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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 Ocean Drilling Program (ODP) Hole 704A was drilled about 2.5° north of the Antarctic Convergence Zone (ACZ) and approximately 5° south of the Subtropical Convergence. The site is located under Subantarctic Surface Water (SSW) present at the northernmost edges of the Antarctic Circumpolar Current (ACC) (Fig. 1). The strong hydrographic gradients make the location of Site 704 sensitive to climatic/oceanographic changes. The main objectives at Site 704 were to document the development of the ACC and the history of major northward excursions of the Polar Front. Another objective was to compare the record from Site 704 to glacialinterglacial fluctuations in the northern North Atlantic. The sedimentary sequence recovered from Site 704 is the thickest and most complete section at high southern latitudes that contains carbonate and abundant microfossils throughout (Shipboard Scientific Party, 1988). In the Norwegian Sea, at the northernmost stretches of the North Atlantic, numerous oscillations of the Arctic Polar Front during the late Quaternary have been documented through quantitative studies of foraminifers and calcareous nannofossils and oxygen isotope data (Kellogg et al., 1978; Belanger, 1982; Gard and Backman, in press). Detailed correlations between the oxygen isotope stratigraphy and nannofossils in the Norwegian Sea show that nannofossil abundance and assemblage variations reflect climatic changes. Layers with abundant nannofossils represent interglacial time periods, and intermediate glacial-full glacial interval layers have few, or no, nannofossils (Gard, 1988). As the species compositions are also observed to vary rapidly through time, some age determinations can be made from the nannofossil assemblages in cores without oxygen isotope stratigraphy. The nannofossil abundance patterns during the late Quaternary are virtually unknown in the high latitudes of the Southern Hemisphere. This study aims (1) to establish an 1 Ciesielski, P. F., Kristoffersen, Y., et al., 1991. Proc. ODP, Sci. Results, 114: College Station, TX (Ocean Drilling Program). 2 Department of Geology, University of Stockholm, S-106 91, Stockholm, Sweden. 3 BP Exploration, 5151 San Felipe, P.O. Box 4587, Houston, TX, 77210. upper Quaternary quantitative nannofossil biostratigraphy at Hole 704A in the southern South Atlantic, (2) to obtain an absolute chronology for the biostratigraphy by correlating the nannofossil datum events to the oxygen isotope stratigraphy and other available absolute ages, (3) to interpret the nannofossil abundance patterns in paleoceanographic terms, and (4) to compare the nannofossil abundance patterns to those in the northern North Atlantic. In a wider context, this study aims to contribute toward the understanding of Pliocene-Pleistocene climatic change by documenting paleoceanographic evolution within a reliable chronostratigraphic framework. In order to achieve these objectives, the nannofossil biostratigraphy needs to be integrated with results from other studies, particularly of oxygen isotope stratigraphy and other microfossil groups. The present paper reports on the preliminary results obtained from semiquantitative studies of calcareous nannofossils. MATERIALS AND METHODS ODP Hole 704A was drilled on the central southern part of the Meteor Rise in the southeastern South Atlantic (46°53'S, 07°25'E; water depth of 2532 m) (Figs. 1 and 2). The hole was cored continuously using the advanced hydraulic piston corer and extended core barrel to recover an upper Miocene to Quaternary sedimentary sequence. The topmost three cores studied in the present paper penetrated 26.2 m, averaging an apparent recovery of over 100%, which suggests that core loss was minimal. The sediments are highly variable in color and lithology at intervals of about 20 to 100 cm. Generally, the lighter color intervals (light yellow and light gray to white) correspond to high carbonate content, whereas the darker colors (olive and pale olive) correspond to diatom-rich intervals and low carbonate values (Shipboard Scientific Party, 1988). The contacts between the lithologic and color changes are generally sharp. During sampling, efforts were made to avoid intervals that showed signs of disturbance. Calcareous nannofossils recovered from ODP Hole 643A (67°43'N, 01°02'E; water depth 2764 m) (Fig. 2) in the Norwegian Sea have been studied previously (Eldholm, Thiede, et al., 1987; Gard, 1988; Gard and Backman, in press). The Norwegian Sea is today influenced by the Norwegian Current, a northern extension of the Gulf Stream. The surface waters at

Preliminary Results from Hole 704A: Arctic-Antarctic Correlation through Nannofossil Biochronology