Middle Miocene Expansion of the East Antarctic Ice Sheet Triggered by pCO2 decline

Add to your list(s) Download to your calendar using vCal

• Gavin Foster, National Oceanography Centre, Southampton
• Tuesday 23 November 2010, 16:30-17:30
• Tilley Lecture Theater, Department of Earth Sciences.

If you have a question about this talk, please contact John Maclennan.

The global cooling from the early Cenozoic ice-free world (~50 Ma) to today’s bipolar icehouse world has long been ascribed to declining levels CO2 levels (Berner et al., 1983, Raymo et al., 1988). This deterioration in climate is recorded by a ~4 ‰ increase in deepwater benthic foraminiferal d18O, reflecting both a ~12 °C cooling, and the formation of Earth’s continental ice sheets (Lear et al., 2000). Roughly half of this signal occurs between the Miocene Climatic Optimum (~16 Ma; MCO ) and today, including a ~1 ‰ step marking the establishment of a permanent East Antarctic ice sheet during the Middle Miocene Climate Transition (MMCT) at ~14 Ma (Zachos et al., 2001). Although most pCO2 reconstructions show an overall decline associated with early Cenozoic cooling, estimates of pCO2 during the Miocene Climatic Optimum are either higher (stomatal index; Kürshner et al. 2008), lower (boron isotopes in foraminifera; Pearson and Palmer, 2000), or around the same (d13C of alkenones; Pagani et al., 1999) as pre-industrial levels, leading to suggestions that either existing proxy records are flawed (Ruddiman, 2010), or climate and pCO2 have been decoupled for some portions of Earth’s history (Kerr, 1999; Pagani et al., 1999). Here I use new boron isotope measurements in planktonic foraminifera to show that the Miocene Climatic Optimum was associated with elevated pCO2 and that drawdown from this maximum coincided with orbitally-paced organic carbon burial during subsequent climatic cooling. Contrary to previous studies (e.g. Pagani et al., 1999) our new boron based pCO2 record therefore reaffirms the link between CO2 , climate and the cyrosphere for this important part of the Cenozoic.

This talk is part of the Department of Earth Sciences Seminars (downtown) series.

This talk is included in these lists:

• Department of Earth Sciences Seminars (downtown)
• Department of Earth Sciences seminars
• Tilley Lecture Theater, Department of Earth Sciences
• ps635

Note that ex-directory lists are not shown.