The Oceanic System

Once in the photic zone, P is readily incorporated into biogenic particles (2) via the photosynthetic activities of plants and begins to sink. The majority of these particles decompose in the surface layer or in shallow sediments and the P is recycled directly back into the photic zone (3) to be reincorporated into biological particles. A small portion of the particles produced in the surface layers, however, does escape the surface layers and sinks into the deep ocean. Most of these particles eventually decompose (4), and the cycle is repeated. A very small fraction of these particles, however, escapes decomposition and is incorporated into the sediments (6). 

The dominant forms in which P is removed from seawater appear to be (1) the burial of organic P compounds that escape decomposition (2) the burial of P adsorbed onto CaCOs surfaces and (3) the formation of apatite in continental margin sediments. To a lesser degree, the decomposition of fish debris and the adsorption of P onto iron oxyhydroxide phases also contribute to the removal of P from seawater (Froelich et al., 1977,1982,1983). 

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The ocean system is separated into three major reservoirs that best represent the dominant pools and pathways of P transport within the ocean. The surface ocean reservoir (5) is defined as the upper 300 m of the oceanic water column. As discussed in an earlier section and displayed in Fig. 14-6, the surface layer roughly corresponds to the surface mixed layer where all... 

It seems much more likely that Mo isotopes are fractionated within the ocean system during removal from seawater, as hrst proposed hy Barling et al. (2001). This possibility is considered helow with respect to Mo removal to ferromanganese oxides, euxinic sediments and suboxic sediments. 

Fig. 2. Logarithmic activity diagram depicting equilibrium phase relations among aluminosilicates and sea water in an idealized nine-component model of tire ocean system at the noted temperatures, one atmosphere total pressure, and unit activity of H20. The shaded area represents (lie composition range of sea water at the specified temperature, and the dot-dash lines indicate the composition of sea water saturated with quartz, amotphous silica, and sepiolite, respectively. The scale to the left of the diagram refers to calcite saturation foi different fugacities of CO2. The dashed contours designate the composition (in % illite) of a mixed-layer illitcmontmorillonitc solid solution phase in equilibrium with sea water (from Helgesun, H, C. and Mackenzie, F T.. 1970. Silicate-sea water equilibria in the ocean system Deep Sea Res.).

Phytoplankton is at one of the initial levels of the trophic hierarchy of the ocean system. As field observations have shown, the World Ocean has a patchy structure formed by a combination of non-uniform spatial distributions of insolation, temperature, salinity, concentration of nutrient elements, hydrodynamic characteristics, etc. The vertical structure of phytoplankton distribution is less diverse and possesses rather universal properties. These properties are manifested by the existence of one to four vertical maxima of phytoplankton biomass. 

There are several different ways to approach the cycles of Ca, Mg, C, and other elements in the oceanic system depending on the choice of boundary conditions. For example, discussion can be restricted to the water column bounded by continents, atmosphere, and the sediment-water interface. In this case, the various fluxes between the sea-floor and the water column must be defined. Another approach is to include the marine sediments in the oceanic system and to... 

Inputs and outputs of calcium, magnesium, and carbon can be balanced for the modern ocean. This balance necessitates reverse weathering reactions in the ocean system in which CO2 consumed in weathering on land is released to the ocean-atmosphere system during the formation of minerals in the ocean. If this were not the case, regardless of juvenile emissions of CO2 to the ocean-atmosphere system, atmospheric CO2 concentrations could be reduced to vanishingly small values in less than 5000 years. 

Figure 10.34. Two scenarios of the fate of excess carbon input to the ocean because of human activities. A. Most excess carbon is respired and oxidized to CO2. B. Excess carbon is stored in the oceanic system and the CO2 evasion flux is maintained at the geologic rate. See text for discussion. Fluxes are in units of 1012 moles C y-1. (After Wollast and Mackenzie, 1989.)...

Helgeson, H.C. and Mackenzie, F.T. Silicate-sea water equilibria in the ocean system. Deep-Sea Res. 17, 877-892 (1970). 

Increased density of sampling of the ocean system has made it possible to explore the extent... 

Nitrogen fixation. The two aspects of the nitrogen cycle having the greatest impact on the biological pump are nitrogen fixation and denitrification. The first provides a mechanism for drawing on the extensive atmospheric pool of N2 gas in support of primary production. The second provides a pathway for DIN to be converted back to N2 gas and removed from the ocean system. 

The control processes of chelation and adsorption are in turn partially dependent on the route of entry of the trace metal into the ocean system. Transport via stream or river is a complex process which varies from metal to metal. For example, analysis of trace metal transport for Fe, Cu, Co, and Mn, with respect to five possible processes was carried out22). These processes included ... 

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