6. Air–Water CO₂ Flux in Shallow Coastal Waters: Theory, Methods, and Empirical Studies

The fact that the ocean is one of the largest sinks of atmospheric CO₂ on Earth is an important consideration in the prediction of future climate changes and identification of possible mitigation strategies for global climate change. Recently, carbon storage in vegetated coastal habitats (blue carbon ecosystems) has been explored as a new option to mitigate climate change. However, the complexity of the mechanisms that control air–water CO₂ fluxes in shallow coastal ecosystems has precluded their adequate quantification. Spatiotemporal extension of accurate values of these fluxes will be an important milestone for assessing the contribution of blue carbon ecosystems to mitigation of climate change. In this chapter, we explain the theoretical understanding of air–water CO₂ fluxes and methods for their measurement. We then discuss results of empirical measurements of air–water CO₂ fluxes in shallow coastal waters. We conclude that statistical analyses of augmented air–coastal-water CO₂ flux data based on long-term measurements and multiple methods should lead to a quantitative understanding of the current status and future air–water CO₂ fluxes in shallow coastal waters at national and global scales.