Date of Award

8-2012

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Physics

Advisor

C.T. Hess

Second Committee Member

Aria Amirbahman

Third Committee Member

Steve Norton

Abstract

Several processes change the radionuclide profiles in lake sediment cores. Two important processes are sediment mixing by worms and microbes, and molecular diffusion in the pore waters. Simple diffusion is used to estimate these influences upon the 210Pb distribution using an analytic solution to the Constant Flux Constant Sedimentation (CFCS) model. Diffusion coefficients are calculated by fitting Gaussian curves to 137Cs distributions before diffusion (based on fallout measured in precipitation during nuclear testing) and after diffusion (distributions measured in sediment cores). Diffusion coefficients ranged from 0.01 cm2/yr to over 2 cm2/yr, with an average value of 0.64 cm2/yr. When significant diffusion is seen, corrections must be applied to the dates calculated using CFCS and Constant Rate of Supply (CRS) models. Using 22 lakes dated by the University of Maine Department of Physics, the corrections resulted in an average increase in the age of sediment at a given depth by 36%.

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