The Pan‐Arctic Continental Slope as an Intensifying Conveyer Belt for Nutrients in the Central Arctic Ocean (1985–2015)

Primary production in the Central Arctic Ocean (CAO) is limited by light and bioavailable nutrients. With the decline of the sea‐ice cover in recent decades, and the resulting increase in light availability, nitrate limitation has been speculated to become more prominent. We used an eddy‐permitting biogeochemical model simulation to estimate nitrate advective fluxes at different spatio‐temporal scales (synoptic, mesoscale and sub‐mesoscale) over the 1985–2015 period. We found that the pan‐Arctic continental slope contributes disproportionately to the Dissolved Inorganic Nitrogen supply and that this supply is intensifying through two main processes: lateral eddy transport and upwelling. Despite this increasing supply in nitrate and an intensification of ocean dynamics, the nutrient supply is decreasing everywhere else in the central basins and the simulation indicates that the CAO is still shifting from light to nutrient limitation. Plain Language Summary Microscopic algae called phytoplankton are the base of the trophic chain, sustaining the entire Arctic Ocean (AO) ecosystem. In the central parts of the AO, multi‐year sea‐ice used to limit transmission of light in the surface ocean and therefore control phytoplankton growth and primary productivity. However, the massive loss in sea‐ice during the last 3 decades allowed more and more light to penetrate the water column, making nutrient availability the main bottom‐up control of the AO productivity. A major part of the bio‐available nutrients reaching the surface in the central AO are transported with ocean currents from the adjacent North Atlantic and Pacific and from deeper water masses. Using a biogeochemical model resolving processes at high spatial resolution, we were able to quantify the different transport pathways of nutrients with ocean currents and revealed that despite increasing supply along the anticlockwise flowing boundary current, the central AO is still running into more severe nutrient limitation. Key Points The pan‐Arctic continental slope contributes disproportionately to the transport of nutrients in the Central Arctic Ocean (CAO) The nutrient supply intensifies along the slope through upwelling and lateral eddy transport but decreases in the interior basins Despite an intensification of ocean dynamics, the CAO is still shifting from a light‐limited to a nutrient‐limited system