pH Distributions and Determining Processes Along the U.S. East Coast
Date
2024-09-11
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Journal of Geophysical Research: Oceans
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 pHT (in total proton scale) from a synoptic summer cruise in 2018. We examine the processes controlling pHT 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 pHT 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 pHT features in each subregion, including an onshore upwelling of the low pHT slope water in the SAB, a seasonal low pHT feature on the bottom of the MAB shelf associated with the Cold Pool water, and an inflow of low pHT slope water to the bottom of the GoM. Our findings suggest that net biological production plays a prominent role in regulating sea-surface pHT, driving it away from the air-sea equilibrated pHT and mitigating the pHT decrease caused by the anthropogenic carbon dioxide (CO2) uptake. Furthermore, net biological respiration dominates the interior pHT 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.
Key Points
- The subsurface pH minimum layer extends from the slope bottom in the south to the middle layer of the slope in the north
- Each subregion has a distinct low-pH feature, including onshore upwelling, Cold Pool water, and Gulf bottom water
- Surface pH deviates from air-sea gas equilibrium due to net biological production, while interior ocean pH is dominated by respiration
Plain Language Summary
Given that pH is a crucial index for assessing ocean acidification, understanding pH distribution patterns and its controlling factors in coastal oceans is essential. This study investigates pH from a summer 2018 cruise along the entire U.S. East Coast. We found that the surface-water pH deviates from the atmospheric equilibrium, primarily due to net biological production. Subsurface pH patterns are also mainly controlled by biological factors. Along the slope, a continuous low pH band is associated with the oxygen minimum zone, extending from the bottom in the SAB to the middle depth in the MAB and GoM. On the shelf, each subregion has unique subsurface low pH features, including a shoreward upwelling of the low pH slope water in the SAB, a seasonal low pH feature in the MAB Cold Pool, and an inflow of low pH slope water in the bottom of GoM. This research provides new insights into the processes controlling pH distribution and lays a foundation for interpreting current and future pH decadal trends in the context of climate change.
Description
This article was originally published in Journal of Geophysical Research: Oceans. The version of record is available at: https://doi.org/10.1029/2024JC020993.
© 2024. American Geophysical Union. All Rights Reserved.
This article will be embargoed until 03/11/2025.
Keywords
pH distribution, inorganic carbon system, U.S. East Coast, ocean acidification
Citation
Li, X., Xu, Y.-Y., & Cai, W.-J. (2024). pH Distributions and determining processes along the U.S. East Coast. Journal of Geophysical Research: Oceans, 129, e2024JC020993. https://doi.org/10.1029/2024JC020993