Geologists digging into West Antarctica’s vast ice sheet have discovered the remains of an ancient river system that once flowed nearly a thousand miles.
The discovery offers a glimpse into Earth’s history and indicates how extreme climate change could change the planet, according to their findings, published June 5 in the journal Science Advances.
“When we think about potentially severe climate change in the future, we need to learn from periods in Earth’s history when this was already happening,” says Johann Klages, co-author of the study and sedimentologist at the Alfred Wegener Institute Helmholtz Center for Polar and Marine. Research in Germany, LiveScience told.
Between 34 million and 44 million years ago, an epoch known as the middle to late Eocene, Earth’s atmosphere changed dramatically. As carbon dioxide levels plummeted, global cooling caused the formation of glaciers on an ice-free Earth.
Scientists are interested in investigating how this major climate event occurred in Antarctica, especially as carbon dioxide levels on Earth continue to rise due to human-induced 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 predicted in about 150 to 200 years if greenhouse gas levels continue to rise, Klages said.
But uncovering the past has proven to be a challenge. Most of West Antarctica is covered in ice today, making it difficult to access sedimentary rocks, which are critical for studying early environments. Geologists often rely on the types of grains, minerals, and fossils trapped in these sediments to determine the conditions that characterize an area.
In 2017, Klages and other scientists aboard the research vessel Polarstern traveled from the southernmost part of Chile across the rugged Drake Passage to the western part of the icy continent. Equipped with advanced seabed drilling equipment, Klages and his team looked for cores from soft sediments and hard rocks in the frozen seabed.
After drilling almost 30 meters into the seabed, the researchers retrieved sediments with layers from two different periods.
By calculating the half-life of radioactive elements, such as the ratio of uranium and lead in the sediment, they found that the lower part of the sediment was formed during the mid-19th century.Cretaceous period, about 85 million years ago. This sediment contained fossils, spores and pollen typical of a temperate rainforest that existed at the time. The upper part of the sediment contained mainly sand from the middle to late Eocene, about 30 million to 40 million years ago.
Upon closer inspection, they recognized a highly layered pattern in the Eocene sand layer that resembled that from a river delta, very similar to something you would encounter in the Mississippi or Rio Grande Rivers, Klages said.
The scientists conducted a lipid biomarker analysis, quantifying the amount of lipids and sugar in the sediment, and found a unique molecule common in cyanobacteria living in freshwater. The find confirmed their suspicion that an ancient river once meandered across the continent.
The researchers traced the Eocene grains to a distinct salt zone in the Transantarctic Mountains, crossing an area that stretched about 1,500 kilometers before emptying into the Amundsen Sea.
“This is exciting – just having the exciting image in your brain that there was a gigantic river system flowing through Antarctica that is now covered in miles of ice,” Klages said.
Klages and his team are now analyzing parts of the core sediments that belong to a more recent Oligocene-Miocene period, about 23 million years ago. That will help refine models to better predict future climate.