Investigation of Basal Carbon Pools and Microbial Communities Associated with a High Arctic Glacier

The base of glaciers contains unique and novel subsystems such as basal ice and ponded meltwaters. The basal ice layer reflects a long-term integration of subglacial processes, including the physical glacier-bedrock interactions that form and enrich it with bedrock-derived nutrients, organic matter and microbes in the form of debris. In contrast, ponded meltwaters, accumulated at basal margins and originating from late-season surface and ice-marginal runoff, can offer a snapshot of the effects of dilute meltwaters being incubated overwinter in dark, oxic environments with limited bedrock contact. Exploring different basal subsystems could help identify features and processes unique to the subglacial environment. In May 2018, before the onset of the melt season, samples of basal ice and ponded meltwaters from an open channel near the margins were collected from Sverdrup Glacier, a polythermal high Arctic tidewater glacier. Dissolved organic matter (DOM) composition via fluorescence spectroscopy and ultra-high resolution mass spectrometry (FT-ICR-MS), and microbial diversity (via 16S) and functional potential (from taxonomic data) were measured. Ponded meltwaters had higher diversity of DOM compounds shown by FT-ICR-MS, higher fractions of humic-like fluorescence, and lower microbial compositional and functional potential for aerobic/anaerobic chemoheterotrophy and chemolithoautotrophy than basal ice. These differences may be due to site-specific basal conditions such as diverse water sources reaching the margins, rock-water contact, oxygen availability, and freeze-thaw processes. Incubations of debris-rich and debris-poor melted basal ice were also used to track changes in dissolved organic carbon (DOC) levels and microbial diversity so as to compare with ponded meltwaters incubated in situ overwinter. Higher DOC depletion and increase in microbial diversity in the debris-rich incubation versus debris-poor incubation show the role of debris amount in regulating basal ice microbial metabolism, whereas for ponded meltwaters, the water sources and freeze-thaw processes may provide the materials needed for in situ microbial activity. These results could help improve our baseline knowledge of the complex and diverse processes present in novel subsystems in the subglacial environment.