Date of Award

8-2011

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography

Advisor

Lawrence M. Mayer

Second Committee Member

Emmanuel S. Boss

Third Committee Member

Neil V. Blough

Abstract

Organic carbon contained in suspended, coastal marine sediments photochemically dissolves under high doses of artificial sunlight in the laboratory, suggesting that sunlight might induce large changes in the form and fate of organic matter present in suspended particles along turbid, low-latitude coastlines. The primary goal of the work presented here was to develop a quantitative method of predicting the particulate organic carbon (POC) "photodissolution" rate in the coastal waters of Louisiana near the deltas of the Mississippi and Atchafalaya rivers. Pursuit of this objective required measurements of the reaction rate and apparent quantum yield, determination of sediment light absorption properties, and development of a novel method to retrieve the optical properties of coastal water from remotely-sensed reflectance measurements. This dissertation first describes dissolved inorganic carbon (DIC) production and oxy-gen consumption accompanying photodissolution. The ratio of DIC production to O2 consumption was lower for POC than in previously-described reactions of colored dis-solved organic matter (CDOM), suggesting greater photochemical incorporation of oxy-gen into organic matter. Particle light absorption properties control, in part, the rate of photodissolution. Absorption coefficients of suspended sediment samples from the study region are a weak function of organic carbon content but a strong function of reducible iron content. Photodissolution rate measurements and radiative transfer modeling were used to determine the wavelength-dependent apparent quantum yield for the reaction and to constrain the temperature dependence and sample composition-induced variability in the rate. Initial photodissolution rates scaled linearly with the reducible iron content of sediments but the rate was independent of composition over longer periods. High spatial-resolution optical properties of study region waters were obtained from a novel satellite reflectance inversion calibrated using the local mass-normalized optical properties of sus-pended sediments. Lab-based photodissolution rate measurements were scaled to match field optical conditions determined from available satellite observations. Empirical relationships between local weather and the satellite-based photodissolution predictions allowed estimates of rates on days without satellite imagery. Annually-integrated rates were small relative to river POC inputs, but results suggested photodissolution rates similar in magnitude to CDOM photoreactions.

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