Before the ice, Antarctica had a rainforest near South Pole: Fossils reveal a 90-million-year-old secret

Antarctica was once home to a rainforest, with vegetation growing near the South Pole about 90 million years ago despite months of darkness each year, as per aa TOI report. Evidence preserved in a seabed sediment core, including fossilised roots, pollen and spores, shows that the continent supported a wet, temperate ecosystem long before it became dominated by its vast ice sheet.

Climate evidence suggests the ancient forest experienced an average annual temperature of around 12°C. Later analysis of the same core also identified tiny fragments of amber, providing further evidence that resin-producing trees once grew in the region.

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Fossil roots provide evidence of ancient Antarctic forest

The sediment core was collected during a 2017 expedition aboard the German research icebreaker Polarstern in the Amundsen Sea, near the Pine Island and Thwaites glaciers. Drilling was conducted in waters almost a kilometre deep.

Scientists found an unusual layer containing ancient soil and a network of fossilised roots. X-ray computed tomography was used to examine the root structures, while microscopic analysis revealed substantial quantities of pollen and spores.

The roots provide particularly strong evidence that vegetation grew at the site because they developed within the soil where the plants lived. Pollen and spores, by contrast, can be carried elsewhere by wind and water.

Researchers combined the fossilised roots and plant remains with soil and chemical evidence to reconstruct a wet, forested environment during the Cretaceous Period.

A study published in Nature, titled ‘Temperate rainforests near the South Pole during peak Cretaceous warmth’, dated the core to the Turonian-Santonian interval, approximately 92 to 83 million years ago. The evidence indicated that a lowland temperate rainforest existed at a palaeolatitude of about 82 degrees south.

Forest survived months without sunlight

The forest’s location made its survival particularly unusual. Being close to the South Pole, the region would have experienced several months each year when the Sun remained below the horizon.

Despite the prolonged polar darkness, the vegetation persisted through repeated cycles of winter darkness and summer growth.

The reconstructed environment was considerably warmer than present-day Antarctica. Scientists estimated the mean annual air temperature at around 12°C, while summer temperatures may have averaged about 19°C. Water in rivers and swamps could have reached approximately 20°C.

Researchers described the ecosystem as a temperate rainforest rather than a tropical forest because it combined high moisture levels with a relatively cool climate and extreme seasonal variations in daylight.

Higher carbon dioxide linked to warmer conditions

Climate modelling conducted as part of the research indicated that the Antarctic conditions would have been difficult to reproduce without a largely ice-free continent and atmospheric carbon dioxide concentrations considerably higher than those recorded before modern industrialisation.

The simulations generated plausible conditions with carbon dioxide concentrations ranging from approximately 1,120 to 1,680 parts per million. These figures are model-dependent, and scientists cannot directly measure ancient atmospheric carbon dioxide in the same way as modern instruments.

The absence of a major continental ice sheet would also have influenced the climate. Ice reflects incoming sunlight, while its disappearance can change the surface heat balance. Ocean circulation and atmospheric conditions would have further affected how heat was distributed around Antarctica.

Amber provides another clue about ancient trees

The same core yielded additional evidence in 2024, when scientists reported tiny pieces of amber from a layer containing lignite, a form of coal produced from compressed plant material.

The amber was reportedly named Pine Island amber after the region where the core was collected. Because amber originates as tree resin, its presence provides another indication that resin-producing trees grew there.

The fragments measured around a millimetre before preparation. Some appeared to preserve possible traces of bark, while other features were consistent with resin flowing from damaged parts of a tree.

Researchers are continuing to examine the material because amber can sometimes preserve microscopic biological remains.

Sediment core preserves vanished Antarctic landscape

The ancient soil and fossilised root network provide a direct record of vegetation growing at the location represented by the core. Pollen and spores offer additional clues about the wider plant community, while chemical evidence helps scientists reconstruct the environmental conditions.

Over millions of years, the ancient soil was buried beneath layers of sediment. Geological processes eventually transformed material that had once formed on land into part of the seabed.

The sediment core therefore preserves traces of an ecosystem that existed tens of millions of years before modern Antarctica became dominated by its vast ice sheet. Together, the roots, pollen, spores and amber offer a detailed glimpse of a forest that once grew near the South Pole.