Seminar Series – Dr. Julie Granger: Insights on Nutrient Dynamics in the Western Arctic Ocean from Nitrate Isotope Ratios

Dr. Julie Granger, University of Connecticut

Insights on Nutrient Dynamics in the Western Arctic Ocean from Nitrate Isotope Ratios

The rapid warming of the Arctic has manifested in a decrease in extent and duration of sea ice cover in the Arctic Ocean, as well as a freshening of surface ocean due to increased riverine input and freshwater influx at Bering Strait. The longer ice free season has resulted in higher productivity of the shelf regions, but its impact on the productivity of the open basins remains unclear. Here I present insights from recent GEOTRACES efforts in the western Arctic Ocean, where my group measured the nitrogen and oxygen isotope ratios of nitrate on the Chukchi shelf and in the Canada Basin. Nitrate isotope ratios reveal that shelf processes influence the size and depth-distribution of the subsurface nutrient reservoir in the Canada Basin downstream. In particular, benthic denitrification on the shallow shelf results in a sizeable N deficit in the subsurface nutrient reservoir. The growth of phytoplankton and the subsequent remineralization of biomass at the shallow sediment interface result in the sequestration of nutrients in a water mass that ultimately reside well below the depth of winter mixing – limiting nutrient availability to phytoplankton. The biogeochemical properties of Canada Basin coherently evince a weak biological pump. I examine these observations in light of anticipated changes in circulation and ice cover of the western Arctic Ocean.

Host: Adrian Marchetti