Other
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992e%26psl.114...85f&link_type=abstract
Earth and Planetary Science Letters, Volume 114, Issue 1, p. 85-99.
Other
2
Scientific paper
A numerical model for the time-dependent behavior of particle-associated tracers in sediments has been developed. The model is based on the advection-diffusion equation for a tracer and includes a sediment density that increases with depth as a modified power function, and a diffusion coefficient that follows a half-Gaussian function versus depth with maximal diffusivity at the sediment-water interface. The solution procedure is based on finite elements or finite differences. The density function is developed from soil mechanics concepts and includes mixing effects through a Young's modulus that is increased in the top layer according to a half-Gaussian function. The new density function provides a better fit to 15 out of 17 sediment cores from Lake Michigan than a frequently used exponential expression.
The tracer model provides an excellent fit for the 137Cs distributions in all of the 17 Lake Michigan cores that were investigated. Our fit to the 137Cs profile of a southern Lake Michigan core that has been examined by others, is significantly better than previous fits, particularly near the top of the core. From two different forms of the governing equation for a tracer, and the resultant fits to experimental data, it appears that 137Cs is associated with colloidal and 210Pb with settling particles.
A previously developed time domain method to extract the historical input record of a tracer from its sedimentary profile, influenced by mixing, has been further improved by including m depth and n time intervals, where m >= n, and by fitting the influx to a polynomial. The improved method is demonstrated for the Cd input to a northern Lake Michigan core (NLM84B). Although the time resolution obtained ( ~ 5 yr) is better than the previous resolution ( ~ 15 yr), it is clear that the method needs to undergo further development in order to decrease the error of the reconstructed influx and particularly to avoid negative fluxes.
Christensen Erik R.
Fukumori Eiji
Klein Richard J.
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