About 50 million years ago, the Antarctic summer was subtropical, winter temperatures were above freezing and there was a tropical rainforest on the coast. These are the remarkable results of a research cruise to eastern Antarctica aboard a drilling vessel, led by expedition leader Henk Brinkhuis from Utrecht University and the Royal Netherlands Institute for Sea Research. The international research team will publish their results in the authoritative scientific journal Nature later this week.
In spring 2010, Expedition 318 of the Integrated Ocean Drilling Program (IODP) left for eastern Antarctica aboard the drilling vessel Joides Resolution. Close to the Antarctic coastline, they drilled through the ocean floor and hauled up 50-million-year-old sediment. This sediment is now about 1.000 meters below the ocean floor. Analyzing these sediment samples, they found large concentrations of pollen grains from tropical and subtropical plants, such as palms, baobab (adansonia) and tropical fruit and nut trees. These species all grow within a specific temperature range and are certainly not frost-hardy.
The Dutch scientists on the team did not just analyze pollen grains, but also fossil molecules of soil bacteria. These analyses also revealed that 50 million years ago, summer temperatures at Antarctica must have been over 25ºC. The method they used for establishing past temperatures has been developed by Stefan Schouten and his colleagues at the Royal Netherlands Institute for Sea Research.
Super Greenhouse World
The early Eocene period, 56 to 48 million years ago, is known as the 'super greenhouse world' with extremely high, natural concentrations of the greenhouse gas CO2 in the atmosphere. Up to now, the climate history of Antarctica from this period was largely unknown because any fossil remains from the period are covered by an immense ice cap. For a better understanding of the effects of high CO2 concentrations it is crucial to learn more about the climate history of this period.
North and South Poles
These first results correspond to results from earlier Arctic drillings by the same research group, which revealed remains of palm trees from the early Eocene in the Arctic. The present results show that during that period CO2 concentrations were probably 4 to 5 times higher than they are now and on this 'greenhouse Earth' subtropical forests reached both Poles. This offers insight into the dynamics of a world affected by such concentrations.
Twenty-five countries, including the Netherlands, participate in the Integrated Ocean Drilling Program. This program is partly funded by the Netherlands Organisation for Scientific Research (NWO). NWO pays the Dutch membership fee to the IODP European branch, so that Dutch research groups can participate in drilling expeditions.
Jörg Pross, Lineth Contreras, Peter K. Bijl, David R. Greenwood, Steven M. Bohaty, Stefan Schouten, James A. Bendle, Ursula Röhl, Lisa Tauxe, J. Ian Raine, Claire E. Huck, Tina van de Flierdt, Stewart S.R. Jamieson, Catherine E. Stickley, Bas van de Schootbrugge, Carlota Escutia, Henk Brinkhuis and IODP Expedition 318 Scientists. ‘Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch’. Nature, DOI: 10.1038/nature11300.
Roy Keeris, press officer Universiteit Utrecht, 030 – 253 2411, firstname.lastname@example.org.
The scientists used the drillship JOIDES Resolution to recover sediment cores off the Antarctic coast. Drilling reached a depth of more than 1,000 m below the sea floor. Image credit: Rob Dunbar, Stanford University.
The scientists analyzed pollen and spores that had been produced by plants on Antarctica 52 Million years ago. After their transport into the ocean through winds and rivers, the pollen and spores were preserved in the marine sediment cores shown. Image credit: Kevin Welsh, University of Queensland.
52-Million-year-old palm pollen (left) and pollen grain (right) from Antarctica. The pollen grain, which has been produced by ancestors of today’s tropical Baobab trees, provides evidence that near-tropical forests grew along the Wilkes Land margin of Antarctica during that time. Size of pollen grain is 45 x 37 microns. Image credit: Lineth Contreras, Goethe University Frankfurt.
52 Million years ago, the Wilkes Land coast of Antarctica was covered by near-tropical forests as they today occur in NE Australia (shown here). Copyright Sven Brenner – Fotolia.com.