Geologists digging into the massive West Antarctic ice sheet have uncovered the remains of an ancient river system that once flowed for nearly a thousand miles.
The discovery provides a glimpse into Earth’s history and hints at how extreme climate change could alter the planet, according to their findings, published June 5 in the journal Science Advances.
“If we think about potentially severe climate change in the future, we need to learn from the periods of Earth’s history where this has already happened,” Johann Klages, co-author of the study and a sedimentologist at the Alfred Wegener Helmholtz Center for Polar and Marine Institute. Research in Germany, told Live Science.
Between 34 million and 44 million years ago, an epoch known as the middle and late Eocene, Earth’s atmosphere was drastically transformed. As carbon dioxide levels fell, global cooling caused glaciers to form on an ice-free Earth.
Scientists are interested in investigating how this major climate event unfolded in Antarctica, especially as Earth’s carbon dioxide levels continue to rise due to human-caused climate change. The amount of carbon dioxide during the late Eocene was almost double the amount we have today. However, it could be similar to levels projected in about 150 to 200 years if greenhouse gas levels continue to rise, Klages said.
But uncovering the past has proved challenging. Most of West Antarctica today is covered in ice, making access to sedimentary rocks, which are critical for studying early environments, difficult. Geologists often rely on the type of grains, minerals, and fossils trapped within these sediments to determine the type of conditions that characterize an area.
In 2017, Klages and other scientists aboard the expedition research vessel Polarstern traversed from the southernmost tip of Chile, through the rugged Drake Passage and into the western part of the icy continent. Equipped with advanced seabed drilling equipment, Klages and his team set out to collect cores from the soft sediments and hard rocks within the frozen seabed.
After drilling about 100 feet (30 meters) into the sea floor, the researchers found layered sediments from two different periods.
By calculating the half-lives of radioactive elements, such as the ratio of uranium to lead in the sediment, they found that the lower part of the sediment formed during the middleCreative period, about 85 million years ago. This sediment contained fossils, spores and pollen characteristic of a temperate rainforest that existed at that time. The upper part of the sediment contained mainly sand from the middle to late Eocene epoch, about 30 million to 40 million years ago.
Upon closer inspection, they recognized a strongly layered pattern in the Eocene sand layer that resembled those coming from a river delta, very similar to something one would encounter in the Mississippi River or the Rio Grande, Klages said.
The scientists performed a lipid biomarker analysis, in which they quantified lipids and sugar in the sediment, and found a unique molecule commonly found in cyanobacteria that live in freshwater. The discovery confirmed their suspicions that an ancient river once meandered through the continent.
The researchers traced the Eocene grains to a distinct salt region in the Transantarctic Mountains, traversing an area that stretched about 930 miles (1,500 kilometers) before draining into the Amundsen Sea.
“That’s exciting — just having this exciting image in your mind that there’s this giant river system that flows through Antarctica that’s now covered by kilometers of ice,” Klages said.
Klages and his team are now analyzing core sediment pieces that date back to a more recent Oligocene-Miocene period, about 23 million years ago. This will help refine models to better predict future climate.