Osmium (Os)
| Atomic number: |
76 |
| Atomic weight: |
190.2 |
| Average concentration in ocean: |
15 - 56 fmol/kg |
| Residence time: |
16,000 -
65,000 years |
Distribution in ocean
The processes controlling osmium concentrations are not well understood because
there is not yet agreement on the oceanic distribution. A conservative
distribution with constant vertical profiles
and similar values in the Atlantic and Pacific was found by Sharma et al.
(1997). A constant vertical profile
was also found in the Indian Ocean (Levasseur et al., 1998), but values are
offset about 30 fmol/kg higher from the Pacific and Atlantic values (data).
Lack of isotopic tracer equilibration in the Atlantic and Pacific data during
analysis was suggested as the reason for the offset. More recently,
Woodhouse et al. (1999) found a non-conservative profile with low osmium
concentrations in the oxygen minimum and values intermediate between the two
studies mentioned above. Additional work needs to be done.
Speciation
Osmium may be present as H3OsO6- ion.
Residence time
The osmium residence time is from Levasseur et al. (1998). It was
calculated from the global average river input.
Analysis
Osmium is determined by isotope dilution, thermal ionization mass spectrometry.
References & Notes