Geologists digging into the massive ice sheet of West Antarctica 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 suggests 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 have to learn from periods in Earth’s history where it has already happened,” Johann Klages, study co-author and sedimentologist at the Alfred Wegener Helmholtz Center for Polar and Marine Research. Research in Germany, he told Live Science.
Between 34 and 44 million years ago, an epoch known as the Middle to Late Eocene, Earth’s atmosphere changed drastically. As carbon dioxide levels plummeted, global cooling triggered the formation of glaciers on an ice-free Earth.
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Scientists are interested in investigating how this major Antarctic climate event unfolded, 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. But it may resemble levels predicted in about 150 to 200 years if greenhouse gas levels continue to rise, Klages said.
But uncovering the past proved challenging. Most of present-day West Antarctica is covered in ice, making access to sedimentary rocks crucial to studying early environments difficult. Geologists often rely on the type of grains, minerals, and fossils captured in these sediments to determine the kind of conditions that characterize a given area.
In 2017, Klages and other scientists aboard the research vessel Polarstern Expedition traveled from the southernmost part of Chile through the rugged Drake Passage and into the western part of the icy continent. Equipped with modern seabed drilling equipment, Klages and his team set out to collect cores from soft sediments and hard rocks on the frozen seabed.
After drilling nearly 100 feet (30 meters) into the sea floor, the researchers recovered sediments with layers from two distinct periods.
By calculating the half-life 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 MiddleCretaceous period, about 85 million years ago. This sediment contained fossils, spores and pollen characteristic of the temperate rainforest that existed at the time. The upper part of the sediment contained mostly sand from the middle to late Eocene period, about 30 million to 40 million years ago.
Upon closer inspection, they recognized a highly stratified structure in the Eocene sand layer that resembled those from a river delta, very similar to something one would encounter in the Mississippi River or the Rio Grande, Klages said.
The researchers performed a lipid biomarker analysis in which they quantified the amount of lipids and sugar in the sediment and found a unique molecule commonly found in cyanobacteria that live in fresh water. The find confirmed their suspicion that an ancient river once wound its way through the continent.
The researchers traced the Eocene grains to a prominent salt area in the Transantarctic Mountains, which traversed an area that spanned about 1,500 kilometers before reaching the Amundsen Sea.
“It’s exciting — to have this exciting image in your brain that there’s this gigantic river system running through Antarctica that’s now covered in kilometers of ice,” Klages said.
Klages and his team are now analyzing parts of the core sediments that belong to the more recent Oligocene-Miocene period, about 23 million years ago. This will help improve models to better predict future climate.