Declining coccolithophore blooms in the North Atlantic and Western Barents Sea.

Coccolithophores are vital to marine ecosystems and play a central role in the global carbon cycle. Although abundant in the temperate North Atlantic and Barents Sea, their long-term bloom dynamics remain poorly understood. Using two decades of satellite observations, we reveal a substantial decline in coccolithophore blooms between 2003 and 2022, with a 36.1% reduction in bloom area and a 51.2% decrease in bloom frequency. The decline is most pronounced in the temperate North Atlantic and western Barents Sea, while the eastern Barents Sea shows notable increases. Decreasing sea surface temperatures (SSTs) in the North Atlantic and warming in the eastern Barents Sea are identified as key drivers of these trends. However, SST changes alone do not explain the asymmetric patterns across the Barents Sea, suggesting additional environmental drivers and phytoplankton competition. Our study provides the most spatially and temporally resolved assessment of coccolithophore bloom trends in this region to date, with broader implications for marine ecosystems and carbon cycling.