A continuous 10,000-year record of alpine glacier fluctuations in Wyoming's Teton Range suggests that some glacial ice in the western U.S. persisted in a reduced, essentially dormant state during periods of early Holocene warming. The findings challenge the paradigm that all Rocky Mountain glaciers completely disappeared during these warm, dry conditions, instead indicating that they may have taken the form of smaller glaciers covered by debris or caked with rocks, which insulated the lingering ice from the heat. This insight may help scientists better understand how glaciers in the region may respond to future warming. "The long-term survival of glacial ice through warm conditions highlights the potential role of debris-covered glaciers and/or rock glaciers to continue providing ecosystem services into the future, despite unfavorable climatic conditions," says Darren Larsen, the lead author of the study. Retreating glaciers are a hallmark of modern climate change, but due to an incomplete glacial record, little is known about how western U.S. glaciers responded to temperature and precipitation changes thousands of years ago. To construct a continuous record, Larsen and colleagues sampled sediment cores from two lake basins in the Tetons - Delta Lake, a glacial lake basin that provided a complementary record of glacier activity, and other nearby lakes including Surprise Lake, a nonglacial lake basin that provided a record of climate variability. By using accelerator mass spectrometry radiocarbon dating, the researchers developed composite rock layer sequences that documented changes in the glaciers as they endured shifts in climate over ten millennia. While sediment flux and meltwater from the Teton Glacier appeared to decrease during a warm period between about 10,000 and 6,300 years ago, Delta Lake sediments maintained distinctly glacial characteristics that suggest glacial ice remained.
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