Baobab and palm trees once thrived on today’s icy coasts of Antarctica about 52 million years ago, a new study led by the Goethe University and the Biodiversity and Climate Research Center in Frankfurt has suggested.
An iceberg floating near the Antarctic coast (Roy Davis / Integrated Ocean Drilling Program)
Given the predicted rise in global temperatures in the coming decades, climate scientists are particularly interested in warm periods that occurred in the geological past. Knowledge of past episodes of global warmth can be used to better understand the relationship between climate change, variations in atmospheric carbon dioxide and the reaction of Earth’s biosphere.
The study, published in the journal Nature, shows that tropical vegetation, including palms and relatives of today’s tropical Baobab trees, was growing on the coast of Antarctica 52 million years ago. These results highlight the extreme contrast between modern and past climatic conditions on Antarctica and the extent of global warmth during periods of elevated atmospheric carbon dioxide levels.
Around 52 million years ago, the concentration of the greenhouse gas carbon dioxide in the atmosphere was more than twice as high as today.
“If the current carbon dioxide emissions continue unabated due to the burning of fossil fuels, carbon dioxide concentrations in the atmosphere, as they existed in the distant past, are likely to be achieved within a few hundred years,” said lead author Prof Jörg Pross, a paleoclimatologist at the Goethe University.
“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,” he added.
52-million-year-old palm pollen, left, and pollen from the ancestors of today’s baobab trees, found by the team (Lineth Contreras / Goethe University Frankfurt)
The scientists analyzed rock samples from drill cores on the seabed, which were obtained off the coast of Wilkes Land, Antarctica, as part of the Integrated Ocean Drilling Program. The rock samples are between 53 and 46 million years old and contain fossil pollen and spores that are known to originate from the Antarctic coastal region. The researchers were thus able to reconstruct the local vegetation on Antarctica and, accordingly, interpret the presence of tropical and subtropical rainforests covering the coastal region 52 million years ago.
The scientists’ evaluations show that the winter temperatures on the Wilkes Land coast of Antarctica were warmer than 10 degrees Celsius at that time, despite three months of polar night. The continental interior, however, was noticeably cooler, with the climate supporting the growth of temperate rainforests characterized by southern beech and Araucaria trees of the type common in New Zealand today. Additional evidence of extremely mild temperatures was provided by analysis of organic compounds that were produced by soil bacteria populating the soils along the Antarctic coast.
The findings also imply that the temperature difference between the low latitudes and high southern latitudes during the greenhouse phase 52 million years ago was significantly smaller than previously thought.
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Bibliographic information: Pross et al. 2012. Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch. Nature; doi: 10.1038/nature11300
