RAPID AND SYNCHRONOUS DEGLACIATION OF THREE ADJACENT ALPINE VALLEYS IN THE ARKANSAS RIVER VALLEY, CO AT THE HEINRICH STADIAL 1/BØLLING TRANSITION

The last deglaciation (19 – 11 ka) is a time interval marked by considerable global warming and retreat of glaciers and ice sheets worldwide. Precise reconstructions of alpine glacier demise from around the world during this time interval have been used to assess the impact of global versus regional climate forcings. Here, we present chronologies of glacier retreat during the last deglaciation from three adjacent valleys in the upper the Arkansas River basin, Colorado using ¹⁰Be exposure dating of ice-sculpted bedrock outcrops along valley profiles. We present 12 new and 10 previously published ages that constrain the deglaciation of each valley. We take advantage of a production rate calibration from the western US and use LSDn scaling to (re-)calculate both new and previously published exposure ages; these calculations produce significantly younger ages (by as much as 12 – 7%) when compared to other production rate calibrations and scaling schemes. Deglaciation ages in all three valleys range from 16.0 ± 0.4 to 13.7 ± 0.2 ka (after excluding four outliers). We find that by ~16 ka, the three glaciers had only slightly retreated, holding positions at 100 – 70% of their Last Glacial Maximum extents. Each glacier had experienced a period of rapid retreat ~15 – 14 ka and cirques were ice free by 14.2 – 13.7 ka. Our results indicate that glaciers in the upper Arkansas River valley retreated rapidly and synchronously at the Heinrich Stadial 1/Bølling transition, and may provide evidence for teleconnections between climate forcing in the North Atlantic region and climate response in the western US.