Eocene cooling linked to early flow across the Tasmanian Gateway

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 110; no. 24; pp. 9645 - 9650
• Main Authors: Bijl, Peter K., Bendle, James A. P., Bohaty, Steven M., Pross, Jörg, Schouten, Stefan, Tauxe, Lisa, Stickley, Catherine E., McKay, Robert M., Röhl, Ursula, Olney, Matthew, Sluijs, Appy, Escutia, Carlota, Brinkhuis, Henk
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences 11-06-2013; National Acad Sciences
• Subjects: Antarctic Regions; Atmosphere; Biogeography; Carbon dioxide; Carbon Dioxide - metabolism; Climate; Climate models; Cold Temperature; Cooling; Dinoflagellida - growth & development; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fossils; Geography; Geologic Sediments - chemistry; Greenhouse Effect; Ice Cover; Marine Biology; Ocean currents; Ocean temperature; Oceanic climates; Oceans; Oceans and Seas; Paleobotany; Paleoclimatology; Paleontology; Physical Sciences; Plankton - growth & development; Plate tectonics; Sea water; Stratigraphy; Surface water; Tasmania; Temperature; Time Factors; Water Movements; Antarctica; Antarctic region; Wilkes Land; East Antarctica; Antarctic Ocean; polar regions; Australia; Tasmania Australia; Antarctic Regions; Tasmania; microfossils; Paleogene; Australasia; paleo-oceanography; paleoclimate; dinoflagellate cysts; Cenozoic; climate cooling; marine sedimentation; marine sediments; sea water; carbon dioxide; Dinoflagellata; paleoceanography; Tertiary; biomarkers; Eocene; surface water; palynomorphs; paleobiogeography; marine environment; lower Eocene; dinoflagellates; Ocean Drilling Program; Phanerozoic; pollen analysis; biostratigraphy; middle Eocene; organic palaeothermometry
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1220872110

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., CO ₂). 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 CO ₂ 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.