Ancient wildfires near the South Pole shaped Earth's earliest peat bog

Wildfires raging through prehistoric rainforests helped create the earliest known peat bog near the South Pole, according to new research co-led by a Northumbria University scientist.

The study, published in Communications Earth & Environment, was co-led by Professor Ulrich Salzmann of Northumbria University, in collaboration with Dr Johann Klages of the Alfred Wegener Institute (AWI) and Professor Thorsten Bauersachs of RWTH Aachen University, working with an international team of collaborators.

Around 90 million years ago, during the Late Cretaceous period, average annual temperatures near the South Pole reached around 12°C, warm enough to support temperate rainforest despite four months of continuous winter darkness each year.

The discovery of this ancient rainforest, made by an AWI-led team drilling sediment cores from the Amundsen Sea in West Antarctica, was first published in Nature in 2020.

In this new study, the team re-examined the same sediment core using a wider range of techniques and found clear evidence of recurring wildfires, the southernmost ever recorded on Earth.

Microscopic charcoal particles, becoming more abundant in younger layers of the core, showed that mostly soft conifer wood had burned at relatively low temperatures, consistent with surface fires rather than fires that consumed the whole forest canopy.

Fire-damaged tree trunks appear to have produced amber as a protective seal, while abundant peat moss (Sphagnum) spores pointed to the formation of the earliest known raised bog of its kind, closely tied to the recurring fires.

Professor Salzmann, co-first author of the study, said: “Ninety million years ago, just 900 kilometres from the South Pole, a temperate and very swampy Antarctic rainforest with pronounced dry and monsoon seasons gradually silted up and developed into a peatland dominated by peat mosses.

“Wildfires, which became increasingly frequent, clearly played a decisive role in this process. They kept the vegetation open and enabled the development of a peat bog where ground-level smouldering fires then occurred repeatedly, similar to those that have become increasingly common in modern peatlands in recent years."

As the nearest volcanic activity at the time was at least 400 kilometres away, the study shows that lightning strikes, rather than lava or ash, were the likely ignition source for these ancient fires.

Professor Bauersachs of RWTH Aachen University said: "Peatlands play a key role in the climate system, both then and now, as highly effective long-term stores of carbon. In a warm climate, wetlands dry up more quickly and fires that prevent forest development occur more frequently. This can promote the formation of peatlands, where carbon-rich plant material accumulates over long periods."

Dr Klages of AWI added: "The Late Cretaceous was extremely warm and prone to frequent fires. We were surprised to find evidence in our core of an early Antarctic ecosystem that, in many respects, resembled today's Arctic raised bogs and also experienced regular fires."

The findings improve our understanding of how fire and peatland ecosystems interact under warm, high-CO2 conditions, insight that is increasingly relevant as modern peatlands face growing wildfire risk under climate change.

The research draws on samples collected during the RV Polarstern Expedition PS104 to the Amundsen Sea Embayment.

The paper, entitled Co-evolution of wildfires and early Sphagnum-peatlands near the Cretaceous South Pole, is published in Communications Earth & Environment.