LATE NEOGENE CLIMATE EVOLUTION OF THE CENTRAL ARCTIC-OCEAN

Because no sediment of post-Eocene to Late Miocene or Pliocene age has been recovered from the central Arctic Ocean, oceanographic conditions during the middle Cenozoic are unknown. The oldest late Cenozoic sediment is glacial-marine and contains agglutinated foraminifera. A few calcareous organisms are present in the oldest late Cenozoic sediment (with an age of 2-4 Ma) but at approximately the time as deposition of lithostratigraphic unit F, sometime between 2.0 and 1.5 Ma, there was an abrupt and dramatic increase in calcareous species diversity and abundance in the central Arctic Ocean. Many of the newly introduced species are Atlantic in origin. Preliminary evidence suggests that the introduction of a moderately large and diverse calcareous fauna at this time corresponds to the lowering of the Arctic Ocean CCD level and this may be explained by increased circulation with the Northern Greenland Sea. Details of the change in threshold values in the Fram Strait required for the introduction of relatively warmer and carbonate-rich water into the central Arctic Ocean are unknown. There is evidence that spreading rates along the North Atlantic-Nansen Ridge System increased during the Pleistocene and this may have permitted increased circulation between the North Atlantic and the central Arctic Ocean. This important change in Arctic Ocean circulation corresponds to increased Pleistocene seasonality in the Northern Hemisphere. © 1990.