PALEO-GLACIER EQUILIBRIUM LINE ALTITUDES FROM CENTRAL ALASKA: INSIGHTS INTO LAST GLACIAL MAXIMUM AND LATE GLACIAL CLIMATE

Alpine glacier equilibrium line altitudes (ELAs) are useful indicators of climate conditions. Reconstructions of past glacier extent can yield ELAs from periods when glaciers were more expansive, which combined with recent (pre-industrial) ELAs of extant glaciers within the same basins, quantify ELA depression (ΔELA). ΔELAs can be used to infer past temperature and precipitation, and paleo-ELA gradients across space are useful in identifying past moisture and temperature sources. Here, we report new paleo-ELA data from central Alaska, where global climate models depict an anomalously mild Last Glacial Maximum (LGM). Elsewhere in Alaska, LGM ELA depressions have been found to be 200 – 700 m (Brooks Range) and ~560 m (in Denali National Park, Alaska Range). These ΔELA values are lower than others reported elsewhere globally (~1000m ). Our new results span ~11° of longitude in the Alaska Range, and include several outlying glaciated centers across Alaska. Former glacier surfaces (from the LGM, Late-Glacial and Little Ice Age) were mapped using moraines and interpolated using an ArcGIS toolbox. ELAs were calculated with various accumulation area ratio (AAR) values using another ArcGIS add-on. Initial findings show LGM ELAs in the Alaska Range between ~1000 and 1560 m asl (using AAR of 0.65), and a LGM ΔELA of ~200 – 800 m. We will also report Late-Glacial ELA depression values. LGM ELAs appear to be lowest in the southwestern Alaska Range, and highest along the northeastern Alaska Range. Overall, these LGM ΔELA values are difficult to reconcile with modeled mild LGM summer temperature, especially considering that independent proxy evidence suggests arid conditions.