Atlantic inflow is the primary driver of remotely sensed autumn blooms in the Barents Sea

Arctic shelf seas have historically hosted a single spring bloom, contrasting with temperate seas, where additional smaller autumn blooms occur regularly, caused by storm systems mixing nutrient-rich deep waters towards the surface ocean. Post millennium, autumn blooms have increased in frequency in Arctic shelf seas. Delayed sea-ice formation, stronger autumn winds and greater inflows of nutrient-rich temperate waters have all been suggested to support growing annual net primary production and an increasing incidence of autumn blooms. Here, we investigated data sets of remotely sensed September chlorophyll a, sea surface temperature, current and wind speeds. We explored mechanistic drivers of autumn blooms in the Barents Sea, one of the most productive Arctic shelf seas, to better understand the role of strong winds and the ingression of Atlantic waters in the dynamics of autumn blooms. We performed geographically resolved regressions between remotely sensed September chlorophyll a and environmental conditions in the Barents Sea, demonstrating a strong dependency of autumn bloom intensity on Atlantic inflow. This result highlights the importance of increased study of autumn phytoplankton bloom dynamics on Arctic shelf seas, especially the further collection and dissemination of in situ cell count and nutrient data to determine the significance of autumn blooms for wider ecosystem function.