Increased intrusion of warming Atlantic water leads to rapid expansion of temperate phytoplankton in the Arctic

The Arctic Ocean and its surrounding shelf seas are warming much faster than the global average, which potentially opens up new distribution areas for temperate‐origin marine phytoplankton. Using over three decades of continuous satellite observations, we show that increased inflow and temperature of Atlantic waters in the Barents Sea resulted in a striking poleward shift in the distribution of blooms of Emiliania huxleyi, a marine calcifying phytoplankton species. This species' blooms are typically associated with temperate waters and have expanded north to 76°N, five degrees further north of its first bloom occurrence in 1989. E. huxleyi's blooms keep pace with the changing climate of the Barents Sea, namely ocean warming and shifts in the position of the Polar Front, resulting in an exceptionally rapid range shift compared to what is generally detected in the marine realm. We propose that as the Eurasian Basin of the Arctic Ocean further atlantifies and ocean temperatures continue to rise, E. huxleyi and other temperate‐origin phytoplankton could well become resident bloom formers in the Arctic Ocean. This study testifies to one of the most rapid poleward expansions of marine organisms reported so far and attributes the observed biogeographic shift to climate‐change induced increases in the inflow and warming of Atlantic waters into the Arctic Ocean. Using a unique continuous archive of satellite observations, we demonstrate the striking and fast‐paced changes in the distribution of blooms of a temperate‐origin phytoplankton species on an Arctic shelf sea over the last three decades. This study evidences the atlantification of the Arctic Ocean, a process that we expect to continue in the future