Chemical weathering and solute export by meltwater in a maritime Antarctic glacier basin

Solute yields, laboratory dissolution data and both chemical and isotopic markers of rock weathering reactions are used to characterise the biogeochemistry of glacial meltwaters draining a maritime Antarctic glacier. We find that delayed flowpaths through ice-marginal talus and moraine sediments are critical for the acquisition of solute from rock minerals because delayed flowpaths through subglacial sediments are absent beneath this small, cold-based glacier. Here the mechanisms of weathering are similar to those reported in subglacial environments, and include sub-oxic conditions in the early summer and increasingly oxic conditions thereafter. Up to 85% of the NO(3) (-) and 65% of the SO(4) (2-) are most likely produced by bacterially mediated reactions in these ice marginal sediments. However, reactive pyrite phases are sparse in the host rocks, limiting the export of Fe, SO(4) (2-) and cations that may be removed by weathering once pyrite oxidation has taken place. This means that dissolution of Ca(2+) and Na(+) from carbonate and silicate minerals dominate, producing moderate cationic denudation yields from Tuva Glacier (163 I pound*meq(+) m(-2) a(-1)) compared to a global range of values (94-4,200 I pound*meq(+) km(-2) a(-1)). Overall, crustally derived cations represent 42% of the total cationic flux, the rest being accounted for by snowpack sources.