Date of Award

Fall 12-2011

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Marine Science

Committee Chair

Dr. Kevin Yeager

Committee Chair Department

Marine Science

Committee Member 2

Dr. Charlotte Brunner

Committee Member 2 Department

Marine Science

Committee Member 3

Dr. Mark Kulp

Abstract

Annual rates of shallow autocompaction (< 1 m) were calculated in the upper ~one meter of sediment from six cores of a transect in the Pearl River Marsh (PRM), Louisiana, in order to determine the most significant sedimentary property controlling this process. Compaction-free wedge cores were sub-sampled at one centimeter intervals to collect the following data: age control, using 137Cs and 210Pb, and sedimentary variables, specifically, particulate organic carbon, bulk density, median grain size, porosity, and water content. An upper and an underlying sedimentary unit (named the 137Cs and 210Pb units) were defined between radiometric datum levels, and their sedimentary properties were statistically tested for significant differences using the non-parametric Mann-Whitney test. Rates of autocompaction were calculated from the model of Williams (2003), and both rates of autocompaction and sedimentation were tested for significant differences between the upper and lower sedimentary units.

The upper unit in the six cores generally had lower bulk density, higher water content, higher porosity, and higher particulate organic carbon than the underlying unit, but with some interesting exceptions. Additionally, annual autocompaction and sedimentation rates were greatest in the overlying unit at stations PR02 (0.39 ± 0.05 cm/y) and PR05 (0.42 ± 0.03 cm/y) and greatest in the underlying unit at stations PR02 (0.22 ± 0.08 cm/y) and PR03 (0.18 ± 0.06 cm/y). Based on Spearman correlations, rates of autocompaction were most strongly correlated to and influenced by rates of sedimentation rather than the other sedimentary variables: particulate organic carbon, bulk density, median grain size, porosity, and water content. The rates of sedimentation and autocompaction from this study were similar to rates measured in similar studies that use different methodologies to calculate compaction. This study demonstrates that rates of autocompaction are highly variable in near-surface sediments and that these rates significantly decrease with increased depth.

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