Molybdenum concentration ocean

Emerson SR, Huested SS (1991) Ocean anoxia and the concentrations of molybdenum and vanadium in seawater. Marine Chem 34 177-196... 

Uranium (chemical symbol, U) is a slightly radioactive metal that occurs throughout the earth s crust. It is about 500 times more abundant than gold 40 times as silver and about as common as tin, tungsten, and molybdenum. It occurs in most rocks in concentrations of 2-4 ppm, for example, at about 4 ppm in granite, which makes up 60% of the earth s crust. In fertilizers, uranium concentrahon can be as high as 400 ppm (0.04%), and some coal deposits contain uranium at concentrahons of 100 ppm (0.01%). It is also found in the oceans, at an average concentration of 1.3 parts per billion (ppb). 

FIG. 8.4 The arrow through the ocean. Top-. The redox potential of different reduction-oxidation pairs corresponds to the order in which reduced and oxidized forms were encountered and used by life. Elements with lower redox potentials were oxidized earlier than elements with higher redox potentials. For example, ammonia/nitrogen, sulfide, and molybdenum (IV) are more easily oxidized than copper (I) and vanadium (III). Bottom Because iron (III) readily precipitates out of solution as iron oxide, over time iron concentrations decreased. Because copper (II) compounds are generally more soluble than copper (I), oxidation increased overall copper availability. This trend can be summarized by an arrow pointing away from iron and toward copper. 

If we compare the total amounts of trace elements present in solution in sea water with the annual levels of production (Table 40), it is clear that the total dissolution of the global annual production of most elements would have a negligible effect on their concentrations in the ocean. With the notable exception of the element lead, it would require the dissolution of over one hundred years production of every element to double its present concentration in sea water. For some elements like boron, fluorine, molybdenum and nickel, this level of enhancement would require the dissolution in the ocean of thousands of years of production at present levels. This is to say that any significant enhancement of the levels of these elements in ocean water as a result of human activity is impossible. 

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