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Evidence for a 90-million-year-old rainforest near the South Pole

Researchers have found unexpected fossil traces of a temperate rainforest near the South Pole 90 million years ago, suggesting the continent had an exceptionally warm climate in prehistoric times.

A team from the UK and Germany, which includes experts from Northumbria University’s Department of Geography and Environmental Sciences, discovered a forest soil from the Cretaceous period in the seabed near the South Pole.

Their analysis of the pristinely preserved roots, pollen and spores show that the world at that time was a lot warmer than previously thought, with rainforests in Antarctica similar to the forests we have in New Zealand today. The international team’s findings are published today as the lead story in the scientific journal Nature.

Co-author Professor Ulrich Salzmann, a palaeoecologist at Northumbria University, used the preserved pollen and spores to reconstruct the past vegetation and climate. He describes the process of reconstructing past environments and climates as similar to working on a huge jigsaw puzzle, which revealed an amazingly detailed picture of the past Antarctic landscape.

“It was particularly fascinating to see the well-preserved diverse fossil pollen and other plant remains in a sediment deposited some 90 million years ago, near the South Pole,” he said.“The numerous plant remains indicate that the coast of West Antarctica was, back then, a dense temperate, swampy forest, similar to the forests found in New Zealand today.”

When they pieced together their analyses, the international research team found evidence for a mild climate around 500 miles from the South Pole, with annual mean air temperatures of about 12 degrees Celsius. This is roughly the mean temperature of Hobart, Australia, today.

Summer temperatures averaged 19 degrees Celsius and water temperatures in rivers and swamps reached up to 20 degrees. This was despite a four-month polar night, meaning for a third of every year there was no life-giving sunlight at all. They also found that the amount and intensity of rainfall in West Antarctica was similar to that in Wales today.

Such climate conditions could only be achieved with a dense vegetation cover on the Antarctic continent and the absence of any major ice-sheets in the South Pole region, as pictured in the artists’ impression of the landscape above. Carbon dioxide concentration in the atmosphere was also far higher than previously assumed. Read more.

Sea ice-free Arctic makes permafrost vulnerable to thawing

New research published in the journal Nature provides evidence from Siberian caves on the essential role that summer sea ice in the Arctic Ocean plays in stabilising permafrost and its large store of carbon.

Permafrost is ground that remains frozen throughout the year and covers nearly a quarter of the Northern Hemisphere’s land. The frozen state of permafrost enables it to store large amounts of carbon; about twice as much as in the atmosphere. The rate and extent of future thawing of permafrost, and consequent release of its carbon, is hard to predict from modern observations alone.However, a new study has discovered a crucial past relationship between summer sea ice in the Arctic and permafrost. This has significant implications for the future as observations show Arctic sea ice has decreased in recent years.

A team of international researchers, including Dr Sebastian Breitenbach from Northumbria’s Department of Geography and Environmental Sciences, have found that times when permafrost melted in the past did not simply match up with times when the Earth was at its warmest. The new research relies on challenging fieldwork to discover and explore Siberian caves. Caves are a powerful recorder of periods when permafrost was absent in the past.

Why are caves important?

Stalagmites, stalactites and flowstones can only form when there is liquid water, and therefore do not form when overlying land is permanently frozen. The presence of stalagmites in caves under permafrosted land therefore demonstrates that there were periods when permafrost was absent in the past.

The researchers used new approaches to date the formation of stalagmites using the decay of natural uranium to lead.  This allows them to assess the timing of periods when permafrost was absent over the last one and a half million years. They found that stalagmites in Siberian caves grew intermittently from 1.5 million to 400,000 years before the present day and have not grown since, due to the overlying land being frozen.

The timing of stalagmite formation during the absence of permafrost does not relate simply to global temperatures in the past but was notably more common when the Arctic Ocean was free of summer sea-ice. The researchers say that several processes may lead to the relationship between Arctic sea-ice and permafrost. Read more.

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