Ocean Drilling Program, United States

While onboard ship during Leg 177, we used variations in sediment physical properties (mainly percent color reflectance) in conjunction with biomagnetostratigraphy to correlate among sites and predict the position of marine isotope stages (MISs). Our working assumption was that physical properties of Leg 177 sediments are controlled mainly by variations in carbonate content. Previous studies of Southern Ocean sediment cores have shown that carbonate concentrations are relatively high during interglacial stages and low during glacial stages at sites located within the Polar Frontal Zone (PFZ). Today, the PFZ marks a lithologic boundary in underlying sediment separating calcareous oozes to the north and silica-rich facies to the south. Although there is debate whether the position of the "physical" PFZ actually moved during glacial-interglacial cycles the "biochemical" PFZ, as expressed by the CaCO (sub 3) /opal boundary in sediments, certainly migrated north during glacials and south during interglacials. This gave rise to lithologic variations that are useful for stratigraphic correlation. At Leg 177 sites located north of the PFZ and at sublysoclinal depths, we expected the same pattern of carbonate variation because cores in the Atlantic basin are marked by increased carbonate dissolution during glacial periods and increased preservation during interglacials. Since the end of Leg 177 in January 1998, we have analyzed stable isotopic ratios of foraminifers in thousands of samples from Ocean Drilling Program (ODP) Sites 1088, 1089, 1090, 1093, and 1094. These data provide a test of our preliminary shipboard stratigraphic interpretations. Here, we describe the methodology employed for stable isotope analysis and provide the resultant data. We present all oxygen isotope signals vs. meters composite depth (mcd) and compare them to variations in carbonate content or percent red reflectance (a proxy for carbonate content). For those records that are continuous enough to be correlated to oxygen isotope reference signals, we present the 18O signals vs. time. The paleoceanographic interpretations of the oxygen and carbon isotope results are presented in papers listed in the bibliography and several manuscripts in preparation.