Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 113, Issue 42, Pages 11782-11787Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1608100113
Keywords
Eocene-Oligocene climate transition; coccolith-based proxies; Atlantic equatorial SSTs; Cenozoic pCO(2); meridional temperature gradient
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Funding
- Centre National de la Recherche Scientifique [SYSTER 884402]
- Natural Environment Research Council [NE/H015523/1]
- NERC [NE/H015523/1] Funding Source: UKRI
- Natural Environment Research Council [NE/H015523/1] Funding Source: researchfish
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Growth of the first permanent Antarctic ice sheets at the Eocene-Oligocene Transition (EOT), similar to 33.7 million years ago, indicates a major climate shift within long-term Cenozoic cooling. The driving mechanisms that set the stage for this glaciation event are not well constrained, however, owing to large uncertainties in temperature reconstructions during the Eocene, especially at lower latitudes. To address this deficiency, we used recent developments in coccolith biogeochemistry to reconstruct equatorial Atlantic sea surface temperature (SST) and atmospheric pCO(2) values from pelagic sequences preceding and spanning the EOT. We found significantly more variability in equatorial SSTs than previously reported, with pronounced cooling from the Early to Middle Eocene and subsequent warming during the Late Eocene. Thus, we show that the Antarctic glaciation at the Eocene-Oligocene boundary was preceded by a period of heat accumulation in the low latitudes, likely focused in a progressively contracting South Atlantic gyre, which contributed to cooling high-latitude austral regions. This prominent redistribution of heat corresponds to the emplacement of a strong meridional temperature gradient that typifies icehouse climate conditions. Our equatorial coccolith-derived geochemical record thus highlights an important period of global climatic and oceanic upheaval, which began 4 million years before the EOT and, superimposed on a long-term pCO(2) decline, drove the Earth system toward a glacial tipping point in the Cenozoic.
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