Changes of lead and barium with time in California off-shore basin sediments
- Creators
- Ng, Amy
- Patterson, Clair C.
Abstract
During ancient times the natural deposition fluxes of lead which can be leached with dilute acid from sediments in Santa Barbara, Santa Monica and San Pedro basins offshore from the Los Angeles Urban complex, were about 0.7, 0.1 and 0.2 μg Pb/cm^2 yr respectively. Since there was little difference in biological productivity in surface waters of these basins, it is proposed that clay is a major transport vehicle for sequestered soluble lead, which then explains why the lead deposition flux within the Santa Barbara basin was so much larger compared to the other basins. The fluxes of silicate mud in the basins in ancient times were about 92, 19 and 30 mg/cm^2 yr in Santa Barbara, Santa Monica and San Pedro basins respectively. Today deposition fluxes of acid soluble lead within these three basins are 3- to 9-fold greater, being about 2.1, 1.1 and 1.8 μg Pb/cm^2 yr respectively, partly in the form of directly deposited large sewage particles, which account for none, 2/3 and 3/4 of the total industrial lead deposition fluxes in the respective basins. Concentrations of leachable lead in varve dated sediment layers increase with time and isotopic compositions of these leads change in accordance with corresponding known changes of isotopic compositions of industrial lead in the Los Angeles atmosphere. Lead remaining in acid leached sediment residues originates from igneous and clay minerals, exhibiting no change in concentration or isotopic composition since pre-industrial times. Deposition fluxes of total barium in sediments among the three basins were proportional to mass deposition fluxes before 1950 in the same manner as for lead. Afterwards, there are barium concentration maxima with time in both Santa Monica and San Pedro Basin sediments which are attributable to industrial sewage rather than to episodic erosion from barium-rich sedimentary evaporite strata exposed locally along the shore. An increase of barium concentrations in present day Santa Barbara basin sediments may reflect dispersal of barium-rich drilling mud from local drilling operations.
Additional Information
© 1982 Pergamon Press Ltd. Received October 13, 1981; accepted in revised form August 17, 1982. We thank A. Soutar and coworkers (Univ. Calif. SIO) for collecting, slicing and x-raying the sediments and for providing PIT samples, K. Bruland and coworkers (Univ. Calif. Santa Cruz) for determining 210Pb ages in them, and R. F1egal and coworkers (Calif. State Univ. Moss Landing) for advice regarding lead deposition mechanisms. We thank reviewers for constructive criticism, including S. Luoma (U.S. Geol. Survey, Menlo Park, Calif.) for pointing out that isotopic relationships show that most of the acid leachable lead is probably sorbed on lithic substrates in fresh waters before they enter the ocean. This work was supported by a grant from the U.S. Bureau of Land Management, Department of Interior, 1977.Additional details
- Eprint ID
- 48698
- Resolver ID
- CaltechAUTHORS:20140819-154143581
- Bureau of Land Management (BLM)
- Created
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2014-08-19Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field