Date of Award

2014

Document Type

Open Access Thesis

Department

Marine Science

First Advisor

Claudia Benitez-Nelson

Abstract

In order to understand the biogeochemical cycling of phosphorus (P) in a coastal marine ecosystem, the chemical composition and the sinking flux of particulate P was analyzed within sediment trap particles collected in the Cariaco Basin, Venezuela. Total, inorganic and organic P composition was examined across the time series (1995-2010) using a modified Aspila method and sequential extraction techniques. Particulate inorganic P (PIP) dominated the total particulate P (TPP) pool (~52%) when averaged over the entire water column. Relationships between particulate nitrogen (PN) and particulate organic carbon (POC) fluxes versus TPP fluxes followed expected canonical Redfield ratios except for a series of samples that were comprised with extraordinarily high fluxes of PIP. This suggests that a significant fraction of PIP is marine derived, with the high PIP flux events likely due to coastal margin and terrigenous inputs. PIP composition in both high and low flux events associated with Redfield and non-Redfield particulate nutrient ratios were examined in detail using SEDEX, a sequential chemical extraction method that focuses on inorganic P associations. Results indicate that most of the "extra" PIP is in the form of labile and oxide bound P, suggesting that it is likely to be bioavailable to marine organisms on relatively short timescales. Indeed, a significant fraction of this "high" PIP was rapidly remineralized with increasing depth. Low terrigenous fluxes and a lack of strong detrital or authigenic P source suggest that the higher PIP fluxes are likely due to remobilization of marine organic matter of lithogenic origin from the Unare platform.

Techniques were also tested for examining specific compounds within sediment trap material using the Miyata & Hattori (M&H) sequential extraction method. The M&H method was optimized using known P compounds as spikes and combining the extraction with solid and liquid state 31P-NMR. Specifically we were able to verify the presence of two P compounds that were spiked and extracted using M&H via 31P-NMR, DNA and sodium hexametaphosphate. A limited number of sediment trap samples were analyzed using the M&H method and our results suggest that > 50% of the P present in the samples are comprised of nucleotides, sugar phosphates and orthophosphate, followed by lipids, polyphosphates and nucleic acids, compounds previously observed in sediments. In contrast, Miyata & Hattori (1986) found orthophosphate and nucleic acids to be the most abundant types of P in phytoplankton, followed by polyphosphates and lipids.

The biogeochemical cycling of P is complicated and various factors need to be considered, for example remineralization and sources (terrestrial, biological, etc.). However, the use of SEDEX, M&H and 31P-NMR, together and individually, help us better understand the behavior and composition of this important nutrient.

Rights

© 2014, Anne S Opseth

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