Year Established: 2013 Start Date: 2013-03-01 End Date: 2014-02-28
Total Federal Funds: $18,000 Total Non-Federal Funds: $36,000
Principal Investigators: Susan Kaspari, Carey Gazis
Abstract: Seasonal snowpack and glaciers provide an important source of water in Washington State. Most of the annual precipitation falls during the winter-spring and is stored in the snowpack. The majority of spring-summer runoff is derived from the melting snowpack, with glacier melt contributing as much as 50% to May-September runoff in watersheds with high concentrations of glaciers. Meltwater is relied on to refill reservoirs and to supply crucial summer flows to rivers used for fisheries, hydropower, irrigation, navigation, recreation and drinking water. In recent decades spring snowpack levels have decreased and glaciers have retreated, affecting the timing of runoff and availability of water resources. Warming temperatures are commonly identified as the dominant cause of this decline, but the deposition of light absorbing impurities (LAI) onto snow and glacier surfaces can be an even larger driver of melt. LAI include black carbon (BC) produced by the incomplete combustion of fossil and biofuels, and dust emissions from desert regions and land use change. When deposited on highly reflective snow and glacier ice, LAI cause darkening of the surface, resulting in greater absorption of solar energy, heating of the snow/ice, and accelerated snow and glacier melt. For snowpack and glaciers with substantial deposition of LAI, these impurities are more important than temperature in driving melt. We propose to analyze the previously collected South Cascade Ice Core from the North Cascades in Washington State for BC and dust to assess variations in LAI deposited on snow and glacier surfaces since 1750 AD. We will be able to assess changes in the frequency and magnitude of LAI deposited onto snow/glaciers in the region since prior to industrialization, and the associated impacts on albedo and melt. Furthermore, the ice core record will be used to differentiate the sources of the LAI between natural (e.g., from forest fires and background dust levels) versus anthropogenic sources (e.g. fossil fuel burning, land use change). The South Cascade ice core will be processed at the National Ice Core Laboratory in Denver, CO, and shipped frozen to Central Washington University. Samples will be analyzed for black carbon using Kaspari’s Single Particle Soot Photometer (SP2), and select samples will be analyzed for elemental carbon using a Sunset EC/OC to facilitate method inter-comparison. Dust mass will be determined gravimetrically by filtering samples through pre-weighed .45μm Millipore filters. Select samples will be analyzed for trace elements, which will further aid in characterizing the dust signal and tracing black carbon from fossil vs. bio-fuel sources. The ice core will be dated using 210Pb and tritium. We will use the Snow, Ice, and Aerosol Radiation [SNICAR, Flanner et al., 2007] model to infer the albedo of the snow according to the measured BC and dust impurities. We can therefore create a record of BC, dust and albedo expanding back to 1750, which in turn can be used to infer changes to the energy balance of the snow/glacier, and hence melt. Interpretation of results will focus on the extent to which BC and dust in the North Cascades snowpack have affected water resources. One MS student and one undergraduate student will be trained as part of this research, and we expect the study will result in a minimum of one publication in the international peer-reviewed literature and two theses (one undergraduate and one MS).