Saba et al. Observing Ocean Acidification With Gliders routinely clean and swap out sensors can address this challenge. The data presented here demonstrate the ability for gliders to routinely provide high resolution water column data on regional scales that can be applied to acidification monitoring efforts in other coastal regions.

Ocean acidification alters the oceanic carbonate system, increasing potential for ecological, economic, and cultural losses. Historically, productive coastal oceans lack vertically resolved high-resolution carbonate system measurements on time scales relevant to organism ecology and life history. The recent development of a deep ion-sensitive field-effect transistor (ISFET)-based pH sensor system integrated into a Slocum glider has provided a platform for achieving high-resolution carbonate system profiles. From May 2018 to November 2019, seasonal deployments of the pH glider were conducted in the central Mid-Atlantic Bight. Simultaneous measurements from the glider's pH and salinity sensors enabled the derivation of total alkalinity and calculation of other carbonate system parameters including aragonite saturation state. Carbonate system parameters were then mapped against other variables, such as temperature, dissolved oxygen, and chlorophyll, over space and time. The seasonal dynamics of carbonate chemistry presented here provide a baseline to begin identifying drivers of acidification in this vital economic zone. Plain Language Summary Seawater chemistry affects the ability of organisms to survive in the ocean. Past monitoring of seawater chemistry has missed key times and locations that are important to natural life cycles. In order to fill in those gaps, we put a chemical sensor into a deep-sea robot that we can control from land. This robot, called a Slocum glider, glides from the top of the ocean down to 200-m depth and collects ocean chemistry data along the way. We used our Slocum glider to measure how seawater chemistry differs between seasons in the Mid-Atlantic, which will help us understand how organisms might be affected by water conditions.

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In shallow coastal shelves like the Mid‐Atlantic Bight (MAB), ocean acidification due to increased atmospheric carbon dioxide (CO2) is compounded by highly variable coastal processes including riverine freshwater inputs, nutrient loading, biogeochemical influence, coastal currents and water mass mixing, and seasonal transitions in physical parameters. Past deconstructions of carbonate system drivers in the MAB have focused on nearshore zones or single season data, and thus lack the spatial and temporal resolution required to assess impacts to important species occupying the shelf. Deconstructing highly resolved data collected during four seasonal Slocum glider deployments in the MAB, this study uses a Taylor Series decomposition to quantify the influence of temperature, salinity, biogeochemical activity, and water mass mixing on pH and aragonite saturation state from sea surface to bottom. Results show that water mass mixing and biogeochemical activity were the most significant drivers of the carbonate system in the MAB. Nearshore water was more acidic year‐round due to riverine freshwater input, but photosynthesis reduced acidity at certain depths and times. Water mass mixing increased acidity in bottom water on the shelf, particularly in summer. Gulf Stream intrusions at the shelf break during fall acted to mitigate acidification on the shelf in habitats occupied by carbonate‐bearing organisms. The relationships quantified here can be used to improve biogeochemical forecast models and determine habitat suitability for commercially important fin and shellfish species residing in the MAB.

Increased atmospheric carbon dioxide (CO2) has led to global climate change and ocean acidification (OA) via the absorption of atmospheric CO2 by the ocean. Coastal shelves are also affected by various processes that influence the acidity of seawater, causing acidity to vary over time and space. These variations in ocean acidity can negatively impact marine species, especially calcifying organisms such as surfclams and sea scallops. In the Mid-Atlantic Bight (MAB), a subsection of the U.S. Northeast Shelf (NES), this variation in acidity generates ecological and economic concerns as the MAB is home to some of the nation’s most productive and profitable estuaries and fisheries. In this study, Rutgers University (southern MAB) and Stony Brook University (northern MAB, Hudson Canyon) deployed two gliders equipped with sensors measur-ing depth, temperature, salinity, pH, dissolved oxygen, and chlorophyll to monitor winter 2021 carbonate chemistry conditions on the shelf as well as in slope waters of the MAB. For both deployments, measured pH and calculated aragonite saturation state (Ωarag) showed opposing patterns, with high pH and low Ωarag in shelf/nearshore and low pH and high Ωarag in slope waters. These trends were attributed to different driving factors whereas pH was more influenced by biological processes (i.e. photo-synthesis) and Ωarag was influenced mostly by thermodynamics and chemical factors (i.e. temperature, total alkalinity). The results of this study underscore the importance of monitoring coastal acidity to understand potential impacts on important species.