Initial Diatom Record of Sites 657 and 658: On the History of Upwelling and Continental Aridity

Abstract

Detailed analyses of samples recovered from the high-resolution Quaternary section cored at Ocean Drilling Program Site 658 reveal that very high abundances (6.4-8.3 x I0 7 valves/g dry sediment) of marine diatoms occur in interglacial oxygen isotope stages 7.5 and 9.3. Smaller abundance peaks (29-300 x I0 5 valves/g dry sediment) are present near oxygen isotope stage boundaries 1/2, 5/6, 9/10, 11/12, and 13/14. Therefore, high abundances of diatoms, interpreted as high productivity, are related to terminations. The Quaternary freshwater diatoms have their highest abundances mainly in sediments deposited during interglacial periods, but they are also recorded during glacial intervals (oxygen isotope stages 2 and 8), and near terminations (stage boundaries 7/8 and 15/16). The Pliocene freshwater diatom record indicates a frequency decrease at 2.8 Ma. It is suggested that the freshwater diatom frequency decrease indicates either a change to a more humid climate (assuming eolian transport) or a change to a more arid climate (assuming fluvial transport).