Palm trees thrived in Antarctica 52 million years ago, study shows - 03/08/2012
Balmy tropical temperatures and frost-sensitive vegetation prevailed on the coast of Antarctica 52 million years ago, according to a study of drill cores from under the seafloor off the coast of Antarctica.
Tropical vegetation, similar to what can be seen on the Queensland coast today, was growing in the area now known as Wilkes Land due south of Australia, the study has shown.
And summer temperatures in coastal Antarctica ranged between 20 and 27 degrees Celsius.
The finding, published in the science journal Nature this week, confirmed what earlier studies had indicated – that Antarctica would have been an ideal summer playground.
It also underlined the extreme contrast between modern and past climate conditions in Antarctica and the extent of global warming during periods of elevated carbon dioxide levels in the atmosphere.
The exceptionally warm period 55 to 48 million years ago was the warmest era in the Earth’s history during the past 70 million years.
The study was undertaken by an international team, led by Goethe University and the Biodiversity and Climate Research Centre in Frankfurt, Germany. The team included micro-paleontologist Dr Ian Raine of GNS Science.
Operating from the ocean drilling ship JOIDES Resolution, the scientists recovered a number of drill cores from the seabed off the coast of Wilkes Land in 2010 as part of the Integrated Ocean Drilling Programme.
The sub-seafloor rock samples were between 53 and 46 million years old and contain fossil pollen and spores that are known to originate from the Antarctic coastal region. Using this information, the researchers were able to reconstruct the local vegetation on Antarctica and deduced the presence of tropical and subtropical rainforests covering the coastal region 52 million years ago.
About 52 million years ago, the concentration of the greenhouse gas carbon dioxide in the atmosphere was more than twice as high as today.
Dr Raine said if CO2 emissions from fossil fuels continued unabated, CO2 concentrations in the atmosphere, as they existed in the distant past, were likely to be reached within a few hundred years.
Studies of warm periods in the geological past increased the knowledge of climate system mechanisms. This contributed enormously to improving our understanding of current human-induced global warming, Dr Raine said.
Computer models indicate that future climate warming will be particularly pronounced in regions 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.
While the coast of Antarctica was tropical, the continental interior was noticeably cooler, with the climate supporting the growth of temperate rainforests similar to beech forests in the South Island 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.
However, the scientists believe the CO2 content of the atmosphere 50 million years ago was not enough on its own to explain the almost tropical conditions in the Antarctic.
Warm ocean currents reaching Antarctica were also an important factor in transferring heat to the continent.
When the warm ocean current collapsed and the Antarctic coast came under the influence of cooler ocean currents, the tropical rainforests and lush coastal palm trees also disappeared.
In allied research, scientists have been able to refine proxy techniques that are used to estimate sea surface temperatures around the globe 50 million years ago, when the Earth was about 10 degrees Celsius warmer than today.
When deciphering the Earth’s climate history, scientists use a range of geochemical and paleontological proxies to estimate past temperatures of the ocean. However, these techniques vary greatly in reliability and accuracy.
The research published online in Earth and Planetary Science Letters aims at increasing the confidence in proxy-based temperature estimates. Three of authors were Chris Hollis, James Crampton and Erica Crouch – all of GNS Science.
The scientists revisited the assumptions that underlie the various proxy measurements and temperature equations. One of the proxy techniques is the measurement of oxygen isotope ratios in fossil sea shells.
By adjusting the calibration of the techniques, they were able to make the proxy techniques more accurate and reliable. This is seen as a significant development and it is hoped that it will lead to an improved understanding of greenhouse climate dynamics and the development of a climate history for the Cenozoic era - the last 65 million years.