Analysis of two small rocks collected in Antarctica allowed scientists to reconstruct how the ice cover of this frozen continent responded to climatic changes across more than 100,000 years during the Late Pleistocene. The study confirms that warming in the surrounding ocean drove the gradual melting of the ice-floe edges in the distant past, a process that aligns with what is happening today due to human-caused climate change.
The East Antarctic Ice Sheet is the globe’s largest ice body. Understanding its sensitivity to climate change is crucial for predicting future sea level rise as global temperatures climb. Recent research suggests this ice sheet may be more susceptible to loss than previously thought.
The new study, published on September 15 by University of California scientists in Nature Communications, shows how conditions at the base of the Antarctic ice sheet varied with cyclical climate shifts during the Pleistocene. Those variations are recorded in mineral deposits at the ice sheet base, which include rocks only a few centimeters long that researchers recently analyzed.
Hot water eats Antarctica’s edges
“One key finding is that the ice sheet responds to temperature changes in the Southern Ocean,” said co-author Terrence Blackburn, associate professor of Earth and planetary sciences at UC Santa Cruz. “Warm water erodes the edges of the ice sheet, increasing ice flow toward the interior. This reaction reaches deep into the ice sheet.”
The rock samples examined in the study consist of alternating layers of opal and calcite that form as minerals at the base of the ice sheet and record cyclical changes in subglacial fluids.
“Each layer represents a shift at the bottom of the ice sheet driven by changes in ice movement,” said first author Gavin Piccione. In dating these layers, researchers found a striking correlation between mineral deposits and the historical record of polar sea surface temperatures from ice cores. Opal appeared during cold periods, while calcite formed in warmer periods.
“These climate oscillations alter the behavior of the ice sheet, which in turn changes the chemistry and hydrology beneath it,” added co-author Slawek Tulaczyk. The climate cycles behind these mineral strata are relatively minor fluctuations that occur every few thousand years within glacial–interglacial cycles that peak roughly every 100,000 years during the Pleistocene. Glacial–interglacial cycles are mainly driven by variations in Earth’s orbit around the Sun.
Smaller millennial climate cycles include oscillations in polar temperatures caused by changes in a large ocean current known as the Atlantic Meridional Circulation (AMOC), which transports large amounts of heat northward across the Atlantic.
Tulaczyk noted that the new findings reveal the Antarctic ice sheet’s susceptibility to short-term climate fluctuations. “As important as this ice sheet is, we still know relatively little about its response to climate variability. It has contributed about 17 meters of sea-level rise since the last glacial maximum. We understand the last 20,000 years fairly well, but beyond that we were nearly blind. That’s why these results are striking. People have been pressing for decades to understand this,” he said.
Two stones that make everything clear
The two rock samples studied were collected from glacial moraines formed in different periods over more than 100,000 years and located more than 900 kilometers apart. In essence, they record similar cycles beneath the ice over a broad region and across long timescales.
“The chemistry of the two samples matched despite the great distance, confirming a large-scale, systematic process was at work,” Piccione explained.
To form a calcite layer on opal, a flow of glacial meltwater containing carbon is required. AMOC tends to strengthen during warm intervals in climate cycles when ocean currents slow, bringing warmer water into contact with floating ice shelves. As this warm water erodes the base of the ice shelves, the land-ice line recedes, and ice moves faster from the interior toward the edges.
Tulaczyk described how the movement of ice over bedrock generates heat and increases meltwater at the base, likening the process to a map where meltwater expands during warm periods and contracts like a heartbeat during cold periods.
The interaction of freeze-thaw cycles at the ice floor helps explain the observed opal and calcite layering in the rocks studied.
CO2 warms sea and melts Antarctica
The findings point to water temperatures in the Southern Ocean as the primary mechanism driving the Antarctic ice sheet’s response to global climate changes. Antarctic temperatures are so cold that a few degrees of warming will not instantly melt surface ice, but previous warming episodes show partial ice sheet collapse. Blackburn emphasized that ocean warming appears to be the driving force.
“If one looks at places currently losing ice, they tend to be at the ice sheet margins where it meets the warming ocean,” Tulaczyk noted. “Atmospheric carbon dioxide largely drives ocean warming, not AMOC.” He added that the ice sheet may recede during warm periods and recover during subsequent cooling, suggesting a threshold of uncontrolled melting is unlikely in the near term. “Ice is sensitive to short-term fluctuations, but the magnitude of loss seems recoverable with cooling,” he stated.
Attribution: Nature Communications study (Nature Communications).