NEW EVIDENCE OF A WARMER BOTTOM WATER MASS LEADING UP TO THE PALEOCENE EOCENE THERMAL MAXIMUM: STABLE ISOTOPE RECORDS FROM DSDP LEG 22 SITE 215

Moderately-high resolution (20 kyr) stable isotope (δ¹³C and δ¹⁸O) records were developed from the Deep Sea Drilling Program Indian Ocean Site 215 to investigate paleoceanographic changes during the late Paleocene (54.8-59 Ma) leading up and including to the Paleocene-Eocene Thermal Maximum (PETM). Site 215 was drilled in water depth of 5,300 meters in ponded sediments of the Ninetyeast Ridge, in the central Indian basin at 8° 12’S, 86° 50’E. This site was chosen to study the Paleocene because of the thin overlying sediment cover. This occurred due to the site subsiding below the CCD by the Early Eocene. As a result, Paleocene sediments are only buried by 100 meters of sediments, making Site 215 an ideal site to recover well-preserved foraminifera. A total of 195 stable isotopic measurements from benthic foraminifera were analyzed in this study that spanned between 54.8 Ma and 59 Ma. A chronostratigraphic framework was developed using foraminiferal biostratigraphic data and converted to the Gradstein et al. (2012) timescale.

The results from Site 215 showed similar trends as previous studies, with a long-term warming trend seen in the δ¹⁸O isotope record and progressively lighter δ¹³C values leading up to the PETM. A significant difference between our record and other global records (e.g., ODP Site 1209) is that bottom water temperatures (BWT) appear to increase sooner at Site 215, starting about ~ 1 myr earlier, resulting in a more gradual increase in BWT leading up to the PETM. This results in an δ¹⁸O offset of about 0.5‰ or about 2˚ C. As this is the deepest water site with stable isotope records, we speculate that a warm bottom water mass began to bathe deepest parts of the world’s oceanic basins leading up to the PETM.