Nitrogen Cycling in the Canadian Arctic and Sub-Arctic: Constraints from Dual Nitrate Isotope Data
Nitrate isotope values in the western Archipelago show a pronounced relative enrichment in 15N and a coincident minimum in δ18O in the upper halocline layer, indicative of both benthic denitrification upstream on the Bering and Chukchi shelves and remineralization along the transit. This subsurface peak in nitrate δ15N associated with the cold Pacific-derived halocline shows a progressive decrease along a west-to-east transect, from ~8‰ in the Canada Basin to ~7‰ in southern Lancaster Sound and ~6‰ in western Baffin Bay. The concurrent minimum in nitrate δ18O in the upper halocline seems largely preserved throughout its transit through the Archipelago, with values slightly increasing from ~0‰ in the western Archipelago to ~0.5‰ in southern Lancaster Sound. The Baffin Island Current and the Labrador Current subsequently carry this 15N-enrichment and relatively low-δ18O signature southward along the western Baffin Bay and into the Labrador Sea.
The observed trends in nitrate isotope ratios described here will be discussed in the context of regional circulation patterns and N biogeochemistry in the central Archipelago and further downstream in the sub-Arctic North Atlantic.