MINERALIZATION AND BURIAL OF ORGANIC-CARBON IN SEDIMENTS OF THE SOUTHERN WEDDELL SEA (ANTARCTICA)

Benthic fluxes of oxygen, alkalinity (A(T)), total carbonate (C-T or S igma CO2) and dissolved organic carbon (DOG) were measured during sedi ment-water incubations al 16 stations in the southern Weddell Sea (Ant arctica) with water depths between 280 and 2514 m. The total sediment oxygen consumption rates (TSOC) were in general low (1.74-3.61 mmol m( -2) day(-1)) and more comparable to measurements in slope and deep-sea sediments at a few thousand meters water depth. The decrease of TSOC with water depth was lower than that observed in many other seas. The mean carbon to nitrogen ratio (C/N) in the solid phase of surficial se diment was 8.3. Measured benthic fluxes of alkalinity, corrected for c ontributions from nitrification and denitrification, were quantitative ly used to correct the fluxes of total carbonate for dissolution of so lid phase carbonates. The Sigma CO2 fluxes, originating from carbonate dissolution (0.166- 1.77 mmol m(-2) day(-1)), were 2.6-71% of the Sig ma CO2 fluxes (0.984-3.73 mmol m(-2) day(-1)) resulting from organic c arbon oxidation. Measured benthic fluxes of oxygen, Sigma CO2 and nitr ate were, together with estimated denitrification rates and sediment C /N ratios, used to model respiration quotients (RQ) for organic carbon oxidation and estimate composition of the organic matter undergoing d egradation. Modelled RQ varied roughly between 2/3 and 1 (mean 0.87). Measured fluxes of Sigma CO2 were 1.6-3.2 times higher than integrated organic C mineralization rates (measured during closed incubations of sieved, homogenized sediment), indicating macrofaunal (plus possibly meiofaunal) respiration to be important. However, low abundances of bi oirrigating benthic macrofauna and small differences in benthic fluxes of oxygen, Sigma CO2 and alkalinity found between replicate sediment cores, suggested that macrofaunal respiration was quantitatively unimp ortant in these sediments. The higher measured fluxes of Sigma CO2, co mpared to the integrated mineralization rates, were therefore most lik ely caused by a large fraction of the respiration occurring directly o n the sediment surface. This degradation of newly deposited organic ma tter was not reflected in the integrated organic C mineralization rate s. Also, there was no obvious effect of this surficial degradation pro cess on the pore water distributions of Sigma CO2. Benthic mass balanc es of carbon revealed that benthic fluxes of DOC were 3-147% of the co rrected fluxes of Sigma CO2, and the recycling efficiencies (E) were u p to 35% higher if the DOC fluxes were included in the calculations of E, rather than the inorganic Sigma CO2 flux alone. The recycling effi ciencies, including the benthic flux of DOG, ranged between 57 and 88% (mean 78%). Measured rates of inorganic C accumulation (for most stat ions <0.3 mmol C m(-2) day(-1)) were a factor of 6-7 lower than organi c C accumulation rates (0.457-1.94 mmol C m(-2) day(-1)). (C) 1997 Pub lished by Elsevier Science Ltd.