Publication Date:
2015-04-30
Description:
The outer Western Crimean Shelf of the Black Sea is a natural laboratory to investigate effects of stable oxic vs. varying hypoxic conditions on seafloor biogeochemical processes and benthic community structure. Bottom water oxygen concentrations varied between normoxic (175 μmol O2 L−1) and hypoxic (〈 63 μmol O2 L−1) or even anoxic/sulfidic conditions within a few kilometres 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 in the oxic zone to 〈 9 mmol m−2 d−1 in the hypoxic zone, correlating with changes in macrobenthos composition. Benthic diffusive oxygen uptake rates, comprising microbial respiration plus reoxidation of inorganic products, were around 4.5 mmol m−2 d−1, but declined to 1.3 mmol m−2 d−1 at oxygen concentrations below 20 μmol L−1. Measurements and modelling of pore water profiles indicated that reoxidation of reduced compounds played only a minor role in the diffusive oxygen uptake, leaving the major fraction to aerobic degradation of organic carbon. Remineralization efficiency decreased from 100% in the oxic zone, to 50% in the oxic-hypoxic, 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.
Print ISSN:
1810-6277
Electronic ISSN:
1810-6285
Topics:
Biology
,
Geosciences
