Effects of fluctuating hypoxia on benthic oxygen consumption in the Black Sea (Crimean shelf)
Effects of fluctuating hypoxia on benthic oxygen consumption in the Black Sea (Crimean shelf)
The outer western Crimean shelf of the Black Sea is a natural laboratory to investigate effects of stable oxic versus varying hypoxic conditions on seafloor biogeochemical processes and benthic community structure. Bottom-water oxygen concentrations ranged from normoxic (175 ?mol O2 L?1) and hypoxic (< 63 ?mol O2 L?1) or even anoxic/sulfidic conditions within a few kilometers' distance. Variations in oxygen concentrations between 160 and 10 ?mol L?1 even occurred within hours close to the chemocline at 134 m water depth. Total oxygen uptake, including diffusive as well as fauna-mediated oxygen consumption, decreased from 15 mmol m?2 d?1 on average in the oxic zone, to 7 mmol m?2 d?1 on average in the hypoxic zone, correlating with changes in macrobenthos composition. Benthic diffusive oxygen uptake rates, comprising respiration of microorganisms and small meiofauna, were similar in oxic and hypoxic zones (on average 4.5 mmol m?2 d?1), but declined to 1.3 mmol m?2 d?1 in bottom waters with oxygen concentrations below 20 ?mol L?1. Measurements and modeling of porewater profiles indicated that reoxidation of reduced compounds played only a minor role in diffusive oxygen uptake under the different oxygen conditions, leaving the major fraction to aerobic degradation of organic carbon. Remineralization efficiency decreased from nearly 100 % in the oxic zone, to 50 % in the oxic–hypoxic zone, to 10 % in the hypoxic–anoxic zone. Overall, the faunal remineralization rate was more important, but also more influenced by fluctuating oxygen concentrations, than microbial and geochemical oxidation processes.
5075-5092
Lichtschlag, A.
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Donis, D.
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Janssen, F.
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Jessen, G. L.
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Holtappels, M.
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Wenzhöfer, F.
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Mazlumyan, S.
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Sergeeva, N.
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Waldmann, C.
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Boetius, A.
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27 August 2015
Lichtschlag, A.
f465c42f-b2fd-45a8-ae5b-8b7381d62c13
Donis, D.
e89bb93e-ee40-4203-a9cd-a1e63156be27
Janssen, F.
d7b53d12-6f59-462f-8014-c7b8f11f2ba1
Jessen, G. L.
23626d82-742a-491c-ad5e-34504f4fb0f2
Holtappels, M.
86d82c53-cc6a-4438-9582-229567c2e33d
Wenzhöfer, F.
00241e86-32a9-4b80-b23c-82392fa88c27
Mazlumyan, S.
13458491-16e7-4161-997b-418c0f5a54b9
Sergeeva, N.
f04187e5-771e-4169-babf-595637829958
Waldmann, C.
e657a676-77ae-45ce-a762-ac04ea007310
Boetius, A.
87e266e8-a5f5-44ae-9a24-21b9a872fb45
Lichtschlag, A., Donis, D., Janssen, F., Jessen, G. L., Holtappels, M., Wenzhöfer, F., Mazlumyan, S., Sergeeva, N., Waldmann, C. and Boetius, A.
(2015)
Effects of fluctuating hypoxia on benthic oxygen consumption in the Black Sea (Crimean shelf).
Biogeosciences, 12 (16), .
(doi:10.5194/bg-12-5075-2015).
Abstract
The outer western Crimean shelf of the Black Sea is a natural laboratory to investigate effects of stable oxic versus varying hypoxic conditions on seafloor biogeochemical processes and benthic community structure. Bottom-water oxygen concentrations ranged from normoxic (175 ?mol O2 L?1) and hypoxic (< 63 ?mol O2 L?1) or even anoxic/sulfidic conditions within a few kilometers' distance. Variations in oxygen concentrations between 160 and 10 ?mol L?1 even occurred within hours close to the chemocline at 134 m water depth. Total oxygen uptake, including diffusive as well as fauna-mediated oxygen consumption, decreased from 15 mmol m?2 d?1 on average in the oxic zone, to 7 mmol m?2 d?1 on average in the hypoxic zone, correlating with changes in macrobenthos composition. Benthic diffusive oxygen uptake rates, comprising respiration of microorganisms and small meiofauna, were similar in oxic and hypoxic zones (on average 4.5 mmol m?2 d?1), but declined to 1.3 mmol m?2 d?1 in bottom waters with oxygen concentrations below 20 ?mol L?1. Measurements and modeling of porewater profiles indicated that reoxidation of reduced compounds played only a minor role in diffusive oxygen uptake under the different oxygen conditions, leaving the major fraction to aerobic degradation of organic carbon. Remineralization efficiency decreased from nearly 100 % in the oxic zone, to 50 % in the oxic–hypoxic zone, to 10 % in the hypoxic–anoxic zone. Overall, the faunal remineralization rate was more important, but also more influenced by fluctuating oxygen concentrations, than microbial and geochemical oxidation processes.
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Published date: 27 August 2015
Organisations:
Marine Geoscience
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Local EPrints ID: 381159
URI: http://eprints.soton.ac.uk/id/eprint/381159
ISSN: 1726-4170
PURE UUID: 1c073397-43bd-4636-b3b0-57d3b8a6a253
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Date deposited: 02 Sep 2015 10:53
Last modified: 14 Mar 2024 21:11
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Author:
A. Lichtschlag
Author:
D. Donis
Author:
F. Janssen
Author:
G. L. Jessen
Author:
M. Holtappels
Author:
F. Wenzhöfer
Author:
S. Mazlumyan
Author:
N. Sergeeva
Author:
C. Waldmann
Author:
A. Boetius
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