Variability in biogeochemical Arctic outflow through Davis Strait

Polar ocean ecosystems are a key source of nutrients such as nitrogen (N) and phosphorus (P) to the rest of the world’s oceans. Climate change is already altering many processes affecting elemental cycling at the poles, but interruption of polar nutrient export could suppress global primary productivity and fisheries by around a quarter over multi-century timescales. It is thus essential to constrain both the mechanisms and variability of these fluxes, and their global implications.

The Arctic specifically exports an excess of P relative to N, equivalent to ~90% of the net phosphate flux to the Atlantic at 47°N, and supporting a significant fraction of North Atlantic N-fixation. Of the gateways into the Atlantic, Davis Strait has the strongest net southwards transport. A mooring array has been tracking volume and freshwater transports there since 2004, yet biogeochemical transports remain poorly quantified. To move towards addressing this gap, two autonomous water samplers were deployed at the western boundary of Davis Strait; targeting the P*-rich core of the Baffin Bay outflow (~100db) enabled the monitoring of nutrient transport of waters being exported into the North Atlantic, and the variability in their N:P relationship. 

Deployed in Ocober 2022, samples were collected at ~2 week intervals and analysed for inorganic and organic nutrients, oxygen isotopes and pH, forming the first two years of a dedicated biogeochemical time series of the western boundary outflow.  

Initial results show substantial chemical variability across all measured parameters, with a clear seasonal cycle in salinity-normalised nutrients and oxygen isotopes. When combined with velocity fields then concentration difference drive varialbity in the transports. While temperature and salinity also vary strongly on seasonal (and shorter) timescales, their cycles showed some temporal offsets, suggesting different underlying forcing mechanisms. Differences between the slope and off slope sites (a stronger amplitude in both concentrations and transports closer to the shelf)also highlight spatial structure in the exported water masses. 

Across the Straits then preliminary P* transport estimates underscore the dominant role of the western core in total nutrient export through Davis Strait. Early indications are of longer-term changes in N:P ratios in the outflow. Ongoing work will further refine transport estimates and assess implications for Arctic–Atlantic nutrient connectivity.