Evidence points to renewed Barnes Ice Cap growth about 2,000 years ago

Barnes Ice Cap is a surviving fragment of the Laurentide Ice Sheet. According to Ars Technica, its ice is frozen to the ground rather than sliding over it, allowing buried tundra plants to remain intact.

The study’s team used radioactive beryllium-10 in exposed rock surfaces to estimate when ice had withdrawn. Radiocarbon dating of mosses then established when advancing ice killed the plants. Together, these methods reconstruct retreat followed by renewed expansion.

Rock-exposure dating places the retreat of the Laurentide remnant within today’s ice margin by about 3,600 years ago, with further shrinkage probable around 3,000 years ago. This reconstructs an earlier retreat rather than a continuous measurement record.

The proposed start of renewed growth remains an inference for Barnes itself. Older plants are still buried there; the roughly 2,000-year timing comes from nearly 200 plant-death dates previously collected at neighboring ice caps sharing the same climate. None was older than that. At Barnes, the article reports that retreat since 1960 has exposed plants killed from about 1000 CE onward, while the ice margin has withdrawn 200–800 meters.

Lead author Nicolás Young interprets the renewed advance as the beginning of another glaciation, not evidence that a full ice-age climate had already arrived. He says development of large ice sheets would have taken several tens of thousands of years. The finding therefore concerns the earliest reversal toward growth—and its reported interruption—not an imminent ice age avoided by warming.