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article imageAntarctica was home to a rainforest 90 million years ago

By Karen Graham     Apr 5, 2020 in Science
The South Pole is surrounded by a harsh, frozen landscape of year-round ice and snow — but it hasn't always been this way. Imagine Antarctica as being home to an ancient, swampy rainforest full of diverse animal and plant life.
A team of researchers led by geoscientists from the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research in Germany and scientists from Imperial College London, UK. have discovered fossil soil dating to the mid-Cretaceous Period, about 90 million years ago, suggesting that the climate was exceptionally warm at the time.
Their analysis of the preserved roots, pollen, and spores show that dense concentrations of atmospheric CO2 would have created much hotter global temperatures, melting polar ice sheets, and sending sea levels soaring to up to 170 meters (558 feet) higher than they are today. Their work was published in the journal Nature on April 1, 2020.
Co-author Professor Tina van de Flierdt, from the Department of Earth Science & Engineering at Imperial, said, per Science Daily: "The preservation of this 90-million-year-old forest is exceptional, but even more surprising is the world it reveals. 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."
FS Polarstern in front of a mighty iceberg in Inner Pine Island Bay  West Antarctica.
FS Polarstern in front of a mighty iceberg in Inner Pine Island Bay, West Antarctica.
JP Klages, Alfred Wegener Institute
Attention-grabbing sediment layer
During an expedition in 2017, aboard the RV Polarstern in the Amundsen Sea, researchers drilled deep underneath the seabed of West Antarctica, close to the location of the Pine Island and Thwaites glaciers, and only about 900 kilometers (560 miles) away from the South Pole.
What they pulled up from a depth of about 30 meters "quickly caught our attention. It clearly differed from the layers above it," lead author Dr. Johann Klages, a geologist at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research in Germany, said in a press release.
"The first analyses indicated that, at a depth of 27 to 30 meters (88 to 98 ft) below the ocean floor, we had found a layer originally formed on land, not in the ocean."
First author Dr. Johann P. Klages (AWI) and co-author Prof. Dr. Tina van de Flierdt (Imperial Colleg...
First author Dr. Johann P. Klages (AWI) and co-author Prof. Dr. Tina van de Flierdt (Imperial College London) try to remove heavily solidified sediment from the MeBo core catchers.
Thomas Ronge; Alfred Wegener Institute
No one has ever pulled a Cretaceous Period sample out of the ground from such a southern point on the planet before - but the research team was not prepared for what they would find out after a further examination of the sediment was done with X-ray computed tomography (CT) scans.
Back on land, the CT Scans revealed soil that was so well-preserved that it still contained traces of pollen, spores, and remnants of flowering plants. Even intact individual cell structures could be observed. This all pointed to the preserved remains of an ancient rainforest that existed in Antarctica approximately 90 million years ago.
"The numerous plant remains indicate that the coast of West Antarctica was, back then, a dense temperate, swampy forest, with many conifers and tree ferns similar to the forests found in New Zealand today," says palaeoecologist Ulrich Salzmann from Northumbria University in the UK.
Station meeting of geologists and geophysicists in the sounder center of the FS Polarstern.
Station meeting of geologists and geophysicists in the sounder center of the FS Polarstern.
JP Klages, Alfred Wegener Institute
An interesting reason for the unprecedented find
So how could it have been possible for a rainforest to grow and thrive at the South Pole? We do know that the mid-Cretaceous was the heyday of the dinosaurs - but was also the Earth's warmest period in the past 140 million years, with ocean temperatures thought to be as high as 95 degrees Fahrenheit.
Then, as now, the South Pole would have been subjected to four months of unyielding darkness during the Antarctic winter. How could this ancient rainforest thrive, deprived of the Sun for so long? Based on biological and geochemical data contained in the soil sample, researchers used modeling to reconstruct what the ancient climate of this long-gone forest region might have been like.
They found out that atmospheric CO2 levels would have needed to be significantly higher than scientists realized. It was a super-heated environment, with an average air temperature of around 12 degrees Celsius or 54 degrees Fahrenheit in the Antarctic.
"Before our study, the general assumption was that the global carbon dioxide concentration in the Cretaceous was roughly 1,000 parts per million (ppm)," explains geoscientist Torsten Bickert from the University of Bremen in Germany. "But in our model-based experiments, it took concentration levels of 1,120 to 1,680 ppm to reach the average temperatures back then in the Antarctic."
There is still one big question to be answered: If Antarctica used to be so warm, what caused it to dramatically cool, asks CBS News, allowing the formation of ice sheets? According to co-author and AWI climate modeler Dr. Gerrit Lohmann, in all of their climate simulations, researchers were "unable to find a satisfactory answer."
More about Antarctica, Rainforest, cretaceous period, carbon dioxide levels, lack of glaciation
 
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