Abstract
Observations and model experiments highlight the importance of ocean heat in forcing ice sheet retreat during the present and geological past, but past ocean temperature data are virtually missing in ice sheet proximal locations. Here we document paleoceanographic conditions and the (in)stability of the Wilkes Land subglacial basin (East Antarctica) during the mid-Miocene (~17–13.4 million years ago) by studying sediment cores from offshore Adélie Coast. Inland retreat of the ice sheet, temperate vegetation, and warm oligotrophic waters characterise the mid-Miocene Climatic Optimum (MCO; 17–14.8 Ma). After the MCO, expansion of a marine-based ice sheet occurs, but remains sensitive to melting upon episodic warm water incursions. Our results suggest that the mid-Miocene latitudinal temperature gradient across the Southern Ocean never resembled that of the present day. We demonstrate that a strong coupling of oceanic climate and Antarctic continental conditions existed and that the East Antarctic subglacial basins were highly sensitive to ocean warming.
Highlights
Observations and model experiments highlight the importance of ocean heat in forcing ice sheet retreat during the present and geological past, but past ocean temperature data are virtually missing in ice sheet proximal locations
We demonstrate that marine-based ice sheets are absent or extremely reduced compared to present day during the Miocene Climatic Optimum (MCO) at the Wilkes Land
Deposition occurred in an open-water environment where only occasional erosion or reworking of older marine sediments and transport to the core location took place
Summary
Observations and model experiments highlight the importance of ocean heat in forcing ice sheet retreat during the present and geological past, but past ocean temperature data are virtually missing in ice sheet proximal locations. Inland retreat of the ice sheet, temperate vegetation, and warm oligotrophic waters characterise the mid-Miocene Climatic Optimum (MCO; 17–14.8 Ma). Observational data and modelling studies suggest consistently that influx of warm waters onto the Antarctic continental shelf invigorates ice retreat[1,2,3]. Studying ice sheet instability and ice–ocean interactions during past warm geologic episodes, when atmospheric CO2 was analogous to present day or higher, can shed light on the longterm stability of continental cryosphere for our future. For the mid-Miocene epoch, geological records show major variations in Antarctic ice sheet volume, global sea level, ocean temperatures, and marine fauna and flora[8,9,10,11]. Climatic Optimum (MCO, ~17–15 Ma) represents one of the warmest intervals since the inception of Antarctic glaciation[12], with atmospheric CO2 per million by volume concentrations as high (ppmv)[13,14,15,16,17], analogous as to
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