Thule to Summit: Using the physical and chemical properties of shallow firn to describe glacier facies, accumulation, and 55 years of change

Between 1952 and 1955, Carl Benson and the US Army Snow, Ice and Permafrost Research Establishment undertook a series of traverses of the Greenland Ice Sheet (GIS). Employing a number of physical measurements, Benson (1962) characterized the GIS via mapping of the spatial distribution of annual net accumulation and classifying the diagenetic glacier facies. Recent advances in remote sensing techniques now provide a number of ways to assess the state of the GIS, but these techniques still require some component of in situ verification. In the springs of 2010 and 2011, we undertook a 1200 km traverse along a nearly-identical route on the GIS from Thule Air Base to Summit Station. Along the traverse route, we characterized the physical stratigraphy of the near-surface (0-10 m depth) snow using an array of observations such as density, grain size, hardness, optical stratigraphy and temperature. We collected a total of 30 snow pits and 14 shallow firn cores over the two field seasons. These measurements allow us to make comparisons with Benson's results, identifying changes in glacier facies and accumulation patterns over the past 55 years. In addition to physical stratigraphy, we measured snowpit chemical stratigraphy (major ions, trace elements and stable water isotopes) at 5-10 cm resolution. These measurements allow us to date horizons seen in the physical stratigraphic record, and to explore questions about the spatial variability of species deposition. Here, we present an initial analysis of these snowpits, shallow cores, and BOS logs, co-located with near infrared imagery, ground-penetrating radar and kinematic GPS data (see Lutz et al. and Overly et al., both this session), which will be useful in quantifying spatial and temporal changes in glacier facies, accumulation rates, and geochemical cycling on the GIS. Benson, CS. 1962. Stratigraphic studies in the snow and firn of the Greenland Ice Sheet. SIPRE Research Report, 70, 89 pp.