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Ocean acidification (OA), an alteration of seawater chemistry caused primarily by anthropogenic carbon emissions, is a global issue. However, the local expression of OA can vary widely in nearshore waters around the world. This is due to localized factors such as river input, eutrophication, topography, location (e.g., temperature), and sensitivity of local species. Human impacts from OA also vary depending on societal uses of the ocean and its resources. Managers, policy­makers, and governments need to understand the status and susceptibility of their regions in order to make effective decisions and drive policy. In the early 2000s, scientists recognized the need for a global ocean acidification observing system and called for a coordinated approach to effectively assess global as well as local status with consistent methods. As a result, the Global Ocean Acidification Observing Network (GOA-ON) was formed in 2012 with three goals: (1) to improve understanding of global OA conditions, (2) to improve understanding of ecosystem responses to OA, and (3) to acquire and exchange data and knowledge necessary to optimize modeling of OA and its impacts (Newton et al., 2015; Tilbrook et al., 2019). 

Ocean Acidification (OA) is negatively affecting the physiological processes of marine organisms, altering biogeochemical cycles, and changing chemical equilibria throughout the world’s oceans. It is difficult to measure pH broadly, in large part because accurate pH measurement technology is expensive, bulky, and requires technical training. Here, we present the development and evaluation of a hand-held, affordable, field-durable, and easy-to-use pH instrument, named the pHyter, which is controlled through a smartphone app. We determine the accuracy of pH measurements using the pHyter by comparison with benchtop spectrophotometric seawater pH measurements, measurement of a certified pH standard, and comparison with a proven in situ instrument, the iSAMI-pH. These results show a pHyter pH measurement accuracy of ±0.046 pH or better, which is on par with interlaboratory seawater pH measurement comparison experiments. We also demonstrate the pHyter’s ability to conduct both temporal and spatial studies of coastal ecosystems by presenting data from a coral reef and a bay, in which the pHyter was used from a kayak. These studies showcase the instrument’s portability, applicability, and potential to be used for community science, STEM education, and outreach, with the goal of empowering people around the world to measure pH in their own backyards. 

Abstract Marine microbes produce extracellular reactive oxygen species (ROS) such as superoxide and hydrogen peroxide (H₂O₂) as a result of regulated and nonregulated physiological and metabolic reactions. ROS production can be a sink and cryptic recycling flux of dissolved oxygen that may rival other key fluxes in the global oxygen cycle; however, the low abundance and high turnover rate of ROS makes this figure difficult to constrain. One key step in determining the disparity between the gross production of ROS and the net sink of dissolved oxygen lies in understanding the degradation pathways of H₂O₂in the marine water column. In this study, we use isotope‐labeling techniques to determine the redox fate of H₂O₂in a range of marine environments off the West Coast of California. We find that H₂O₂reduction is greater than or equal to H₂O₂oxidation at most sampled depths, with notable exceptions in some surface and intermediate water depths. The observation that H₂O₂oxidation can exceed reduction in the dark ocean indicates the presence of an oxidizing decay pathway that is not among the known suite of microbially mediated enzymatic pathways (i.e., catalase and peroxidase), pointing to an abiotic and/or a nonenzymatic decay pathway at intermediate water depths. These results highlight the complexity and heterogeneity of ROS decay pathways in natural waters and their unconstrained regulation of oxygen levels within the ocean.