Chemical Weathering of Phosphate and Germanium in Glacial Meltwater Streams: Effects of Subglacial Pyrite Oxidation

Data from three glacial meltwater streams draining Mt. Tronador in the southern Argentine Andes $(72\circW$, $41\circS)$ show that subglacial pyrite oxidation and the subsequent precipitation of iron oxides strongly influences dissolved phosphate concentrations but do not appear to affect dissolved germanium concentrations. Total-Fe (TFe) and total-P (TP) concentrations are high in all three glacial streams, but the ratios of soluble reactive phosphate (SRP) to TP are very different. The Upper Manso Streams that drains the Manso Glacier has relatively low SRP $(0.01-0.23 \mu M)$, representing a small fraction of its TP (0.1-5%). The SRP of the two streams draining smaller side glaciers $(0.12-0.69 \muM)$ represents a much larger portion of their TP (20-32%). TFe, dissolved sulfate, and $\delta ^34 S$ data suggest that pyrite oxidation is the most likely weathering reaction contributing sulfate to the Upper Manso Stream but not to the two smaller glacial-fed streams, in which atmospheric inputs can account for all of the sulfate. Dissolved Ge appears to show no preferential sorption relative to dissolved silica, in contrast to the speculation that Ge preferentially sorbs on fresh iron hydroxyoxide surfaces.