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SUMMARY:Middle Miocene Expansion of the East Antarctic Ice Sheet Triggered
  by pCO2 decline - Gavin Foster\, National Oceanography Centre\, Southampt
 on
DTSTART:20101123T163000Z
DTEND:20101123T173000Z
UID:TALK26149@talks.cam.ac.uk
CONTACT:John Maclennan
DESCRIPTION:The global cooling from the early Cenozoic ice-free world (&#1
 26\;50 Ma) to today’s bipolar icehouse world has long been ascribed to d
 eclining levels CO2 levels (Berner et al.\, 1983\, Raymo et al.\, 1988). T
 his deterioration in climate is recorded by a &#126\;4 ‰ increase in dee
 pwater benthic foraminiferal d18O\, reflecting both a &#126\;12 °C coolin
 g\, and the formation of Earth’s continental ice sheets (Lear et al.\, 2
 000). Roughly half of this signal occurs between the Miocene Climatic Opti
 mum (&#126\;16 Ma\; MCO) and today\, including a &#126\;1 ‰ step marking
  the establishment of a permanent East Antarctic ice sheet during the Midd
 le Miocene Climate Transition (MMCT) at &#126\;14 Ma (Zachos et al.\, 2001
 ). Although most pCO2 reconstructions show an overall decline associated w
 ith early Cenozoic cooling\, estimates of pCO2 during the Miocene Climatic
  Optimum are either higher (stomatal index\; Kürshner et al. 2008)\, lowe
 r (boron isotopes in foraminifera\; Pearson and Palmer\, 2000)\, or around
  the same (d13C of alkenones\; Pagani et al.\, 1999) as pre-industrial lev
 els\, leading to suggestions that either existing proxy records are flawed
  (Ruddiman\, 2010)\, or climate and pCO2 have been decoupled for some port
 ions of Earth’s history (Kerr\, 1999\; Pagani et al.\, 1999). Here I use
  new boron isotope measurements in planktonic foraminifera to show that th
 e Miocene Climatic Optimum was associated with elevated pCO2 and that draw
 down from this maximum coincided with orbitally-paced organic carbon buria
 l during subsequent climatic cooling. Contrary to previous studies (e.g. P
 agani et al.\, 1999) our new boron based pCO2 record therefore reaffirms t
 he link between CO2\, climate and the cyrosphere for this important part o
 f the Cenozoic.
LOCATION:Tilley Lecture Theater\, Department of Earth Sciences
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