Salinity and Its Effects on the Buffering Capacity of Seawater on the East Coast Acidification Cruise

• Kyle Marchese, Marine Science, University of Delaware

• Wei-Jun Cai, College of Earth, Ocean & Environment., University of Delaware

Total alkalinity (TA) and its relationship with salinity (S) along the Eastern coast of the United States and Canada were examined in this study. Over the past decade, NOAA, in partnership with select universities, has been tracking changes in ocean acidification along the U.S. East Coast. Total alkalinity is a crucial indicator of environmental carbon cycles, allowing for ecosystem modeling and inorganic carbon system calculations. All samples in this study were taken as part of the 2026 East Coast Ocean Acidification survey (ECOA-4) using the CTD aboard the NOAA vessel Henry B. Bigelow. Seawater was sampled from varying depths along the coast. Samples were titrated with 0.15 M HCl using Apollo SciTech Alkalinity Titrators to determine TA. The S values of specific samples were compared to their respective TA values. To observe preliminary patterns, TA was plotted against S from the Delaware transect alone. Within the Delaware transect, there was a strong positive correlation (R2 = 0.9495) between TA and S. These results are as expected because both TA and S are influenced by similar oceanic processes. As the amount of freshwater in a system increases (via precipitation, melting, or runoff), S decreases (due to a decrease in Na+ and Cl– ions), and TA also decreases (due to a decrease in HCO3– and CO32- ions). The strong relation allows researchers to rely on salinity-based models rather than extensive TA measurements. These estimates can then be used to calculate other carbonate system parameters, including dissolved inorganic carbon (DIC), thereby improving the efficiency of large-scale oceanographic surveys.