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Eocene cooling linked to early flow across the Tasmanian Gateway
Peter K Bijl1, James A P Bendle, Steven M Bohaty
1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD Utrecht, The Netherlands.
Summary
The Early Eocene Climatic Optimum ended with cooling, leading to Antarctic glaciation. New data suggest the Tasmanian Gateway opening, not just CO2, initiated this Eocene climate transition.
Area of Science:
- Paleoclimatology
- Oceanography
- Geology
Background:
- The Early Eocene Climatic Optimum (52-50 Ma) represents the warmest global temperatures in 85 million years.
- This greenhouse period transitioned to an icehouse climate, marked by Antarctic glaciation from 34 Ma.
- Previous hypotheses for this transition focused on tectonic gateway openings or declining CO2 levels, lacking empirical data.
Purpose of the Study:
- To investigate the causes of the Eocene greenhouse-to-icehouse climate transition.
- To evaluate the roles of ocean gateway dynamics and atmospheric CO2.
- To provide empirical data from the Wilkes Land Margin, East Antarctica.
Main Methods:
- Analysis of marine microfossil and organic geochemical records.
- Dinoflagellate biogeography and sea surface temperature paleothermometry.
- Biomarker and pollen-based paleothermometry for regional cooling.
Main Results:
- Earliest throughflow of a westbound Antarctic Counter Current initiated around 49-50 Ma via the southern Tasmanian Gateway.
- Simultaneous regional surface water and continental cooling of 2-4 °C occurred.
- This cooling coincided with the opening of the Tasmanian Gateway.
Conclusions:
- The opening of the Tasmanian Gateway and subsequent Antarctic Counter Current flow initiated surface water cooling.
- This cooling influenced global intermediate waters via deep convection.
- Gateway dynamics offer a better explanation for Southern Ocean and deep ocean cooling than CO2 forcing alone during this period.
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