The role of sulfur in chemical weathering and atmospheric CO2 fluxes: Evidence from major ions, [delta]13CDIC, and [delta]34SSO4 in rivers of the Canadian Cordillera

@article{citeulike:2642053, abstract = {Water samples from the Fraser, Skeena and Nass River basins of the Canadian Cordillera were analyzed for dissolved major element concentrations (HCO3-, SO42-, Cl-, Ca2+, Mg2+, K+, Na+), [delta]13C of dissolved inorganic carbon ([delta]13CDIC), and [delta]34S of dissolved sulfate ([delta]34SSO4) to quantify chemical weathering rates and exchanges of CO2 between the atmosphere, hydrosphere, and lithosphere. Weathering rates of silicates and carbonates were determined from major element mass balance. Combining the major element mass balance with [delta]34SSO4 (-8.9 to 14.1[per mille sign]CDT) indicates sulfide oxidation (sulfuric acid production) and subsequent weathering of carbonate and to a lesser degree silicate minerals are important processes in the study area. We determine that on average, 81\% of the riverine sulfate can be attributed to sulfide oxidation in the Cordilleran rivers, and that 25\% of the total weathering cation flux can be attributed to carbonate and silicate dissolution by sulfuric acid. This result is validated by [delta]13CDIC values (-9.8 to -3.7[per mille sign] VPDB) which represents a mixture of DIC produced by the following weathering pathways: (i) carbonate dissolution by carbonic acid (-8.25[per mille sign]) > (ii) silicate dissolution by carbonic acid (-17[per mille sign]) [approximate] (iii) carbonate dissolution by sulfuric acid derived from the oxidation of sulfides (coupled sulfide-carbonate weathering) (+0.5[per mille sign]). [delta]34SSO4 is negatively correlated with [delta]13CDIC in the Cordilleran rivers, which further supports the hypothesis that sulfuric acid produced by sulfide oxidation is primarily neutralized by carbonates, and that sulfide-carbonate weathering impacts the [delta]13CDIC of rivers. The negative correlation between [delta]34SSO4 and [delta]13CDIC is not observed in the Ottawa and St. Lawrence River basins. This suggests other factors such as landscape age (governed by tectonic uplift) and bedrock geology are important controls on regional sulfide oxidation rates, and therefore also on the magnitude of sulfide-carbonate weathering--i.e., it is more significant in tectonically active areas. Calculated DIC fluxes due to Ca and Mg silicate weathering by carbonic acid (38.3 x 103 mol C [middle dot] km-2 [middle dot] yr-1) are similar in magnitude to DIC fluxes due to sulfide-carbonate weathering (18.5 x 103 mol C [middle dot] km-2 [middle dot] yr-1). While Ca and Mg silicate weathering facilitates a transfer of atmospheric CO2 to carbonate rocks, sulfide-carbonate weathering can liberate CO2 from carbonate rocks to the atmosphere when sulfide oxidation exceeds sulfide deposition. This implies that in the Canadian Cordillera, sulfide-carbonate weathering can offset up to 48\% of the current CO2 drawdown by silicate weathering in the region.}, author = {Spence, Jody and Telmer, Kevin }, citeulike-article-id = {2642053}, doi = {10.1016/j.gca.2005.07.011}, journal = {Geochimica et Cosmochimica Acta}, keywords = {13c, 34s, atmosphericco2, canada, carbon, carbonates, co2, dic, dic13, geochemistry, isotopes, pyrite, rivers, silicates, sulfur, temperate, weathering}, month = {December}, number = {23}, pages = {5441--5458}, posted-at = {2008-04-08 17:23:28}, priority = {4}, title = {The role of sulfur in chemical weathering and atmospheric CO2 fluxes: Evidence from major ions, [delta]13CDIC, and [delta]34SSO4 in rivers of the Canadian Cordillera}, url = {http://dx.doi.org/10.1016/j.gca.2005.07.011}, volume = {69}, year = {2005} }

TY - JOUR ID - citeulike:2642053 L3 - citeulike-article-id:2642053 TI - The role of sulfur in chemical weathering and atmospheric CO2 fluxes: Evidence from major ions, [delta]13CDIC, and [delta]34SSO4 in rivers of the Canadian Cordillera JF - Geochimica et Cosmochimica Acta VL - 69 IS - 23 SP - 5441 EP - 5458 N2 - Water samples from the Fraser, Skeena and Nass River basins of the Canadian Cordillera were analyzed for dissolved major element concentrations (HCO3-, SO42-, Cl-, Ca2+, Mg2+, K+, Na+), [delta]13C of dissolved inorganic carbon ([delta]13CDIC), and [delta]34S of dissolved sulfate ([delta]34SSO4) to quantify chemical weathering rates and exchanges of CO2 between the atmosphere, hydrosphere, and lithosphere. Weathering rates of silicates and carbonates were determined from major element mass balance. Combining the major element mass balance with [delta]34SSO4 (-8.9 to 14.1[per mille sign]CDT) indicates sulfide oxidation (sulfuric acid production) and subsequent weathering of carbonate and to a lesser degree silicate minerals are important processes in the study area. We determine that on average, 81% of the riverine sulfate can be attributed to sulfide oxidation in the Cordilleran rivers, and that 25% of the total weathering cation flux can be attributed to carbonate and silicate dissolution by sulfuric acid. This result is validated by [delta]13CDIC values (-9.8 to -3.7[per mille sign] VPDB) which represents a mixture of DIC produced by the following weathering pathways: (i) carbonate dissolution by carbonic acid (-8.25[per mille sign]) > (ii) silicate dissolution by carbonic acid (-17[per mille sign]) [approximate] (iii) carbonate dissolution by sulfuric acid derived from the oxidation of sulfides (coupled sulfide-carbonate weathering) (+0.5[per mille sign]). [delta]34SSO4 is negatively correlated with [delta]13CDIC in the Cordilleran rivers, which further supports the hypothesis that sulfuric acid produced by sulfide oxidation is primarily neutralized by carbonates, and that sulfide-carbonate weathering impacts the [delta]13CDIC of rivers. The negative correlation between [delta]34SSO4 and [delta]13CDIC is not observed in the Ottawa and St. Lawrence River basins. This suggests other factors such as landscape age (governed by tectonic uplift) and bedrock geology are important controls on regional sulfide oxidation rates, and therefore also on the magnitude of sulfide-carbonate weathering--i.e., it is more significant in tectonically active areas. Calculated DIC fluxes due to Ca and Mg silicate weathering by carbonic acid (38.3 x 103 mol C [middle dot] km-2 [middle dot] yr-1) are similar in magnitude to DIC fluxes due to sulfide-carbonate weathering (18.5 x 103 mol C [middle dot] km-2 [middle dot] yr-1). While Ca and Mg silicate weathering facilitates a transfer of atmospheric CO2 to carbonate rocks, sulfide-carbonate weathering can liberate CO2 from carbonate rocks to the atmosphere when sulfide oxidation exceeds sulfide deposition. This implies that in the Canadian Cordillera, sulfide-carbonate weathering can offset up to 48% of the current CO2 drawdown by silicate weathering in the region. KW - 13c KW - 34s KW - atmosphericco2 KW - canada KW - carbon KW - carbonates KW - co2 KW - dic KW - dic13 KW - geochemistry KW - isotopes KW - pyrite KW - rivers KW - silicates KW - sulfur KW - temperate KW - weathering AU - Spence, Jody AU - Telmer, Kevin PY - 2005/12/01/ UR - http://dx.doi.org/10.1016/j.gca.2005.07.011 ER -