Millions of years ago, Antarctica looked very different from the icy landscape we know today.
A research expedition led by the Alfred Wegener Institute revealed the hidden secret. Geologists have discovered evidence of an ancient river system by studying sediment samples from the Amundsen Sea.
This suggests that around 34 million years ago, Antarctica supported a temperate climate during which lush forests thrived and a vast network of rivers carved their way across the landscape.
Investigation of sediments
Earth went through a period of dramatic cooling between 34 and 44 million years ago. This “Middle to Late Eocene” period saw a drastic drop in carbon dioxide levels and created the first glaciers on an otherwise ice-free Earth.
Scientists have long wondered how this event took place in Antarctica, a continent now dominated by ice.
Antarctica was not a lonely continent at the time. Until 100 million years ago, it was part of the huge continent known as Gondwana. When Gondwana broke up, Antarctica moved south and established its continent.
Even as Antarctica moved toward the South Pole, it experienced moderate climatic conditions until the end of the Eocene, about 34 million years ago.
This new study involved an international team of researchers studying minerals and rock fragments found in sediment samples from the Amundsen Sea off the coast of West Antarctica. The samples were taken during an expedition aboard the research icebreaker Polarstern.
Surprisingly, most of these minerals and fragments came from somewhere other than West Antarctica, where they were found. Instead, they point to a distant source – the Transantarctic Mountains on the opposite side of the continent, thousands of kilometers away.
As the press release states, this mountain range was not always so high. However, they have been gradually increasing since the end of the Eocene.
This uplift is associated with a geological formation called the West Antarctic Rift System. This division divides Antarctica into two geographic masses: East and West.
Lifting mountains
So how does all this relate to the ancient river?
The uplift of the Transantarctic Mountains produced a huge amount of erosional debris consisting of weathered and displaced rocks and minerals.
The newfound river system most likely moved this debris a long distance (about 1,500 kilometers) across the West Antarctic Rift System before depositing it in the Amundsen Sea.
“The existence of such a transcontinental river system shows that – unlike today – large parts of West Antarctica must have been above sea level as vast flat coastal plains,” said Professor Cornelia Spiegel from the University of Bremen.
According to the press release, West Antarctica had low topography at the end of the Eocene. Despite being at the South Pole, West Antarctica was not cold enough to form permanent ice sheets due to its low altitude.
In contrast, the mountainous regions of East Antarctica, which had higher altitudes and lower temperatures, already witnessed the beginnings of glaciers at that time.
Researchers suggest that similar river systems exist today in places with geological features such as the West Antarctic Rift System. For example, the Rio Grande flows through the Rio Grande Rift, while the Rhine River flows through the Upper Rhine Graben.
ABOUT THE EDITORIAL
Mrigakshi Dixit Mrigakshi is a science journalist who enjoys writing about space exploration, biology and technological innovation. Her professional experience spans both broadcast and digital media, allowing her to learn a variety of storytelling formats. Her work has been featured in well-known publications including Nature India, Supercluster and Astronomy magazine. If you have any offers in mind, feel free to email her.