Energy Balance and Snow Melt on the Kahiltna Glacier, Central Alaska Range
As of 2002, Degree of Master of Science (MS) Quaternary and Climate Studies published under the auspices of the Climate Change Institute.
Abstract
Paleoclimate and mass balance studies depend on the determination of the physical and chemical relationships between melt water and the snowpack, particularly in Central Alaska where glaciers have had consistent negative mass balances for several decades and are among the leading contributors to global sea level rise. To explore these relationships in Central Alaska, I constructed a surface energy balance model based on meteorological observations from May 26, 2010 to June 11, 2010, at Kahiltna Base Camp in Denali National Park, in order to determine the principal modes of energy transfer into the ice and how they are affected by atmospheric variables. The physical properties of grain size, snow hardness, water content and density were measured within the top 1.8 meters of snowpack twice daily between May 26-June 10, 2010 to determine the effects of melt on snow stratigraphy. Snowpit samples were collected and analyzed for 8D, major ion, and trace metal concentrations. At one site, samples were collected on May 13 and June 10, 2010 while at a nearby site samples were collected during the morning and evening of June 7. Through the analysis of these samples the changes in chemical profiles imposed by melt can be assessed on timescales of one day and one month. Results indicate that incoming solar radiation is the dominant source of energy transferred to the ice with an average flux of 47 W/m2. Both temperature index and energy balance models may be appropriate at this site, although high (r2=0.61) correlations with temperature and melt rate are due to the positive relation between air temperature and incoming solar radiation rather than to large sensible and longwave fluxes. The energy balance model was applied to the period 1971-2000 across the Central Alaska Range to produce a realistic equilibrium line altitude at 2000 meters elevation and glacial mass balance of -0.60 meters per year. The mass of surface snow melted at Kahiltna Base Camp is significantly correlated (r2=0.56) with both snowpack density and total mass of melt layers (r2=0.398) within the upper 1.8 meters of the snowpack. At this site, only 53% of the melt water retained in the snow is reconstituted in melt layers, while the other 47% is distributed evenly within existed layers, leading to a homogenization of the stratigraphic profile. Melting smoothes the 8D profile with an average 8.6 %o enrichment in the uppermost meter of snow. After one day of melt trace metals are concentrated by 300-400% in areas just above melt layers, leading us to conclude that chemical stratigraphy at Kbase primarily reflects post-depositional processes rather than atmospheric concentrations. Studies in ice core paleoclimatology and mass balance estimates from surface lowering must account for the physical and chemical changes imposed by melt in sites experiencing similar conditions.