Millions of years ago, Antarctica looked very different from the icy landscape we know today.
A research expedition led by the Alfred Wegener Institute has uncovered a hidden secret. Geologists discovered evidence of an ancient river system by studying sediment samples from the Amundsen Sea.
This suggests that Antarctica supported a temperate climate about 34 million years ago, in which lush forests flourished and an extensive network of rivers wound their way through the landscape.
Examination of sediments
The Earth underwent a dramatic cooling period between 34 and 44 million years ago. This period of the ‘middle to late Eocene’ saw a drastic drop in carbon dioxide levels, causing the first glaciers to form on an otherwise ice-free Earth.
Scientists have long wondered how this event played out in Antarctica, a continent now dominated by ice.
Antarctica was not a lonely continent at the time. Until about 100 million years ago it was part of a huge continent known as Gondwana. When Gondwana broke up, Antarctica moved south and established its continent.
Although it shifted towards the South Pole, Antarctica experienced moderate climatic conditions until the end of the Eocene, about 34 million years ago.
This new study involved an international team of researchers who examined the minerals and rock fragments found in sediment samples from the Amundsen Sea off the West Antarctic coast. The samples were collected 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 other side of the continent, thousands of miles away.
According to the press release, this mountain range has not always been this high. However, since the late Eocene they have grown gradually.
This increase is associated with a geological feature called the West Antarctic Rift System. This split separates Antarctica into two geographic masses: East and West.
Raising mountains
How does all this relate to the ancient river?
The uplift of the Transantarctic Mountains created a huge amount of erosional debris, consisting of weathered and displaced rocks and minerals.
The newly found river system most likely moved this debris a long distance (about 1,500 kilometers) via 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,” says Professor Cornelia Spiegel of the University of Bremen.
According to the press release, West Antarctica had a low topography at the end of the Eocene. Despite being located at the South Pole, West Antarctica was not cold enough to form permanent ice caps due to its low elevation.
In contrast, the mountainous areas of East Antarctica, which had higher altitudes and lower temperatures, were already witnessing the onset of glaciers at that time.
The 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 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 innovations. Her professional experience spans both television 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 pitches in mind, don’t hesitate to email her.