Chemical denudation and the role of sulfide oxidation at Werenskioldbreen, Svalbard

•Chemical denudation in the Werenskioldbreen basin ranges from 1601 to 1762meqm−2yr−1.•Chemical weathering intensity ranges from 876 to 964meqm−3yr−1.•Sulfide oxidation predominates in subglacial channel-dominated outflows.•Carbonation accompanies sulfide oxidation in subartesian outflows.•Sulfide oxidation is a good indicator to distinguish drainage system configuration. This study aims to determine the rate of chemical denudation and the relationships between dominant geochemical reactions operating in the proglacial and subglacial environments of the polythermal glacier Werenskioldbreen (SW Svalbard) during an entire ablation season. Water sampling for major ion chemistry was performed at a proglacial hydrometric station and from subglacial outflows from May to September 2011. These data were combined with measurements of discharge and supraglacial ablation rates. The slopes and intercepts in best-fit regressions of [*Ca2++*Mg2+ vs. *SO42−] and [HCO3− vs. *SO42−] in meltwater from ice-marginal subglacial channels were close to the stoichiometric parameters of sulfide oxidation and simple hydrolysis coupled to carbonate dissolution (*concentrations corrected for input of sea-salt). This shows that these relationships predominates the meltwater chemistry. Our findings also show that sulfide oxidation is a better indicator of the configuration of subglacial drainage systems than, for instance, Na+ and K+. In the proglacial area and in sub-artesian outflows, the ion associations represent sulfide oxidation but other processes such as ion exchange and dissolution of Ca and Mg efflorescent salts may also contribute to the solute variations. These processes may cause enhanced fluxes of Ca2+ and HCO3− from glacierized basins during the early ablation and peak flow seasons as the proglacial salts re-dissolve. The overall chemical denudation rate in the basin for 2011 (ranging from 1601 to 1762meqm−2yr−1 (121.9 to 132.2tkm−2yr−1)) was very high when compared to other Svalbard valley glaciers suggesting that the high rate of chemical denudation was mostly caused by the high rates of discharge and ablation. Chemical weathering intensities (876 and 964meqm−3yr−1) exceeded previously reported intensities in Svalbard.