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The isotopic composition of foraminiferal shells (oxygen, carbon) holds the key to a number of central problems in paleoceanography, such as paleotemperature determination, discovery of the nature of the age cycles, and the evolution of climate and circulation during the last 100 million years. The Pleistocene cyclicity appears tied to the Milankovitchmechanism; however, the peculiar shape of the 100,000 year “saw-tooth” cycle calls for certain feedback mechanisms. In particular, the deglaciation events suggest strong positive feedback, which may derive from salinity stratification of the ocean. There is evidence for such stratification during the last deglaciation. The Tertiary oxygen isotope stratigraphy indicates an overall cooling trend for high latitudes, while the tropics tend to stay warm. During the Eocene high latitudes were characterized by (isotopically light) low salinity surface waters. During the Neogene, a strong thermocline developed, and confined the vertical mixing of upper waters to privileged regions including upwelling areas. The steplike transitions in isotope stratigraphy (Eocene- Oligocene, Cretaceous-Tertiary) are of fundamental importance in the avolution of climate and of life.

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