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The ocean has absorbed anthropogenic carbon dioxide (C_anthro) from the atmosphere and played an important role in mitigating global warming. However, how much C_anthrois accumulated in coastal oceans and where it comes from have rarely been addressed with observational data. Here, we use a high-quality carbonate dataset (1996–2018) in the U.S. East Coast to address these questions. Our work shows that the offshore slope waters have the highest C_anthroaccumulation changes (ΔC_anthro) consistent with water mass age and properties. From offshore to nearshore, ΔC_anthrodecreases with salinity to near zero in the subsurface, indicating no net increase in the export of C_anthrofrom estuaries and wetlands. Excesses over the conservative mixing baseline also reveal an uptake of C_anthrofrom the atmosphere within the shelf. Our analysis suggests that the continental shelf exports most of its absorbed C_anthrofrom the atmosphere to the open ocean and acts as an essential pathway for global ocean C_anthrostorage and acidification. 

Abstract This study examines the seasonal and spatial variabilities of total alkalinity (TA) and dissolved inorganic carbon (DIC) concentrations and fluxes in the Parker River, part of the Plum Island estuary, the largest macro tidal saltmarsh system in northeastern US. Our investigation reveals that the Parker River estuary is a net source of TA and DIC, with outwelling fluxes ranging 8.9–13.2 mmol m⁻² d⁻¹for TA and 10.4–18.1 mmol m⁻² d⁻¹for DIC. Porewater fluxes from marshes contributed to 71% (55%–96%) and 59% (51%–78%) of the TA and DIC outwelling flux, respectively. Spatial heterogeneity is pronounced, with high‐salinity section porewater fluxes nearly three times higher than in low‐salinity section. TA fluxes peak in summer and are lowest in the spring, with the seasonal changes controlled by both hydrology and marsh phenology. The interplay of primary production and aerobic and anaerobic respiration governs carbon transformations in the estuary, leading to net DIC export and contributing to the acidification of adjacent coastal waters. Overall, approximately 20% saltmarsh net primary production is laterally exported to the coastal ocean as TA during 2023, providing potential long‐term carbon sinks comparable to about 40% of sediment organic carbon burial. Our research underscores the spatial and temporal variabilities in TA and DIC fluxes driven by biotic processes and the importance of considering both TA and DIC fluxes to fully understand the carbon sequestration potential of saltmarshes. 

Abstract. As the largest active carbon reservoir on Earth, the ocean is a cornerstone of the global carbon cycle, playing a pivotal role in modulating ocean health and regulating climate. Understanding these crucial roles requires access to a broad array of data products documenting the changing chemistry of the global ocean as a vast and interconnected system. This review article provides a comprehensive overview of 60 existing ocean carbonate chemistry data products, encompassing compilations of cruise datasets, derived gap-filled data products, model simulations, and compilations thereof. It is intended to help researchers identify and access data products that best align with their research objectives, thereby advancing our understanding of the ocean's evolving carbonate chemistry.