Ancient Dust Suggests Ross Shelf shrank in Last Warmth

ancient Antarctic – A new study using a coastal Antarctic ice core traces the source of volcanic and mineral dust during the Last Interglacial (about 129,000 to 116,000 years ago). The dust shift—from southern South America during colder ice to volcanic rock material near the Ros

For tens of thousands of years. the ice at Antarctica’s Allan Hills Blue Ice Area has been quietly storing a record of winds. landscapes. and the ice itself. In a new study published in Nature Geoscience. scientists say that record now shows something startling about Earth’s last warm period—how much smaller the Ross Ice Shelf and the West Antarctic Ice Sheet may have been.

The warm interval they focused on is the Last Interglacial, dated to approximately 129,000 to 116,000 years ago. In that time window. the chemistry and even the physical shape of dust trapped in Antarctic ice appear to change dramatically. And that shift. the researchers argue. is not just a fingerprint of climate—it’s a map of where parts of the Ross Sea region may have become exposed as ice retreated.

Instead of dust arriving from the same far-off place. the team found that volcanic dust from nearby Antarctic ice-free regions replaced dust that had dominated during colder conditions. During glacial times preceding the Last Interglacial. the dust had a chemical signature consistent with southern South America. a well-established source for Antarctic dust in glacial climates. But as the interglacial warmth arrived. the ice began to record young volcanic rock material associated with ice-free regions near McMurdo Sound in the West Antarctic Rift System.

The volcanic clue mattered because Antarctic ice from warm periods typically contains much less dust than glacial ice. In other words, there wasn’t just a new source—it was a rare one. Coauthor Sarah Aarons. a geochemist at the Lamont-Doherty Earth Observatory. part of the Columbia Climate School. described it as perplexing at first.

“We found a volcanic signature rarely seen before in Antarctic ice from a warm period, and it was really perplexing at first,” Aarons said. She added that seeing volcanic rock material in the dust record suggested parts of the Ross Sea region may have been exposed during that warm period.

The researchers also leaned on how the dust was layered—or, crucially, how it wasn’t. They found no distinct volcanic layers in the ice core, which supports their interpretation that the material came from exposed Antarctic terrain rather than isolated volcanic eruptions.

Then there was the texture. Along with changes in chemical signatures. the dust particles themselves became different: larger. more angular grains during the warm interval. including coarse particles that are difficult for wind to carry over long distances. Lead author Austin Carter. a postdoctoral research associate at Princeton University. said the grain size helped them make the case that the dust was coming from much closer to Antarctica.

“The bigger the particle, the faster it will fall out of the atmosphere,” Carter said. “Ice from the Last Interglacial contained more of these coarse particles, which points to a dust source much closer to Antarctica rather than material transported across the Southern Ocean.”

The ice core study was possible because of where it was drilled. The work centered on an ice core extracted at the Allan Hills Blue Ice Area in East Antarctica. That site lies close to the margin of the East Antarctic Ice Sheet and within about 60 miles (100 km) of the Ross Sea. putting it in a position to pick up environmental changes along the Antarctic coast.

Blue ice areas expose very old Antarctic ice unusually close to the surface through a mix of ice flow and surface weathering. That exposure gave the scientists relatively direct access to ice that recorded both the colder glacial conditions before the Last Interglacial and the transition into the warm period. The team measured the concentration. size. and chemical composition of mineral dust preserved in the ice core. using the dust’s properties as a way to trace where it came from as the climate changed.

To connect the dust evidence to what might have happened to ice in the Ross Sea region. the researchers paired the ice-core record with climate model simulations. They tested three different Ross Sea ice sheet scenarios—preindustrial. partially collapsed. and fully collapsed—to see which one could reproduce the dust record.

“Our simulations show that the loss of Ross Ice Shelf ice results in increased dust flux. snow accumulation. and wind speed along the Ross Sea coastline toward the Allan Hills ice core site. ” Carter said. “This supports the idea of an open Ross Sea and even a diminished West Antarctic Ice Sheet during the Last Interglacial.”.

The logic is tied to physics that already governs much of the region’s vulnerability. The floating Ross Ice Shelf acts as a barrier that slows the movement of ice from the West Antarctic Ice Sheet into the ocean. Much of the West Antarctic Ice Sheet rests on bedrock below sea level. making it particularly vulnerable to retreat if the Ross Ice Shelf weakens or disappears.

In the real world. the Last Interglacial stands out because it’s one of the clearest natural tests of how Antarctica responds to only modest warming. Temperatures during that period are estimated to have been between 0.5 and 1.5 degrees Celsius above preindustrial levels. yet sea levels were still significantly higher than they are today.

For researchers studying Antarctica’s ice sheets, that combination is difficult to ignore. Aarons said the implication for the future is unsettling: if the Ross Ice Shelf was little or absent and the West Antarctic Ice Sheet was diminished during the Last Interglacial. it may not bode well for West Antarctic ice sheet stability under warming.

“If we know that during the Last Interglacial we probably had little or no Ross Ice Shelf and a diminished West Antarctic Ice Sheet, it may not bode well for future West Antarctic ice sheet stability,” Aarons said.

The stakes are not just academic. Previous modeling studies referenced in the research suggest that melting of the West Antarctic Ice Sheet could raise global sea levels by between three and five meters. With a warmer-than-today past now written—literally—into Antarctic ice. the new findings add a clearer sense of what “retreat” can look like when the planet warms by relatively limited amounts.

Antarctica Ross Ice Shelf West Antarctic Ice Sheet Last Interglacial ice core volcanic dust wind patterns climate simulations sea level rise Nature Geoscience