150 Years of Light Absorbing Impurity Deposition on South Cascade Glacier, Washington State USA

Glaciers and seasonal snowpack in Washington State have undergone significant decline over the past 50 years. While warming global temperatures are widely recognized as the cause of glacial decline, the deposition of black carbon (BC) can also contribute to increased melt. BC, commonly referred to as soot, is produced by the incomplete combustion of fossil and biofuels. These particles are subject to atmospheric transport and are deposited on snow by wind and precipitation events. When BC is deposited, it lowers the albedo of the glacial surface resulting in increased energy absorption and melt. We used a 158 m long ice core collected from the South Cascade Glacier in the North Cascades of Washington State to reconstruct 20th century BC deposition. The ice core was processed into 1,989 segments averaging 7.75 cm and BC was measured using a Single Particle Soot Photometer (SP2). Background and peak BC concentrations increased over the top third of the core, peaking at a depth of 52 meters. Concentrations decreased gradually over the lower two thirds of the core, with the higher concentrations indicating higher atmospheric BC loading. Several segments of the ice core contained visible impurity layers and analysis determined 26 outlying samples that contained BC concentrations exceeding 100ng/g. These outliers are randomly distributed through the entire length of the core and may originate from regional forest fire activity, a major natural source of BC