Changes of oxygen and carbon isotopic composition of foraminifera: a tracer for oceanic circulation during the last glacial maximum and last deglaciation

Oxygen and carbon isotopic composition of benthic foraminifera from different oceanic sediment cores have been used to reconstruct the pattern of intermediate and deep ocean circulation during last glacial maximum (≅18,000 years BP) in the Indian and Pacific oceans. Results show that the glacial oceanic circulation was significantly different from the modem one. A deep hydrological front separated intermediate water of the Indian and Equatorial Pacific from underlying deep water. Glacial intermediate water was well ventilated and has approximately the same temperatures than today. By contrast, glacial deep water was cooler by several degrees than modern one. In the Pacific ocean, deep water was more ventilated than that in the southern Indian ocean indicating the formation of relatively ventilated deep water in the South Pacific or the increase of the influence of the North Pacific Intermediate Water. As late as 12,500 yr BP deep oceanic circulation was similar to the glacial one. The decrease of the influence of the North Pacific Intermediate Water has appeared at about 12,500 yr BP and the onset of the active formation of the North Atlantic Deep Water has appeared at about 9,000 yr BP. Holocene conditions have been reached at about 8,000 yr BP in all oceans and at all water depths. (author)