Anaerobic mineralization of marine sediment organic matter: Rates and the role of anaerobic processes in the oceanic carbon economy

Abstract

Fluxes of total CO2, 02, NO3-+NO2-, NH,', DON (dissolved organic nitrogen) and HSwere measured across the interface of a coastal bay sediment for 43 d. The seawater overlying the defaunated sediment cores was changed continuously. Two treatments were employed: oxygenated overlying water (OX-cores) and anoxic water (AN-cores). Fluxes were measured before and after addition of an organic substrate, and loss of POM (particulate organic matter) was measured at the end of the experiment. Loss of POC (particulate organic carbon) from the sediment was the same under aerobic and anaerobic conditions. However, the highest efflux of CO2 was measured in the OX-cores, and the highest efflux of DOC occurred in the AN-cores before and after addition of fresh substrate. Similarly, loss of PON (particulate organic nitrogen) from the sediment was the same in the 2 treatments, but the highest fluxes of NH,' and DON were measured In the AN-cores. Our conclusion is that degradation of POM is the same under both aerobic and anaerobic condltlons, but that mineralization of organic molecules is less effective under anaerobic condlhons. Before substrate addit~on there was an influx of NO3-in both OX-and AN-cores, and the estimated nitrification rate in the OX-cores was 1 to 2 mm01 m-' d-l The estimated denitrification rate contributed 3 to 6 '10 to total carbon respiration. After addition of the substrate, fluxes of all constituents increased. The estimated denitrification rate constituted < 3 '10 of total respiration. There was a large efflux of HS-in AN-cores During the experimental period, the losses of original POC and PON were calculated to be 2.6 and 4.0 %, respectively. Relative to the initial values, the pore water constituents increased with incubation, and the integrated AN/OX ratios for N H d f , DON and total CO2 were 1.2, 1.5 and 1.6, respectively, after 43 d.

Redfield revisited: 2. What regulates the oxygen content of the atmosphere?

“…Existing evidence suggests that new production and therefore the concentration of limiting nutrient in the surface ocean exert the dominant control on marine organic carbon burial [Betts and Holland, 1991;Pedersen and Calvert, 1990]. On the basis of data relating primary production to sedimentation rate [Miiller and Suess, 1979] and sedimentation rate to organic carbon burial [Henrichs and Reeburgh, 1987], organic carbon burial is assumed to be a quadratic function of new production, given by (3) and independent of ocean anoxia. The nonlinearity implies that increases in new production occur primarily in the shelf environments where a greater fraction of production is preserved than in the deep ocean [Van Cappellen and Ingall, 1994].…”

Microbial breakdown of Phaeocystis mucopolysaccharides

“…Remineralization of Phaeocystis mucus under anoxic conditions may have important consequences for oceanic C cycling. Sedimentation of organic C into anoxic sediments accounts for Ͼ90% of the annual burial of C (Henrichs and Reeburgh 1987), and Phaeocystis mucus may contribute a considerable fraction (Wassman et al 1990;Passow and Wassman 1994;Riebesell et al 1995;Hong et al 1997).…”

Changes in kerogen composition across an oxidation front in Madeira Abyssal Plain turbidites as revealed by pyrolysis GC-MS

“…Generally, there are two schools of thought. One argues that the presence or absence of O 2 has little or no effect on organic matter preservation (e.g., Henrichs and Reeburgh, 1987;Pedersen and Calvert, 1990;, whereas the other school states the opposite (e.g., Demaison and Moore, 1980;Pratt, 1984;Canfield, 1989Canfield, , 1993Paropkari et al, 1992).…”