Wednesday, June 12, 2013

Eocene Cooling Linked to Early Flow Across Tasmanian Gateway

Eocene cooling linked to early flow across the Tasmanian Gateway


1. Peter K. Bijl (a)
2. James A. P. Bendle (b)
3. Steven M. Bohaty (c)
4. Jörg Pross (d,e)
5. Stefan Schouten (f)
6. Lisa Tauxe (g)
7. Catherine E. Stickley (h)
8. Robert M. McKay (i)
9. Ursula Röhl (j)
10. Matthew Olney (k)
11. Appy Sluijs (a)
12. Carlota Escuti (a,l)
13. Henk Brinkhuis (a,f)
14. Expedition 318 Scientists


a. Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD, Utrecht, The Netherlands

b. Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom

c. Ocean and Earth Science, University of Southampton, Southampton SO14 3ZH, United Kingdom

d. Paleoenvironmental Dynamics Group, Institute of Geosciences, University of Frankfurt, 60438 Frankfurt, Germany

e. Biodiversity and Climate Research Centre, 60325 Frankfurt, Germany

f. NIOZ Royal Netherlands Institute for Sea Research, 1790 AB, Den Burg, Texel, The Netherlands

g. Geosciences Research Division, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093-0220

h. Department of Geology, University of Troms, N-9037 Troms, Norway

i. Antarctic Research Centre, Victoria University of Wellington, Wellington 6140, New Zealand

j. MARUM–Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany

k. Department of Geology, University of South Florida, Tampa, FL 33620

l. Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Cientificas (Spain)–Universite de Granada, 18002 Granada, Spain


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 ∼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 °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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