Geochemical mass balance ocean

Bulk rock chemistry of hydrothermally altered midoceanic ridge basalt has been well studied and used to estimate the geochemical mass balances of oceans today (Wolery and Sleep, 1976 Humphris and Thompson, 1978 Mottl, 1983). In contrast, very few analytical data on hydrothermally altered volcanic rocks that recently erupted at back-arc basins are available. However, a large number of analytical data have been accumulated on the hydrothermally altered Miocene volcanic rocks from the Green tuff region in the Japanese Islands which are inferred to have erupted in a back-arc tectonic setting (section 1.5.3). 

Geochemical mass balance dissolved chemical inflow and outflow from the ocean... 

The removal processes for potassium and magnesium have remained obscure. Sillen (1961), who considered seawater to be in equilibrium with the underlying oceanic sediments, was impressed by the potential ion exchange capacity of marine clay minerals. Indeed, in geochemical mass balances most potassium and much magnesium are recovered in shales. Following Sillen s proposal a number of workers (e.g., MacKenzie and Garrels, 1966 Siever, 1968 Pytkowicz, 1975) have advocated the reconstitution of silicates in the ocean s sediments by reactions such as... 

A direct geochemical check on the particle flux of organic matter from the euphotic zone determined by sediment traps is achieved by using the mass balance of thorium isotopes in surface waters. Since decay systematics and chemistry of the uranium series isotopes were introduced in Chapter 5, we will only briefly reiterate them here. is relatively unreactive in oxic seawater and exists in the ocean as a conservative element, i.e. the concentration normalized to salinity is everywhere the same to within measurement error. decays to which is very reactive to particles and has a relatively short radioactive half life of 24.1 d ... 

In the ocean, the material advected by the rivers participates in the formation of new sediments whereby the geochemical cycle is closed. The suspended load is redeposited in the continental shelf regions. The dissolved elements are temporarily stored in the ocean reservoir before they, too, are incorporated into sedimentary deposits. In the long run, the river influx must be balanced by an appropriate sedimentary output for each element considered. A certain degree of accumulation is nevertheless evident from the higher concentrations of the principal ions in seawater as compared to those in river water (Table 11-7, columns 6 and 7). Residence times in the ocean can be computed by means of Eq. (4-11) from the ratio of the reservoir s mass content to the observed river influx. The residence times... 

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