(A) Aldegondabreen in Grønfjorden, the study site in Svalbard

<p><strong>Figure 1.</strong> (A) Aldegondabreen in Grønfjorden, the study site in Svalbard. (B) Location of the sampling sites on the surface of Aldegondabreen. Transects (A)–(B) are numbered from the lowest point upstream. In transect (B) only the point B2 was analysed. (C) Northern margin of Aldegondabreen with sampling points A3 and A4 as seen from point A2 with marked areas of bird nesting activity and occurrence of large cryoconite granules. White circles indicate the area in the slopes of Productustoppen (527 m) with nesting seabirds. (D) Large cryoconite aggregate in detail with visible cyanobacterial mat on its surface. (E) View on the glacier surface at transect (A). The scale was derived from an 3 m long avalanche probe with cm scale. The probe is visible in the lower right part of the shot. The cryoconite aggregates cover the surface without producing deep melt ponds due to prevailing effect of conductive heat flux. (F) Large cryoconite sediment aggregates at point A2.</p> <p><strong>Abstract</strong></p> <p>The aggregation of surface debris particles on melting glaciers into larger units (cryoconite) provides microenvironments for various microorganisms and metabolic processes. Here we investigate the microbial community on the surface of Aldegondabreen, a valley glacier in Svalbard which is supplied with carbon and nutrients from different sources across its surface, including colonies of seabirds. We used a combination of geochemical analysis (of surface debris, ice and meltwater), quantitative polymerase chain reactions (targeting the 16S ribosomal ribonucleic acid and <em>amoA</em> genes), pyrosequencing and multivariate statistical analysis to suggest possible factors driving the ecology of prokaryotic microbes on the surface of Aldegondabreen and their potential role in nitrogen cycling. The combination of high nutrient input with subsidy from the bird colonies, supraglacial meltwater flow and the presence of fine, clay-like particles supports the formation of centimetre-scale cryoconite aggregates in some areas of the glacier surface. We show that a diverse microbial community is present, dominated by the cyanobacteria, Proteobacteria, Bacteroidetes, and Actinobacteria, that are well-known in supraglacial environments. Importantly, ammonia-oxidizing archaea were detected in the aggregates for the first time on an Arctic glacier.</p>