Researchers Uncover a Vast Ancient River System Beneath Antarctic Ice
A research icebreaker, Polar stern, positioned in front of a massive iceberg in the Amundsen Sea. Researchers aboard this vessel have uncovered evidence of an enormous ancient river that once traversed West Antarctica. (Image credit: Johann Klages)
Geologists drilling into the expansive ice sheet of West Antarctica have unearthed the remnants of a colossal river system that spanned nearly a thousand miles. This discovery offers insights into Earth’s history and suggests how extreme climate change could transform the planet, according to their findings published on June 5 in the journal Science Advances.
“To understand potential severe climate changes in the future, we need to study periods in Earth’s history where such changes have already occurred,” said Johann Klages, co-author of the study and a sedimentologist at the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research in Germany.
Between 34 million and 44 million years ago, during the middle-to-late Eocene epoch, Earth experienced significant atmospheric changes. A steep decline in carbon dioxide levels led to global cooling and the formation of glaciers on what was previously an ice-free Earth. Scientists are keen to understand how this major climate shift played out in Antarctica, especially as current carbon dioxide levels continue to rise due to human activities. The late Eocene period had nearly double the carbon dioxide levels we have today, a scenario that might recur in 150 to 200 years if greenhouse gas emissions continue unabated, Klages noted.
However, investigating the past is challenging, as most of West Antarctica is covered in ice, making it difficult to access sedimentary rocks vital for studying ancient environments. Geologists rely on grains, minerals, and fossils trapped in these sediments to reconstruct historical conditions.
In 2017, Klages and his team embarked on an expedition aboard the research vessel Polar stern, traveling from southern Chile, across the turbulent Drake Passage, to the western part of Antarctica. Utilizing advanced seafloor drilling equipment, they collected core samples from the frozen seabed’s soft sediments and hard rocks.
Researchers aboard the Polar stern found evidence of an ancient river in West Antarctica that existed 40 million years ago, using sophisticated drilling tools. (Image credit: Karsten Gohl)
By drilling nearly 100 feet (30 meters) into the seafloor, they retrieved sediments with layers from two distinct periods. Analyzing the ratio of radioactive elements such as uranium and lead, they determined that the lower sediment layer formed around 85 million years ago during the mid-Cretaceous period, indicating the presence of a temperate rainforest. The upper sediment layer, primarily sand from the mid-to-late Eocene epoch, dated back 30 to 40 million years.
Closer examination revealed a stratified pattern in the Eocene sand layer, resembling a river delta similar to the Mississippi River or Rio Grande. A lipid biomarker analysis confirmed the presence of a unique molecule found in freshwater cyanobacteria, validating the existence of an ancient river system across the continent.
The researchers traced the Eocene grains to a specific region in the Transantarctic Mountains, showing that the river spanned about 930 miles (1,500 kilometers) before emptying into the Amundsen Sea.
“This discovery is thrilling,” Klages said. “Imagining a gigantic river system flowing through Antarctica, now buried under kilometers of ice, is extraordinary.”
Klages and his team are currently analyzing core sediments from the more recent Oligocene-Miocene period, about 23 million years ago, to refine models for predicting future climate changes.
