Date of Award

12-2012

Degree Type

Masters Thesis

Department

Marine Science

Abstract

Coastal regions influenced by large freshwater inputs exhibit large variability in absorption and associated optical properties. Therefore, understanding coastal ecosystem processes requires intensive, ongoing sampling. Analysis of the Mississippi and Atchafalaya River plumes took place on board the RIV Pelican on two separate cruises. MagMix-1 occurred from May 1 to May 8, 2008 and corresponded to the highest discharge periods for both rivers for 2008; MagMix-11 took place October 31 to November 6, 2008 and corresponded to the lowest discharge periods for both rivers for 2008. Samples were collected along four transects in the northern Gulf of Mexico and were divided into three different spatial groupings for analysis: Atchafalaya River outflow region/Mississippi River outflow region, near shore stations/offshore stations and surface samples/samples taken at the bottom of the water column. A central hypothesis for this work was that there were fundamental differences in the partitioning of total absorption in Atchafalaya and Mississippi outflow regions due to the differences in hydrology and associated biogeochemistry. This hypothesis was rejected as MagMix data could not support this claim with data from chromophoric dissolved organic matter absorption, total particulate absorption, phytoplankton pigment absorption or detrital absorption (acoou ap, aph, or adet). Only actual Mississippi or Atchafalaya River samples taken during MagMix-II had any significant differences with respect to acooM, but neither rivers' respective outflow regions were significantly different from one another. Furthermore, it was hypothesized that coastal and offshore waters will exhibit fundamental differences in partitioning attributable to differences in allocthonous and autochthonous source terms. Both acooM and ap had significant differences when their near shore stations were compared to their offshore stations, for both cruises. When comparing the surface samples and deep samples, variability was significant for acooM, for both MagMix-I and MagMix-II_ Differences in ap were not significant when one compared the surface samples to samples taken at depth.

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