Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 110, Issue 24, Pages 9645-9650Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1220872110
Keywords
climate cooling; dinoflagellate cysts; organic palaeothermometry; paleoceanography
Categories
Funding
- Netherlands Organization for Scientific Research [86610110]
- LPP Foundation
- Natural Environmental Research Council (NERC)
- IODP-Unite Kingdom for Standard Research Grant [NE/I00646X/1]
- Cruise Participation Grant [NE/H014616/1]
- NERC [NE/H020098/1, NE/J019801/1]
- German Research Foundation [PR 651/10, RO 1113/6]
- Biodiversity and Climate Research Center (BIK-F) within the Hessian Initiative for Scientific and Economic Excellence (LOEWE)
- National Science Foundation [OCE 1058858]
- European Research Council [259627]
- NERC [NE/I006257/1, NE/I00646X/1, NE/H020098/1, NE/I00646X/2, NE/J019801/1, NE/H025162/1, NE/H014616/1] Funding Source: UKRI
- Natural Environment Research Council [NE/J019801/1, NE/H020098/1, NE/I00646X/2, NE/H014616/1, NE/I006257/1, NE/H025162/1, NE/I00646X/1] Funding Source: researchfish
- Directorate For Geosciences
- Division Of Ocean Sciences [1058858] Funding Source: National Science Foundation
- Division Of Ocean Sciences
- Directorate For Geosciences [1129101] Funding Source: National Science Foundation
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The warmest global temperatures of the past 85 million years occurred during a prolonged greenhouse episode known as the Early Eocene Climatic Optimum (52-50 Ma). The Early Eocene Climatic Optimum terminated with a long-term cooling trend that culminated in continental-scale glaciation of Antarctica from 34 Ma onward. Whereas early studies attributed the Eocene transition from greenhouse to icehouse climates to the tectonic opening of Southern Ocean gateways, more recent investigations invoked a dominant role of declining atmospheric greenhouse gas concentrations (e.g., CO2). However, the scarcity of field data has prevented empirical evaluation of these hypotheses. We present marine microfossil and organic geochemical records spanning the early-to-middle Eocene transition from the Wilkes Land Margin, East Antarctica. Dinoflagellate biogeography and sea surface temperature paleothermometry reveal that the earliest throughflow of a westbound Antarctic Counter Current began similar to 49-50 Ma through a southern opening of the Tasmanian Gateway. This early opening occurs in conjunction with the simultaneous onset of regional surface water and continental cooling (2-4 degrees C), evidenced by biomarker- and pollen-based paleothermometry. We interpret that the westbound flowing current flow across the Tasmanian Gateway resulted in cooling of Antarctic surface waters and coasts, which was conveyed to global intermediate waters through invigorated deep convection in southern high latitudes. Although atmospheric CO2 forcing alone would provide a more uniform middle Eocene cooling, the opening of the Tasmanian Gateway better explains Southern Ocean surface water and global deep ocean cooling in the apparent absence of (sub-) equatorial cooling.
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