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Respiration and sequestering of organic carbon was investigated in northern Aegean Sea sediments (NE Mediterranean). Benthic total carbonate (CT, also called ∑CO2 or dissolved inor- ganic carbon, DIC) fluxes and O2 uptake rates were measured in situ using a benthic lander. Dis- solved 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 col- lected by the chambers of the benthic lander. Chl a distributions were used as a tracer of high-qual- ity sedimentary organic carbon. The measured benthic CT fluxes were positively correlated with the O2 uptake rates. The obtained average apparent respiration ratio (CT flux:O2 flux) of 0.90 ± 0.36 sug- gests a clear dominance of aerobic respiration in these organic carbon-poor shelf sediments. The CT efflux, the O2 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 ben- thic respiration rates or organic carbon sequestering rates. A strong positive correlation between both the CT and O2 fluxes and the mean chl a concentration in surficial sediment suggests that benthic res- piration, to a large extent, was controlled by the availability of labile phytodetrital organic matter. There was no influence of macrofaunal biomass (dry weight) on CT fluxes or oxygen uptake rates. The calculated benthic DOC fluxes made up 7.2 to 27% (average 14 ± 8.1%) of the CT fluxes, indi- cating that their contribution to the overall recycling of organic carbon in these sediments was impor- tant. The organic carbon burial efficiency ranged from 0.1 to 5.3%, but at Stn KA1 it was consider- ably 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 pri- mary production (PP) for the Aegean Sea at Stn KA1, and to less than 0.1% of PP at the other stations.

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