title: Eocene cooling linked to early flow across the Tasmanian Gateway.
abstract: 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.
authors.affiliation: Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD Utrecht, The Netherlands.
authors.forename: Peter K
authors.initials: PK
authors.lastname: Bijl
authors.forename: James A P
authors.initials: JA
authors.lastname: Bendle
authors.forename: Steven M
authors.initials: SM
authors.lastname: Bohaty
authors.forename: Jörg
authors.initials: J
authors.lastname: Pross
authors.forename: Stefan
authors.initials: S
authors.lastname: Schouten
authors.forename: Lisa
authors.initials: L
authors.lastname: Tauxe
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Stickley
authors.forename: Robert M
authors.initials: RM
authors.lastname: McKay
authors.forename: Ursula
authors.initials: U
authors.lastname: Röhl
authors.forename: Matthew
authors.initials: M
authors.lastname: Olney
authors.forename: Appy
authors.initials: A
authors.lastname: Sluijs
authors.forename: Carlota
authors.initials: C
authors.lastname: Escutia
authors.forename: Henk
authors.initials: H
authors.lastname: Brinkhuis
mesh_terms: D000864:Antarctic Regions; D001272:Atmosphere; D002245:Carbon Dioxide / Q000378:metabolism*; D002980:Climate; D003080:Cold Temperature; D004141:Dinoflagellida / Q000254:growth & development; D005580:Fossils; D005843:Geography; D019015:Geologic Sediments / Q000737:chemistry; D017752:Greenhouse Effect; D046448:Ice Cover; D008386:Marine Biology; D009792:Oceans and Seas; D010933:Plankton / Q000254:growth & development; D013648:Tasmania; D013997:Time Factors; D014872:Water Movements
chemical_list: D002245:Carbon Dioxide
keywords: climate cooling; dinoflagellate cysts; organic palaeothermometry; paleoceanography