210Po in the western Indian Ocean: Distributions, disequilibria and partitioning between the dissolved and particulate phases

Seven GEOSECS stations in the western Indian Ocean were measured for dissolved 210Po, and five of these were also measured for particulate 210Po. Dissolved phase 210Po is lower than 210Pb in the deep water north of Madagascar, with values in the Arabian Sea being lower by about 4 dpm/100 kg (≅ 30%) for almost the entire water column. South of Madagascar, 210Po is essentially in equilibrium with 210Pb in the deep water, but with 210Po excess in subsurface water south of the Crozet basin. In the benthic boundary layer, 210Po is consistently lower than 210Pb for all the stations. In the particulate phase 210Po shows a general increase with depth and is highest in the benthic boundary layer. In general, 210Po is lower than 210Pb in the particulate phase, but at the one Somali basin station where data are available, deep water 210Po is systematically higher than 210Pb. A mid-depth maximum of particulate 210Pb is generally associated with that of dissolved 210Pb. The partition of 210Po between the particulate and dissolved phases is not significantly different from that of 210Pb. The activities of the two nuclides in the particulate phase are generally less than 10% of those in the dissolved phase. The range is from 1% to 60%. High particulate and low dissolved activities are observed in the deep water, especially in the benthic boundary layer. (orig.)