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Publication . Article . 2015

Effects of fluctuating hypoxia on benthic oxygen consumption in the Black Sea (Crimean shelf)

Open Access
Published: 27 Aug 2015 Journal: Biogeosciences (issn: 1726-4189, Copyright policy )

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 μmol O2 L−1) and hypoxic (< 63 μmol O2 L−1) or even anoxic/sulfidic conditions within a few kilometers' distance. Variations in oxygen concentrations between 160 and 10 μmol 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 μmol 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.

Subjects by Vocabulary

Microsoft Academic Graph classification: Biogeochemical cycle Benthic zone Seafloor spreading Black sea Oceanography Oxygen chemistry.chemical_element chemistry Biology Community structure Hypoxia (environmental)


Earth-Surface Processes, Ecology, Evolution, Behavior and Systematics

Funded by
In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and land-locked water bodies
  • Funder: European Commission (EC)
  • Project Code: 226213
  • Funding stream: FP7 | SP1 | ENV
Related to Research communities
European Marine Science
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License: cc-by
Providers: UnpayWall