| Summary: | This dataset contains water column measurements, dissolved organic matter compositions, and hydrographical profiles collected from the Norskebanken seep site at Northern Svalbard, Arctic Ocean. Data are presented along with the R codes for the replication of analyses, and figures that were added in our submitted paper. We recommend using R (v4.3.1) and R Studio (2023.06.1) to run R project file (.Rproj) which can access all codes and data. Running codes in the given order will create corresponding data tables and all the figures that were used in the article. Cold seeps release methane (CH4) from the seafloor to the water column, which fuels microbially mediated aerobic methane oxidation (MOx). Methane oxidising bacteria (MOB) utilise excess methane, and the MOB biomass serves as a carbon source in the food web. Yet, it remains unclear if and how MOx modifies the composition of dissolved organic matter (DOM) in cold seeps. We investigated MOx rates, DOM compositions and the microbial community during ex-situ incubations of seawater collected from an active cold seep site at Norskebanken (north of the Svalbard archipelago) in the Arctic Ocean. For comparison, we used seawater collected from a control site (a non-seep environment). Samples were incubated with and without methane amendments. Samples amended with methane (~1 µM final concentration) showed elevated rates of MOx in both seep and non-seep incubations. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses showed that the number of DOM formulas (i.e., molecular diversity) increased by up to 39 % in these incubations. In contrast, the number of formulas decreased by 20 % in samples not amended with methane, both from non-seep and seep locations. DOM composition was thus altered towards a more diverse and heterogeneous composition along with elevated methanotrophic activity in methane-amended conditions. In addition to microbial DOM production, abating microbial diversity indicates that elevated DOM diversity was potentially ...
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