Abstract

Mountain glaciers in the Sawtooth Mountains responded strongly to reinvigorated atmospheric moisture transport following the last ice-sheet maximum. The glaciers constructed an extensive moraine belt in the southeastern Sawtooth Mountains, allowing determination of a detailed radiocarbon chronology from lake and marsh cores. Moraine morphometry and soil data indicate construction of seven to nine moraines in each of four valleys during two main late Pleistocene ice advances. A basal radiocarbon date from marsh cores in the Alturas valley documents that the maximum advance during marine oxygen isotope stage 2 occurred shortly before ca. 16,900 calibrated (cal.) yr B.P. Minimum limiting dates on glacial-lacustrine sediment in lake and marsh cores from three valleys, clustered around 13,950 cal. yr B.P., document the maintenance or reestablishment of extensive ice volume during early late-glacial time. The ca. 16,900 cal. yr B.P. advance postdates the last ice-sheet maximum by ∼4000 yr and is broadly correlative with maximum advances of the North Yellowstone outlet glacier and the Puget Lobe of the Cordilleran Ice Sheet and a near-maximum advance of Wallowa Mountain glaciers. These synchronous advances indicate response of a variety of ice systems to reinvigorated moisture transport following the ice-sheet maximum, as does the subsequent Sawtooth advance during early late-glacial time. Together, these responses indicate strong sensitivity of certain ice systems to moisture-delivery fluctuations.

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