Physical and Biogeochemical Influences on Nutrients Through the Canadian Arctic Archipelago: Insights From Nitrate Isotope Ratios

The Canadian Arctic Archipelago (CAA) provides a gateway for the flow of nutrients from the North Pacific to the North Atlantic. The transport and biogeochemical cycling of nutrients throughout the CAA, however, are sparsely documented. Here, we report water column nitrogen and oxygen isotope ratios of nitrate (delta N-15(NO3) and delta O-18(NO3)) collected in a throughflow of the CAA into Baffin Bay, providing insights on inherent nutrient dynamics. The nitracline shoaled eastward into the CAA, wherein large subsurface chlorophyll maxima and coincident increases in delta N-15(NO3) and delta O-18(NO3) indicated enhanced nitrate assimilation relative to the oligotrophic Canada Basin. High delta N-15(NO3) values characteristic of Pacific Winter Water (PWW) pervaded the Archipelago and Baffin Bay, decreasing eastward due to mixing with underlying Atlantic water (AW)-from the Canada Basin west of Barrow Strait, and from Baffin Bay east thereof. Nearly 25% of nutrients in the central CAA were of Atlantic origin, a substantially larger fraction than surmised previously. Nutrient properties in the CAA were notably not influenced by benthic denitrification. Those in underlying AW in the western CAA, however, were modified by remineralization of Pacific-sourced nutrients, manifested from increases in delta N-15(NO3) relative to the Canada Basin. Properties in the eastern CAA exposed the complex hydrography of Baffin Bay, characterized by lateral intrusions of nutrient-poor winter waters into PWW and of cold mode waters in underlying AW. High delta N-15(NO3) values in AW revealed the presence of a substantial fraction of N from remineralization, stemming from the high productivity in Baffin Bay fueled by Pacific nutrients.