Regulation of surface carbon dioxide distributions and air–sea fluxes by temperature, biology, and mixing along the North American Atlantic Coastal Ocean Margin

Abstract

The North American Atlantic Coastal Ocean Margin (NAACOM) was recognized as an atmospheric carbon dioxide (CO2) sink, with large uncertainties in its northern areas due to complex dynamics in controlling the spatiotemporal variability of surface partial pressure of CO2 (pCO2) and limited pCO2 observations. Here, we used a regional reconstructed product to investigate the spatial and seasonal variability of pCO2 and air–sea CO2 fluxes across the region during 1993–2021. Decomposition of pCO2 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 pCO2 elevation, and spring phytoplankton production significantly influencing pCO2 drawdown. These regional differences in local dynamics result in greater air–sea CO2 disequilibrium in the north, driving larger seasonal pCO2 amplitudes, and a pronounced south‐to‐north decreasing gradient. We identified the entire region as a CO2 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 < 200 m) and wide (distance from shoreline < 400 km) ocean margins. The updated wide‐margin CO2 uptake is 61% lower than previous reports. This 29‐yr analysis elucidates the drivers of pCO2 variability across the diverse NAACOM, highlighting the importance of regional pCO2 products for improving coastal carbon systems projections in a changing climate.