Date of Award

Spring 2026

Document Type

Open Access Thesis

Department

Marine Science

First Advisor

Subrahmanyam Bulusu

Abstract

The Gulf of Mexico (GoM) is a dynamic semi-enclosed basin where mesoscale and submesoscale circulation regulate the distribution of freshwater, nutrients, and biological productivity. The Loop Current System (LCS), which includes the Loop Current (LC), Loop Current Eddies (LCEs), and Loop Current Frontal Eddies (LCFEs), exerts the dominant control on basin-wide circulation. These features interact with freshwater input from the Mississippi-Atchafalaya River System (MARS) and with saline inflow from the Caribbean, resulting in variability in sea surface salinity (SSS) and chlorophyll-a (Chl-a) across a range of spatial and temporal scales. A primary focus of this work is understanding how the timing and magnitude of freshwater discharge and the evolution of the LC affect salinity, Chl-a distribution, and frontal eddy activity throughout the basin.

An investigation is made to examine how freshwater discharge and LC variability shape sea surface salinity distribution in the GoM. Stepwise linear regression shows that the Atchafalaya River variability, when it leads SSS by four months, is the strongest predictor of basin-wide salinity variability. The analysis further demonstrates that variability in SSS during flood and drought years cannot be explained by discharge alone but instead depends on the interaction between river input and LC positioning. This interaction determines whether freshwater is exported through the Florida Straits, recirculated in the central basin, or retained near the shelf. In addition to salinity, chlorophyll-a (Chl-a) distribution is examined in relation to LCFE activity.

Chl-a distributions (2018–2024) are further examined in relation to LCFE activity. Submesoscale activity along the LC boundary plays a critical role in redistributing nutrients on seasonal and interannual timescales. LCFEs are divided into three categories based on their location in relation to the LC. Each category shows unique seasonal patterns of Chl-a, with elevated concentrations arising from both vertical mixing during winter and horizontal advection of nutrient-rich river water during summer. This is quantified by the amount of Chl-a is transported within individual LCFEs. By linking freshwater discharge and Chl-a signals to LCFE activity, and other forcings, this study provides new insight into how physical processes in the GoM regulate nutrient availability and surface productivity in one of the most biologically and economically important regions of the western Atlantic.

Rights

© 2026, Pamela Jo Lee

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