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During the ablation season, active microbial communities colonise large areas of the Greenland Ice Sheet surface and produce dissolved organic matter (DOM) that may be exported downstream by surface melt. Meltwater flow through the bare ice interfluvial area, characterized by a porous weathering crust, is slow (~ 10-2 m d-1), meaning that it presents a potential site for photochemical and/or microbial alteration of supraglacial DOM. Transformations of supraglacial DOM during transport through the supraglacial drainage system remain unexplored, limiting our understanding of supraglacial DOM inputs to downstream subglacial and coastal ecosystems. Here, we employ negative-ion electrospray ionization 21 tesla Fourier transform ion cyclotron resonance mass spectrometry to catalogue the molecular composition of DOM in supraglacial dark ice, weathering crust meltwater, and supraglacial stream water sampled in a hydrologically connected supraglacial micro- catchment to address this knowledge gap. Dark ice DOM contained significantly more aromatic (25 ± 3 %) and less biolabile (13 ± 4 %) DOM than weathering crust meltwater (3 ± 0 and 50 ± 0 %, respectively), pointing to retention of DOM on the ice surface and microbial, as well as photochemical alteration of DOM during transit through the supraglacial drainage system. These findings have implications for our understanding of supraglacial biogeochemical cycling, highlighting the importance of including the weathering crust photic zone when assessing supraglacial inputs to subglacial and downstream ecosystems. [ABSTRACT FROM AUTHOR]

The article discusses the impact of melting glaciers on freshwater flow, water availability, and downstream water resources due to global warming and climate change. It also highlights the presence of environmental pollutants in glaciers, including toxic elements and anthropogenic contaminants, which are released into water bodies as glaciers melt, affecting downstream ecosystems.

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+, Mg2+, Ca2+, Cl−, SO42− and NO3−) and total 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. [ABSTRACT FROM AUTHOR]