A sediment core preserves evidence of a temperate rainforest near the West Antarctic coast roughly 90 million years ago.
A sediment core recovered from the Amundsen Sea preserves roots, pollen and spores from a temperate rainforest near the West Antarctic coast roughly 90 million years ago. Published in 2020, the study reconstructs conditions at that ancient site; it does not establish that forests covered the whole continent.
The mid-Cretaceous was a period of high global temperatures. The study examines how a forest could have grown so close to the South Pole.
An ancient Antarctic Rainforest
In 2017, during an expedition aboard the RV Polarstern in the Amundsen Sea, researchers drilled the surface under West Antarctica’s seabed, near Pine Island and the Thwaites glaciers. The ancient forest site lay about 900 kilometres from the South Pole at the time the sediment formed.
What they extracted, particularly from a depth of 30 meters, contrasted sharply with the composition of the sediments on the rest of the surface. “During onboard assessments, the unusual coloration of the sediment layer quickly caught our attention,” explained geologist Johann Klages of the Helmholtz Center for Polar and Marine Research at the Wegener Institute in Germany.
As revealed by the researchers, the first analysis pointed towards the fact that at a depth of between 27 and 30 meters from the ocean floor, they had found a layer that was originally on land, not under the ocean.
The core gave researchers a rare record of conditions in Cretaceous Antarctica.
The studies showed an intricate network of fossilized plant roots back on land. Microscopic studies also found evidence of pollen and spores, pointing to the preserved remains of a temperate rainforest that existed in Antarctica approximately 90 million years ago, eons before the landscape was transformed into an icy desert.
The numerous plant remains indicate that the West Antarctic coast was, at the time, a swampy temperate rainforest, similar to those that currently exist in New Zealand. The forest grew despite a polar night that kept the site dark for about four months each year.
To find out more about life in Antarctica millions of years ago, the researchers used plant remains and chemical indicators in the soil to reconstruct the local climate.
The researchers used the reconstructed temperatures and vegetation to test climate simulations. Their model reproduced the conditions with high atmospheric carbon dioxide, dense Antarctic vegetation and no large Antarctic ice sheet. That continent-scale vegetation is a model condition, distinct from the forest remains observed in the core.
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