Sources and molecular composition of cryoconite organic matter from the Athabasca Glacier, Canadian Rocky Mountains

Cryoconite is a dark coloured, dust like material found on the surfaces of glaciers. Cryoconite has received much interest recently because cryoconite holes, which are produced by accelerated ice melt, act as habitats for microbes on glacier surfaces. To the best of our knowledge, cyroconite organic matter (COM) has not yet been chemically characterized at the molecular level. In this study, organic matter biomarkers and a host of NMR techniques were used to characterize COM from the Athabasca Glacier in the Canadian Rocky Mountains. Solvent extracts contained large quantities of fatty acids, n-alkanols, n-alkanes, wax esters and sterols. A large contribution of C23, C25 and C27 relative to C29 and C31 n-alkanes suggests that allochthonous COM is mainly from lower order plants (mosses, lichens). This is confirmed by the absence of lignin phenols (after copper (II) oxidation) in extracts and NMR analyses of COM. Solution state 1H NMR reveals prominent signals from microbial components, while solid state 13C CP-MAS-NMR analysis shows an atypically high alkyl/O-alkyl ratio, suggesting that COM is significantly different from organic matter found in nearby soils. The NMR results suggest that COM is dominated by microbially derived compounds, which was confirmed by phospholipid fatty acid analysis, revealing a significant microbial contribution, primarily from bacteria with minor contributions from microeukaryotes. Both biomarker and NMR data suggest that COM supports active microbial communities on the Athabasca Glacier. Given that such material is incorporated within the glacier in the accumulation zone or flushed by meltwaters into subglacial environments, reworked COM may provide nutrient sources for active microbial communities found within and under glaciers.