Constraining the large scale glaciation of Antarctica during the Eocene-Oligocene Transition using hydrogen isotopes of alkenones
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The Eocene/Oligocene Transition (EOT) (34 Ma) represents a fundamental moment in the history of the Earth. A 1.5‰ positive oxygen isotope excursion marks the transition from an Earth that was warm and largely ice-free towards one of significant glacial ice and cooler temperatures, which still resides today. The EOT is also associated with the origination of the Antarctic Ice Sheet (AIS), however despite much study the cause of this momentous episode of ice growth is widely disputed. Here, the hydrogen isotopes of C37 alkenones are used to reconstruct ice growth over the EOT from three Atlantic sediment cores. The results presented here show a strong positive ~20‰ hydrogen isotope excursion occurring with the EOT suggesting significant Antarctic ice growth. More significantly though, this hydrogen isotope excursion occurs prior to the major oxygen isotope excursion suggesting glaciation prior to abyssal temperature decrease. This is supported by a SST reconstruction showing major cooling of ~5oC occurring after the hydrogen isotope shift. This trend of ice growth first and subsequent abyssal cooling suggests atmospheric carbon dioxide drawdown as the cause for the origin of Antarctic glaciation.