Oxygen consumption depth profiles

Figure 11. Depth profiles of oxygen consumption. The profile defined by the solid circles (m) was calculated from ETS activity measurements (o) as reported previously (55). The profile defined by the open triangles (a) is based on bacteriological studies (84). The family of continuous profile lines between A and B was generated by Suess s (93) model of oxygen-consumption rates.

These dissolved constituents of seawater have concentration versus depth profiles characterized by surface water depletion and deep water enrichment caused by plant consumption in the euphotic zone and release at depth when the biological material dies, sinks and degrades. Examples of these elements are nutrients required for ph5d oplankton growth (P, NO3 and HCO3), oxygen consumed during... 

Fig. 6.5 Measured and simulated profiles of oxygen and nitrate of station GeoB 1711 from the continental slope off Namibia at a water depth of approximately 2000 m. Degradation of organic matter with a C/N ration of 3.7 was assumed for simulation. Bars indicate oxygen consumption rates required for model fit (after Hensen et al. 1997).

One of the first applications of ocean radiocarbon data was as a constraint on the vertical diffusivity, upwelling, and oxygen consumption rates in the deep waters below the main thermocline. As illustrated in Figure 2, the oxygen and radiocarbon concentrations in the North Pacific show a minimum at mid-depth and then increase toward the ocean seabed. This reflects particle remineralization in the water column and the inflow and gradual upwelling of more recently ventilated bottom waters from the Southern Ocean. Mathematically, the vertical profiles for radiocarbon, oxygen (O2), and a conservative tracer salinity (5) can be posed as steady-state, 1-D balances ... 

Dissolved N2O is produced by nitrification and is both produced and consumed by denitrification. The marine flux of N2O is perhaps one-third of the global flux of this greenhouse gas to the atmosphere therefore, an understanding of the mechanisms of N2O production and their regulation in the ocean is an important goal. Culture studies indicate that bacterial production of N2O by nitrification and denitrification produces gas depleted in N and relative to the source material. Consumption of N2O by denitrification leaves the residual gas enriched in N and with d N of N2O as high as 40%o measured in the Arabian Sea. In oxygenated waters of the open ocean, nitrification likely dominates N2O production and its isotopic profile. A depth profile in... 

The methane content of the porewater profiles shows increasing concentration from the surface to 20-30 cm depth and then remains nearly constant. For a surface water temperature and sediment water temperature of 30°C the saturation of methane occurs at approximately 1 mM, which is exceeded by many of the porewaters at depths below 25 cm. Presumably this supersaturation is required for ebullition to be significant. The decrease in methane toward shallower water is probably due to consumption in the oxygenated zone and escape by diffusion and ebullition from the porewater to the atmosphere. It is interesting to note that at site JC-3 (July 91), the sediment below 25 cm has more than twice as much methane as does the sediment below a 5. patens mat (Fig. 5a). Because the mat is not completely floating all the time, we suggest that when the mat is close to or contacts the sediment it disturbs the sediment sufficiently to cause methane release. Another possibility is that the plant stem and/or roots connection of the mat to the sediment causes disturbance and release of the trapped methane. 

Results of experiments performed with oxidized PP doped with secondary HAS Tinuvin 770 show high concentration of nitroxides in the vicinity of both surfaces due to the DLO. This was observed after continuous exposure to radiation in the Weather-Ometer on the irradiated (front) and non-irradiated (back) surfaces as well as on the both surfaces of the samples e qjosed thermally in hot air oven. Very low concentration of nitroxides was present inside of the samples. The concentration profiles are of characteristic U-shape and indicate preferential surface oxidation of PP, with a specific response to thermal and photochemical stress (Fig. 2). The assumed complex HAS mechanism is thus more explicitly confirmed in thick samples than by monitoring nitroxide concentration in PP films. It is consistent with surface consumption of oxygen in thick plaques and lower availability of oxygenated products in the depth of the PP matrix necessary for a direct development of nitroxides from HAS as well as for nitroxide regeneration from O-alkylhydroxylamine >NOP within the regenerative cycle (7). 

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