Biogeochemical evolution of cryoconite holes on Canada Glacier, Taylor Valley, Antarctica

The cryoconite holes of the McMurdo Dry Valleys are simple, closed biogeochemical systems involving water, ice, mineral and organic debris, which serve as ecosystems for consortia of microorganisms. This study is the first to document the seasonal and annual chemical evolution of solutes in cryoconite holes. Samples of glacier ice, frozen cryoconite holes and those containing water were collected during the austral summer of 2005-2006. The isolation age was calculated from the excess Cl- in the holes, and varied from 0 to 5 years ( a), consistent with the last hot summer when the cryoconite holes were open to the atmosphere. The holes progressively deepen with isolation age. Variations in DIC, DOC, K+ and SO42- suggest that dissolution of primary minerals in the cryoconite debris, cyclical precipitation and dissolution of secondary carbonates, net photosynthesis over summer and net respiration during the autumnal freeze are the principal reactions which perturb the seasonal and annual solute concentrations in the holes. DOC is generated in the holes at a rate of 7.5 mu g C cm(-2) a(-1), and non-sea-salt K+ accumulates in frozen holes at a rate of 0.073 mu eq cm(-2) a(-1). We infer that C cycling is complex even in these otherwise simple systems.