Modeling variability in Pb-210 and sediment fluxes near the Whites Point Outfalls, Paleo Verdes Shelf, California
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abstract
Many researchers have had difficulty interpreting sediment data collected from the Palos Verdes Shelf, southern California. Factors that have been difficult to reconcile include the distribution of 210Pb and metals, the depth and extent of bioturbation, and the rate of sedimentation. This paper presents a simple model that includes these elements and simulates the flux of 210Pb, sediment, and metals to the sea floor near the Whites Point wastewater outfalls. The model uses known particle and metals emission rates from the outfalls and 210Pb fluxes to the sediments that vary in proportion to the flux of sediment mass to the sea floor. Model-predicted metals and 210Pb concentration profiles in the sediments agree well with data from cores collected at three locations on the Palos Verdes Shelf between 1972 and 1997. The implication of the model results is that 210Pb fluxes to the sediments in this area have varied greatly over the past 60 years. The model suggests that subsurface 210Pb maxima and uniform 210Pb concentrations to depths within the sediments of roughly 30 cm have resulted from time-variable 210Pb fluxes to the sediments and relatively shallow bioturbation and that natural sedimentation rates are relatively high (roughly 500-1000 mg cm-2 yr-1, or about 0.7-1.3 cm yr-1 of unconsolidated sediment).
