EVIDENCE FOR YOUNGER DRYAS GLACIER ACTIVITY IN THE TETON MOUNTAIN RANGE, WYOMING

Warming at the end of the last glaciation was interrupted by the Younger Dryas (YD), a ~1200-year-long cold event (~12.9 to 11.7 ka) characterized by both its severity and abruptness. Despite uncertainty regarding its cause, this event presents a valuable opportunity to assess environmental responses to abrupt climate change centered in the North Atlantic. The expression of the YD at lower latitudes is of particular interest, given uncertainty in the global nature of the event and the proximity of lower latitude sites to population centers. Although some sedimentary and moraine records hint that alpine glaciers in the western US were influenced by YD cooling, such records are sparse and often equivocal. Additional well-dated glacier and climate records are required to definitively demonstrate the influence of this short-lived event in the region. We explore the nature of YD glacier activity in Teton mountain range, WY, by using cosmogenic ¹⁰Be to precisely date a Late Pleistocene moraine fronting the modern Teton and Teepee glaciers in Glacier Gulch. Five of six moraine boulders statistically overlap and fall within the YD interval, suggesting that deglaciation during the latest Pleistocene was interrupted by either a stillstand or a re-advance due to YD cooling. Lake sediment records from nearby high and low elevation sites exhibit a marked shift from glacier-dominated to organic-dominated sediments at ~11.5 ka, indicating that glaciers retreated rapidly at the end of the YD. Taken together, the moraine ages and lake sediment records provide compelling evidence that YD cooling influenced the pattern of deglaciation in the Teton Range, likely halting glacial retreat and resulting in glacier configurations greater than at any time in the Holocene, including the Little Ice Age. Constraining the sensitivity of alpine glaciers in the western US to abrupt climate oscillations centered in the North Atlantic is critical for predicting glacier response to modern warming.