Ancient Antarctic Dust Shows Ross Ice Shelf Was Reduced

A new Nature Geoscience study reads volcanic and mineral dust trapped in an East Antarctica ice core to infer that the Ross Ice Shelf and the West Antarctic Ice Sheet were likely far smaller during the Last Interglacial warm period about 129,000–116,000 years

On a stretch of East Antarctica ice that has been dragged close to the surface by flow and weathering, an ice core drill cuts down into time. The ice it extracts is old enough to remember a world that was only modestly warmer than today—yet the dust inside it tells a much bigger story.

A new study published in Nature Geoscience examines mineral dust trapped in a coastal Antarctic ice core that records the Last Interglacial warm period. approximately 129. 000 to 116. 000 years ago. The work points to a reshaped Ross Sea environment during that interval. suggesting the Ross Ice Shelf and the West Antarctic Ice Sheet were far smaller than they are now.

The key clue is where the dust came from.

During colder portions of the record leading into the Last Interglacial. the dust carried a chemical signature consistent with southern South America. a well-established source of Antarctic dust in glacial climates. But as the climate warmed. the ice began to record a different kind of material: dust containing volcanic signatures and young volcanic rock material from ice-free regions near McMurdo Sound in the West Antarctic Rift System. The researchers say the shift means dust sources around the Ross Sea changed as the climate warmed. and that it reflects major environmental and wind-pattern changes tied to retreat of the West Antarctic Ice Sheet.

What makes the volcanic signal especially striking is how rarely it appears in Antarctic ice from warm periods. “We found a volcanic signature rarely seen before in Antarctic ice from a warm period. and it was really perplexing at first. ” said coauthor Sarah Aarons. a geochemist at the Lamont-Doherty Earth Observatory. part of the Columbia Climate School.

Aarons said the volcanic rock material in the dust record suggested that parts of the Ross Sea region may have been exposed during that warm period. “Seeing volcanic rock material in the dust record suggested that parts of the Ross Sea region may have been exposed during that warm period. ” she said. adding that she is also an assistant professor in Columbia’s Department of Earth and Environmental Sciences.

At the Allan Hills Blue Ice Area in East Antarctica. the study team had a practical advantage: the site lies within about 60 miles (100 km) of the Ross Sea and close to the margin of the East Antarctic Ice Sheet. making it especially sensitive to environmental changes along the Antarctic coast. Blue ice areas expose very old Antarctic ice unusually close to the surface through a combination of ice flow and surface weathering. which gave the researchers relatively easy access to ice that captured both the colder glacial conditions before the Last Interglacial and the transition into it.

In the lab, the scientists measured the concentration, size, and chemical composition of mineral dust preserved in the core. They found that during the warm interval, dust particles became larger and more angular, including coarse particles. Those grain characteristics matter because coarse particles are difficult for wind to transport over long distances.

That particle evidence, the study says, strengthens the case that the dust’s warm-period source was local rather than transported across the Southern Ocean.

Lead author Austin Carter, a postdoctoral research associate at Princeton University, tied the grain sizes to geography. “The bigger the particle, the faster it will fall out of the atmosphere,” he 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 researchers also looked for patterns that might point to isolated eruptions instead of exposed terrain. They said the absence of distinct volcanic layers in the ice core supports their interpretation that the material originated from exposed Antarctic terrain rather than from isolated volcanic eruptions.

To connect the dust record to what the Ross Sea may have been doing during the Last Interglacial. the team combined the ice core data with climate model simulations. They tested three Ross Sea ice sheet scenarios—preindustrial. partially collapsed. and fully collapsed—to see whether the models could reproduce the dust record.

Carter said the simulations pointed in the same direction as the dust measurements. “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. ” he said. “This supports the idea of an open Ross Sea and even a diminished West Antarctic Ice Sheet during the Last Interglacial.”.

A mechanism underlies that logic: the floating Ross Ice Shelf acts as a barrier that slows the movement of ice from the West Antarctic Ice Sheet into the ocean. And because much of that ice sheet rests on bedrock below sea level. it can be especially vulnerable to retreat if the Ross Ice Shelf weakens or disappears.

The Last Interglacial itself is a rare benchmark for ice sheet behavior because it is one of the clearest natural examples scientists have of a world only marginally warmer than today. Temperatures then were between 0.5 and 1.5 degrees Celsius above preindustrial levels. yet sea levels are estimated to have been significantly higher than they are now.

For Antarctic researchers, that makes the dust record more than a curiosity. It is a way to ask how the ice system responds to a relatively modest warming—and what that could imply for what comes next.

“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.

Previous modeling studies referenced by the research team suggest that melting of the West Antarctic Ice Sheet could raise global sea levels by between three and five meters. In that context. the message carried by the dust trapped in Antarctic ice feels stark: when warming arrived in the past. the Ross Sea likely opened. winds changed. and the ice shelf that helps slow the system appears to have shrunk.

The drill’s descent at the Allan Hills Blue Ice Area is now offering scientists something rare—direct evidence, in the language of particles, that a warmer Earth can remake the Ross region far more quickly and completely than many people might expect.

Antarctica Ross Ice Shelf West Antarctic Ice Sheet Last Interglacial ice core mineral dust volcanic signature Ross Sea climate simulations sea-level rise Nature Geoscience