Introduction

The proglacial zone is an area of potentially high geochemical activity, because it contains a variety of comminuted glacial debris, is subject to glaciofluvial reworking and can be colonized by vegetation (Anderson et al., 2000; Cooper et al., 2002). Chem by sulphide oxidation (Equation 7) is ultimately deposited as carbonate in the oceans, and this gives rise to a net release of CO2 to the atmosphere (Equation 10).

Ca2+(aq) + 2HCO3-(aq) ^ CaCO3(s) + H2OQ) + CO2(g) (10)

The impact of major ions in glacial runoff on global geochemi-cal cycles is presently very limited. This is because the runoff is dilute when compared with riverine concentrations, and because the volume of glacial runoff is small when compared with riverine discharge to the oceans. However, during deglaciation, when global glacial discharge is believed to have equalled global riverine discharge to the oceans, there may have been short periods when glacial solutes made similar contributions to riverine fluxes of major ions (Tranter et al., 2002a).

To date, modelling that attempts to determine the impact of glacial chemical weathering on atmospheric CO 2 concentrations has not found any significant perturbations (Ludwig et al., 1998; Jones et al., 2002; Tranter et al., 2002a). However, linkage of terrestrial chemical erosion models to ocean carbon cycle models is still at an early stage of development. It may well be the case that the next generation of ocean carbon cycle models will be able to explore in greater detail the changes in dissolved inorganic carbon species at depth that arise from changes in ocean circulation (Broecker, 1995; Dokken & Jansen, 1999). Atmospheric CO2 perturbations from changing terrestrial chemical erosion may be amplified as a consequence, as it is anticipated that enhanced terrestrial chemical erosion during times of reduced sea level is less well buffered by slower deep water turnover (Jones et al., 2002).

ical weathering reactions resemble those in subglacial environments (Anderson et al., 2000; Wadham et al., 2001a), with sulphide oxidation/carbonate dissolution dominating in recently deglacierized moraines, and carbonation of silicates becoming more important in older moraines as the reactive sulphides and carbonates are exhausted (Anderson et al., 2000). Significant dif and other ice masses (after Knight, 1999)

Table 14.3 Volumes of terrestrial ice contained in ice sheets and other ice masses (after Knight, 1999)

Region

Current Volume

Volume at LGM

(106km3)

(106km3)

Antarctica 26 26

Greenland 2.6 3.5

Laurentide 30

Cordilleran 3.6

Scandinavian 13

Other ice masses 0.2 1.1

Total 28.4 77.2

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