Uncovering an ancient Antarctic rainforest

New research indicates that the icy continent was once home to a temperate rainforest, Shruti Sundaresan reports.

An artist’s impression of the temperate rainforest now known to have existed in West Antarctica during the Cretaceous period. Image credit: J. McKay/Alfred-Wegener-Institut.

When one speaks of Antarctica, we tend to automatically think of snow, ice, glaciers and penguins. However, research shows that the icy continent once had quite a temperate-rainforest-like climate!.

The study was carried out by an international team of researchers, led by geoscientists from the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research in Germany and scientists from the Imperial College of London.

In 2017, the team drilled a narrow hole into the seabed, near the Pine Island and Thwaites glaciers in west Antarctica – around 2000km from what we know now as the south pole. 

On drilling the seabed using a remotely operated rig, the initial few metres showed glacial sediments, followed by sandstone. However, this discovery was not of much interest to the team. As they progressed with the drilling, a giant moving glacier approached them. It posed a grave danger to the expedition. Dr Johann Klages of the Alfred Wegener Institute and the team decided to dig for a few more metres before evacuating the core site. And that’s when they hit the jackpot: a section of the core caught the attention of the researchers with its eye-catching colour. 

The discovered forest soil was CT scanned and dated back to the Cretaceous period, around 90 million years ago. In order to reconstruct the environment of the forest, the team analysed the temperature and precipitation indicators within the sample.

The soil included samples of fossil roots, spores and pollen that indicated that the atmosphere in Antarctica had been a lot warmer than general assumption. These samples were so well preserved that individual cell structures were clearly visible. The material showed the remains of more than 65 different kinds of plant.

“The annual temperatures of the continent would have been around 12-13 degrees Celsius. The south pole, which houses darkness for four months during winter, would only possibly have such a warm atmosphere if the concentration of greenhouse gases were much higher and land surface was covered in vegetation”, said Klages, revealing the results of computer modelling.

The analysis of chemicals deposited by cyanobacteria further revealed that surface water maintained a temperature of 20 degrees Celsius. 

Professor Tina van de Flierdt, from the Department of Earth Science & Engineering at Imperial, said that the very discovery of the 90 million-year old forest sample was unbelievable, but the information it offers has further surprised them. “Even during months of darkness, swampy temperate rainforests were able to grow close to the South Pole, revealing an even warmer climate than we expected.” 

Before this study, the general assumption was that global CO2 concentration during the Cretaceous period was around 1000ppm. However, model-based experiments indicate that CO2 levels needed to be 1120 to 1680 ppm to reach the temperatures now detected in Antarctica.“This discovery is of immense importance to understand past and future climate change”, said Dr James Bendle, geoscientist from the University of Birmingham. “If we were to have an atmosphere of more than 1000 ppm of CO2, the planet would have little or no ice. Antarctica would ultimately be completely vegetated without any ice cover.” 

Written by Shruti Sundaresan and edited by Ailie McWhinnie.

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