Variations in Atlantic water influx and sea-ice cover drive taxonomic and functional shifts in Arctic marine bacterial communities

Abstract

The Arctic Ocean is experiencing unprecedented changes as a result of climate warming, necessitating detailed analyses on the ecology and dynamics of biological communities to understand current and future ecosystem shifts. Here we show the pronounced impact that variations in Atlantic water influx and sea-ice cover have on bacterial communities in the East Greenland Current (Fram Strait) using two, 2-year high-resolution amplicon datasets and an annual cycle of long-read metagenomes. Densely ice-covered polar waters harboured a temporally stable, resident microbiome. In contrast, low-ice cover and Atlantic water influx shifted community dominance to seasonally fluctuating populations enriched in genes for phytoplankton-derived organic matter degradation. We identified signature populations associated with distinct oceanographic conditions and predicted their ecological niches. Our study indicates progressing "Biological Atlantification" in the Arctic Ocean, where the niche space of Arctic bacterial populations will diminish, while communities that taxonomically and functionally resemble those in temperate oceans will become more widespread.

The Arctic summer microbiome across Fram Strait: Depth, longitude, and substrate concentrations structure microbial diversity in the euphotic zone

“…On average, ASVs from signature populations constituted a relative abundance of 66%, with a maximum of 78% in the lower-photic western Strait (Table S2). The maximum in subsurface Arctic waters supports the notion of a stable community in "true" polar conditions, which might be affected by progressing Atlantification (Priest, von Appen, et al, 2023). Each cluster displayed a specific taxonomic composition (Figure 7B).…”

“…Rhodopirellula can degrade complex sulfated polysaccharides (Wegner et al, 2013); possibly counteracting the lower concentrations of labile substrates in western Fram Strait (Figure 2B). Detection of SUP05 ( Thioglobus ) mirrors its wide distribution in “true” Arctic habitats, based on comparison with TARA and MOSAiC datasets (Priest, von Appen, et al, 2023). Defluviicoccales might persist on stored glycogen or unsaturated aliphatics (Burow et al, 2007; Lucas et al, 2016).…”

“…These patterns underscore that specific organic compounds prevail under Arctic versus Atlantic influence (Engel et al, 2019; Priest, Vidal‐Melgosa, et al, 2023; von Jackowski et al, 2020). Consequently, bacterial communities in polar waters are enriched in genes targeting terrestrial compounds, compared to genes targeting phytoplankton‐derived compounds under Atlantic influence (Priest, von Appen, et al, 2023). Over vertical scales, concentrations of CHO, AA, sugar acids, amines, chl‐a, and DOC peaked in surface and chl‐max depths, independent of the sampling site (Wilcoxon rank‐sum test, p < 0.001; Figures 2B and S1).…”

“…Subsurface MAGs shared several CAZymes not found in surface MAGs (Figure 8A), including GH88 (chitosan or gellan hydrolase) and PL1 (pectate lyase). Most subsurface CAZymes were found in the verrucomicrobial Arctic97B‐4 clade, harbouring 81 CAZyme and 54 sulfatase genes potentially targeting semi‐refractory polysaccharides (Priest, von Appen, et al, 2023).…”

“…Bacterial cell numbers are an order of magnitude higher in the eastern Fram Strait, which has been attributed to higher water temperatures (Cardozo‐Mino et al, 2021). Overall, Atlantic‐influenced waters are more productive and characterized by stronger seasonal dynamics (Wietz et al, 2021), with major implications for the biological carbon pump (Fadeev, Rogge, et al, 2021; Flores et al, 2019; Priest, von Appen, et al, 2023; Ramondenc et al, 2022; Rapp et al, 2018; von Appen et al, 2021). In addition to regional differences, bacterial communities in the Fram Strait distinctly vary with depth.…”