High-resolution ice-volume estimates for the early Miocene: Evidence for a dynamic ice sheet in Antarctica

摘要

Ice-volume estimates for the early Miocene (23-16 Ma ATS) were determined by applying delta O-18 to sea-level calibrations to high-resolution delta O-18 records from ODP Sites 1090 and 1218. These calibrated records indicate that ice-volume ranged between 50% and 125% of the present day East Antarctic Ice Sheet (EAIS) during most of the early Miocene (23-17 Ma). Maximum ice-volume occurred at each of the early Miocene isotopic events (i.e., Mi-events) concomitant with bottom water temperatures generally between similar to 1 and 2 degrees C. Rapid ( 1 myr) and high amplitude ice-volume changes also occurred intermittently during this period, with some fluctuations ranging from a fully glaciated East Antarctic continent to a partial collapse of the ice sheet (equivalent to a 50-70% reduction in the EAIS). These large-scale ice-volume changes often occurred at < 100 kyr time scales suggesting an orbitally driven dynamic EAIS existed during the early Miocene. In contrast, the calibrated delta O-18 record from Site 1090 indicates significantly less ice-volume (25-70% of the present-day EAIS) was present between 17 and 16 Ma. These results are supported by numerical climate-ice sheet modeling Studies that show increased orbitally driven ice-volume variability with elevated levels of atmospheric CO2.