153
© Springer Nature Singapore Pte Ltd. 2019
T. Kuwae, M. Hori (eds.), Blue Carbon in Shallow Coastal Ecosystems,
https://doi.org/10.1007/978-981-13-1295-3_6
Chapter 6
Air–Water CO 2 Flux in Shallow Coastal
Waters: Theory, Methods, and Empirical
Studies
Tatsuki Tokoro, Kenta Watanabe, Kazufumi Tada, and Tomohiro Kuwae
Abstract The fact that the ocean is one of the largest sinks of atmospheric CO 2 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 CO 2 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 CO 2 fluxes and methods for their measurement. We then discuss results of empirical measurements of air–water CO 2
fluxes in shallow coastal waters. We conclude that statistical analyses of augmented
air–coastal-water CO 2 flux data based on long-term measurements and multiple
methods should lead to a quantitative understanding of the current status and future
air–water CO 2 fluxes in shallow coastal waters at national and global scales.
6.1 Introduction
CO 2 is a very soluble gas in water. At 25 °C and 1 atmosphere pressure, approximately 1.4 g of CO 2 are dissolved in 1 L of freshwater, about 100 times the amount
of dissolved N 2 . CO 2 is more soluble in seawater than in freshwater (except for very
hard water) because the capacity of CO 2 dissociation into bicarbonate ions (HCO 3
−
)
and carbonate ions (CO 3
2−
) in seawater is larger than that in freshwater.
The amount of carbon stored in the global ocean is estimated to be about 38,000
Pg-C (about 50 times the amount of carbon present as CO 2 in the atmosphere), and
the ocean is the largest carbon reservoir on the Earth’s surface (Ciais et al. 2013).
T. Tokoro · K. Watanabe · K. Tada · T. Kuwae (*)
Coastal and Estuarine Environment Research Group, Port and Airport Research Institute,
Yokosuka, Japan
e-mail: kuwae@p.mpat.go.jp
© Springer Nature Singapore Pte Ltd. 2019
T. Kuwae, M. Hori (eds.), Blue Carbon in Shallow Coastal Ecosystems,
https://doi.org/10.1007/978-981-13-1295-3_6
Chapter 6
Air–Water CO 2 Flux in Shallow Coastal
Waters: Theory, Methods, and Empirical
Studies
Tatsuki Tokoro, Kenta Watanabe, Kazufumi Tada, and Tomohiro Kuwae
Abstract The fact that the ocean is one of the largest sinks of atmospheric CO 2 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 CO 2 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 CO 2 fluxes and methods for their measurement. We then discuss results of empirical measurements of air–water CO 2
fluxes in shallow coastal waters. We conclude that statistical analyses of augmented
air–coastal-water CO 2 flux data based on long-term measurements and multiple
methods should lead to a quantitative understanding of the current status and future
air–water CO 2 fluxes in shallow coastal waters at national and global scales.
6.1 Introduction
CO 2 is a very soluble gas in water. At 25 °C and 1 atmosphere pressure, approximately 1.4 g of CO 2 are dissolved in 1 L of freshwater, about 100 times the amount
of dissolved N 2 . CO 2 is more soluble in seawater than in freshwater (except for very
hard water) because the capacity of CO 2 dissociation into bicarbonate ions (HCO 3
−
)
and carbonate ions (CO 3
2−
) in seawater is larger than that in freshwater.
The amount of carbon stored in the global ocean is estimated to be about 38,000
Pg-C (about 50 times the amount of carbon present as CO 2 in the atmosphere), and
the ocean is the largest carbon reservoir on the Earth’s surface (Ciais et al. 2013).
T. Tokoro · K. Watanabe · K. Tada · T. Kuwae (*)
Coastal and Estuarine Environment Research Group, Port and Airport Research Institute,
Yokosuka, Japan
e-mail: kuwae@p.mpat.go.jp