Date of Award

Summer 8-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Ocean Science and Engineering

Committee Chair

Alan M. Shiller

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Stephan D. Howden

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Scott P. Milroy

Committee Member 3 School

Ocean Science and Engineering

Committee Member 4

Kevin S. Dillon

Committee Member 4 School

Ocean Science and Engineering

Committee Member 5

Karen H. Johannesson

Abstract

We investigated various dissolved trace element (dTE) distributions in two distinct areas: the coastal northern Gulf of Mexico and the eastern tropical Pacific Ocean.

A multi-year (2007‒2011) chemical time series of eight stations in the western Mississippi Sound (MS) and northwestern Mississippi Bight (MB) was undertaken to examine the factors affecting chemical distributions in this dynamic region. Key findings include the frequent development of bottom water hypoxia in MB during late spring-summer, the likely contribution of submarine groundwater discharge (SGD) to the material flows, and observation of effects of episodic events including tropical storms and the opening of the Bonnet Carré Spillway. In hypoxic bottom waters, enriched nutrients, Mn, and Ba as well as depleted V and Cr were commonly observed.

Contrasting with the northern Gulf section, we also examined dTE distributions in the eastern tropical Pacific Ocean in late 2013. Generally, a conservative dissolved Mo (dMo) distribution and surface dissolved V (dV) depletion were observed in the East Pacific Zonal Transect (EPZT) from Peru to Tahiti. Depleted dMo and dV in the oxygen deficient zone (ODZ) coincided with the nitrite maximum, suggesting association of these elements with the nitrogen cycle. Particulate Mo (pMo) and V (pV) enrichments in the ODZ indicate scavenging by Fe oxyhydroxides and/or biogenic particles. Depleted dMo and dV in hydrothermal plumes suggest a sink for Mo and V. Within the plumes, pV and pMo are adsorbed onto Fe oxyhydroxide and Fe/Mn (oxy)hydroxides, respectively.

Low surface water dissolved Ga and Al, as well as high and variable surface Ga/Al ratios along the EPZT reflect low aeolian input and a longer Ga residence time than Al. Intermediate water dissolved Ga (removal) and Al (addition) behaved non-conservatively in the EPZT, having contrasting behaviors that remain to be explained. Generally, elevated Ga and Al concentrations were observed in deep water, indicating inputs from hydrothermal activity and resuspended sediments. Hydrothermal flux estimates for Ga and Al showed that hydrothermal inputs of these elements are likely to be of local, not global importance, with dust input still the likely major influence on the distributions of these elements.

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