Publication Date:
2021-03-29
Description:
Water column samples taken in summer 2008 from
the stratified Gotland Deep (central Baltic Sea) showed a
strong gradient in dissolved methane concentrations from
high values in the saline deep water (max. 504 nM) to low
concentrations in the less dense, brackish surface water
(about 4 nM). The steep methane-gradient (between 115 and
135 m water depth) within the redox-zone, which separates
the anoxic deep part from the oxygenated surface water
(oxygen concentration 0–0.8 mL L
−
1
), implies a methane
consumption rate of 0.28 nM d
−
1
. The process of micro-
bial methane oxidation within this zone was evident by a
shift of the stable carbon isotope ratio of methane between
the bottom water (
δ
13
C CH
4
=−
82.4 ‰) and the redox-
zone (
δ
13
C CH
4
=−
38.7 ‰). Water column samples be-
tween 80 and 119 m were studied to identify the microor-
ganisms responsible for the methane turnover in that depth
interval. Notably, methane monooxygenase gene expression
analyses for water depths covering the whole redox-zone
demonstrated that accordant methanotrophic activity was
probably due to only one phylotype of the aerobic type I
methanotrophic bacteria. An imprint of these organisms on
the particular organic matter was revealed by distinctive
lipid biomarkers showing bacteriohopanepolyols and lipid
fatty acids characteristic for aerobic type I methanotrophs
(e.g., 35-aminobacteriohopane-30,31,32,33,34-pentol), cor-
roborating their role in aerobic methane oxidation in the
redox-zone of the central Baltic Sea.
Keywords:
Aerobic methanotrophy; pelagic redox-zone; Gotland Deep: Baltic Zone
;
551
Language:
English
Type:
article
,
publishedVersion
Format:
9
