Australia’s breaking away from Antarctica caused climate cooling
27-05-2013 The tectonic opening of the Tasmanian strait between Australia and Antarctica was a contributory factor to the earth beginning to cool down 49 million years ago. This is the result of a study carried out by an international research team led by paleoclimatologists from Utrecht University. With this cooling, the then ice-free greenhouse world eventually changed into the ice capped earth we know today. The results of the study will be published on May 27 in the leading scientific journal Proceedings of the National Academy of Science (PNAS).
Land bridges and straits
Until about 49 million years ago, the land bridge between Australia and Antarctica had a major impact on ocean circulation in the Southern Ocean. Just as the narrow landmass at Panama prevents ocean water today from being exchanged between the Pacific and Atlantic oceans, the Tasmanian land bridge ensured then that the ocean could not flow round Antarctica. 49 million years ago, plate tectonics caused an opening in this land bridge resulting in ocean waters being able to circulate around Antarctica. 
"Thanks to tectonic reconstructions it was already known that Australia and Antarctica slowly drifted apart," says Peter Bijl, Antarctic paleoclimate expert at Utrecht University and lead author. "What we did not know was how and when exactly, this drifting apart influenced the ocean circulation. It now appears that these new ocean currents caused cooling of the climate."
Fossils
The researchers traced back the changing ocean currents by studying fossils of single-cell organisms (dinoflagellates) from sediment cores taken around Tasmania and Antarctica. These cores became available after ocean drilling expeditions of the Integrated Ocean Drilling Program (IODP). Prior to the tectonic opening, there was a significant difference in species composition of fossil algae between the two oceans, indicating a strict separation of the two bodies of water by the Tasmanian land bridge. Around 49 million years ago, the species composition of the two oceans was similar, suggesting exchange of water through the newly formed Tasmanian strait.
Climate change
On the basis of fossil molecules, the team of researchers could demonstrate that simultaneously with the emergence of the new ocean currents through the Tasmanian strait, the seawater temperature and Antarctic air temperature significantly decreased. This decrease was the beginning of a long-term cooling and the end of the fossil super-greenhouse world of the Eocene epoch. Finally, through this long and gradual cooling, large ice masses came into being on Antarctica. "Our research shows that the opening of tectonic straits has had a profound effect on the climate evolution on Earth," says Bijl.
This research was partly made possible by the Dutch Organisation for Scientific Research (NWO) through financial support to IODP and for the scientific research on the sediment cores.
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Publication:
P.K. Bijl, J.A. Bendle, S.M. Bohaty, J. Pross, S. Schouten, L. Tauxe, C.E. Stickley, R.M. McKay, U. Röhl, M. Olney, A. Sluijs, C. Escutia, H. Brinkhuis and Expedition 318 Scientists. ‘Eocene cooling linked to early flow across the Tasmanian Gateway’. PNAS.
Expedition:
Members of the research team participated in an international drilling expedition off the coast of the Antarctic continent. Their experiences could be followed in various blogs:
www.pooljaar.nl/broeikaswereld
www.kennislink.nl
For film clips of the expedition to the South Pole and other IODP expeditions, see YouTube.
More information:
Roy Keeris, press officer Utrecht University, +31 30 253 2411
Images:
The Integrated Ocean Drilling Program’s (IODP) research vessel, JOIDES. This research vessel is capable of bringing to the surface miles of ocean history, stored in the ocean floor sediments. In 2000, the ship drilled around Tasmania and in 2010 she drilled on the Antarctic coastline. Photo: William Crawford, IODP-Texas A&M University.
Photo of a sediment core from the Southern Ocean, cut in half. Multidisciplinary research helps scientists to obtain a great deal of information from the fossilized ocean floor. Photo: Shipboard Scientific Party IODP Leg 318.
Schematic representation of the opening of the Tasmanian strait between Antarctica and Australia during the Eocene epoch (~50 million years ago) and the consequences that the opening had for the ocean circulation. Continents are shown in dark grey, shallow seas in light grey, the deep ocean floor in white. NZ stands for New Zealand.