Researchers Uncover Ancient River System in Antarctica, Revealing Temperate Climate 34 Million Years Ago

Antarctica was not always an isolated ice-covered land mass. Until about 100 million years ago, it formed the central part of the supercontinent Gondwana. It was only after the supercontinent broke up that it became established as an independent continent. Despite its south polar location, temperate climate conditions prevailed in Antarctica until the end of the Eocene around 34 million years ago, and the continent was crossed by extensive river systems. Researchers from the University of Bremen and the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, together with German, British, Irish and Swedish universities and research institutes, have now discovered the largest of these river systems to date and described it in the journal Science Advances.

The team examined sediment samples that they had obtained from the Amundsen Sea off the West Antarctic coast during an expedition on the research icebreaker Polarstern. The analyses show that most of the minerals and rock fragments in these samples do not come from West Antarctica, but from the Transantarctic Mountains on the edge of East Antarctica, thousands of kilometers away. Since the late Eocene, these mountains have been rising as a steep shoulder of a continental trench, the West Antarctic Rift System, which today divides Antarctica into the two land masses of East and West Antarctica. Since then,
the uplift and erosion of the Transantarctic Mountains have produced large quantities of debris, which the newly discovered current transported over a distance of more than 1,500 km through the West Antarctic Rift System into what is now the Amundsen Sea, where it was deposited in a swampy river delta. Modern examples of large river systems in a similar geological environment are the Rio Grande in the Rift of the same name or the Rhine in the Upper Rhine Graben.

Professor Cornelia Spiegel from the University of Bremen: “The existence of such a transcontinental river system shows that – unlike today – large parts of West Antarctica must have been located above sea level as extensive, flat coastal plains.” Due to the low topography, West Antarctica was still ice-free at the end of the Eocene, while the mountainous regions of East Antarctica were already beginning to freeze over.