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Late Eocene to early Miocene ice sheet dynamics and the global carbon cycle

Record type: Article

Paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial Pacific Ocean Drilling Program Site 1218. The records include the two largest abrupt (<1 Myr) increases in the Cenozoic benthic oxygen isotope record: Oi-1 in the earliest Oligocene (34 Ma) and Mi-1 in the earliest Miocene (23 Ma). The paired Mg/Ca and oxygen isotope records are used to calculate seawater d18O (dw). Calculated dw suggests that a large Antarctic ice sheet formed during Oi-1 and subsequently fluctuated throughout the Oligocene on both short (<0.5 Myr) and long (2–3 Myr) timescales, between about 50 and 100% of its maximum earliest Oligocene size. The magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy. The transient expansion of the Antarctic ice sheet at Mi-1 is marked in the benthic d18O record by two positive excursions between 23.7 and 22.9 Ma, each with a duration of 200–300 kyr. Bottom water temperatures decreased by 2C over the 150 kyr immediately prior to both rapid d18O excursions. However, the onset of each of these phases of ice growth is synchronous, within the resolution of the records, with the onset of a 2C warming over 150 kyr. We suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as Antarctic basement silicate rocks became blanketed by an ice sheet. This represents a negative feedback process that might have operated during major abrupt growth phases of the Antarctic ice sheet.

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Citation

Lear, C.H., Rosenthal, Y., Coxall, H.K. and Wilson, P.A. (2004) Late Eocene to early Miocene ice sheet dynamics and the global carbon cycle Paleoceanography, 19, (4), PA4015. (doi:10.1029/2004PA001039).

More information

Published date: 2004
Keywords: Cenozoic paleoceanography, Antarctic ice sheet, silicate weathering, Mg/Ca paleoceanography, sea level, Ocean Drilling Program, ODP Site 1218

Identifiers

Local EPrints ID: 15391
URI: http://eprints.soton.ac.uk/id/eprint/15391
ISSN: 0883-8305
PURE UUID: bb300a7e-60e4-469f-a062-b91860db6076

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Date deposited: 07 Apr 2005
Last modified: 17 Jul 2017 16:49

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Contributors

Author: C.H. Lear
Author: Y. Rosenthal
Author: H.K. Coxall
Author: P.A. Wilson

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