Ice ages occurred much more frequently in Antarctica
Scientific archives worldwide represent an enormously valuable treasure trove of knowledge, because the samples stored there still hold many secrets, even if they have already been analyzed. Some of them, however, were not even examined after sampling. This was also the case with a sediment core recovered from Antarctica almost 20 years ago. And this core now revealed that ice ages in Antarctica occurred much more frequently than previously known.
Geologist Dr. Christian Ohneiser of the University of Otago in New Zealand, lead author of the current study, was conducting research in another project to reconstruct the retreat of the Ross Ice Shelf after the last ice age when he also analyzed a sediment core just over six meters long that was recovered in 2003 and stored in an archive in the United States. Ohneiser assumed to find information from the last 10,000 years in it.
“I conducted a paleomagnetic analysis on the core, which reconstructs changes in the earth’s magnetic field, and found a magnetic reversal showing it was much older and had a record spanning more than 1 million years,” Ohneiser said in a University of Otago news release.
Using sediment and magnetic mineral indicators, he reconstructed the size of the Ross Ice Shelf and the West Antarctic Ice Sheet that feeds it in the study published in the journal Nature Geoscience. “Ice bergs, which come from the ice shelf, have sediment and rocks attached to their underside. When icebergs break off they float out to sea and drop the rocks and sediment as it melts, these rocks and sediments can also come directly from the ice shelf if the ice was over the core site,” Ohneiser explains. “By figuring out how much of this debris is in the core through time we can build a picture of the changes in the size of the ice sheet.”
Knowledge of the frequency of ice ages has been based on assumptions and incomplete data sets. Only Ohneiser’s analyses showed that ice ages in Antarctica occurred much more frequently than previously assumed. “Until this research, it was common knowledge that over the last million years global ice volume, which includes Antarctica’s ice sheets, expanded and retreated every 100,000 years. However, this research shows they actually advanced and retreated much more often – every 41,000 years – until at least 400,000 years ago,” he says. In view of climate change, knowledge about the frequency of ice ages in Antarctica is very important, he said.
“Antarctica’s ice sheets have the capacity to increase sea-level significantly over the coming centuries,” Ohneiser points out. “Antarctica’s ice sheets have the capacity to increase sea-level significantly over the coming centuries.”
“Because the response of ice sheets to any change in climate occurs very slowly, reconstructions on past ice sheet behaviour provide constraints on how big or small the ice sheets were and how quickly they have retreated and regrown under different climate conditions. These reconstructions provide baseline information on natural behaviour of ice sheets in the past before humans started messing with the atmosphere,” Ohneiser continues.
In the coming year, the Antarctic Science Platform project team, for which Ohneiser provides data, will drill for sediment deposits near the baseline of the West Antarctic Ice Sheet as part of the SWAIS 2C international drilling project and, together with its international partners, will investigate, among other things, the climatic conditions under which the West Antarctic Ice Sheet collapses.
Julia Hager, PolarJournal
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