210Pb in the Pacific: the GEOSECS measurements of particulate and dissolved concentrations

Details 210Pb in the Pacific: the GEOSECS measurements of particulate and dissolved concentrations 210Pb in the Pacific: the GEOSECS measurements of particulate and dissolved concentrations

Nov 1983

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983e%26psl..65..406c&link_type=abstract

Earth and Planetary Science Letters, Volume 65, Issue 2, p. 406-432.

Computer Science

14

Scientific paper

We report here on particulate and dissolved 210Pb profiles at 16 stations, and on total 210Pb profiles at 3 stations, all occupied during the Pacific GEOSECS expedition. Comparison with measurements at Yale on GEOSECS library samples indicates that during separation of particulate lead from dissolved lead, our filtered water samples suffered some loss of 210Pb in the filtration system; this effect appears to have reduced the dissolved 210Pb activities by ~ 20% in stations where the water was filtered. However, for these first Pacific data on the 210Pb distribution between the two phases, this effect does not significantly interfere with our recognition of the major features of both particulate and dissolved 210Pb distributions.
The dissolved 210Pb profiles in general vary geographically, following the 226Ra profiles. In deep water, 226Ra increases northward and eastward from the southwest Pacific, from ~ 22 dpm/100 kg, to over 40 dpm/100 kg in the northeast Pacific. Our dissolved 210Pb profiles show a similar increase in deep water, varying from about 10 to 20 dpm/100 kg along this line, and are commonly characterized by a mid-depth maximum. This 210Pb maximum reflects the mid-depth 226Ra maximum of the Pacific Deep Water observed along the western boundary current.
In surface water at low latitudes there is a significant 210Pb flux from the atmosphere, which produces a 210Pb/226Ra activity ratio generally greater than unity. This flux penetrates as deep as 600 m, as indicated by an ``induced'' 210Pb minimum caused by the surface maximum. The surface water 210Pb excess decreases toward high southern latitudes and vanishes in the Circumpolar region.
The particulate 210Pb profiles show a general increase with depth, from ~ 0.3 dpm/100 kg in subsurface water to ~ 1.5 dpm/100 kg in bottom water, with or without a mid-depth maximum that reflects the 226Ra or dissolved 210Pb maximum. The particulate 210Pb normally comprises about 2% of the total 210Pb in subsurface water, and this fraction increases to about 10% near the bottom. As the filtration loss is not taken into account, the fraction of particulate 210Pb quoted here is an upper limit. Since the particulate matter concentrations are quite uniform in the water column below a few hundred meters, the 210Pb activity of the particulate matter also increases with depth. The particulate matter has a 210Pb concentration of ~ 100 dpm/g in subsurface water, but the concentration increases to ~ 500 dpm/g or more toward the bottom. This indicates that there is a cumulative adsorption of Pb onto the suspended particles as they are sinking through the water column.

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