This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A journey back in time to the Late Cretaceous: A swampy rainforest with conifers and tree ferns stretches as far as the eye can see, dinosaurs roam through the misty wetlands, and the climate is mild and warm. The average annual temperature is 12°C (54°F)—around two degrees higher than in present-day Germany.
There is plenty of water, too, as dry periods are regularly followed by monsoon-like rainy seasons. Just one thing seems unusual: For around four months of the year, the forest is shrouded in continuous darkness. This is because the ecosystem described here lies close to the South Pole, in what is now West Antarctica, where the polar night also occurred during the Late Cretaceous.
When the international team led by marine geologist Dr. Johann Klages of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), published the results of a Polarstern expedition in Nature in 2020, the discovery caused quite a stir. "In a sediment core from the Amundsen Sea in West Antarctica, we found an extremely well-preserved forest soil dating back around 90 million years, containing abundant pollen and spores and a dense network of roots," Klages explains.
"During the Cretaceous, tectonic conditions meant that this temperate rainforest lay even farther south, just 900 kilometers (560 miles) from the South Pole. Today, average annual temperatures at this location are around -30°C (-22°F), and everything is covered by an ice sheet several kilometers thick. Our discovery showed that during the warmest period of the Cretaceous, when atmospheric CO₂ levels were four to six times higher than today, a relatively warm and humid climate prevailed—even close to the South Pole." The researchers have now followed up with a new study in Communications Earth & Environment.
Klages, co-first author of the study, notes: "We took another very close look at the core using a different range of methods and found clear evidence of recurring wildfires. The sediments recovered contain evidence of the southernmost wildfires ever recorded on Earth." Throughout the Late Cretaceous section of the core, the team found microscopic charcoal particles that became increasingly abundant in the younger sediments. Analysis of the particles showed that mainly soft conifer wood had burned at relatively low temperatures, as is typical of surface fires that do not spread through the entire forest canopy.
Further evidence of fire came from amber—fossilized tree resin—which appears to have formed a kind of protective seal over fire-damaged areas of tree trunks. Finally, countless spores of peat moss (genus: Sphagnum) provided evidence of the earliest raised bogs, the formation of which was closely linked to the occurrence of recurring fires. From these clues, the researchers were able to develop a scenario that may also be highly relevant today.
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