Introduction

Glaciers are the largest freshwater reservoir on Earth (Knight, 1999), containing some 28 x 106km3 of water (Table 14.1). Glaciers are acknowledged as powerful agents of physical erosion (Paterson, 1994; Hallet et al., 1996). Globally significant volumes of sediment may be transported and deposited from glacial runoff (Syvitski et al., 1987). By contrast, glacial chemical erosion is less well documented (Sharp et al., 1995; Anderson et al., 1997), but globally significant quantities of solute may be transported by glacial runoff in relatively brief periods during deglaciation (Tranter et al., 2002a).

Chemical erosion in glaciated regions proceeds at rates comparable to those of temperate catchments with comparable specific runoff (Anderson et al., 1997). The factors usually associated with elevated rates of chemical weathering in other environments, such as the continual presence of water, soil and vegetation (Drever, 2003), are not definitive features of glacial environments. Glaciated regions are largely frozen for significant periods each year, the residence time of liquid water in the catchment is low (Knight, 1999), there are thin, skeletal soils at best and vegetation is either absent or limited (French, 1997). Even so, chemical erosion rates in glaciated terrain are usually near to or greater than the continental average (Sharp et al., 1995; Wadham et al., 1997, Hodson et al., 2000). This is because glaciated catchments usually have high specific runoff, there are high concentrations of freshly comminuted rock flour, and adsorbed organic matter or surface precipitates that may hinder water-rock interactions are largely absent (Tranter, 1982). In short, the rapid flow of water over fine-grained, recently crushed, reactive mineral surfaces maximizes both the potential rates of chemical weathering and chemical erosion.

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