SEASONAL TRANSPORT OF DISSOLVED INORGANIC CARBON AND TOTAL ALKALINITY ACROSS THE LOUISIANA SHELF

Author

Michelle M. Anderson, Louisiana State University and Agricultural and Mechanical CollegeFollow

Semester of Graduation

Summer 2020

Degree

Master of Science (MS)

Department

Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

Rivers and wetlands are a major source of terrestrial derived carbon for coastal ocean margins. Unfortunately, Louisiana’s wetlands are threatened by ongoing high rates of erosion, deterioration, and unprecedented rates of river water discharge that changes seasonally, leading to a net loss of terrestrial carbon into the northern Gulf of Mexico (nGOM). There exists a current lack of understanding about the distribution of dissolved inorganic carbon (DIC) and total alkalinity (TAlk) within the shallowest regions of the Louisiana shelf. Even less is known about how the transport of DIC alters seasonally with changes in river outflow and shelf currents. Quantifying seasonal shifts in carbon transport is critical to comprehending coastal water quality, as dissolved constituents from these terrestrial fresh water sources can change the nGOM’s ability to buffer decreases in pH and aragonite saturation states (Ω_A). This study investigated the DIC and TAlk dynamics in the shelf regions adjacent to the Wax Lake Delta (WLD) and Barataria Bay (BB), which represent contrasting areas of net land gain and net land loss along the Louisiana coast, respectively. DIC and TAlk samples were collected, in conjunction with short-lived radium isotopes ²²⁴Ra (t_1/2= 3.66 days) and ²²³Ra (t_1/2 = 11.43 days) samples for the month of June and September in 2019, to quantify cross-shelf transportation processes. Our results suggest that the buffering capability of surface water on the Louisiana shelf during the summer months were weaker than what has been reported by previous studies. Net cross shelf transport of DIC was found to be higher for the WLD region compared to BB, highlighting the importance of freshwater discharge in exporting DIC across the shelf. Extrapolating our study for the entire Louisiana shelf indicates that 9.7 x 10¹⁰ mol C d^-1 and 1.85 x 10¹⁰ mol C d^-1 in the form of DIC was exported across the shallow region of the shelf (isobath) during high and low river flow seasons. Predicted future changes in freshwater discharge are thus estimated to have a major impact on DIC transported into the interior nGOM and the Loop Current.

Recommended Citation

Anderson, Michelle M., "SEASONAL TRANSPORT OF DISSOLVED INORGANIC CARBON AND TOTAL ALKALINITY ACROSS THE LOUISIANA SHELF" (2020). LSU Master's Theses. 5171.
https://repository.lsu.edu/gradschool_theses/5171

Committee Chair

Maiti, Kanchan

DOI

10.31390/gradschool_theses.5171