Abstract
The North American Atlantic Coastal Ocean Margin (NAACOM) was recognized as an atmospheric carbon dioxide (CO 2 ) sink, with large uncertainties in its northern areas due to complex dynamics in controlling the spatiotemporal variability of surface partial pressure of CO 2 ( p CO 2 ) and limited p CO 2 observations. Here, we used a regional reconstructed product to investigate the spatial and seasonal variability of p CO 2 and air–sea CO 2 fluxes across the region during 1993–2021. Decomposition of p CO 2 variability reveals temperature as the primary driver in southern sub‐regions (Gulf of Mexico, South and Mid Atlantic Bight), while both thermal and nonthermal processes dominate in the north (Gulf of Maine, Scotian Shelf, Gulf of St. Lawrence, and Grand Banks), with winter deep mixing leading to p CO 2 elevation, and spring phytoplankton production significantly influencing p CO 2 drawdown. These regional differences in local dynamics result in greater air–sea CO 2 disequilibrium in the north, driving larger seasonal p CO 2 amplitudes, and a pronounced south‐to‐north decreasing gradient. We identified the entire region as a CO 2 sink, with fluxes of −0.63 ± 0.19 and −0.60 ± 0.21 mol C m −2 yr −1 (10.14 ± 3.00 and 24.24 ± 8.31 Tg C yr −1 ), respectively, in the narrow (depth 2 uptake is 61% lower than previous reports. This 29‐yr analysis elucidates the drivers of p CO 2 variability across the diverse NAACOM, highlighting the importance of regional p CO 2 products for improving coastal carbon systems projections in a changing climate.