This data comprises geographical and seasonal patterns in water quality and carbonate chemistry parameters in Narragansett Bay, RI, USA. Direct measurements of salinity, temperature, dissolved oxygen concentration, dissolved oxygen percent saturation, pH on the NBS scale, dissolved inorganic carbon concentration, and total alkalinity concentration were performed during monthly sampling cruises carried out over three years. The information provided by carbonate chemistry analysis allowed for the characterization of acidification in this estuary. Portions of this dataset are inaccessible because: NA. They can be accessed through the following means: NA. Format: NA. This dataset is associated with the following publication: Pimenta, A.R., A. Oczkowski, R. McKinney, and J. Grear. Geographical and seasonal patterns in the carbonate chemistry of Narragansett Bay, RI. Regional Studies in Marine Science. Elsevier B.V., Amsterdam, NETHERLANDS, 62(September 2023): 102903, (2023).