Open Access210 Po and 210 Pb distributions and residence times in the nearshore region of Lake Superior
Author(s) -
Chai Yingtao,
Urban Noel R.
Publication year - 2004
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2003jc002081
Subject(s) - settling , water column , sediment , sediment trap , isotope , particulates , seawater , fractionation , geology , oceanography , hydrology (agriculture) , environmental science , chemistry , geomorphology , physics , chromatography , quantum mechanics , environmental engineering , geotechnical engineering , organic chemistry
The naturally occurring radionuclide, 210 Pb, and its decay daughter, 210 Po, were measured in the Keweenaw Peninsula region of Lake Superior. Water, suspended particles, sediment trap material (settling particles), and sediment cores and grab samples were collected along three transects that stretched from 1 to 20 km from shore. Departures from secular equilibrium (activity ratio of 210 Po: 210 Pb = 1) were observed for most samples. 210 Po‐deficiency was observed in both suspended particles (TSP) with a ratio of 0.43 ± 0.05 (±95% confidence interval (CI)) and settling particles with a ratio of 0.57 ± 0.04; higher ratios in the settling particles resulted from an admixture of resuspended sediments. Ratios in the dissolved phase were 0.45 ± 0.12. Approximately 83% and 85% of total 210 Po and 210 Pb in the water column was in the particulate phase. No evidence of biological uptake of Po was found. Seasonal and spatial variability in activities and ratios was small. Using steady state solutions to the mass balance equations for both isotopes, similar residence times in the water column were calculated for 210 Po and 210 Pb (55 ∼ 75 days in a 150‐m‐deep water column). It was possible to calibrate a one‐box model for the paired isotopes so that the model output closely matched rates of sediment and isotope resuspension estimated from sediment traps. However, this calibration required a fractionation of the isotopes during resuspension. The particle settling velocity was estimated to be 2.3 m d −1 , which also is in agreement with the estimate (2.4 ± 2.2 m d −1 ) from sediment traps. These results indicate rapid fluxes of radioisotopes and sediments through the water column largely driven by resuspension of sediments in nearshore areas.