性质羽流之内。地下水中星状体层中 dAl 和 dMn 浓度的增加表明铁的沉积源也可能很重要的区域。根据这两年的夏季和秋季数据，dAl 和 dMn 在 NGA 架子上的地表水中的停留时间估计平均为 31 天 (dAl) 和 42 天 (dMn)。dMn 的 4E-14）突出了这些金属在羽流中的准保守性质。地下水中星状体层中 dAl 和 dMn 浓度的增加表明铁的沉积源也可能很重要的区域。根据这两年的夏季和秋季数据，dAl 和 dMn 在 NGA 架子上的地表水中的停留时间估计平均为 31 天 (dAl) 和 42 天 (dMn)。dMn 的 4E-14）突出了这些金属在羽流中的准保守性质。地下水中星状体层内 dAl 和 dMn 浓度升高表明沉积铁源也可能很重要的区域。根据这两年的夏季和秋季数据，dAl 和 dMn 在 NGA 架子上的地表水中的停留时间估计平均为 31 天 (dAl) 和 42 天 (dMn)。