(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2000-09)
Laarkamp, Kirsten L.
Phosphorus, an essential nutrient, is removed from the oceans only through burial
with marine sediments. Organic phosphorus (Porg) constitutes an important fraction (ca.
25%) of total-P in marine sediments. However, given the inherent lability of primary Porg
biochemicals, it is a puzzle that any Porg is preserved in marine sediments. The goal of this
thesis was to address this apparent paradox by linking bulk and molecular-level Porg
information.
A newly-developed sequential extraction method, which isolates sedimentary Porg
reservoirs based on solubility, was used in concert with 31P nuclear magnetic resonance
spectroscopy (31P-NMR) to quantify Porg functional group concentrations. The coupled
extraction/31P-NMR method was applied to three sediment cores from the Santa Barbara
Basin, and the first-ever high-resolution depth profiles of molecular-level Porg distribution
during diagenesis were generated.
These depth profiles were used to consider regulation of Porg distribution by biomass
abundance, chemical structure, and physical protection mechanisms. Biomass cannot
account for more than a few percent of sedimentary Porg. No evidence for direct structural
control on remineralization of Porg was found. Instead, sorptive protection appears to be
an important mechanism for Porg preservation, and structure may act as a secondary
control due to preferential sorption of specific Porg compound classes.
