During the Cretaceous period, a balmy forest grew 900 kilometres from the South Pole, according to new research that uncovered ancient spores and roots.
Millions of years ago, Earth’s atmosphere had several times more carbon dioxide than it does even today, making the Cretaceous one of the warmest periods of the planet. But scientists have few records of what Antarctica was like during this time. A recent voyage to drill beneath the continent revealed dozens of species of plants via their fossilized pollen grains and spores dating back 90 million years, in a region that was only 900 kilometres from the South Pole during that period.
“We went there with a special seafloor drill rig—that was the first time anyone could penetrate this layer of the Amundsen Sea,” study first author Johann Klages from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, told Gizmodo. “We knew it must be old and could go back to the Cretaceous, but what part and what we would find, no one really knew. We were quite astonished when the first material came up.”
The team travelled on the research icebreaker RV Polarstern in 2017 to a trough in West Antarctica’s Amundsen Sea, located at 73.54°S. Past glaciers had compacted this region’s sediment, making it difficult to penetrate. But they’d brought with them the MARUM- MeBo70 seafloor drill rig, a portable, remotely operated rig capable of drilling up to 80 metres beneath the seafloor. They needed to monitor the area using satellite images and on-board helicopters to look out for icebergs that could disrupt the drilling sessions, which could go for multiple days. Luckily, however, a treasure trove revealed itself just 30 meters (98 feet) beneath the seafloor.
Analysis of the drill samples, including CT scans, revealed at least 62 species of plants represented by fossilized pollen and spores, as well as a network of fossilized roots. The identified species include southern hemisphere conifer trees and ferns, according to the paper published today in Nature. Though the site today is deep under the ocean off the Antarctic Coast, an analysis of the tectonic activity in the area suggests it used to be at a latitude of 82°S and part of the now-sunken continent of Zealandia, whose sediment and fossils date back 90 million years.
Taken together, the work reveals that a temperate rainforest—like the kind of coniferous rainforest found in parts of New Zealand or the United States’s Pacific Northwest—existed around 900 kilometers (560 miles) from the Cretaceous-period South Pole. “We found an amazing diversity for that latitude,” said Klages.
The team then built a model to determine what temperatures would support such plant life and calculated annual average temperature of 13 degrees Celsius—a similar climate and environment to Seattle. But in order to support these temperatures in a region with four months of night, Earth would have had to have extremely high concentrations of carbon dioxide in the atmosphere, perhaps between 1,120 and 1,680 parts per million. The CO2 levels in the atmosphere today are around 415 ppm.
Dietmar Muller, a geophysics professor at the University of Sydney in Australia who reviewed the paper, told Gizmodo it was quite convincing. He thought that the most exciting advance of the paper was the implication that there was no Antarctic ice during the Cretaceous. However, he warned that such might be the fate of the world again if humans continue to pump CO2 into the atmosphere unchecked. Some models estimate that we might increase the atmospheric concentration of CO2 to 1,000 ppm by the year 2100. If so, and if all of the Antarctic ice melts, the planet could stay in a hothouse state for a very, very long time, perhaps millions of years, he said.
Klages told Gizmodo that his team hopes to continue working on models of what the Cretaceous climate would have been like in order to maintain a rainforest so far south.