Organic carbon and metal concentrations shape surficial benthic microbial communities in Arctic fjords

Ocean warming and Arctic climate change have a significant impact on the biogeochemistry and ecology of Svalbard fjords. Glacier melt and permafrost thaw introduce terrigenous material from the rivers and glacial runoff into these fjords. This study focused on benthic bacterial community structure and the influence of environmental factors in three climate-sensitive Arctic fjords located in the northern and western regions of Svalbard. Our findings revealed significant differences in bacterial community structure between the surface sediments of the northern and western Svalbard fjords (PERMANOVA, R² = 0.215, p-value = 0.001). Notably, the western fjord exhibited higher bacterial diversity compared to the northern fjord. In the northern fjord, the dominant bacterial phyla were Bacteroidetes (41 %), Proteobacteria (37 %), and Firmicutes (18 %). In contrast, the western fjord was characterised by a prevalence of Proteobacteria (46 %), Firmicutes (25 %), Bacteroidota (8 %), and Actinobacteriota (7 %). Significant differences in the TOC/TN ratio and metal concentrations (Fe, Mn, Ni, Co, Cu, Zn, Cr, and Pb) between the northern and western fjords were revealed (ANOVA), with p-values of ≤0.05 for TOC/TN, Fe, Mn, and Ni; ≤ 0.01 for Co, Cu, Zn, and Cr; and ≤ 0.001 for Pb. These results underscore the influence of the organic carbon content and varying metal concentrations on shaping the bacterial community structure across the northern and western Svalbard fjords.