We compiled a splice of benthic foraminiferal δ18O records over the past 66 Myr and scaled to sea level using a smoothed record (>2 Myr) of Cenozoic Mg/Ca variations to account for long-term effects of temperature changes. We assume that shorter term (Milankovitch scale, 104-105 year) temperature changes comprise ~20% of the benthic foraminiferal δ18O changes, as in the Quaternary, and a calibration of 0.13±0.02‰ δ18Oseawater/10m. Our record provides an estimate of ice-volume and attendant Global Mean Sea Level changes due to ice (GMSL-I) with errors of approximately ±10 m, but is not a complete estimate of GMSL because it does not account for changes in the volume of the ocean basin, other tectonic effects, or changes due to sediment input. We compare our GMSL-I records with independent estimates of Myr-scale sea-level changes derived from passive margin (New Jersey, USA, and Marion Plateau, Australia) by backstripping, progressively accounting for the effects of compaction, loading, and thermal subsidence. Both GMSL-I and backstripped records show synchronous 20-60 m variations on the Myr scale during the Icehouse World of the Oligocene-Miocene, suggesting that we have constrained changes in ice volume on this scale.
WHAT’S NEXT: We are analyzing an early Paleogene (48-66 Ma) record from Site 1209 for Mg/Ca building on the oxygen isotopic record of Westerhold et al. (2019).