The mid-Pliocene (3.3 -3 Ma) has long been considered an analogue for future global warming with atmospheric CO2 concentration of 400 ppm, average surface temperatures 2-3 °C higher than pre-industrial and a lack of large continental ice sheets in the Northern Hemisphere. This period of equable climate was terminated by global cooling coincident with a 100ppm drop in CO2 and the development of Northern Hemisphere continental ice sheets during the late Pliocene.
I’ll present a new high-resolution (~1kyr) continuous sea-level record for this interval, derived from a shallow-marine continental margin, Whanganui Basin, New Zealand, using a newly-developed sediment grainsize water-depth relationship. An integrated age model, independent of the global benthic δ18O stack, was developed from magnetostratigraphy, tephrochronology and biostratigraphy. Back-stripping technique was used to remove the effects of subsidence and loading from the paleobathymetry. Glacio-isostatic adjustment modelling for the mid-Pliocene suggests the Whanganui site approximates eustatic sea-level.
The resulting relative sea-level record is characterised by glacial-interglacial precession-paced fluctuations of 15±8m during the mid-Pliocene, and obliquity-paced cycles of 20±8m for the Late Pliocene. Four paleomagnetic reversals allow correlation to orbital time-series, demonstrating sea-level fluctuations in phase with southern high-latitude insolation, implying an Antarctic dominated meltwater source for eustatic sea-level during the mid-Pliocene. An Antarctic ice-rafted debris record also suggests that the marine margins of the Antarctic ice sheets continued to be paced by local insolation (precession) through the Late Pliocene. The emergence of obliquity in the record from 2.9 Ma is driven by developing northern hemisphere ice sheets.
I will discuss the implications of this sea-level record for the sensitivity of the marine-based sectors of Antarctic ice sheet, and interpretation of the benthic oxygen isotope proxy record for global ice volume.