Chemical weathering in glacial environments

Do glaciers enhance or inhibit chemical weathering rates relative to other environments? The importance of glaciers in the global carbon cycle and climate change hinges on the answer. We show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge. Silica denudation rates are distinctly lower in glacier-covered catchments than in their nonglacial counterparts. Because sediment yields are high from glaciers, this suggests that water flux, rather than physical erosion, exerts the primary control on chemical erosion by glaciers. Potassium and calcium concentrations are high relative to other cations in glacial water, probably due to dissolution of soluble trace phases, such as carbonates, exposed by comminution, and cation leaching from biotite. Preferential weathering of biotite may result in higher ⁸⁷Sr/⁸⁶Sr in glacial runoff than expected from whole-rock compositions. Thus, although glaciers do not influence total chemical denudation rates at a given runoff, they may yield compositionally distinctive chemical fluxes to the oceans. Disruption of mineral lattices by grinding increases dissolution rates; this and high surface area should make glacial sediments exceptionally weatherable. Weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles.