LAST GLACIAL MAXIMUM EQUILIBRIUM LINE ALTITUDES FROM MOUNTAIN GLACIERS ACROSS ALASKA

We report new paleo-equilibrium line altitude (ELA) data from alpine glaciers across Alaska with the goal of producing a data-model comparison for Last Glacial Maximum (LGM) climate. Our dataset spans nearly 12° of latitude and 30° of longitude. LGM and pre-industrial glacier extents were constrained using LGM ice limits from the Alaska PaleoGlacier Atlas and Landsat8 imagery. Glacier surfaces were interpolated using GlaRe, an ArcGIS toolbox. ELAs of these glacier surfaces were then calculated with another ArcGIS toolbox using accumulation area ratio values between 0.55 and 0.65. Our results show statewide LGM ELAs ranging from ~300 m asl in the western Ahklun Mountains (SW Alaska) to ~1800 m asl in the eastern Brooks Range (NE Alaska). This SW-NE rise in ELA values suggests the strong influence of a North Pacific moisture source. Additionally, LGM ΔELA (preindustrial ELA minus LGM ELA) values, thus far most of which are available from the Alaska Range, range from -200 to -800 m with an average of 420 ± 195 m. Abundant proxy data from Alaska suggest drier than modern conditions during the LGM. Thus, deriving temperatures depressions derived using simplistic atmospheric lapse rates can be used to estimate maximum temperature depressions. ΔELA values yield a maximum summer temperature depression of 4.2 ± 2.0°C – contrary to some global climate models that show Alaska being warmer than present during the LGM but still consistent with relatively mild temperature depressions from some local climate proxy reconstructions and a recent global synthesis. Future work will focus on reconstructing ΔELAs elsewhere in Alaska to supplement the ΔELA values in the Alaska Range.