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

Lear, Caroline Helen, Rosenthal, Y., Coxall, Helen Kathrine and Wilson, P. A. 2004. Late Eocene to early Miocene ice sheet dynamics and the global carbon cycle. Paleoceanography 19 (4) , pp. 1-11. 10.1029/2004PA001039

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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 ?18O (?w). Calculated ?w 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 ?18O 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 ?2°C over the 150 kyr immediately prior to both rapid ?18O 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 2°C 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.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Additional Information: Publisher's copyright requirements "Permission to Deposit an Article in an Institutional Repository. Adopted by Council 13 December 2009. AGU allows authors to deposit their journal articles if the version is the final published citable version of record, the AGU copyright statement is clearly visible on the posting, and the posting is made 6 months after official publication by the AGU." See
ISSN: 08838305
Last Modified: 04 Jun 2017 01:39

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