Abstract
Selenium in sea water is present in four different forms, i.e., dissolved inorganic (IV and VI), dissolved organic and particulate organic form. The total content of selenium in dissolved forms is controlled by following factors:
- Exchange of water between the shallow and deep layers of the ocean.
- Biological production in which dissolved inorganic selenium is transferred into particulate organic form.
- Regeneration of dissolved selenium (inorganic and organic) from the particulate organic form of selenium.
The content of either inorganic or organic selenium in dissolved form is controlled also by oxidative decomposition of dissolved organic selenium.
It is considered that the ocean can be divided into two layers, i.e., the first layer (0-1,000 m) and the second layer (1,000-5,000 m).
Mean concentration of Se(IV), Se(VI) and organic selenium dissolved in the first and the second layer in the western North Pacific are as follows:
| | | | | (μg 1-1) |
| | IV | VI | Org. | Total |
| The 1st | 0.042 | 0.028 | 0.014 | 0.083 |
| The 2nd | 0.058 | 0.063 | 0.008 | 0.13 |
By assuming appropriate values of rates of different processes controlling the total content of dissolved selenium, the calculation was done concerning the cycle among the different forms of selenium in the ocean. The results of calculation showed that the observed values of the total content of dissolved selenium in two different layers can be explained on the assumption that a steady state is kept in the vertical direction with respect to selenium contents in various forms.
In the next place, dynamical equilibrium among the different chemical forms of selenium, i.e., selenium IV, selenium VI and organic selenium in both dissolved and particulate forms was studied in the same way as the above. The results showed a fairly good agreement between observation and calculation concerning contents of selenium in various chemical forms in sea water in the two different layers of the ocean.
