Seasonal shifts of microbial methane oxidation in Arctic shelf waters above gas seeps

Abstract

The Arctic Ocean subseabed holds vast reservoirs of the potent greenhouse gas methane (CH 4 ), often seeping into the ocean water column. In a continuously warming ocean as a result of climate change an increase of CH 4 seepage from the seabed is hypothesized. Today, CH 4 is largely retained in the water column due to the activity of methane-oxidizing bacteria (MOB) that thrive there. Predicted future oceanographic changes, bottom water warming and increasing CH 4 release may alter efficacy of this microbially mediated CH 4 sink. Here we investigate the composition and principle controls on abundance and activity of the MOB communities at the shallow continental shelf west of Svalbard, which is subject to strong seasonal changes in oceanographic conditions. Covering a large area (364 km 2 ), we measured vertical distribution of microbial methane oxidation (MOx) rates, MOB community composition, dissolved CH 4 concentrations, temperature and salinity four times throughout spring and summer during three consecutive years. Sequencing analyses of the pmoA gene revealed a small, relatively uniform community mainly composed of type-Ia methanotrophs (deep-sea 3 clade). We found highest MOx rates (7 nM d −1 ) in summer in bathymetric depressions filled with stagnant Atlantic Water containing moderate concentrations of dissolved CH 4 (< 100 nM). MOx rates in these depressions during spring were much lower (< 0.5 nM d −1 ) due to lower temperatures and mixing of Transformed Atlantic Water flushing MOB with the Atlantic Water out of the depressions. Our results show that MOB and MOx in CH 4 -rich bottom waters are highly affected by geomorphology and seasonal conditions.

Aerobic oxidation of methane significantly reduces global diffusive methane emissions from shallow marine waters

“…MOx rates varied between 0.01 and 7.5 nmol L −1 d −1 (Fig. 1d ), and fell within reported ranges 14 , 18 , 27 – 31 , and were comparable to rates observed in a number of methane seep impacted waters 32 – 34 . In contrast to the high rates driven by elevated methane concentrations near seeps 33 , 35 – 37 , rapid turnover times and correspondingly high MOx rates reflect the inherent capacity of methane oxidizing communities to consume methane at the low concentrations typical of the ECS.…”

Biogeochemistry and timing of methane-derived carbonate formation at Leirdjupet fault complex, SW Barents sea

“…These findings are consistent with a number of studies demonstrating that seepage activity can vary both spatially and temporally (Judd and Hovland, 2007;Suess, 2014;Ferré et al, 2020;Dølven et al, 2022), influencing subsurface biogeochemical processes (e.g. AOM, carbonate precipitation) (Rooze et al, 2020), the composition and distribution of seafloor chemosynthetic communities (Levin, 2005;Fischer et al, 2012) as well as local water-column biogeochemistry (Sert et al, 2020;Zhang et al, 2020;Gründger et al, 2021). We conducted thermodynamic modelling of the oxygen isotopic composition of aragonite cements forming in equilibrium with coeval bottom waters (8 ka BP and 4 ka BP) to check whether samples recorded some influence from gas hydrates.…”

The marine methane cycle in the Canadian Arctic Archipelago during summer

“…In almost all the incubations there was occurrence of Chloroplast genome. Summarizing, our dataset emphasized the occurrence of Chloroplast genome, Oleispira, Planctomarina, and Aurantivirga in the methane oxidations (similar outcome of Uhlig et al, 2018 andGründger et al, 2021). However, little is still known about this relationship, stimulating open questions on the drivers of methane oxidation activity in the Arctic Ocean.…”

“…Alphaproteobacteria and Gammaproteobacteria include known MOB, however, Oleispira and Planctomarina are not yet classified as such. Nevertheless, these taxa were found in Arctic methane incubations by Uhlig et al (2018), andGründger et al (2021), and are therefore likely associated with methane oxidation. The Flavobacteria are known to be secondary consumers of methane, oil, or cellular decay products (Redmond & Valentine, 2012).…”

“…CC BY 4.0 License. sources, such as the Arctic shelf gas seeps (Steinle et al 2015(Steinle et al , 2017Gründger et al, 2021) showed that methane oxidation rates are sometimes mitigated by the seasonal variations of the hydrographical regimes, which trigger a system-wide switch of the efficiency of water column methane oxidizers. In our study, we detected higher microbial methane oxidation rates within the upper 200 m depth (see Fig.…”