Impact of Marine Heatwaves on Air-Sea CO2 Flux Along the US East Coast

Marine heatwaves (MHWs) are extremely warm ocean temperature events that significantly affect marine environments, but their effects on the coastal carbonate system are still uncertain. In this study, we systematically quantify MHWs' impacts on air-sea carbon dioxide (CO2) flux anomalies (FCO2 ') in the Mid-Atlantic Bight (MAB) and South Atlantic Bight (SAB) from 1992 to 2020. During the longest MHW in both regions, oceanic CO2 uptake capabilities substantially decreased, primarily due to significant increases in the seawater partial pressure of CO2 (pCO(2sea)). For all cases, MHWs played a more significant role in driving pCO(2sea) changes in the MAB than the SAB, where non-thermal drivers dominated pCO(2sea) variability. In the MAB, weakened wind speeds related to wintertime atmospheric perturbations increase ocean temperatures and pCO(2sea), further reducing CO2 uptake during winter MHWs. This work is the first to connect extreme temperatures to coastal air-sea CO2 fluxes. The reduction in CO2 absorption noted during MHWs in this study has important implications for coastal regions to act as continued sinks for excess CO2 emissions in the atmosphere.