The Bering and the Barents Seas are very productive high-latitude shelf seas connecting the Arctic Ocean with the North Pacific and Atlantic Oceans, respectively. Because of their proximity to the ice edge, they are expected to respond rapidly to global warming. Using over three decades of continuous satellite observations of phytoplankton blooms and the physical environment (ice cover and temperature), we examine to which extent climatic changes impact blooms of calcifying and non-calcifying phytoplankton. We show that increased intrusion and warming of waters from the South have lead to the emergence and the subsequent rapid poleward expansion of blooms of Emiliania huxleyi (Ehux), a marine calcifying phytoplankton species typically associated with temperate waters. We suggest that Ehux blooms may be considered as harbingers for blooms of other temperate-origin phytoplankton species, including harmful ones, and may be an indicator for the borealization of the entire marine food web, a manifestation of climate change that we expect to continue in the future.