Publication Date:
2017-01-31
Description:
Abstract. The bacterially mediated aerobic methane oxidation
(MOx) is a key mechanism in controlling methane (CH4)
emissions from the world’s oceans to the atmosphere. In
this study, we investigated MOx in the Arctic fjord Storfjorden
(Svalbard) by applying a combination of radio-tracerbased
incubation assays (3H-CH4 and 14C-CH4), stable CCH4
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
60m of the water column, Arctic water (ArW) between
60 and 100 m, and brine-enriched shelf water (BSW) down to
140 m. CH4 concentrations were supersaturated with respect
to the atmospheric equilibrium (about 3–4 nM) throughout
the water column, increasing from �20nM at the surface to
a maximum of 72nM at 60m and decreasing below. MOx
rate measurements at near in situ CH4 concentrations (here
measured with 3H-CH4 raising the ambient CH4 pool by
〈2 nM) showed a similar trend: low rates at the sea surface,
increasing to a maximum of �2.3nMday−1 at 60 m,
followed by a decrease in the deeper ArW/BSW. In contrast,
rate measurements with 14C-CH4 (incubations were spiked
with �450nM of 14C-CH4, providing an estimate of the
CH4 oxidation at elevated concentration) showed comparably
low turnover rates (〈1nMday−1) at 60 m, and peak rates
were found in ArW/BSW at �100m water depth, concomitant
with increasing 13C values in the residual CH4 pool.
Our results indicate that the MOx community in the surface
MW is adapted to relatively low CH4 concentrations. In contrast,
the activity of the deep-water MOx community is relatively
low at the ambient, summertime CH4 concentrations
but has the potential to increase rapidly in response to CH4
availability. A similar distinction between surface and deepwater
MOx is also suggested by our molecular analyses. The
DGGE banding patterns of 16S rRNA gene fragments of the
surface MW and deep water were clearly different. A DGGE
band related to the known type I MOx bacterium Methylosphaera
was observed in deep BWS, but absent in surface
MW. Furthermore, the Polymerase Chain Reaction (PCR)
amplicons of the deep water with the two functional primers
sets pmoA and mxaF showed, in contrast to those of the surface
MW, additional products besides the expected one of
530 base pairs (bp). Apparently, different MOx communities
have developed in the stratified water masses in Storfjorden,
which is possibly related to the spatiotemporal variability in
CH4 supply to the distinct water masses.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
Format:
application/pdf
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