Award: OCE-1713677

The Arctic Ocean is undergoing significant changes related to a warming climate, including rapid ice melt, permafrost thaw, and increased riverine discharge. While the focus of these effects on the hydrologic cycle and physical oceanography have been directly studied, the biogeochemical impacts are more complex and thus harder to constrain. A portion of this puzzle is the role of trace metals on Arctic Ocean biogeochemistry, since many trace metals (iron, zinc, copper, manganese, nickel, and cadmium) play a role as essential nutrients for the enzyme centers of photosynthesizing plankton in the surface ocean. Prior to this project, there was little known about the trace metal distributions, sources, and sinks in the Western Arctic, as existing decades-old datasets were plagued by contamination issues and narrow spatial and depth resolution. We collected samples and measured concentrations to produce the first full-depth sections of dissolved metal distributions in the Western Arctic Ocean. We learned that dissolved metal distributions in the Arctic Ocean are profoundly different than in all other global ocean basins. Profile shapes that define marine trace metal behavior were flipped upside-down for some metals in the Arctic (e.g. zinc, copper, nickel). We applied chemical tracers to determine which oceanographic processes resulted in these unique distributions, and we were able to attribute high surface concentrations to riverine and/or sedimentary inputs from the extensive shallow continental shelves. The low and homogenous deep water concentrations were attributed to the nearly non-existent biological pump below the perennially ice-covered central Arctic; instead, deep water metals in the Arctic were nearly equal in concentration to the incoming Atlantic waters from which they were derived. The highest concentrations of many metals (e.g. iron, manganese, zinc, cadmium) were found over the Chukchi Shelf and in waters of the subsurface halocline, a water mass formed from brine rejection during sea ice formation over the continental shelves and transported offshore below the fresh surface layer. The Western Arctic halocline carries Pacific-influenced waters that we showed were injected with margin-derived sedimentary inputs during their transport toward the Central Arctic. We also observed a major concentration maximum of many metals (e.g. iron, copper, nickel) in the Central Arctic, associated with Eurasian riverine inputs that were quickly carried across the North Pole in the Transpolar Drift Current. Altogether, this assessment confirmed the processes that are controlling trace metal distributions in the current Arctic Ocean, including potential limitation of phytoplankton growth by iron based on nutrient ratios, which will serve as a critical baseline against which future climate changes to the Arctic Ocean can be evaluated. The project provided significant professional development and training opportunities for participating personnel. It was the first project as Lead-PI for this female early career scientist. It also provided support for the training of a female PhD student, whose dissertation is based mostly on this project; this student successfully defended her PhD and is continuing her Arctic Ocean biogeochemical research in a postdoctoral fellowship. This project also provided support for the training of three undergraduate students (two female), one of whom is now a PhD student studying trace metal oceanography in the Pacific Ocean. Finally, this project supported two young lab technicians (one female), one of whom will be moving on to a PhD in heavy metal contaminant cycling as a result of this project. Finally, this project also funded the creation of four weekly public radio shows on the oceanography of the Arctic Ocean on the KAMU "On the Ocean" radio show in College Station, Texas. It also supported two presentations to ~120 K-12 students in Miami, Florida (>50% under-represented) on "What makes a scientist?" and "Science is fun!" Last Modified: 06/08/2020 Submitted by: Jessica N Fitzsimmons