The anomalously warm waters that bathed the sea floor 95 million years ago developed in shallow shelf seas in an ocean circulation pattern very different from today’s, according to research published online this week in Nature Geoscience.
Oliver Friedrich and colleagues studied the shells of bottom-dwelling micro-organisms collected in deep-sea drill cores in the region equivalent to the modern tropical North Atlantic Ocean. They found evidence of extremely warm water temperatures at intermediate depths associated with intervals of high salinity conditions. The team suggests that warm surface temperatures during this time led to high rates of evaporation in the shallow seas that lined the proto-North Atlantic. The remaining salty waters became increasingly dense and began to flow off the shelves and sink into the deep ocean.
Such a circulation pattern is markedly different from modern deep-water formation, in which water in the polar regions cools to freezing temperature before sinking and flowing towards lower latitudes.