Calibration between eustatic estimates from backstripping and oxygen isotopic records for the Oligocene

Eustatic estimates from the backstripping of Oligocene sections are compared quantitatively with δ¹⁸O data. Each of the nine Oligocene δ¹⁸O events (maxima) identified in previous studies correlates with a stratigraphically determined sea-level lowstand. Oxygen isotopic records from planktonic foraminifers from western equatorial Atlantic Ocean Drilling Program (ODP) Site 929 indicate an isotopic increase of 0.16‰ per 10 m decrease in the depth of the ocean (apparent sea level, ASL). Amplitudes of ASL change also correlate with moderate- and high-resolution benthic foraminiferal δ¹⁸O records from ODP Sites 803 (western tropical Pacific) and 929 and from Deep Sea Drilling Project (DSDP) Site 522 (South Atlantic Ocean), with an isotopic change of 0.22‰ per 10 m of ASL change (r² = 0.807 and 0.960, respectively), and with records from ODP Site 689 (Southern Ocean; 0.13‰ per 10 m of ASL change; r² = 0.704). This correlation suggests that Southern Ocean deep-water temperature changes were smaller than tropical sea-surface temperature changes between million year-scale glacials and interglacials. It also suggests that the deep-sea Southern Ocean records may provide the best means to calibrate sea level to oxygen isotopes.