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Eocene bipolar glaciation associated with global carbon cycle changes

Fig. 1a. Reconstructions of CCD based on carbonate mass accumulation rate (MAR) for 0-50 Myr ago. Black line is the low-resolution CCD history based on DSDP sediments. Eocene sediments (dotted line) were poorly recovered during past drilling in the Pacific Ocean. Blue line is our revised CCD history for the greenhouse-icehouse transition, based on sediments recovered during ODP Leg 199. Grey bars at bottom mark CCD deepenings that coincide with transient benthic d18O increases and vertical grey line marks Oi-1 glaciation. Eocene bipolar glaciation associated with global carbon cycle changes
Nature Vol. 436, Number 7049, pp.341-346, 21 July 2005 doi: 10.1038/nature03874.

Aradhna Tripati1, Jan Backman2, Henry Elderfield1 and Patrizia Ferretti1

1 Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK

2 Department of Geology and Geochemistry, Stockholm University, Kungstensgatan 45, S-10691, Stockholm, Sweden

ABSTRACT:
The transition from the extreme global warmth of the early Eocene 'greenhouse' climate, ~55 million years ago to the present glaciated state is one of the most prominent changes in Earth's climatic evolution. It is widely accepted that large ice sheets first appeared on Antarctica ~34 million years ago, coincident with decreasing atmospheric carbon dioxide concentrations and a deepening of the calcite compensation depth in the world's oceans, and that glaciation in the Northern Hemisphere began much later, between 10 and 6 million years ago. Here we present records of sediment and foraminiferal geochemistry covering the greenhouse-icehouse climate transition. We report evidence for synchronous deepening and subsequent oscillations in the calcite compensation depth in the tropical Pacific and South Atlantic oceans from ~42 million years ago, with a permanent deepening 34 million years ago. The most prominent variations in the calcite compensation depth coincide with changes in seawater oxygen isotope ratios of up to 1.5 per mil, suggesting a lowering of global sea level through significant storage of ice in both hemispheres by at least 100 to 125 metres. Variations in benthic carbon isotope ratios of up to ~1.4 per mil occurred at the same time, indicating large changes in carbon cycling. We suggest that the greenhouse-icehouse transition was closely coupled to the evolution of atmospheric carbon dioxide, and that negative carbon cycle feedbacks may have prevented the permanent establishment of large ice sheets earlier than 34 million years ago.

Download data from the WDC Paleo archive:
Carbonate and stable isotope data and calculated Calcite Compensation Depth and 0% isopleth depth,
Text or Microsoft Excel format.

See also Paleocene-Eocene Thermal Maximum Isotope and Mg/Ca data from
Tripati and Elderfield Science v. 308, 24 June 2005.

To read or view the full study, please visit the Nature website.
It was published in Nature, Vol. 436, Number 7049, pp.341-346, 21 July 2005 doi: 10.1038/nature03874.
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