OXYGEN ISOTOPE PALEOTEMPERATURES ACROSS THE CRETACEOUS SUPERGREENHOUSE AT SOUTHERN HIGH LATITUDES (NATURALISTE AND AGULHAS PLATEAU)

New oxygen isotope paleotemperature estimates from δ⁸O measurements of well-preserved planktic and benthic foraminifera are presented for the middle Albian of Deep Sea Drilling Project DSDP Site 257 and Turonian through early Campanian of DSDP Site 258 (62-63°S paleolatitude, southeast Indian Ocean) and late Campanian piston core sites on southern Agulhas Plateau (62°S paleolatitude; southwest Indian Ocean). Results are consistent with the long-term planktic and benthic foraminiferal paleotemperature records documented from Falkland Plateau (63°S paleolatitude, southern South Atlantic) and global compilations of deep-sea benthic foraminifera. Assuming mean ocean δ_w of -1.2‰ in an ice-free world and standard paleotemperature equation for non-symbiotic foraminifera, southern Indian Ocean middle bathyal δ¹⁸O paleotemperatures warmed from 13°C during the middle Albian to a maximum of 19°C during the Turonian, cooled to 14-16°C during the Coniacian- Santonian, and further cooled to 8°C by the late Campanian. Mixed layer planktonic δ¹⁸O paleotemperatures parallel the benthic record with maximum warmth of 30°C documented during the Turonian, sustained warmth of between 14 and16°C from the Coniacian-Santonian and cooling to 8°C by the late Campanian. Extreme warmth during the Turonian-Santonian has been generally attributed to an increase in atmospheric CO₂ from volcanic sources in the Caribbean and elsewhere, but how such warm global temperatures were maintained for nearly nine million years is not understood. The timing for termination of the Cretaceous Supergreenhouse interval needs to be better constrained, and the cause for the switch to long-term cooling will also require further investigation.