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

Abstract

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.

Assessment of Metal Pollution in Sediments along Sinop peninsula of the Black Sea

“…Higher amounts of some metals in sediments from Sinop Peninsula reflect that the sediments act as a settle and source for these metals. Sediment accumulation rates were around 1 ± 0.5 mm year −1 for the upper 10 cm of the oxic-hypoxic and the hypoxic-sulfidic zone in the Black Sea (Lichtschlag et al, 2015) and sediments are of fine-grain muddy composition with a brownish grayish fluff layer on top about 0.5 cm (Jessen et al, 2017). In general results showed that decreasing of the metal levels with increasing depth of the sediment.…”

Estimating the effect of burrowing shrimp on deep-sea sediment community oxygen consumption

“…Because these relatively large organisms are vulnerable to physical disturbance from human activities such as bottom trawling ( Clark et al, 2016 ), a decrease in their density and/or diversity would likely result in a loss in ecosystem function. Evaluating the magnitude of this loss, which is likely to be greatest in relatively high productivity upper continental slope habitats where large benthic fauna are most abundant ( Leduc, Pilditch & Nodder, 2016 ), may be aided by the application of functional trait assessment approach ( Bremner, Rogers & Frid, 2003 ) and the use of in situ O 2 consumption measurement method capable of integrating larger and therefore more representative areas of the seabed, such as in situ benthic chamber incubations ( Lichtschlag et al, 2015 ) or the eddy correlation flux method ( Berg et al, 2009 ).…”

Soft-shelled foraminifera of the Black Sea and the Sea of Azov

“…По градиенту глубины в Чёрном море выделены четыре зоны в зависимости от концентрации кислорода в придонных водах (Lichtschlag et al 2015): кислородная, глубины <130м (> 63 μmol L -1 ), кислородная/гипоксическая, глубины 130-142 м (> 63 to > 0 μmol L -1 ), гипоксическая/бескислородная, глубины 142-167 m (63-0 μmol L -1 ) и бескислородная/ сульфидная, глубины > 167м (в бескислородной воде присутствует сероводород).…”

“…Условия среды для мейобентосных организмов в зависимости от концентрации кислорода в воде придонных слоев вдоль пограничной зоны на внешнем западном крымском шельфе и в районе Стамбульского пролива Чёрного моря варьировали от нормоксии (175 мкмоль O 2 L -1) к гипоксии (менее <63 мкмоль O 2 L -1) и аноксии с сероводородом на протяжении нескольких километров (Holtappels et al, 2011;Lichtschlag et al, 2015).…”