In the field of observation, chance favours only the prepared mind (Pasteur). Impressive developments in genomics have led microbiology to its third ″Golden Age″. However, conventional metagenomics strategies necessitate retrograde transfer of samples from extreme or remote environments for later analysis, rendering the powerful insights gained retrospective in nature, striking a contrast with Pasteur′s dictum. Here we implement a highly portable USB-based nanopore DNA sequencing platform coupled with field-adapted environmental DNA extraction, rapid sequence library generation and off-line analyses of metagenome profiles to characterize the microbiota of a High Arctic glacier. The profile of the microbial communities produced by this approach are coherent with those from conventional amplicon and shotgun metagenome sequencing of glacier environments, and prompt testable hypotheses regarding microbial community structure and function on the basis of data generated and analysed while in the field. Moreover, we highlight the potential for oligonucleotide mixture model based metagenomic profiling of nanopore reads to deliver off-grid metagenomics analyses. Ultimately, in-field metagenomic sequencing potentiated by nanopore devices raises the prospect of considerably enhanced agility in exploring Earth′s microbiomes.