Giant river system that existed 40 million years ago discovered deep below Antarctic ice

A decent sized boat floats in ocean water next to the vertical incline of an ice cliff.
A research icebreaker Polarstern in front of a giant iceberg in the Amundsen Sea. Researchers on this vessel have discovered evidence of a giant river that once ran across West Antarctica. (Image credit: Johann Klages)

Geologists digging into the massive ice sheet of West Antarctica have discovered the remains of an ancient river system that once flowed for nearly a thousand miles.

The discovery offers a glimpse into the 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 a potentially severe climate change in the future, we need to learn from periods in Earth's history where this already happened," Johann Klages, study co-author and a sedimentologist at the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research in Germany, told Live Science.

Between 34 million to 44 million years ago, an epoch known as the middle-to-late Eocene, Earth's atmosphere transformed drastically. As carbon dioxide levels plummeted, global cooling triggered the formation of glaciers on an ice-free Earth. 

Related: US Space Force satellite data shines light on mystery of Arctic warming

Scientists are interested in investigating how this major climate event unfolded in Antarctica, especially as carbon dioxide levels on Earth continue to rise due to human-caused climate change. The amount of carbon dioxide during the late Eocene period was almost double the amount we have today. However, it may be similar to levels predicted in about 150 to 200 years if levels of greenhouse gases continue to rise, Klages said.

But uncovering the past has proven challenging. Most of West Antarctica today is covered in ice, making it difficult to access sedimentary rocks, which are critical to studying early environments. Geologists often rely on the type of grains, minerals and fossils trapped within these sediments to work out the kind of conditions that characterize an area.

In 2017, Klages and other scientists onboard the research vessel Polarstern expedition traversed from the southernmost part of Chile, across the rough Drake Passage and into the western part of the icy continent. Equipped with advanced seafloor drilling equipment, Klages and his team set out to collect cores from soft sediments and hard rocks within the frozen seabed. 

Researchers aboard the research vessel "Polarstern" found an ancient river in West Antarctica that existed 40 million years ago using advanced drilling equipment. (Image credit: Karsten Gohl)

After drilling nearly 100 feet (30 meters) into the seafloor, the researchers retrieved sediments with layers from two distinct 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-Cretaceous period, about 85 million years ago. This sediment contained fossils, spores and pollens characteristic of a temperate rainforest, which existed at that time. The upper part of the sediment contained mostly sand from the mid-to-late Eocene epoch, about 30 million to 40 million years ago. 

Upon closer inspection, they recognized a strongly stratified 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 Rio Grande, Klages said.

The scientists performed a lipid biomarker analysis, in which they quantified the amount of lipid and sugar in the sediment, and found a unique molecule commonly found in cyanobacteria that live in freshwater. The finding confirmed their suspicions that an ancient river once snaked across the continent. 

The researchers traced the Eocene grains to a distinct salt region in the Transantarctic Mountains, traversing an area that spanned about 930 miles (1,500 kilometers) before draining into the Amundsen Sea.

"This is exciting — just having this exciting image in your brain that there was this gigantic river system flowing through Antarctica that is now covered by kilometers 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.

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Kristel Tjandra
Staff Writer

Kristel is a science writer based in the U.S. with a doctorate in chemistry from the University of New South Wales, Australia. She holds a master's degree in science communication from the University of California, Santa Cruz. Her work has appeared in Drug Discovery News, Science, Eos and Mongabay, among other outlets. She received the 2022 Eric and Wendy Schmidt Awards for Excellence in Science Communications.

  • Parsable
    Between 260 and 340 million years ago, CO2 levels were where they are now. Yet in the middle of that period, temps spiked more than 6 deg C. Also, 160 million years ago, CO2 was at 2500 ppm and has decreased ever since. Yet 60 mil years after that, the Cretaceous Hothouse occurred, with temp spikes for millions of years. (David Falvey, Former Director, British Geological Survey (retired) (1998–2006)) This CO2/temp correlation is nonsense. And for grins, 200 years ago, the CO2 levels worldwide were dangerously low. Plants start dying below 150 ppm. We need more CO2 in the air, not less. This young columnist in Space is simply regurgitating the AGW stuff she's been fed since birth.
  • Classical Motion
    Where's the river? How about a map of the river?

    China and India will show us in short time what CO2 can do. We will see how much fossil generated CO2 is produced, how much CO2 remains in our air and what affect it has on temp.

    It will no longer be theory.
  • Unclear Engineer
    The river isn't surprising. Antarctica has been sliding around the globe over Earth's history, and was even on the equator at one time, 600,000,000 years ago. (but I can't find that link right now) See for a discussion of climate and Antarctica.

    So, it would not be surprising if all of the ice sheets on Earth eventually melt. And, if that happens, sea level will rise more than 300 feet. Even that is not unprecedented. Sea level has already risen 325 feet from its most recent low point about 25,000 years ago, at the peak glaciation in the last ice age. Back in the days of the dinosaurs, with no ice caps at Earth's poles, a lot of our current farm lands were under water - salt water.

    So, things could get drastically different in our not all that distant future, if we continue to warm our planet. Most cities would be flooded, and a lot of farmland would be lost.

    But, that is a far cry from turning Earth into Venus.