Satellite-Based Assessment of Spatially Heterogeneous XCO2 and Marine pCO2 Trends (2015–2020)

Satellite remote sensing has revolutionized the monitoring of atmospheric carbon dioxide (CO2) concentrations, yet its integration into studies of air–sea CO2 flux dynamics remains limited. Leveraging high-resolution observations from the Orbiting Carbon Observatory 2 (OCO-2) and Copernicus Marine Environment Monitoring Service (CMEMS), this study investigated the spatiotemporal heterogeneity of atmospheric column-averaged CO2 (XCO2) and sea surface partial pressure of CO2 (pCO2) between 2015 and 2020. Our analysis reveals pronounced latitudinal gradients, with the Northern Hemisphere exhibiting stronger seasonal XCO2 variability (5.67 ± 0.42 ppm annual amplitude) compared to the Southern Hemisphere (1.2 ± 0.18 ppm). Notably, the XCO2 growth rate was marginally higher in the Southern Hemisphere (2.48 ppm yr−1) than the Northern Hemisphere (2.39 ppm yr−1), while coastal regions showed elevated atmospheric CO2 concentrations, but slower pCO2 increases relative to the open ocean, suggesting a buffering capacity of marginal seas. Furthermore, we identified distinct seasonal phasing between land and ocean XCO2, with oceanic signals lagging terrestrial ones by approximately one month. These findings highlight the utility of satellite data in resolving fine-scale air–sea carbon flux dynamics and provide critical insights into how heterogeneous atmospheric CO2 changes propagate across marine systems.