Microbial and chemical signatures of melting sea-ice: export of bacteria, microeukaryotes, and molecules

Sea-ice loss in the warming Arctic Ocean profoundly affects microbial communities and biogeochemical cycles. Here, we performed a microcosm experiment with sea-ice and seawater from the Fram Strait to identify microbial and chemical signatures of melting ice and the surrounding seawater. Amplicon sequencing across 49 h of incubation showed that approximately one-tenth of bacterial and microeukaryotic taxa were directly traceable between the original ice and meltwater. Exported microbes included diatoms (for example Attheya , Navicula , Bacillaria ), heterotrophic protists (for example Pelagophyceae , MAST-12B, Thoracosphaeraceae ), and bacteria (for example Psychroflexus , Taeseokella , Lewinella ). Size-fractionated filtration showed that mostly larger cells and aggregates, including chytrid fungi and biofilm-forming bacteria, seeded the meltwater microbiome. FT-ICR-MS revealed a prevalence of aliphatic and sulfuric molecular formulae in the original sea-ice. Of the 128 formulae unique to sea-ice, 10 were subsequently detected in meltwater. Up to 26% of organic molecules in sea-ice were shared with other Arctic datasets, indicating pan-Arctic patterns in sea-ice chemistry. Together, the finding of distinct 'ice signatures' in meltwater illustrates microbial and chemical connectivity between these habitats, with implications for the biological carbon pump and cryobenthopelagic coupling.