Ocean organic carbon

The quantity of primary production that is exported from the upper ocean is said to be equivalent to new production (18, 19) New primary production is that associated with allocthonous nutrients (i.e., those upwelled or mixed into the euphotic zone or input via rivers and rain). In order for steady state to be maintained, an equivalent flux out of the euphotic zone is required. Earlier studies (19) suggested that sediment-trap measurements of particulate organic carbon (POC) flux were equivalent to new primary production however, recently it has become clear that these measurements probably represent only a... 

The case of bacterial reduction of sulfate to sulfide described by Berner (1984) provides a useful example. The dependence of sulfate reduction on sulfate concentration is shown in Fig. 5-4. Here we see that for [SO ] < 5 mM the rate is a linear function of sulfate concentration but for [SO4 ] > 10 itiM the rate is reasonably independent of sulfate concentration. The sulfate concentration in the ocean is about 28 mM and thus in shallow marine sediments the reduction rate does not depend on sulfate concentration. (The rate does depend on the concentration of organisms and the concentration of other necessary reactants - organic carbon in this case.) In freshwaters the sulfate concentration is... 

As shown in Fig. 10-13, there is also a flux of O2 produced during net photosynthesis from the ocean to the atmosphere and an export flux of particulate and dissolved organic matter out of the euphotic zone. For a steady-state system, new production should equal the flux of O2 to the atmosphere and the export of organic carbon (Eppley and Peterson, 1979) (when all are expressed in the same units, e.g., moles of carbon). Such an ideal state probably rarely exists because the euphotic zone is a dynamic place. Unfortunately, there have been no studies where all three fluxes were measured at the same time. Part of the difficulty is that each flux needs to be integrated over different time scales. The oxygen flux approach has been applied in the subarctic north Pacific (Emerson et al, 1991) and subtropical Pacific (Emerson et al, 1995, 1997) and Atlantic (Jenkins and Goldman, 1985). The organic carbon export approach has... 

To this point, organic matter in the ocean has been treated primarily as RKR average plankton. We now need to focus on the fate of this biologically produced organic carbon. 

Sediment trap studies in the open ocean show that the flux of organic carbon at any depth is directly proportional to the rate of primary productivity in the surface water and inversely proportional to the depth of the water column (Suess, 1980) ... 

Fig. 10-15 Organic carbon fluxes with depth in the water column normalized to mean annual primary production rates at the sites of sediment trap deployment. The undulating line indicates the base of the euphotic zone the horizontal error bars reflect variations in mean annual productivity as well as replicate flux measurements during the same season or over several seasons vertical error bars are depth ranges of several sediment trap deployments and uncertainities in the exact depth location. (Reproduced with permission from E. Suess (1980). Particulate organic carbon flux in the oceans - surface productivity and oxygen utilization, Nature 288 260-263, Macmillan Magazines.)...

The distribution of dissolved, total particulate, and living particulate organic carbon in the surface (0-300 m) and deep ocean (>300 m) are summarized in Table 10-6. Recent analytical advances have greatly improved our understanding of the distributions of DOC in the ocean (Hedges and Lee, 1993). The important aspects of this compilation are ... 

The organic carbon (and thus the organic matter) in seawater is predominantly in dissolved form (DOC) with an average for the whole ocean being 97%. In general, surface ocean concentrations are about 80/ M and decrease to about 40 /iM below 500 m (Peltzer and Hayward, 1996 Hansell and Peltzer, 1998). 

The main mechanism for removal of organic carbon from the ocean is burial in sediments. This flux is equal to the average global sedimentation rate for marine sediments times their weight percent organic carbon. The total sink... 

To a first approximation the deep ocean distributions shown in Fig. 10-20 can be reproduced if the particulate material dissolving in the deep sea has the ratio of 1 mol CaCOs to 4 mol organic carbon (Broecker and Peng, 1982). 

Emerson, S., Quay, P., Karl, D. et al. (1997). Experimental determination of the organic carbon flux from open-ocean surface waters. Nature 389, 951-954. 

Hansell, D. and Carlson, C. A. (1998). Deep-ocean gradients in the concentration of dissolved organic carbon. Nature 395, 263-266. 

Peltzer, E. T. and Hayward, N. A. (1996). Spatial and temporal variability of total organic carbon along 140 W in the equatorial Pacific Ocean in 1992. Deep-Sea Res. II43, 1155-1180. 

Suess, E. (1980). Particulate organic carbon flux in the oceans-surface productivity and oxygen utilization. Nature 288, 260-263. 

The two prime mechanisms of carbon transport within the ocean are downward biogenic detrital rain from the photic zone to the deeper oceans and advection by ocean currents of dissolved carbon species. The detrital rain creates inhomogeneities of nutrients illustrated by the characteristic alkalinity profiles (Fig. 11-9). The amount of carbon leaving the photic zone as sinking particles should not be interpreted as the net primary production of the surface oceans since most of the organic carbon is recycled... 

Chen, C.-T.A. (1978). Decomposition of calcium carbonate and organic carbon in the deep oceans. Science 201, 735-736. 

Fig. 4.14. Tracing climate change in the Miocene. Shown here are records of ice volume and temperature (based on foraminiferal S 0) and relative organic carbon burial (based on foraminiferal S C), compared with the CO2 estimates of Pagani et al. (1999), and tectonic events that may have affected ocean heat transport. Trends in CO2 are consistent with organic carbon burial and CO2 drawdown during the Monterey Excursion, but cannot explain the Miocene Climatic Optimum (MCO) or expansion of the East Antarctic Ice Sheet (EAIS).

THORIUM AND POLONIUM AS TRACERS FOR ORGANIC CARBON CYCLING IN THE OCEANS... 

Buesseler KO, Ball L, Andrews J, Benitez-Nelson C, Belastock R, Chai F, Chao Y (1998) Upper ocean export of particulate organic carbon in the Arabian Sea derived from thorium-234. Deep-Sea Res II 45 2461-2487... 

Niven SEH, Kepkay PE, Boraie A (1995) Colloidal organic carbon and colloidal dynamics during a coastal phytoplankton bloom. Deep-Sea Res II 42 257-273 Nozaki Y, Thomson J, Turekian KK (1976) The distribution of Pb-210 and Po-210 in the surface waters of the Pacific Ocean. Earth Planet Sci Lett 32 304-312... 

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