During a sampling cruise to the Barents Sea in 10/2021, 50 gravity cores were collected in the Barents Sea from three areas with known hydrocarbon (HC) anomalies and two reference areas. Cores were subsampled and conditioned on site using GFZ’s mobile geomicrobiology laboratory (BugLab). Biogeochemical characterization of the samples included high-resolution pore water profiles, sulfate reduction rates, dissolved gas concentrations, and microbial cell counts. Combined results showed that HC anomalies result in more pronounced biogeochemical trends and steeper gradients in pore water chemistry. Biomolecule extractions were individually optimized on paired samples to reach sufficient yield and quality of DNA, RNA and protein extracts. Metagenomic sequencing of Illumina short- and Oxford Nanopore Technology long-reads was performed on all 50 sediment cores. Bioinformatics processing delivered 165 archaeal and 358 bacterial high-quality metagenome-assembled genomes (MAGs), and >6000 bins via hybrid assembly, achieving thorough characterization of subseafloor microbial taxonomic and functional diversity. Several MAGs prevalent at HC-affected sites exhibited key functions in the anaerobic degradation of alkanes and aromatic HCs. Metatranscriptomic data were obtained for 31 sediment cores, mostly from HC-affected sites. DNA and RNA sequencing data were compiled into a comprehensive database of predicted proteins. For metaproteomics, continuous elution electrophoresis from sample slurry improved the yield and quality of protein extracts. Mass spectrometric data searches resulted in >1,300 taxonomically and functionally assigned peptides per gravity core, highlighting metabolic activities by archaea related to methane and C1 compounds. Statistics on the combined dataset selectively extracted diagnostic features for integration into predictive models. Key markers for inconspicuous seepage included pore water sulfate, trace elements and alkalinity, alongside 9 taxonomic groups and 14 marker genes.
To validate these diagnostic features, 6 gravity cores were collected south-west of the initial sampling area in fall 2023. These were analyzed for biogeochemistry, metagenomics and metaproteomics. Pore water sulfate and alkalinity, microbial reduction rates, predicted functions of prevalent MAGs, and expressed proteins related to C1 metabolism were validated as indicators of thermogenic methane anomalies. Such biogeochemical and omics features were all indicative of sulfate-driven anaerobic oxidation of methane, with a suite of taxa cross-feeding on simple HCs and metabolites. In conclusion, minute supplies of electron donors through seepage result in slightly increased consumption of electron acceptors.
Project dissemination was achieved through conferences, publications and data deposition in public repositories. The sampling campaign video documentary is posted on PROSPECTOMICS social media channels.
