Dissertation Proposal Seminar - EvaLynn Jundt

COASTAL AND MARINE SYSTEM SCIENCE PROGRAM
DEPARTMENT OF PHYSICAL AND ENVIRONMENTAL SCIENCES
TEXAS A&M UNIVERSITY-CORPUS CHRISTI

SUBJECT: Carbonate Chemistry and Ocean Acidification in the Northwestern Gulf of Mexico

MAJOR ADVISOR: Dr. Xinping Hu

ABSTRACT
Ocean acidification (OA) caused by the absorption of anthropogenic CO₂ is a direct threat to many organisms living in the oceans across the globe. The study of OA primarily focuses on the uptake of atmospheric CO₂, resulting in a reduction in both pH and aragonite saturation state (Ω_Arag). The CO₂ absorbed by the ocean has led to a 0.1 unit decrease in pH since pre-industrial levels with an additional decrease of 0.3-0.4 units projected in business-as-usual emission scenarios by end of century. Global trends indicate that despite the lull of 2020, CO₂ emissions are increasing again to reach levels of previous years. Decreasing Ω_Arag in seawater poses serious threats to calcifying organisms, affecting their populations, growth patterns, and shell or skeletal density. The Northwestern Gulf of Mexico (NWGOM) is home to the northernmost tropical coral reefs around the contiguous United States as well as prominent shellfish industry. The health of these species and the ecosystem services they provide, which humans depend on, are likely to be threatened by OA.

With the significant increase in OA studies over the past two decades, there is improved understanding of Ω_Arag distribution and evolution in the global ocean, but research in marginal seas remains limited. The capacity to measure chemical parameters in the lab has improved with the introduction of modern analytical tools. On the other hand, only a few carbonate system variables can be directly measured in situ. Due to methodology limitations, researchers can directly measure five (pCO₂, pH, DIC, TA, and CO₃^2-) of the six (which also include HCO₃^-) carbonate system variables. Of the directly measurable parameters, only pH and pCO₂ have reached accessible autonomous measurements, while autonomous alkalinity measurements are newly available but far less prevalent. However, pH and pCO₂ as the input variable typically produce large errors in speciation calculations. Due to these constraints, direct measurements and calculations or carbonate parameters are spatially and temporally inadequate.

Across the globe, marginal seas lack sufficient data for analysis of trends in carbonate chemistry. As the NWGOM is subject to multiple controlling factors including anthropogenic CO₂ increase, ocean warming, eutrophication induced hypoxia and acidification, and changes in current and weather patterns, it is especially pertinent to obtain adequate data coverage in time and space. This dissertation is composed of three chapters to address the problems. (1) A numerical model will be developed using multilinear regression and a machine learning techniques which are capable of using hydrographic parameters to generate targeted carbonate chemistry parameters. This will be done using data collected on oceanographic cruises. (2) Sensors placed in the Flower Garden Banks National Marine Sanctuary will collect high resolution data, which will be used for an in-depth examination of temporal changes in carbonate chemistry in this sensitive coral habitat. (3) All currently available oceanographic cruise, satellite, and sensor data for the NNWGOM will be combined and used to provide an updated higher resolution an analysis of the evolution of carbonate system and air-sea CO2 fluxes in the NWGOM.