δ18O AND δD FRACTIONATION TRENDS IN SURFACE SNOW ACROSS THE MATTHES-LLEWELLYN DIVIDE, JUNEAU ICEFIELD, ALASKA AND BRITISH COLUMBIA

A lack of understanding of parameters that govern stable isotope fractionation in precipitation in regions of particularly complex meteorological conditions and high relief has long presented problems for paleoclimate and hydrologic studies. With a goal of obtaining high resolution data of local orographic effects on isotopic variation in precipitation, 123 surface snow samples were taken at 0.5 to 1 km increments along a 35 km transect spanning the Matthes and Llewellyn glaciers in southeast Alaska and British Columbia. These samples were obtained during late July to early August 2012 at elevations ranging from ~1260 m to 1870 m and were analyzed for δ18O and δD onsite using an LGR Liquid Water Isotope Analyzer. δ18O and δD were found to decrease with elevation, as expected. Isotopic plots show a strong correlation and are similar to the theoretical global meteoric water line, displaying a linear trend of y = 7.86x – 19.48 and r² = 0.898. In hopes of determining the dominant types of localized weather systems causing these fractionation trends, results are compared alongside open-system Rayleigh fractionation models, NOAA back trajectory air-mass simulations, and nearby-recorded meteorological data. We attempt to place these weather systems into synoptic-scale meteorological contexts as a proxy for delineating orographic fractionation parameters on the Juneau Icefield.