Late Eocene Early Oligocene Cooling

The Eocene to early Oligocene (focus of Chapter 8) represent a time of global cooling which was marked by reorganisation of global ocean circulation patterns and significant turnovers in the marine and terrestrial biota (e.g. Berggren and Prothero, 1992) that culminates in the development of the first Antarctic Ice Sheet and an important expansion of Antarctic ice volume. Global deep-sea oxygen isotope records indicate that this long-term cooling trend was not monotonic, but that it was interrupted by a series of abrupt short-term (ca. 1 million years) excursions in 818O (Zachos et al., 2001). Among these, the Oi-1 cooling event (Miller et al., 1991) at 33.55 Ma marked one of the most significant global climatic deteriorations in the Cenozoic in response to the appearance of the first continent-wide glaciation in Antarctica (e.g. Zachos et al., 1996). Coupled GCM/ice-sheet modelling has already been used to show that the formation of the East Antarctic Ice Sheet was triggered by a combination of gradual pCO2 lowering coupled with ice-climate feedbacks and orbital-forcing-induced cooling, rather than by the cooling associated with the opening of circumpolar seaways during the earliest Oligocene (e.g. Kennett et al., 1974; DeConto and Pollard, 2003; Lawver and Gahagan, 2003).

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