Respiration and sequestering of organic carbon in shelf sediments of the oligotrophic northern Aegean Sea

• Respiration and sequestering of organic carbon was investigated in northern Aegean Sea sediments (NE Mediterranean). Benthic total carbonate (C-T, also called SigmaCO(2) or dissolved inorganic carbon, DIC) fluxes and O-2 uptake rates were measured in situ using a benthic lander. Dissolved organic carbon (DOC) fluxes were calculated from pore water gradients, taking into account the influence of biodiffusion/bioirrigation. Macrofaunal biomass was determined in the sediment collected by the chambers of the benthic lander. Chl a distributions were used as a tracer of high-quality sedimentary organic carbon. The measured benthic C-T fluxes were positively correlated with the O-2 uptake rates. The obtained average apparent respiration ratio (C-T flux:O-2 flux) of 0.90 +/- 0.36 suggests a clear dominance of aerobic respiration in these organic carbon-poor shelf sediments. The C-T efflux, the 02 uptake rate, and the DOC flux were significantly higher in spring than in fall at 2 of the stations. The Black Sea water, which enters the Aegean Sea in the study area, did not influence benthic respiration rates or organic carbon sequestering rates. A strong positive correlation between both the C-T and O-2 fluxes and the mean chl a concentration in surficial sediment suggests that benthic respiration, to a large extent, was controlled by the availability of labile phytodetrital organic matter. There was no influence of macrofaunal biomass (dry weight) on C-T fluxes or oxygen uptake rates. The calculated benthic DOC fluxes made up 7.2 to 27 % (average 14 +/- 8.1 %) of the C-T fluxes, indicating that their contribution to the overall recycling of organic carbon in these sediments was important. The organic carbon burial efficiency ranged from 0.1 to 5.3 %, but at Stn KA1 it was considerably higher (average 4%) than at the other stations (average 0.3%). Except for this station, the obtained burial efficiencies were very low compared to other sediments with similar accumulation rates. The average burial flux of organic carbon corresponded to less than 1 % of the annual mean primary production (PP) for the Aegean Sea at Stn KA1, and to less than 0.1 % of PP at the other stations.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

northern Aegean Sea

sediment

organic carbon

dissolved inorganic

carbon

dissolved organic carbon

oxygen

chlorophyll

benthic lander

CONTINENTAL-MARGIN SEDIMENTS

OXYGEN-UPTAKE

IN-SITU

MOLECULAR-DIFFUSION

INORGANIC CARBON

MARINE-SEDIMENTS

ATLANTIC

OCEAN

BENTHIC FLUXES

MATTER

MINERALIZATION

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