NALED IT: SEASONAL EVOLUTION OF SUBGLACIAL ECOSYSTEMS BENEATH OUTLETS OF THE GREENLAND ICE SHEET

The Greenland Ice Sheet hides a sprawling landscape of waterways. During the melting season, small streams of basal ice melt can grow to fast-moving, interconnected channels when fed by surface meltwater. This shift in flow dynamics greatly influences subglacial geochemistry, bedrock weathering, resource availability, and microbial ecology. Eventually, sediments, nutrients, and microbial cells suspended in drainage and carrying a record of subglacial conditions emerge in proglacial streams. Prior studies have used these indicators in summer outflow to estimate water circulation, geochemical processes, and downstream productivity. However, overwintering chemical and biological activity at the ice-bedrock interface remains largely unknown. By using naled ice, ice consisting of rapidly-frozen layers preserving subsurface meltwater upwelling during winter, we aimed to explore the complete seasonal evolution of subglacial ecosystems beneath the Greenland Ice Sheet and their impact on downstream environments. We collected intra-annual naled ice and proglacial water samples from two land-terminating West Greenland glacier outlets (Isunnguata Sermia and Leverett Glacier). Our objectives were to (i) evaluate whether microbial community composition, biomass isotope fractionation, and dissolved organic matter (DOM) change seasonally, (ii) estimate the connectivity of subglacial flow paths using carbon- and nitrogen-based source identification, and (iii) characterize subsurface biogeochemical potential via metagenomics and quantitative PCR. Here I present 16S rRNA amplicon data from the late melt season (October) and DOM metrics in late, overwinter, and early (May) discharge. We observed spatial and intra-annual differences in microbial community composition, dissolved organic carbon concentrations, and DOM characteristics. Through our findings, we seek to clarify the mechanics underlying subglacial hydrology and better predict downstream consequences of global warming as a shrinking Greenland Ice Sheet disrupts typical drainage.