(9 August 2012)
A team of scientists, including Dr Stewart Jamieson, a glaciologist from Durham University’s Department of Geography, has discovered an intense warming phase occurred in Antarctic climate millions of years ago.
The study shows that tropical vegetation, including palm trees and relatives of today’s Baobab trees normally found in the world’s hottest climates, was growing on the coast of Antarctica 52 million years ago – today one of the world’s coldest regions.
The study was published in the journal Nature, a prestigious international academic journal.
The 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 (CO2) levels. Around 52 million years ago, the concentration of this greenhouse gas in the atmosphere was more than twice as high as today.
Given the predicted rise in global CO2 concentrations and temperatures in the coming decades, climate scientists are particularly interested in warm periods that occurred in the past. Knowledge of such 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 and ice sheets.
Computer models indicate that future climate warming will be particularly pronounced near the poles. The new data gives a valuable insight into the response of Antarctic terrestrial ecosystems under a 'greenhouse' climate with high atmospheric CO2 concentrations.
The international team analysed fragments of plants and bacteria found in a 1 km long drill core. This fossil data was compared against a new map of the ancient Antarctic landscape developed by Dr. Jamieson and colleagues to reconstruct past temperatures and vegetation distributions.
Dr Stewart Jamiesonsaid:“The results are important because they provide a window into a world where CO2 concentrations were high and show just how warm Antarctica has been in the past.
“The data help us understand how climate might respond in the future as greenhouse gas concentrations continue to rise as a result of human activity. This in turn aids efforts to predict the future stability of the Antarctic Ice Sheet and the knock-on implications for global sea level.”
The scientists analysed 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 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 able to reconstruct the local vegetation of Antarctica and interpret the presence of tropical and subtropical rainforests covering the coastal region.
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 characterised 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 phase 52 million years ago was significantly smaller than previously thought. This shows the importance not only of atmospheric CO2 concentrations, but of the evolving role of the oceans in transferring heat around the globe.