Antarctica was once covered with tropical forests. Now researchers have fully charted the slow transition from tropical paradise to icy wasteland, thanks to a single marine sediment core.

The core shows for the first time that temperate forests were a key transitional stage before falling temperatures turned the continent into a white wasteland.

The core was taken from the sea floor off Wilkes Land in East Antarctica as part of the Integrated Ocean Drilling Programme. Pollen grains found inside show how vegetation on the continent changed between the early Eocene, around 54 million years ago and into the Miocene, 12 million years ago.

“The core from Wilkes Land is the first to give the entire story from the Eocene all the way through,” says Ulrich Salzmann of Northumbria University in Newcastle upon Tyne, UK, who presented preliminary results at the European Geosciences Union meeting in Vienna last month. “It seems that vegetation had disappeared completely by 12 million years ago.”

Vanishing monkey puzzles

The core’s story starts in much warmer climes, around 16 °C, in the Eocene between 53.8 and 47.9 million years ago. Back then, the climate was subtropical, the verdant landscape dominated by palms and trees such the monkey puzzle.

By the early Oligocene around 31 to 33 million years ago, the palms and monkey puzzles had disappeared. They gave way to more temperate species, including Huon pines, trees known as living fossils that still thrive in New Zealand and Tasmania today.

Podocarpus conifers began to abound, as did Nothofagus, or southern beeches, which are also still common in New Zealand and Tasmania.

For trees, the transition from the Oligocene to the Miocene 23 million years back was the beginning of the end. Podocarpus trees and southern beeches remained, but their territory was increasingly being invaded by mosses and other plants that are the hallmarks of tundra. The temperatures dropped to around 6°C by this period.

Tundra takeover

“Tundra starts to take over,” says Salzmann. “The vegetation moves down to the lowlands and the tundra becomes dominant. The landscape became very similar to that seen today in Tierra del Fuego in Patagonia.”

But the end for all greenery came around 12.5 million years ago, when even the tundra disappeared. “Then, the glaciers took over and turned Antarctica into a white desert,” says Salzmann. “Wilkes Land must have been the last refuge of woody vegetation.”

“It’s a super-exciting find, and opens the door to this new look at Earth’s history in the Antarctic,” says Jörg Pross, a paleoclimatologist at the University of Heidelberg in Germany. “Obviously, this is particularly important in light of anthropogenic climate change, with Antarctica warming up quickly and its ice sheets becoming potentially unstable.”

But he says that even though Salzmann’s core is a great start, it is like trying to use a single core from Europe to say what the entire climate was like, from southern Spain up to Norway. “To get a grip of what happened, more drill cores around Antarctica are needed,” says Pross.

Source: New Scientist