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message of the UNEP report—that shallow coastal ecosystems contribute greatly to
mitigating global warming. This message has not been adequately communicated to
the public.
1.2.1 What Is Blue Carbon?
In order to understand the contents of the UNEP report, it is necessary to define
some technical terms about the processes involved in the transfer of carbon dioxide
(hereinafter referred to as CO 2 ) from the atmosphere to the ocean, where it may
become blue carbon, and the storage of this blue carbon in the sediments of shallow
coastal areas or the deep ocean floor (Fig. 1.1). In the UNEP report, blue carbon is
defined as green carbon in the sea, and green carbon is defined as carbon that plants
Storage by Sedimentation
Emission via respiration,
mineralization and other
decomposition processes
Atmospheric CO 2
Dissolved CO 2
Bicarbonate ion and carbonate ion
(2) Organic Carbon
in living creatures
(3) Refractory
Organic Carbon
Carbon flow in the food chain
Ecosystem Carbon stock
(4) Carbon buried in Sediment
(5) Other
carbonates
(shells, etc)
(1) Atmosphere-water CO 2 exchange
Absorption by
marine plants
Fig. 1.1 Schematic diagram of major carbon cycle and carbon sequestration/storage in shallow
coastal ecosystems
M. Hori et al.