Seasonal response of air–water CO₂ exchange along the land–ocean aquatic continuum of the northeast North American coast.

Abstract. This regional study quantifies the CO₂ exchange at the air–water interface along the land–ocean aquatic continuum (LOAC) of the northeast North American coast, from streams to the shelf break. Our analysis explicitly accounts for spatial and seasonal variability in the CO₂ fluxes. The yearly integrated budget reveals the gradual change in the intensity of the CO₂ exchange at the air–water interface, from a strong source towards the atmosphere in streams and rivers (3.0 ± 0.5 TgC yr⁻¹) and estuaries (0.8 ± 0.5 TgC yr⁻¹) to a net sink in continental shelf waters (−1.7 ± 0.3 TgC yr⁻¹). Significant differences in flux intensity and their seasonal response to climate variations is observed between the North and South sections of the study area, both in rivers and coastal waters. Ice cover, snowmelt, and intensity of the carbon removal efficiency through the estuarine filter are identified as important control factors of the observed spatiotemporal variability in CO₂ exchange along the LOAC.