Fossil evidence of an ancient rainforest has recently been discovered in West Antarctica. A thriving temperate rainforest grew in West Antarctica about 90 million years ago, according to a new study, based on newly discovered fossil roots, pollen and spores.
The world was different then. In the mid-Cretaceous period (145 to 65 million years ago), dinosaurs roamed the Earth and sea levels were 558 feet (170 meters) higher than they are today. Sea surface temperatures in the tropics reached 95 degrees Fahrenheit (35 degrees Celsius).
This scorching climate allowed tropical forests similar to those seen in New Zealand today to take root in Antarctica, the researchers say.
The remains of a tropical forest were discovered beneath the ice in a sediment core collected from the seafloor near Pine Island Glacier in West Antarctica by a team of international researchers in 2017.
As soon as the team saw the core, they knew there was something unusual. The layer, which formed about 90 million years ago, was a different color. “It was clearly different from the layers above it,” study leader Johann Klages, a geologist at the Alfred Wegener Helmholtz Center for Polar and Marine Research in Bremerhaven, Germany, said in a statement.
Back in the lab, the team placed the core in a CT (computed tomography) scanner. The resulting digital images showed a dense network of roots throughout the soil layer. Ancient pollen, spores, and remains of flowering plants from the Cretaceous period were also found in the dirt.
The operator on the Polarstern vessel controls the MeBo seabed drilling system using remote technology. JP Klages/AWI
By analyzing pollen and spores, study co-author Ulrich Salzmann, a paleoecologist at Northumbria University in England, was able to reconstruct the vegetation and climate of West Antarctica 90 million years ago. “Abundant plant remains indicate that the coast of West Antarctica at that time was a dense, temperate, swampy forest, similar to the forests found in New Zealand today,” Salzmann said in a statement.
Sediment cores show that during the mid-Cretaceous, West Antarctica had a mild climate with average annual air temperatures of about 54 F (12 C), similar to the temperature in Seattle. Summer temperatures were warmer, averaging 66 F (19 C). In rivers and swamps, water could reach 68 F (20 C).
In addition, the researchers found that rainfall at the time was comparable to rainfall in Wales (England) today.
These temperatures are impressively warm, given that Antarctica experienced four months of polar night, meaning it was without life-giving sunlight for a third of each year. But the world was warmer then, in part because atmospheric carbon dioxide levels were high — higher than previously thought, according to sediment core analysis, the researchers say.
“Before our study, the general assumption was that global carbon dioxide concentrations in the Cretaceous were around 1,000 ppm (parts per million),” study co-author Gerrit Lohmann, a climate modeler at the Alfred Wegener Institute, said in a statement. “But in our model experiments, concentration levels of 1,120 to 1,680 ppm were needed to reach the average temperatures of that time in Antarctica.”
The findings show how powerful greenhouse gases like carbon dioxide can cause temperatures to soar, so much so that today’s freezing West Antarctica was once home to a tropical rainforest. What’s more, it shows how important the cooling effects of modern ice sheets are, the researchers say.
Fossils from the lush rainforests of the South Pole, dating back 53 million years, have been discovered in Tasmania. Fifty million years ago, lush rainforests covered what is now Antarctica, Australia, New Zealand and the tip of South America. Now, researchers have discovered new fossils that show what kinds of plants lived in these forests and how they adapted to life near the South Pole.
Recent excavations in western Tasmania have uncovered a number of plant fossils, including the remains of two previously unknown conifer species that were part of a 53-million-year-old ‘polar forest’.
According to a study published August 27 in the American Journal of Botany, the forest flourished during the Eocene Epoch (56 to 33.9 million years ago), when the average surface temperature of the Earth was 80 degrees Fahrenheit (27 degrees Celsius) and the southern continents formed one giant land mass around the South Pole.
“This discovery provides a rare glimpse into a time when global temperatures were much warmer than they are today,” study author Miriam Slodownik, a paleobotanist and recent doctoral graduate from the University of Adelaide in Australia, said in a statement. “Tasmania was much closer to the South Pole, but the warm global climate allowed lush forests to thrive in these regions.”
Plant fossils discovered near Macquarie Harbour in western Tasmania Wiley Periodicals LLC
Global temperatures rose sharply during the Early Eocene Climate Optimum (53-49 million years ago), the period before Australia separated from Antarctica between 45 and 35 million years ago. New fossils discovered near Macquarie Harbour in Tasmania show that tropical plants from the polar forest moved north as the continents drifted apart, seeding the rainforests that exist to this day.
The researchers dug up more than 400 plant fossils and analyzed them in the lab using advanced microscopes and ultraviolet photography. These techniques revealed well-preserved leaves and cellular structures that helped the team identify 12 different plant species. Most of them were ancestors of flora that are still found in Australia, New Zealand and South America, according to the statement. The three landmasses remained connected after the breakup of the ancient supercontinent Gondwana and remained so until at least 49 million years ago.
Of the 12 species, at least nine were conifers, according to the study. “The most impressive fossils are relatives of the kauri (Agathis), bunja (Araucaria bidwillii) and Wollemi (Wollemia nobilis) pines, which provide clues about the evolution of these iconic Australian trees,” Slodownik said.
The researchers, working with the Tasmanian Aboriginal Centre, also identified ferns, a cycad and two new extinct tree species, which they named Podocarpus paralungatikensis and Araucaria timkarikensis. According to the statement, “Paralungatik” is the original name of Macquarie Harbour, and “Timkarik” is the Aboriginal name for the surrounding area in Tasmania.
The analysis showed that ancient plants adapted to a polar environment that 53 million years ago experienced the same extreme seasonal light regimes as today. Plants evolved large leaves to maximize light absorption in the summer and deciduousness to conserve resources in low-light conditions in the winter, according to the study.
“The analysis showed how these plants adapted and thrived in the warm, ice-free conditions of the Southern Hemisphere, even with extreme seasonal changes near the Arctic Circle,” Slodownik said.
But the new fossils reveal details of even larger changes. “These plants tell a story of big climate changes and shifting tectonic plates over millions of years,” Soldovnik said.
Scientists suggest that a decrease in atmospheric CO2 levels would be accompanied by a cooling of the global climate, and would likely push the Earth to a threshold and allow ice sheets to form.
The Antarctic continent also likely experienced local cooling due to plate tectonics. Around this time, South America and Antarctica finally separated, opening what is now called the Drake Passage.
“This has created what we call a circumpolar current, which is water moving around Antarctica in a circle,” Wolf said. “This isolates Antarctica from the rest of the world and makes it much more difficult for warm air to pass through the Southern Ocean, and therefore makes Antarctica colder.”
He added that plate tectonics also directly affects carbon dioxide levels. Rock weathering and volcanic activity are part of the carbon cycle, so over thousands of years, geological processes can shift the balance of gases in the atmosphere.
While some uncertainty remains, researchers are fairly confident about this transition 34 million years ago, thanks to chemical signatures in sedimentary rocks. Oxygen atoms come in two forms: oxygen-16 (normal oxygen) and oxygen-18 (heavy oxygen). Continental ice contains a higher proportion of the lighter oxygen-16, meaning the oceans — and therefore the shells of small sea creatures — contain a higher percentage of oxygen-18 when ice sheets are larger.
“When you look at oxygen isotopes in the carbonate shells of small sea creatures in ocean sediments, you see a jump around 34 million years ago that people think is due to the lighter oxygen isotope moving to the continent of Antarctica,” Wolf explained.
As for whether Antarctica could ever become ice-free again, “It’s definitely possible,” van de Flirdt said. “Planet Earth has done it before. Planet Earth can do it again.” While it’s unlikely that human activity will cause the ice sheet to melt completely, it’s important that we do everything we can to limit ice loss in Antarctica now, she added. “It’s in our hands to avoid the worst-case scenario,” van de Flirdt said.
