MEPS 269:33-48 (2004)  -  doi:10.3354/meps269033

ABSTRACT: Respiration and sequestering of organic carbon was investigated in northern Aegean Sea sediments (NE Mediterranean). Benthic total carbonate (C_T, also called …CO₂ or dissolved inorganic carbon, DIC) fluxes and O₂ 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 O₂ uptake rates. The obtained average apparent respiration ratio (C_T flux:O₂ 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 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 benthic respiration rates or organic carbon sequestering rates. A strong positive correlation between both the C_T and O₂ 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.

KEY WORDS: Northern Aegean Sea · Sediment · Organic carbon · Dissolved inorganic carbon · Dissolved organic carbon · Oxygen · Chlorophyll · Benthic lander