Pacific Ocean surface water alkalinity

Both Die and Ax increase from surface waters to the deep Atlantic, Antarctic and Pacific Oceans as one follows the route of the ocean conveyor helt (Fig. 1.12). Along this transect pH changes from about 8.2 in surface waters to 7.8 in the deep Pacific Ocean, and CO3 decreases from nearly 250 geq kg to less than a third of this value, 75 geq kg. The reason for this change has to do with the ratio of the change in Aj and DIG in the waters and is discussed in the final section of this chapter. Notice that the contribution of the nutrients Si and P to the total alkalinity is only between 0 and 5 geq kg or at most 0.2% of the total alkalinity. Although Si concentrations are much greater than those of P, the two nutrients have nearly equal contributions to the alkalinity (Table 4.4) because the pK values for two phosphate reactions are closer to the pH of seawater than is the pK for sfiicate (see Table 4.1). 

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