pH Distributions and Determining Processes Along the U.S. East Coast

Abstract

pH is a key index in ocean biogeochemical and acidification research. However, there remains a limited understanding of the spatial patterns and drivers of pH across different coastal oceans. In this study, we present the distribution of spectrophotometric pH_T (in total proton scale) from a synoptic summer cruise in 2018. We examine the processes controlling pH_T along the U.S. East Coast, covering the South Atlantic Bight (SAB), Mid-Atlantic Bight (MAB), and Gulf of Maine (GoM). Our findings reveal a continuous low pH_T band associated with the oxygen minimum and CO₂ maximum zone along the slope of the entire east coast, extending from the bottom layer (∼1,000 m) in the SAB to the middle layer (300–500 m) in the MAB and GoM. We also identified unique low pH_T features in each subregion, including an onshore upwelling of the low pH_T slope water in the SAB, a seasonal low pH_T feature on the bottom of the MAB shelf associated with the Cold Pool water, and an inflow of low pH_T slope water to the bottom of the GoM. Our findings suggest that net biological production plays a prominent role in regulating sea-surface pH_T, driving it away from the air-sea equilibrated pH_T and mitigating the pH_T decrease caused by the anthropogenic carbon dioxide (CO₂) uptake. Furthermore, net biological respiration dominates the interior pH_T distributions. Our analysis provides new insights and establishes a foundation for interpreting future pH changes in response to processes such as water masses shifting, ocean warming, and anthropogenic carbon uptake in coastal oceans.