The ice cap in Antarctica formed relatively recently from a geological point of view, experts say. “I think most people would say that 34 million years ago. 2000, an ice sheet first formed in Antarctica, says Eric Wolff, a paleoclimatologist at the University of Cambridge. – [Anksčiau] much of it must have been like northern Canada today – tundra and conifer forests.”
Global temperature is the main factor influencing the extent of ice cover. About 50 million years ago year, the world was about 14 degrees Celsius warmer than now, but during the next 16 million annual temperature has been steadily decreasing. 34 million years ago years – a period called the Eocene-Oligocene boundary – the climate was 8 C° warmer than now.
But what caused such a drop in temperature – and was it enough to cause the glaciers to form?
“There are two factors, and they were probably both important,” says Wolff. “One of them is the change in the concentration of carbon dioxide in the atmosphere, and the other is the movement of the continents, and in particular the opening of the Drake Passage, the strait between South America and Antarctica that connects the South Atlantic to the South Pacific.”
The more carbon dioxide in the atmosphere, the more heat is trapped and the warmer the planet.
About 60-50 million years ago years, the concentration of carbon dioxide in the Earth’s atmosphere was really high – about 1000-2000 parts per million, that is, 2.5-5 times higher than nowsays Tina van de Flierdt, a geochemist at Imperial College London.
“But we know that across that Eocene-Oligocene boundary, CO2 amount in the atmosphere has decreased, she says and adds that with the reduction of CO2 concentration in the atmosphere, the world’s climate must have cooled, which likely determined the Earth’s climatic threshold and allowed the ice sheets to form.
However, it is likely that plate tectonics also caused local cooling in the Antarctic continent, says E. Wolff. Around this time, South America and Antarctica finally separated, opening up what is now the Drake Passage.
“Because of this, the so-called circumpolar current appeared – water goes around Antarctica in a circle,” says the scientist. “This isolates Antarctica from the rest of the world, making it much harder for warm air masses to get through the Southern Ocean, making Antarctica colder.”
Plate tectonics also has a direct effect on carbon dioxide levels, he said. Rock decay and volcanic activity are part of the carbon cycle, so geological processes can change the balance of gases in the atmosphere over thousands of years.
Although some uncertainty remains, based on the chemical signatures in the rock sediments, scientists are fairly confident about this transition 34 million years ago. years. Oxygen atoms come in two forms: oxygen-16 (simple oxygen) and oxygen-18 (heavy oxygen). Continental ice contains more of the lighter oxygen-16 – which means there is more oxygen-18 in the oceans, and therefore the shells of small sea creatures – when the ice cover is greater.
“By looking at the oxygen isotopes in the carbonate shells of small sea creatures found in ocean sediments, we see that around 34 million years ago, years there was a jump that people understand as [lengvesnių] the entry of oxygen isotopes into the Antarctic continent”, explains E. Wolff.
As for whether Antarctica could ever be ice-free again, van de Flierdt says it’s certainly possible: “Planet Earth has done it before. Planet Earth can do it again.”
While it is unlikely that human activity will cause the ice sheet to completely melt, it is important that we do everything possible now to minimize the loss of ice from Antarctica, she adds. “It is in our hands to avoid the worst-case scenario,” says van de Flierdt.
Parengta pagal „Live Science“.
2024-09-10 05:31:37