Selenium concentration ocean

Mercury-selenium interactions are significant in marine mammals and seem to be a factor in loons however, this is not the case in marine birds. Mercury concentrations in oceanic birds were not correlated with selenium concentrations, as evidenced by values in livers of murres, Uria spp. and razorbills Alca torda, and in breast muscle of sooty terns Sterna fuscata. 

Johnson TM, Bullen TD (2004) Mass-dependent fractionation of selenium and chromim isotopes in low-temperature environments. Rev Mineral Geochem 55 289-317 Johnson KS, Gordon RM, Coale KH (1997) What cond ols dissolved iron concentrations in the world ocean ... 

Selenium profiles in sediments from the northeast Atlantic Ocean indicate concentrations of —0.2-0.3 mg kg in the oxic zone, and typically 0.3-0.5 mg kg below the redox boundary reflecting immobilization under reduced conditions (Thomson et al., 2001). Similar increases for cadmium, uranium, and rhenium have also been observed in the suboxic zone. 

Typical concentrations of selenium in seawater are —0.1-0.2 p,g (Table 9) with an estimated mean residence time of 70 yr in the mixed layer and 1,100 yr in the deep ocean. The oceans are, therefore, an important sink for selenium (Haygarth, 1994 Jacobs, 1989). Biogenic volatilization of selenium from seawater to the atmosphere is estimated to be 5,000-8,0001 yr. Amouroux et al. (2001) have demonstrated that biotransformation of dissolved selenium in seawater by blooms of phytoplankton in the spring is a major pathway for the emission of gaseous selenium to the atmosphere. Hence, oceans are an important part of the selenium cycle. 

Volatilization of selenium from volcanoes, soils, sediments, the oceans, microorganisms, plants, animals, and industrial activity all contribute to selenium in the atmosphere. Natural background concentrations of selenium in nonvolcanic areas are only around 0.01-1 ngm , but the short residence time, usually a matter of weeks, makes the atmosphere a rapid transport route for selenium. Volatilization of selenium into the atmosphere results from microbial methylation of selenium from soil, plant, and water, and is affected by the availability of selenium, the presence of an adequate carbon source, oxygen availability, and temperature (Frankenberger and Benson, 1994 Jacobs, 1989). 

Concentrations of many trace element nutrients (zinc, cadmium, iron, copper, nickel, and selenium) increase with depth in the ocean, similar to increases observed for major nutrients (nitrate, phosphate, and silicic acid) (Figures 2—4). In the central North Pacific, filterable concentrations of zinc and cadmium increase by 80-fold and 400-fold, respectively, between the surface and 1000-m depth. The similarity between vertical distributions of these trace elements and major nutrients indicates that both sets of nutrients are subject to similar biological uptake and regeneration processes. In these processes, both major and trace element nutrients are efficiently removed from surface waters through uptake by phytoplankton. Much of these assimilated nutrients are recycled within the euphoric zone by the coupled processes of zooplankton grazing and excretion, viral lysis of cells, and bacterial degradation of organic... 

Figure 4 Depth profiles for concentrations of total selenium and different chemical forms of selenium (selenate, selenite, and organic selenium compounds) in filtered seawater samples from the eastern tropical North Pacific Ocean (18° N, 108° W Oct.-Nov. 1981). Data are from Cutter GA and Bruland KW (1984) The marine biogeochemistry of selenium A reevaluation. Limnology and Oceanography 29 1179-1192.

Se(VI), Te(IV) is the stable form as Te(OH)4. There are few data for this element in the ocean, and profiles of tellurium in the eastern North Pacific (Figures 5D and E) show that its concentrations are 1000 times less than those of selenium and both forms of tellurium show strongly scavenged behavior. It is interesting to note that the most abundant form of tellurium is Te(VI), but it is the least thermodynamically stable. Although there are numerous biological reasons to expect reduced species in oxic waters (i.e., as for arsenic and selenium), this observation is somewhat difficult to explain. The elevated concentrations of Te(VI) at the surface, relative to Te(IV), suggest that the atmospheric or riverine inputs of this element are enriched in this form, but virtually no atmospheric data are available to confirm this speculation. 

Although selenium levels are low in natural waters, fluvial action is important in selenium transport. Bectine and Goldberg [54] estimated that 8,000 tons of selenium are deposited annually in the oceans. The average concentration of selenium in seawater is 0.09 ppb, due to loss by precipitation of selenite-metal hy-drozies. Analysis of rainwater for selenium content [21, 25] have shown a range of 0.04 to 1.4 ppb, and atmospheric selenium in rainwater is correlated to industrial emissions [21]. 

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