2025/02/21 by Emily Lauren Salinas Ortega, Isaac Reister, Seth L. Danielson +1 · 1 voice · 1 citation
Earth and Planetary Sciences · Environmental Science · #Atmospheric and Environmental Gas Dynamics #Geological formations and processes #Geology and Paleoclimatology Research
paper · doi:10.1016/j.marchem.2025.104508
openalex publication_date 2025/02/21 · openalex created_date 2025/10/10 · openalex updated_date 2026/04/09
The Copper River is a major source of freshwater to the Northern Gulf of Alaska (NGA) shelf with a seasonal cycle that reaches peak discharge in summer. This glacially-fed river also provides a large input of dissolved chemicals to the NGA, and because of its large particle load, it impacts the distribution of particle-reactive elements. Summertime sampling of shelf water properties was carried out within the Copper River plume region during two years: first during a period of upwelling-favorable winds and higher river discharge (4–7 July 2019) and later during lower river discharge and more typical downwelling conditions (11–13 July 2020). Although these wind conditions were observed in separate years, both can occur over the course of a single summer. We found that the export of most nutrients to surface shelf waters was enhanced under upwelling-favorable winds accompanied by higher river discharge compared to downwelling conditions and lower discharge. For example, greater cross-shelf plume transport in 2019 resulted in higher mid-shelf surface inventories for nitrate + nitrite (N + N), silicic acid (H 4 SiO 4 ), phosphate (PO 4 3− ), dissolved Fe (dFe), and dissolved Cu (dCu) compared to 2020. Entrainment of relatively macronutrient-rich subsurface waters under upwelling conditions may also have contributed to the enhancement of these mid-shelf nutrient inventories. The observed high N:P ratios in plume waters were likely driven by the scavenging of P within particle-laden plume waters. Similarly, we observed lower than expected [dFe] (1.58 to 6.12 nM) in particle-laden plume waters, likely a result of enhanced scavenging combined with low concentrations of dissolved Fe-binding ligands. Although dNi and dZn have a river source, we observed lower concentrations in surface shelf waters under upwelling conditions, suggesting enhanced dilution by relatively micronutrient-poor subsurface waters. Results highlight the influence of sub-seasonal variations in atmospheric forcing on nutrient distributions and suggest that this forcing also impacts the location and timing of primary production hotspots during summer, adding to the ecological mosaic of the NGA across a range of temporal and spatial scales. Conceptual diagram depicting plume mixing processes under upwelling (left) and downwelling (right) conditions. Top diagrams show wind direction (rosettes), water masses, an inshore-offshore transect across the Copper River plume region (A-B dashed line), and a commonly sampled mid-shelf region (red box). The cross-section of the A-B transect is represented in the bottom diagrams, which show particle settling (small brown arrows), plume direction (light arrows) and mixing (curved arrows), and shelf water transport (large blue arrows). The area of the cross-shelf transect within the mid-shelf region is shown by the red bars in the bottom diagrams. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) • The Copper River is a source of H 4 SiO 4 , N + N, and trace metals to the NGA shelf. • Wind forcing affects nutrient distributions in the Copper River plume region. • Under upwelling conditions, macronutrients, dFe, & dCu are enhanced over the shelf. • Under downwelling conditions, mid-shelf dNi & dZn are enhanced. • Copper River plume transport impacts nutrient ratios of the NGA shelf.