Tropical climate in the Antarctic: Palm trees once thrived on today’s icy coasts 52 million years ago

Tropical climate in the Antarctic

Palm trees once thrived on today’s icy coasts 52 million years ago

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. An international team of scientists, including Claire Huck and Tina van de Flierdt from the Department of Earth Science and Engineering at Imperial College London, has discovered an intense warming phase around 52 million years ago in drill cores obtained from the seafloor near Antarctica — a region that is especially important in climate research. 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.

Today's view of the Wilkes Land coast, Antarctica. 50 Million years ago, Antarctica was ice-free, and lush, near-tropical rainforests thrived along the Antarctic coasts. Image credit: Etienne Classen, Integrated Ocean Drilling Program (IODP).

Around 52 million years ago, the concentration of the greenhouse gas carbon dioxide (CO2) in the atmosphere was more than twice as high as today. If the current CO2 emissions continue unabated due to the burning of fossil fuels, CO2 concentrations in the atmosphere, will be reaching similar levels in the next few hundred years or sooner. ‘The only way we have to understand how the climate system may react to continued human-induced fossil fuel burning and associated increases of atmospheric CO2 concentrations, is to look back into the geological past to times when climatic conditions were similar to what we expect for the future“ explain Claire Huck and Tina van de Flierdt. 

Computer models indicate that future climate warming will be particularly pronounced in high-latitude regions, i.e., near the poles. Until now, however, it has been unclear how Antarctic terrestrial ecosystems responded in the geological past to a greenhouse climate with high atmospheric CO2 concentrations.

The team of scientists tackled this problem by carrying out analyses of 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 (IODP). The rock samples were brought to the surface from more than 4 km of water depth and ~1km of depth below the seafloor. They 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 research team was 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.

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

In an area where the Antarctic ice sheet borders the Southern Ocean today, frost-sensitive and warmth-loving plants such as palms and the ancestors of today’s baobab trees flourished 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. 
These new findings from Antarctica also imply that the temperature difference between the low latitudes and high southern latitudes during the greenhouse climate 52 million years ago was significantly smaller than previously thought. “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”, says the lead author of the study, Jörg Pross from the Goethe University in Frankfurt, Germany.. “Another important factor was the transfer of heat via warm ocean currents that reached Antarctica.” 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.

Paper:

Pross, J., Contreras, L., Bijl, P.K., Greenwood, D.R., Bohaty, S.M., Schouten, S., Bendle, J.A., Röhl, U., Tauxe, L., Raine, J.I., Huck, C.E., van de Flierdt, T., Jamieson, S.S.R., Stickley, C.E., van de Schootbrugge, B., Escutia, C., Brinkhuis, H., IODP Expedition 318 Scientists (2012): Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch. Nature, DOI: 10.1038/nature11300.

Tina van de Flierdt reported in a blog from this research expedition, the science behind it, and what it is like to work on a drilling vessel for 9 weeks. Read it here

See also the following article on the BBC