The abundance of calcareous nannofossils fluctuates strongly in the upper Quaternary interval of ODP Hole 704A in the southern South Atlantic. These fluctuations are tentatively correlated to the oxygen isotope stratigraphy, which shows that intervals rich in nannofossils represent interglacial time periods. The nannofossil assemblages indicate that during about the last 650,000 yr, the surface waters at Site 704 were warmer than at present only in oxygen isotope stage 5, with probable restriction to substage 5e. The environment was interglacial also during oxygen isotope stages 7,11, and 13, whereas stage 3 was characterized by intermediate glacial conditions. The nannofossil assemblages suggest that a significantly colder environment than at present prevailed in isotope stages 2, 4, 6, 8, 10, and 12.The fluctuations in nannofossil abundance in Hole 704A are correlated to nannofossil abundance patterns in the Norwegian Sea. During the last 500,000 yr, total abundances of nannofossils fluctuate in similar patterns in both the subantarctic and subarctic areas studied. Nannofossils were rare in the subarctic area between about 500,000 yr to over 1 m.y. ago, but were deposited in abundance around 650,000 yr ago in the subantarctic area.
BACKGROUND AND OBJECTIVES