Enhancement of glacial solute fluxes in the proglacial zone of a polythermal glacier

Abstract

Annual proglacial solute fluxes and chemical weathering rates at a polythermal high-Arctic glacier are presented. Bulk meltwater chemistry and discharge were monitored continuously at gauging stations located at the castern and western margins of the glacier terminus and at "the Outlet", 2.5 km downstream where meltwaters discharge into the fjord. Fluxes of non-snowpack HCO3-, SO42-, Ca2+ and Mg2+ increase by 30-47% between the glacier terminus and the Outlet, indicating that meltwaters are able to access and chemically weather efflorescent sulphates, carbonates and sulphides in the proglacial zone. Smaller increases in the fluxes of non-snowpack-derived Na+, K+ and Si indicate that proglacial chemical weathering of silicates is less significant. En3hanced solute fluxes in the proglacial zone are mainly due to the chemical weathering of active-layer sediments. The PCO2 of active-layer ground-waters is above atmospheric pressure. This implies that solute acquisition in the active layer involves no drawdown of CO2. The annual proglacial chemical weathering rate in 1999 is calculated to be 2600 meqΣ+m-2. This exceeds the chemical weathering rate for the glaciated part of the catchment (790 meqΣ+m-2) by a factor of 3.3. Hence, the proglacial zone at Finsterwalderbreen is identified as an area of high geochemical reactivity and a source of CO2.