Geologists excavating the massive ice sheet in West Antarctica have discovered the remains of an ancient river system that once flowed nearly 1,000 miles.
The findings, published June 5 in the journal Science Advances, offer a glimpse into Earth’s history and suggest how extreme climate changes could alter the planet.
“If we want to think about possible severe climate change in the future, we need to learn from events that have already happened in Earth’s history,” Johan Klages, a sedimentologist at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research in Germany and co-author of the study, told Live Science.
Between 34 and 44 million years ago, during a period known as the Middle to Late Eocene, Earth’s atmosphere changed dramatically: Carbon dioxide levels dropped suddenly, causing global cooling and the formation of glaciers on an ice-free planet.
Scientists are interested in investigating how this massive climate event occurred in Antarctica as global carbon dioxide levels continue to rise due to human-induced climate change. During the Late Eocene, there was nearly twice as much carbon dioxide as there is today. But if greenhouse gas levels continue to rise, they could be as high as predicted in about 150 to 200 years, Klages said.
But uncovering the past has proven difficult. Today, much of West Antarctica is covered in ice, making it hard to access the sedimentary rocks important for studying early environments. Geologists often work out the conditions characteristic of the region based on the types of particles, minerals and fossils trapped within these sediments.
In 2017, Klages and other scientists boarded the research vessel Polarstern and sailed from the southernmost tip of Chile across the rugged Drake Passage to the icy western part of the continent. Equipped with a state-of-the-art ocean-drilling rig, Klages and his team began the task of extracting cores from the soft sediments and hard rocks of the frozen ocean floor.
Using cutting-edge drilling equipment, researchers aboard the research vessel Polarstern have discovered an ancient river in West Antarctica that existed 40 million years ago. (Image credit: Karsten Gaul)
After drilling about 100 feet (30 meters) into the seafloor, the researchers recovered sediments made up of layers from two different eras.
By calculating the half-lives of radioactive elements, such as the ratio of uranium to lead in the sediments, they determined that the lower part of the sediments formed during the Mid-Cretaceous Period, about 85 million years ago. The sediments contain fossils, spores and pollen characteristic of a temperate rainforest that existed at that time. The upper part of the sediments contains mainly sand from the Middle to Late Eocene, about 30 to 40 million years ago.
Upon closer inspection, the Eocene sands showed a strong layering pattern that came from a river delta and was very similar to that seen in the Mississippi and Rio Grande rivers, Klages said.
The scientists performed lipid biomarker analysis to quantify the amount of lipids and sugars in the sediments and found specific molecules commonly found in freshwater cyanobacteria, which supported their speculation that ancient rivers once meandered through the continent.
The researchers tracked the Eocene particles to a unique salt region in the Transantarctic Mountains, where they crossed a region of about 930 miles (1,500 kilometers) before flowing into the Amundsen Sea.
“Just imagining the exciting image of a huge river system that flows through Antarctica, now covered by kilometers of ice, is thrilling,” Klages said.
Klages and his team are now analyzing some of the core sediments, dating to the more recent Oligocene-Miocene epochs, about 23 million years ago, which will help refine models to more accurately predict future climate.
