Direct Measurement of Femtomoles of Osmium and the ¹⁸⁷ Os/ ¹⁸⁶ Os Ratio in Seawater

Abstract

Two depth profiles of the osmium concentration and the 187Os/186Os isotopic ratio in the Indian Ocean showed that the osmium concentration seems to be unaltered by chemical or biological processes occuring in seawater; accordingly, osmium is conservative. These data were obtained from an experimental method that eliminated the problems related to osmium preconcentration. This method led to a new evaluation of the concentration of osmium in seawater; the mean concentration of osmium and the 187Os/186Os ratio are equal to 10.86 +/- 0.07 picograms per kilogram and 8.80 +/- 0.07, respectively. The results suggest the existence of an organocomplex that dominates the speciation of osmium in seawater.

Osmium contamination of seawater samples stored in polyethylene bottles

“…These observations are in contrast with earlier studies. Levasseur et al (1998) (Sharma et al 2000) supporting Levasseur et al (1998) observations. However, Woodhouse et al (1999) reported a significant (30%) reduction in Os concentrations in the core oxygen minimum zone (OMZ) of the eastern tropical North Pacific (9° 46'N, 104° 22'W), a very different setting from site studied by Levasseur et al (1998).…”

“…Levasseur et al (1998) (Sharma et al 2000) supporting Levasseur et al (1998) observations. However, Woodhouse et al (1999) reported a significant (30%) reduction in Os concentrations in the core oxygen minimum zone (OMZ) of the eastern tropical North Pacific (9° 46'N, 104° 22'W), a very different setting from site studied by Levasseur et al (1998). Woodhouse et al (1999) reconciled their results with those of Levasseur et al (1998) by noting that dissolved O 2 profiles from nearby GEOSECS stations from western Indian Ocean (Leg 5 Station 428; 37°45′S, 57°37'E) show minimal vertical variation.…”

“…These techniques indicated that seawater Os concentration was 4-to 5-fold higher than determined by the previous studies. Levasseur et al (1998) …”

Osmium concentrations and 187Os/188Os ratios of three sediment reference materials

“…The Mn-Fe oxyhydroxides that form this crust scavenge Os from seawater . The Os isotopic ratio obtained for JMS-2 is slightly lower than that of the present seawater, which is approximately 1.0 (Sharma et al, 1997;Levasseur et al, 1998;Woodhouse et al, 1999;Burton et al, 1999). The Os isotopic composition of seawater has gradually increased from 0.5 to 1.0 in the last 50 million years, including a pronounced minimum (0.22-0.27) in the late Eocene between 34 and 34.5 Ma and a subsequent rapid increase to approximately 0.6 by 32 Ma (Ravizza and PeuckerEhrenbrink, 2003).…”

Mantle Sulfides and their Role in Re–Os and Pb Isotope Geochronology

“…Os; Levasseur et al 1998), but also extremely radiogenic ( 187 Os/ 188 Os ~ 1; Levasseur et al 1998) compared with PUM (0.1296, Meisel et al 2001. Rhenium, on the other hand, is enriched in seawater by approximately 740 times compared to Os (Anbar et al 1992).…”