Reservoir ocean basins

Using the rock cycle as an example, we can compute the turnover time of marine sediments with respect to river input of solid particles from (1) the mass of solids in the marine sediment reservoir (1.0 x 10 g) and (2) the annual rate of river input of particles (1.4 X lO g/y). This yields a turnover time of (1.0 x 10 " g)/(14 x lO g/y) = 71 X lo y. On a global basis, riverine input is the major source of solids buried in marine sediments lesser inputs are contributed by atmospheric feUout, glacial ice debris, hydrothermal processes, and in situ production, primarily by marine plankton. As shown in Figure 1.2, sediments are removed from the ocean by deep burial into the seafloor. The resulting sedimentary rock is either uplifted onto land or subducted into the mantle so the ocean basins never fill up with sediment. As discussed in Chapter 21, if all of the fractional residence times of a substance are known, the sum of their reciprocals provides an estimate of the residence time (Equation 21.17). 

Recent pelagic sediments containing over 30% calcium carbonate, by dry weight, cover a quarter of the surface of the earth (see Figure 1). These sediments make up a vast and chemically reactive carbonate reservoir which has a major influence on the chemistry of the oceans and atmosphere. In order to have a predictive understanding of the natural carbon dioxide system and the influence of man on it, the chemical dynamics of calcium carbonate deposition in the deep ocean basins must be known in detail. 

The World Ocean clearly occupies first place among all the water reservoirs on Earth. Its present volume exceeds 50-fold the volume of water in glaciers, which occupies second place. This comparison is important for understanding the correlation between the hierarchical steps of water basins and determining their structure in the model. Within a priori scenarios of anthropogenic activity and possible changes in the biosphere, the correlation between these steps is important. For instance, 1.6%... 

Figure 13.13 illustrates the major fluxes across the boundaries of the basin, as well as sinks (denitrification) and new sources (N2 fixation) of reactive N. The important physical reservoirs included in the budget are estuaries, continental shelves, and the open ocean, each undergoing additions and removals of N by various mechanisms. The estuaries receive N from rivers (540 x 10 mol year ), about half of which (250 X 10 molyear ) is lost from the system via denitrification (Seitzinger, 1988). The bulk of the remainder passes through the system to the shelves, with a small amount lost to the estuarine sediments. Major rivers do not have the conditions... 

Kharaka et al. (1979) and Kharaka and Carothers (1988) were probably the first to present evidence for meteoric water older than Pleistocene in sedimentary basins. These authors presented isotopic and chemical data for formation waters from exploration and producing oil and gas wells from the North Slope of Alaska. The water samples were obtained from reservoir rocks between 700 m and 2,800 m in depth and in age from Triassic to Mississippian. The waters from all formations, however, are remarkably similar in TDS ((1.9-2.4)X lO mgL" ) and in the concentration of the major cations and anions. The least-squares line through the 5D and 5 0 values for these waters (Figure 12) intersects the meteoric water line at 5D and 5 0 values of —65%c and —l%c, respectively. This line does not pass through the values for standard mean ocean... 

The turnover time and fluxes of DOC into the ocean are obtained by comparing the reservoir size and radiocarbon age. The ocean inventory of DOC is —680 Gt, and nearly all of this carbon resides in the deep sea, where concentration profiles and radiocarbon values are constant with depth. DOC ages by —1,000 yr as deep seawater moves from the Atlantic to the Pacific Basin, but even in the Atlantic, DOC radiocarbon values are significantly depleted relative to dissolved inorganic carbon (DIC) (Druffel et al., 1992). DOC persists in seawater through several ocean... 

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