INTRODUCTION

As noted elsewhere in this volume, Ocean Drilling Program (ODP) Site 1002 offers an unusual chance to study tropical climate and paleoceanography at high resolution over many of the late Pleistocene cycles of global ice volume and sea-level change. Data recovered from Site 1002 will help to assess the stability of tropical sea-surface temperatures (SST) on glacial-interglacial time scales and the effects of changes in sea level on oxygenation and carbon burial in the silled Cariaco Basin. In particular, the Cariaco Basin sediments may provide an unusual archive to assess the controversial topic of glacial sea-surface cooling during ice volume maxima (CLIMAP, 1976, 1984; Rind and Peteet, 1985; Broecker, 1986; Mix et al., 1986; Guilderson et al., 1994; Stott and Tang, 1996) and to determine the extent to which millenial-scale climate oscillations such as the Younger Dryas and Dansgaard-Oeschger Events from the North Atlantic (Bond et al., 1993) penetrated to the tropics (Hughen et al., 1996; Curry and Oppo, 1997). Previous work from piston cores has focused on the details of oxygenation, oxygen isotopic, and productivity history from the last glacial maximum (LGM) through the Holocene (Peterson et al., 1991; Hughen et al., 1996; Lin et al., 1997). We discuss here the significance of SST estimates derived from the U^k´₃₇ biomarker approach over a full glacial to interglacial cycle.

The U^k´₃₇ ("alkenone") approach estimates paleotemperatures by measuring the unsaturation index of di- and triunsaturated C₃₇ ketones synthesized by several species of haptophyte algae, of which Emiliania huxleyi and Gephyrocapsa oceanica are believed to be the most important (Volkman et al., 1980, 1995; Marlowe et al., 1984; Lesley et al., 1996). Field and culture studies have defined calibration functions relating the unsaturation index, expressed as

U^k´₃₇ = C_37:2/(C_37:2 + C_37:3)

(Prahl et al., 1988), to growth temperature (Prahl and Wakeham, 1987; Prahl et al., 1988; Brassell, 1993). For this study, we use the Prahl et al. (1988) calibration derived from cultures of E. huxleyi. Core-top studies show that this relationship provides a good fit with a global database comparing unsaturation index to surface-water temperatures (Sikes et al., 1991; Rossell-Mele et al., 1994; Sonzogni et al., 1997; Herbert et al., 1998; Müller et al., 1998). We also discuss trends in the amount of alkenones preserved in Site 1002 sediments as an index of a combination of haptophyte productivity and bottom-water oxygenation. Data reported here provide a high-resolution (~500-yr sampling rate) look at the alkenone record over the last full glacial cycle.