Geologists drilling into the massive ice sheet in 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 hints at how extreme climate change will affect the planet, according to their findings published June 5 in the journal. Advancement of science.
“If we think about possible severe climate change in the future, we need to learn from periods in Earth’s history where this has already happened.” Johann KlagesStudy co-author and sedimentologist at the Alfred Wegener Institute at the Helmholtz Center for Polar and Marine Research in Germany told Live Science.
Between 34 million and 44 million years ago, an epoch known as the Middle to Late Eocene, Earth’s atmosphere radically transformed. As carbon dioxide levels fell, global cooling led to the formation of glaciers on ice-free land.
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 was roughly twice the amount we have today. However, it may be similar to levels expected in about 150 to 200 years if greenhouse gas levels continue to rise, Klages said.
But uncovering the past has proven difficult. Most of western Antarctica today is covered in ice, making it difficult to access sedimentary rocks, which are essential for studying early environments. 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 research vessel Polarstern crossed from the southern tip of Chile, through the rugged Drake Passage to the western part of the icy continent. Equipped with advanced seafloor drilling equipment, Klages and his team set out to collect cores of soft sediment and hard rock within the frozen seafloor.
After drilling nearly 100 feet (30 meters) into the seafloor, the researchers unearthed layered sediments from two different periods.
By calculating the half-lives of radioactive elements, such as the percentage of uranium and lead in the sediments, they found that the bottom of the sediments formed during the mid-20th century.Cretaceous period, about 85 million years ago. These sediments contain fossils, spores and pollen characteristic of the temperate rainforests that existed at that time. The upper part of the deposit contains mostly sand dating from the middle and late Eocene, about 30 to 40 million years ago.
Upon closer inspection, they recognized a strong stratigraphic pattern in the Eocene sand layer that resembled that coming from a river delta, very similar to something one might encounter on the Mississippi River or the Rio Grande, Klages said.
Scientists conducted a lipid biomarker analysis, measuring the amount of fat and sugar in the sediment, and found a unique molecule common to freshwater cyanobacteria. This discovery confirmed their suspicions that an ancient river flowed across the continent.
The researchers traced the Eocene grains to a distinct salt region in the Trans-Antarctic Mountains, crossing a region that extended about 930 miles (1,500 kilometers) before emptying into the Amundsen Sea.
“This is exciting – just having this exciting image in your mind that there is a huge river system flowing through Antarctica that is now covered by kilometers of ice,” Klages said.
Klages and his team are now analyzing parts of core sediments belonging to a more recent Oligocene-Miocene period, about 23 million years ago. This will help improve models to better predict future climate.
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