Intra- and interannual variability in the Atlantic Water inflow region north of Svalbard: sea ice, hydrography, nutrients and the potential for primary production

Abstract

Atlantic Water (AW) is the major source of heat and nutrients to the Arctic Ocean. Changing AW inflow promotes sea ice decline and borealisation of marine ecosystems and affects primary production in the Eurasian Arctic. North of Svalbard, the AW inflow dominates oceanographic conditions along the shelf break and hence the distribution of heat and nutrients in the region. However, interaction with sea ice and Polar Surface Water determines nutrient supply to the euphotic layer. Using a combination of multidisciplinary approaches such as ship-based measurements and sampling, moored sensors, remote sensing and numerical modelling, we have been monitoring and studying the AW boundary current north of Svalbard since 2012. In this presentation, I will show some of our findings with particular focus on repeated measurements from a transect across the AW inflow at 31°E, 81.5°N. Large interannual variability in hydrography, nutrients and chl a indicates varying levels of nutrient drawdown by primary producers over summer. Sea ice conditions impact surface stratification, light availability, and wind-driven mixing, with a strong potential for steering chl a concentration over the productive season. In early winter, nutrient re-supply through vertical mixing varied in efficiency, again related to sea ice conditions. The autumn re-supply elevated nutrient concentrations sufficiently for primary production but likely happened too late as high-latitude light levels limited potential autumn blooms. Multidisciplinary observations are key to gain insight into the interplay between physical, chemical, and biological drivers and to understand ongoing and future changes. They are particularly important in regions like north of Svalbard that can indicate what we can expect in the central Arctic Ocean in the future.