Antarctic rocks reveal a missing chapter of glacier history

Istanbul, Türkiye – Antarctica’s glaciers have been changing long before satellites, weather stations, or cameras captured them, leaving behind clues. Along Marguerite Bay on the Western Antarctic Peninsula, ridges of rocks and debris mark former glacier margins. For decades, scientists lacked direct evidence about when many of these ridges formed.

Now, researchers have assigned dates to some of them, filling a key gap in the region’s glacier history. This study presents the first direct surface-exposure ages for late-Neoglacial, including Little Ice Age, moraines in Marguerite Bay, the largest bay on the Western Antarctic Peninsula. Notably, they dated a moraine on Shoesmith Glacier on Horseshoe Island to 496 ± 79 years ago, placing its formation during the Little Ice Age. Published in Quaternary Science Reviews, these findings offer new physical evidence of how glaciers in this part of Antarctica responded during one of the peninsula’s most recent cooling periods.

“These ridges resemble ancient boundaries formed by ice. Determining when the rocks were exposed allows us to map past glacier positions before direct observations. Marguerite Bay was a key missing piece in that historical puzzle," explained Prof. Attila Çiner of the Eurasia Institute of Earth Sciences at Istanbul Technical University.

A missing period in Antarctica’s glacier timeline

Scientists have extensive knowledge about the much older retreat of ice from Marguerite Bay after the Last Glacial Maximum, when large ice sheets covered the region. However, understanding events over the past several thousand years remains limited. A key period is the Neoglacial, a cooling phase that began around 4,000 years ago and ended roughly 200 years ago. Its later part overlaps with the Little Ice Age, dated from 1300 to 1850 CE, mainly documented in Northern Hemisphere records.

Previous studies indicate that glaciers advanced in parts of the Antarctic Peninsula during this period, as evidenced by lake and marine sediments, raised beaches, buried mosses, and glacial landforms. Researchers have also dated glacier movements around the Peninsula in the Little Ice Age. However, Marguerite Bay was still an unexplored area. It has well-preserved moraines near active glaciers, but prior to this study, no dating data existed for its Neoglacial glacial deposits. This research does not claim to pinpoint the Little Ice Age in Antarctica but offers a vital missing piece by providing directly dated moraines that show when glaciers advanced there during this recent climate period.

Using rocks as clocks

The researchers examined moraines associated with three glaciers: Shoesmith and Erinç on Horseshoe Island and Erol Glacier on the nearby Calmette Peninsula. A moraine is a ridge of rock and sediment deposited or pushed by moving ice. When the glacier retreats and exposes these rocks, they begin to accumulate trace amounts of beryllium-10 produced by cosmic rays. By measuring this isotope, scientists can determine how long a rock surface has been exposed. The clearest record was from the Shoesmith Moraine. After removing samples with older geological signals, the researchers estimated an age of 496 ± 79 years. This suggests the moraine stabilized during the Little Ice Age, at the end of the Neoglacial period. Notably, this finding aligns with broader evidence from the Antarctic Peninsula.

Previous studies using other geological and biological data have also identified glacier advances during similar periods. For example, an advance near Rothera Point, less than 50 kilometers from the study site, occurred around the same time as the Shoesmith Glacier advance. Collectively, these records support the idea that the Little Ice Age was a significant phase of glacier expansion in parts of the Western Antarctic Peninsula, although the timing and behavior of individual glaciers varied.

Not every Antarctic rock tells a simple story

The other two glaciers also illustrate why reconstructing Antarctica’s recent history can be challenging. Rocks from the Erinç Moraine showed a broader age range. The researchers considered various explanations and favor an age of 1,163 ± 403 years, suggesting an earlier late-Neoglacial glacier advance. A nearby, undated ridge, just a few meters from the current glacier, might have formed during the Little Ice Age, but this remains a tentative link. At Erol Glacier, three sampled boulders appeared significantly older than the moraine, ranging from around 2,000 to nearly 10,000 years old, because the rocks retained beryllium-10 from earlier exposure. This indicates that a rock can be older than the glacier ridge it ends up in. Additional evidence clarified the situation: parts of the Erol Moraine overlay previously dated raised beaches, showing the glacier must have advanced after those beaches formed, supporting its connection to the Little Ice Age.

“Antarctic rocks do not always reset their geological clocks to zero when a glacier moves them. Some carry an older history with them. That is why we need to interpret the dates together with the surrounding landscape,” explained Prof. Attila Çiner.

Small ridges, a much bigger climate story

One of the most fascinating findings is the current locations of some of these ancient glacier boundaries. The researchers note that inner moraine ridges linked to Little Ice Age glacier positions are often only about 25–50 meters from current glacier fronts. This may suggest a degree of local stability despite the significant warming observed in the Antarctic Peninsula over recent decades. However, this does not imply the glaciers are immune to future changes.

The researchers emphasize that further studies are necessary to understand how ongoing warming and variations in snowfall might influence these ice masses in the years ahead. Numerous other undated moraines and lakes around Marguerite Bay could serve as additional clues, expanding the record. Ultimately, the study's significance goes beyond dating a ridge of Antarctic rocks. Modern satellite technology allows scientists to monitor changes in Antarctica in greater detail, and moraines can extend our understanding back in time, to before measurement tools existed.

By converting these ancient glacier boundaries into dated records, researchers can compare contemporary changes with centuries or even thousands of years of natural glacier behavior, helping them develop a clearer understanding of how Antarctic ice reacts to climate shifts.

“Satellites reveal the current state of Antarctic glaciers, while the landscape records their past activity. Dating more ancient glacier boundaries extends our timeline for understanding how Antarctic ice reacts to climate change,” said Prof. Attila Çiner.