90 million years ago, Antarctica had a temperate forest just 900 kilometers from the South Pole despite months of darkness. 90 million years later, scientists found its roots, pollen and spores preserved in seafloor sediment beneath today's frozen continent

Today, much of Antarctica is covered by ice. But roughly 90 million years ago, a very different landscape existed near the South Pole. Scientists found evidence of a temperate rainforest growing in what is now West Antarctica, despite the region being close to the pole and experiencing months of darkness each year, as per a report.

What makes the discovery especially striking is what survived. Inside a sediment core recovered from the seabed off West Antarctica, researchers found a dense network of fossil roots preserved in ancient soil, along with pollen and spores from the vegetation that once grew there, as per a Science Blog report.

The evidence shows that this was not simply pollen carried into Antarctica from a warmer region. The roots remained embedded in the soil, preserving the structure of plants that had actually grown there.

Scientists found the ancient forest beneath the sea

The evidence came from sediment core PS104_20-2, recovered during a 2017 expedition aboard the German research icebreaker Polarstern.

The drill reached the seabed in the Amundsen Sea near the Pine Island and Thwaites glaciers, in water almost a kilometre deep.

When researchers examined an unusual section of the core using X-ray computed tomography, they found an intact network of roots running through fine-grained soil.

Microscopic analysis revealed abundant pollen and spores. Chemical indicators preserved in the sediment provided additional information about the climate in which the vegetation had grown.

The findings were reported in a 2020 paper in Nature.

The core dates to the Turonian-Santonian interval, between about 92 and 83 million years ago. The plant remains were consistent with a temperate lowland rainforest at a palaeolatitude near 82 degrees south.

The core represents one location and period rather than a complete picture of Antarctica's ancient environment. But the combination of roots, soil, pollen, spores and organic temperature markers gives researchers several lines of evidence for reconstructing the landscape.

Antarctica was warm despite being near the South Pole

The reconstructed climate was dramatically different from modern Antarctica. Researchers estimated a mean annual air temperature of about 12 degrees Celsius. Summer temperatures averaged around 19 degrees, while river and swamp water reached roughly 20 degrees.

Estimated precipitation was similar to modern Wales.

The vegetation included conifers, ferns and other plants associated with a temperate rainforest environment. Yet the forest existed under an extreme seasonal light cycle.

For about four months each year, the Sun did not rise. That meant plants experienced a productive summer followed by a prolonged period of darkness unlike anything experienced by modern temperate rainforests.

The core cannot show exactly how the vegetation adapted to this extreme seasonal light cycle. What it does preserve is evidence of a forest growing under those conditions.

The forest was not a tropical rainforest

The evidence does not suggest that a tropical rainforest once grew beside the South Pole.

The environment was a temperate rainforest: dense and wet, with conifers, ferns and other vegetation growing in swampy conditions. The distinction matters because Antarctica's ecosystem at the time belonged to a very different world.

Flowering plants were diversifying during the Cretaceous, while conifers and ferns remained important. Antarctica was also positioned differently within Gondwana, ocean circulation differed from today and global sea levels were much higher, as per the Science Blog report.

The ancient forest was therefore not a modern ecosystem transplanted to the pole. It was an ecosystem shaped by Cretaceous conditions.

Climate models point to a very different Antarctica

The 2020 study also used climate modelling to investigate the conditions needed to reproduce the warmth reconstructed from the sediment.

The models found that the Antarctic climate could be reproduced with a vegetated continent without a major ice sheet and atmospheric carbon dioxide concentrations between about 1,120 and 1,680 parts per million.

Those figures come from climate modelling and remain subject to uncertainty, as do estimates of Cretaceous carbon dioxide. But the modelling illustrates how different Antarctica's climate was from the cold, ice-covered landscape that exists today, as per the report.

A small piece of amber added another clue

The same core later produced another piece of evidence about the ancient forest.

In a 2024 paper published in Antarctic Science, researchers described tiny fragments of amber extracted from a layer of lignite. The material was named Pine Island amber after the region where the core was recovered. Amber begins as tree resin, so its presence provides evidence that resin-producing trees lived in the area.

The fragments were tiny, measuring about a millimetre before preparation. They did not contain a spectacular trapped insect, but some appeared to preserve possible remnants of tree bark and signs of resin flow associated with damage.

Researchers are still studying the material to determine what microscopic traces it might contain, as per the Science Blog report.