analysis two small rocks collected Antarctica allowed scientists to reconstruct how the ice cover of this frozen continent was affected by climatic changes. More than 100,000 years during the Late Pleistocene. This made it possible to confirm that it was the warming of the surrounding ocean that caused the gradual melting of the edges of the Antarctic ice floes in the distant past; this is something that aligns with what is happening right now due to human-induced climate change.
The East Antarctic Ice Sheet is the world’s largest ice sheet. To understand sensitivity to climate change is crucial to knowing how much sea level will rise as global temperatures rise. Recent studies suggest that it may be more vulnerable to ice loss than previously thought.
The new study, published Sept. 15, by scientists at the University of California (USA), Nature CommunicationIt shows the variations that occurred at the base of the Antarctic ice sheet in response to cyclical changes in climate during the Pleistocene. These changes are reflected in the minerals deposited at the base of the ice sheet.or some rocks just a few centimeters long that have now been analyzed.
Hot water eats Antarctica’s edges
“One of the key findings is that the ice sheet is affected by temperature changes in the Southern Ocean,” said co-author Terrence Blackburn, associate professor of Earth and planetary sciences at UC Santa Cruz. “Hot water eats up the edges of the ice sheet, making the ice flow faster, and this reaction goes to the heart of the ice sheet.“, added.
The rock samples analyzed in the study consist of alternating layers of opal and calcite that form as mineral deposits at the base of the ice sheet and record cyclical changes in the composition of subglacial fluids.
“Each layer in these samples is a manifestation of a change in the bottom of the ice sheet driven by variations in the movement of ice currents,” says first author Gavin Piccione.
In dating these layers, the researchers found a surprising correlation between the levels of mineral deposits and the record of polar sea surface temperatures from ice cores. Opal was deposited in cold periods and calcite in warm periods.
“These climate oscillations cause changes in the behavior of the ice sheet, thus changing the chemistry and hydrology beneath the ice,” said co-author Slawek Tulaczyk.
The climate cycles that give rise to the mineral strata are relatively minor fluctuations that occur every few thousand years in glacial-interglacial cycles that occur approximately every 100,000 years during the Pleistocene. Glacial-interglacial cycles are primarily driven by changes in Earth’s orbit around the Sun.
Smaller millennial climate cycles include oscillations in polar temperatures caused by the weakening and strengthening of a large ocean current (Atlantic Meridional Circulation or AMOC) that carries large amounts of heat northward across the Atlantic Ocean.
Tulaczyk said new finding reveals susceptibility of Antarctic ice sheet to small short-term climate fluctuations.
“As important as the Antarctic ice sheet is, we really know very little about how it responds to climate variability, as it is responsible for sea level rise of about 17 meters since the last glacial maximum.” said. “We know the last 20,000 years pretty well, but beyond that we were almost blind. That’s why these results are mind-blowing. People have been banging their heads against the wall for this for decades.”
Two stones that make everything clear
The two rock samples analyzed for this study were collected from glacial moraines that were formed in different periods over a total period of more than 100,000 years, located more than 900 kilometers apart. In other words, they record similar cycles under the ice over a wide area and for long periods of time.
“The chemistry of the two samples matched despite coming from a great distance, confirming to us that a large-scale, systematic process was taking place,” Piccione said. Said.
To obtain a layer of calcite on the opal requires a flow of glacial meltwater containing carbon.AMOC occurs at warm intervals in climate cycles when ocean currents slow down. This leads to warming in the southern hemisphere, bringing warm water into contact with floating ice shelves. As the warm water eats away at the bottom of the ice shelves, the line where the ice meets the land begins to recede and the ice flows faster from the interior to the edges.
Tulaczyk explained that the movement of ice on bedrock generates heat and increases the amount of meltwater at the base of the ice sheet. “If you imagine a map with water melting under the ice sheet, that area expands during warm periods and contracts like a heartbeat during cold periods,” he said.
The “freeze-thaw cycles” that occur on the ice floor take into account the alternating layers of opal and calcite in the rocks.
CO2 warms sea melting Antarctica
The findings point to Water temperatures in the Southern Ocean as the main mechanism driving the response of the Antarctic ice sheet to changes in global climate.. Temperatures in Antarctica are so cold that a few degrees of warming won’t cause the surface ice to melt, but scientists know the ice sheet melted in the past and parts of it collapsed, Blackburn said. “It’s been difficult to understand, but this clearly shows that ocean warming is the driving mechanism,” he said.
“If you look at places that are losing ice today, they are concentrated at the edges of the ice sheet where it is in contact with the warming ocean,” Tulaczyk said. “The main driver of ocean warming is atmospheric carbon dioxide, not AMOC.Still, I don’t think he cares what the ice sheet is causing the warming,” he joked.
Tulaczyk added that the findings show that the ice sheet may recede during warm periods and recover during subsequent cooling. “In the context of the threshold question, does the ice sheet sit at a threshold where there will be uncontrolled melting and everything will disappear? That’s not what I’m seeing here,” he said. “Ice is sensitive to these short-term fluctuations, but the magnitude of ice loss is small enough that it can be recovered through cooling.‘ he assured.
Reference work: https://www.nature.com/articles/s41467-022-33009-1
…..
Environment department contact address:[email protected]