Bodies of water may explain why Antarctica froze
Scientists have long said that global warming could reveal an ancient river landscape that persisted beneath the East Antarctic Ice Sheet for millions of years. Now, thanks to research in Antarctica, the scale and time of their occurrence have become known.
Much of Antarctica was ice-free in the past, creating space for river systems that are now frozen. Sediments from the Amundsen Sea were brought here from a mountain range that stretches across the continent, indicating that there was no inland sea between them to trap them.
In total, 40 million years ago it was hotter on Earth, but in Antarctica the difference was most noticeable: while the highlands were covered with ice and the lowlands were covered with snow in winter, the forests flourished.
“The continent was relatively warm, with a climate similar to modern southern South America, like Argentina and Chile,” explains researcher Stuart Jamieson. “Earlier, Durham University found evidence that Antarctica once had tropical vegetation, including palm trees.”
Forests need rain, and regular rain means the appearance of rivers. However, determining where they occur is not easy. According to scientists, the landscape has changed over quite a long time. Therefore, they can't just look at the current position of the land and guess where the water might have flowed and where the lowest point of the continent is.
Drilling through all this ice to determine what it was like a long time ago is not easy, but Professor Cornelia Spiegel from the University of Bremen and her colleagues have found an easier way to identify the missing rivers of Antarctica. They drilled into the sediments around the coast using the icebreaker Polarstern.
In the Amundsen Sea, the team discovered sediments 17–24 meters thick, consisting of minerals that do not match those from nearby West Antarctica. Instead, they were discovered in the Transantarctic Mountains, which separate East and West Antarctica. Unfortunately, it is reported that no fossils have been found in these sediments that would indicate the ecosystem of that era.
“The existence of such a transcontinental river system shows that – unlike today – much of West Antarctica must have been located above sea level in the form of vast, flat coastal plains,” the scientists say.
Sea levels were higher then. , and much less water was frozen, so these West Antarctic plains must have been slightly higher than they are today. On the other hand, they could not have been too high, otherwise they would have been covered with ice even in the warmer conditions of that time.
The researchers concluded that a number of events, including sedimentation in the Amundsen Sea, widened the seafloor and the rise of the Transantarctic Mountains, began at about the same time: 44–40 million years ago.
“Given the erosion or subsidence that has occurred since then, we cannot expect the return of such a river when West Antarctica will be freed from ice, which could happen very soon,” the study authors conclude. However, they argue that only by understanding what the world was like back then can we understand how it changed to become what it is today, with permanent ice sheets.
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