Abstract
Dinoflagellates in Late Quaternary sediments from deepwater cores in the Black Sea appear to fall into two ecological categories that are dependent upon paleosalinity relationships. Sediments deposited there during the last 7,000 years contain cosmopolitan, euryhaline species of common marine genera and represent the brackish‐water Old Black Sea Stage of Soviet authors. Older sediments whose ages did not exceed 23,000 years in our cores contain a unique assemblage that comprises essentially two species, Tectatodinium psilatum Wall and Dale and Spiniferites cruciformis Wall and Dale. These dinoflagellates apparently lived in the almost freshwater “lake‐sea” of the New Euxinic Stage and were displaced abruptly 7,000 years ago when saline water from the Mediterranean began to flow into the Black Sea.