Vertical distribution of methane oxidation and methanotrophic response to elevated methane concentrations in stratified waters of the Arctic fjord Storfjorden (Svalbard, Norway)

• Published in: Biogeosciences
• Main Authors: S. Mau, J. Blees, E. Helmke, H. Niemann, E. Damm
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2013
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Arctic; Svalbard; Norway; Storfjorden
• Online Access: https://doi.org/10.5194/bg-10-6267-2013; https://doaj.org/article/99adf4ae0f6340e799a61608be76c778

The bacterially mediated aerobic methane oxidation (MO x ) is a key mechanism in controlling methane (CH 4 ) emissions from the world's oceans to the atmosphere. In this study, we investigated MO x in the Arctic fjord Storfjorden (Svalbard) by applying a combination of radio-tracer-based incubation assays ( 3 H-CH 4 and 14 C-CH 4 ), stable C-CH 4 isotope measurements, and molecular tools (16S rRNA gene Denaturing Gradient Gel Electrophoresis (DGGE) fingerprinting, pmoA - and mxaF gene analyses). Storfjorden is stratified in the summertime with melt water (MW) in the upper 60 m of the water column, Arctic water (ArW) between 60 and 100 m, and brine-enriched shelf water (BSW) down to 140 m. CH 4 concentrations were supersaturated with respect to the atmospheric equilibrium (about 3–4 nM) throughout the water column, increasing from ∼20 nM at the surface to a maximum of 72 nM at 60 m and decreasing below. MO x rate measurements at near in situ CH 4 concentrations (here measured with 3 H-CH 4 raising the ambient CH 4 pool by <2 nM) showed a similar trend: low rates at the sea surface, increasing to a maximum of ∼2.3 nM day −1 at 60 m, followed by a decrease in the deeper ArW/BSW. In contrast, rate measurements with 14 C-CH 4 (incubations were spiked with ∼450 nM of 14 C-CH 4 , providing an estimate of the CH 4 oxidation at elevated concentration) showed comparably low turnover rates (<1 nM day −1 ) at 60 m, and peak rates were found in ArW/BSW at ∼100 m water depth, concomitant with increasing 13 C values in the residual CH 4 pool. Our results indicate that the MO x community in the surface MW is adapted to relatively low CH 4 concentrations. In contrast, the activity of the deep-water MO x community is relatively low at the ambient, summertime CH 4 concentrations but has the potential to increase rapidly in response to CH 4 availability. A similar distinction between surface and deep-water MO x is also suggested by our molecular analyses. The DGGE banding patterns of 16S rRNA gene fragments of the surface MW ...