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Fossil evidence shows frost-sensitive and warmth-loving plants such as palms and the ancestors of today's baobab trees flourished 52 million years ago in Antartica.
A recent expedition found that the winter temperatures 52 million years ago were warmer than 10 degrees Celsius at that time, and rainforests flourished despite three months of polar night.
"By studying naturally occurring climate warming periods in the geological past, our knowledge of the mechanisms and processes in the climate system increases. This contributes enormously to improving our understanding of current human-induced global warming," explained Prof. Jörg Pross, a paleoclimatologist at the Goethe University and member of the Biodiversity and Climate Research Centre (BiK-F) in Frankfurt, Germany
The scientists working with Pross analysed rock samples from drill cores obtained off the coast of Wilkes Land, Antarctica, as part of the Integrated Ocean Drilling Program (IODP). Between 53 and 46 million years old, these rock samples contained fossil pollen and spores that are known to originate from the Antarctic coastal region. The samples indicated the presence of tropical and subtropical rainforests covering the coastal region 52 million years ago.
"The CO2 content of the atmosphere as assumed for that time interval is not enough on its own to explain the almost tropical conditions in the Antarctic", added Pross. "Another important factor was the transfer of heat via warm ocean currents that reached Antarctica."
The scientists concluded that when the warm ocean current collapsed and the Antarctic coast came under the influence of cooler ocean currents, the tropical rainforests including palms and Baobab relatives also disappeared.
The scientists used the drillship JOIDES Resolution to recover sediment cores off the Antarctic coast. Photo credit: Rob Dunbar, Stanford University