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The Danian coccolithosphores and planktonic foraminifers probably developed in an isolated and brackish Arctic Ocean during Late Cretaceous time, and when the Greenland Sea–Norwegian Sea passage opened to the North Atlantic, the Arctic Ocean water spread out as a surface layer over the world ocean. The presence of this low-salinity surface layer caused the catastrophic extinction of marine biota that has been labeled the terminal Cretaceous event.
Gärtner et al. (Sun,) studied this question.