Exceptional 2023 marine heat wave reshapes North Atlantic coccolithophore blooms

The North Atlantic Ocean is undergoing rapid transformation driven by long-term warming and the increasing frequency of extreme marine heatwaves. In 2023, surface temperatures across the basin reached record highs, raising concerns about the resilience of phytoplankton ecosystems. This study examines the response of Emiliania huxleyi, a key calcifying phytoplankton species, using satellite-derived ocean colour data. The 2023 marine heatwave significantly disrupted bloom intensity and phenology, revealing contrasting trends between two bloom regions. While bloom intensity and extent declined in the Celtic Sea, conditions in the Barents Sea became increasingly favorable for growth. These shifts reflect the immediate impacts of the heatwave superimposed on long-term environmental changes, influenced by processes such as Atlantification, sea-ice retreat, and vertical stratification. The resulting changes have critical implications for carbon cycling and trophic interactions, underscoring the need for sustained, high-resolution monitoring to track both extreme events and persistent trends in phytoplankton dynamics. As high-latitude regions emerge as potential refuges, their long-term stability is highly uncertain under continued warming, ocean acidification, and ecosystem restructuring. A deeper understanding of these dynamics is essential for predicting future carbon cycle feedbacks and for managing ocean ecosystem services in a rapidly changing climate.