Microbial community abundance and metabolism close to the ice-water interface of the Blomstrandbreen glacier (Kongsfjorden, Svalbard): a sampling survey using an Unmanned Autonomous Vehicle

Polar marine environments host a complex assemblage of cold-adapted auto- and heterotrophic microorganisms that affect water biogeochemistryand ecosystem func-tions. However, due to logistical difficulties, remote regions like those in close proxim-ity to glaciers have received little attention, resulting in a paucity of microbiological data. To fill this gaps and obtain novel insights on microbial structure and function in Arctic regions, a survey of microbial communities in an area close to the Blomstrand-breen glacier in Kongsfjorden (Svalbard Archipelago; Arctic Ocean) was carried out during an early summer period. An Unmanned Autonomous Vehicle designed to safely obtain seawater samples from offshore-glacier transects (PROTEUS, Portable RObotic Technology for Unmanned Surveys) was equipped with an automatic remotely con-trolled water multi-sampler, so that it could sample just beneath the glacier, where ac-cess from the sea is difficult and dangerous. The samples were analysed by Image Analysis for: abundance of total prokaryotes, viable and respiring cells, their morpho-logical traits and biomass; by flow cytometry for: autotrophic and prokaryotic cells (with high and low nucleic acid contents) as well as virus-like particle counts; by BI-OLOG ECOPLATES for potential community metabolism; and by fluorimetry for po-tential enzymatic activity rates on organic polymers. Contextually, the main physical and chemical (temperature, salinity, pH, dissolved oxygen and nutrients) parameters were detected. Altogether, besides the PROTEUS vehicle suitability for collecting sam-ples from otherwise inaccessible sites, the multivariate analysis of the overall dataset allowed the identification of three main sub-regions differently affected by the haline gradient (close to the glacier) or terrigenous inputs coming from the coast. A complex microbiological scenario was depicted by different patterns of microbial abundance and metabolism among the transects, suggesting that ice melting and Atlantic water inflow differently supported the microbial growth.