Antarctic ice loss could add three meters to sea-level rise
Researchers from the University of California found evidence demonstrating a huge loss of ice in East Antarctica during a warm interglacial period, recorded 400,000 years ago.
Researchers from the University of California found evidence demonstrating a huge loss of ice in East Antarctica during a warm interglacial period, recorded 400,000 years ago. The results were published in the journal Nature.
As global temperature increases, ecosystems are presenting irreparable environmental damage. Antarctica is one of them. Recently, it was found that the East Antarctic Ice Sheet, the world's largest ice sheet, may be at greater risk of collapse danger than previously thought.
A study, published in Nature, reveals that 400,000 years ago a large part of that layer, of approximately 295,000 km², collapsed in the ocean during a period of relatively mild heat. This detachment caused the sea level to rise more than three meters. The worrying thing, researchers at the University of California warn, is that this could happen again.
Terrence Blackburn, professor of Earth and planetary sciences at the University of California and lead author, explains that “At the time of the previous collapse, the amount of carbon dioxide in the atmosphere had reached approximately 300 parts per million (ppm). It is now at 400 ppm. This has led to serious consideration of the possibility of the ice sheet being reduced. ”
For the study, the researchers focused on the Wilkes Basin, one of several basins that are considered vulnerable to melting. Currently, this area contains enough ice to raise the sea level from 3 to 4 meters. Blackburn says that ice flows slowly through the basins from the interior of the continent to the floating ice shelves on the margins.
Therefore, the loss of ice causes the grounding line to move inland. This line, adds the researcher, is the point at which the ice loses contact with the ground and begins to float. "Our data shows that the grounding line in the Wilkes Basin receded 700 kilometers inland during one of the last really hot interglacials when global temperatures were 1 to 2 degrees Celsius warmer than they are now," he says.
For Blackburn, the retraction of the grounding line, most likely, contributed to the sea level rising from three to four meters. The researchers made a comparison with current greenhouse gas emission scenarios and found that it could lead to sea levels rising by 13 meters. However, he cautions, it wouldn't happen all at once because it takes so long to melt so much ice.
To calculate estimates of sea-level rise caused by melting glaciers, the researchers used a technique based on measurements of isotopes in mineral deposits that record past changes in subglacial fluids. They found that in Antarctica water is trapped at the base of the ice sheet and moves very slowly as long as the ice is stable.
As the ice remains stable, adds the researcher, it accumulates at very high levels over long periods, U-234, which is an isotope of uranium that accumulates very slowly in water that is in contact with rocks. "The ice sheet acts as an insulating blanket, so heat from the Earth's interior causes melting at the base," says Blackburn.
"The water flowing under the ice begins to freeze over again at the edges, concentrating all dissolved minerals until it becomes supersaturated and the minerals precipitate to form opal or calcite deposits. Those deposits trap uranium-234, so we can date the deposits and measure their composition, and we can trace that overtime to get a deep history of the composition of the water under the ice cap, ”he says.
The study suggests that U-234 in subglacial water in the Wilkes Basin was ejected during the interglacial period 400,000 years ago when the ice melted and the ground line was removed. "We have opened the freezer door, but that block of ice is still cold and not going anywhere anytime soon. To understand what will happen on longer time scales, we need to see what happened under comparable conditions in the past, "says the researcher.