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Cryoconite holes play a significant role in the nutrient cycling on glaciers and can be regarded as a storehouse of nutrients that are generated through microbial and photochemical activities. In this work, the chemical characteristics of hydrologically connected and isolated cryoconite holes from three geographically distinct regions of coastal Antarctica, namely Larsemann Hills, Amery Ice Shelf and central Dronning Maud Land were studied. Major ions (Na + , K + , Mg 2+ , Ca 2+ , Cl − , SO 4 2− and NO 3 − ) andtotal organic carbon in the hydrologically isolated, closed cryoconite holes showed significantly higher enrichment (6-26 times and 9 times, respectively) over the conservative tracer ion Cl − possibly due to sediment dissolution and microbial synthesis during isolation period. In contrast, depletion of major ions and organic carbon were observed in the open, hydrologically connected holes due to their discharge from the cryoconite holes through interconnected streams. This study suggests that the contribution of cryoconite holes to the nutrient and microbial transport to downstream environments may vary with the extent of hydrological connectivity by virtue of the fact that nutrients and organic carbon which accumulate in the isolated cryoconite holes during isolation could get washed to downstream environments in the event that they get connected through surface or subsurface melt channels.

While the role of supraglacial environments such as the cryoconite holes and surface snow in cycling of carbon and nutrients has gained momentum in the last decade, little has been done to assess how interactions with sunlight and microbes control the dissolved organic matter cycling in these environments. In this study, the cryoconite holes, which are subjected to different light conditions, were monitored in the coastal Antarctica during the summer in order to determine how the geochemistry of these environments varied through the melt season. Additionally, mesocosm experiments were conducted to understand the impact of photochemical and microbial activities on dissolved organic carbon (DOC) and ionic constituents in the snow and cryoconite holes. In situ measurements of primary and bacterial production carried out in the surface snow and cryoconite holes showed that the primary production rates were higher than the bacterial production rates. Both photochemical and microbial processes resulted in changing the concentration of DOC, carboxylate, and nitrate ions in these environments. Sunlight-induced production of biologically labile compounds, such as acetate and formate, and photochemical degradation of oxalate were also observed. Microbial activity had the opposite effect, resulting in an increase in oxalate and decrease in acetate and formate concentrations. Consequences of these combined processes would determine the fate of DOC and associated nutrients in the Antarctic supraglacial environments and potentially influence the local productivity within these systems.