The Northern Gulf of Alaska (NGA) shelf is a subpolar ecosystem, which is impacted by seasonal freshwater input from rivers fed by glacial and snow melt in addition to precipitation. This input contributes to the temporal and spatial patterns of micro- and macronutrients observed in the vicinity of, and along the Alaska Coastal Current (ACC), a defining feature of the NGA shelf that acts as an alongshore transport mechanism and a barrier between the inner shelf and further offshore waters. The sediment-laden Copper River is the largest source of freshwater to the ACC (and the NGA) providing large input of dissolved and particulate trace elements and silicic acid, but little nitrate and phosphate to the shelf region. A survey of the Copper River plume at peak flow in July of 2019, highlighted its impact on the biogeochemstry of the shelf. Differences in nutrient ratios (N:P) delineated “fresh” and “aged” plume waters and reflected a combination of particle scavenging of P and inhibition of primary production in turbid waters. Concentrations of H₄SiO₄ were approximately double (20.0±5.46 µM) in the “fresh” plume compared to “aged” plume waters (10.26±2.81 µM). Trace metal concentrations declined rapidly as plume waters aged and mixed with surrounding coastal water. For example, labile particulate Fe decreased by several orders of magnitude, and dissolved Fe ranged from 6.09 to 0.05 nM across the study region.

Primary Presenter: Emily Ortega, University of Alaska Fairbanks (elortega@alaska.edu)

Authors:

Emily Ortega, University of Alaska Fairbanks  (elortega@alaska.edu)

Ana Aguilar-Islas, University of Alaska Fairbanks  (amaguilarislas@alaska.edu)