242
Regardless of pelagic or coastal waters, photosynthetic organisms are affected
by OA, and the effects can be compounded with other chemical/physical factors.
Most previous studies have been carried out in the laboratory under controlled
conditions. Due to data deficiency, it is still difficult to characterize the mechanisms
of OA effects on photosynthesis and related ecological processes in complex environments (Riebesell and Gattuso 2015).
12.3 UV and Its Effect on Marine Photosynthetic
Carbon Fixation
12.3.1 UV Radiation
Ultraviolet radiation is divided into UV-A (315–400 nm), UV-B (280–315 nm), and
UV-C (<280 nm). The ozone layer completely absorbs UV-C (most harmful to
organisms). Most of the UV-B is also absorbed by the ozone in the atmosphere
(mainly in the stratosphere). Only a fraction of UV-B reaches the ground through
the stratosphere and the upper troposphere. With little attenuation by the atmosphere
and ozone, most UV-A and visible light reach the ground. Since the mid of the last
century, the ozone layer has been destroyed with increasing accumulation of
anthropogenic CFCs (chlorofluorocarbons) and chlorinated organic compounds.
The ozone decreased in the stratosphere and ozone holes were discovered in the
atmosphere above Antarctica resulting in increased UV-B radiation at the ground,
to a different extent at different latitudes. Since the Montreal Protocol was enforced,
the amount of released CFCs has been reduced; however, the destroyed ozone layer
has not yet recovered due to the long lifetimes of CFCs in the atmosphere (Bais
et al. 2015). Additionally, several new gases destructive to the ozone layer are rapidly accumulating in the atmosphere (Laube et al. 2014). Ozone holes have also
been discovered over the Arctic (Manney et al. 2011). Therefore, more attention
should be given to the increased UV-B and other global environmental change drivers
(Häder and Gao 2015).
At the same time increased ocean temperature results in the shoaling of the
upper mixed layer, which increases the exposure of the plankton in this layer to UV
radiation. In addition, this temperature-dependent increased stratification reduces
the amount of nutrients transported upward through the thermocline into the UML
(Gao et al. 2012a).
In marine environments, seawater itself and particles (including phytoplankton)
and dissolved matters absorb and scatter solar radiation. The degree of absorption
and scattering depends on the wavelength. The solar radiation transmitted into the
water undergoes exponential attenuation (Piazena and Häder 1997). The energy
ratio of light with different wavelengths to the total light energy varies with depth
(Hargreaves 2003). In estuary and coastal ecosystems, particulate organic matters
K. Gao and D.-P. Häder
Regardless of pelagic or coastal waters, photosynthetic organisms are affected
by OA, and the effects can be compounded with other chemical/physical factors.
Most previous studies have been carried out in the laboratory under controlled
conditions. Due to data deficiency, it is still difficult to characterize the mechanisms
of OA effects on photosynthesis and related ecological processes in complex environments (Riebesell and Gattuso 2015).
12.3 UV and Its Effect on Marine Photosynthetic
Carbon Fixation
12.3.1 UV Radiation
Ultraviolet radiation is divided into UV-A (315–400 nm), UV-B (280–315 nm), and
UV-C (<280 nm). The ozone layer completely absorbs UV-C (most harmful to
organisms). Most of the UV-B is also absorbed by the ozone in the atmosphere
(mainly in the stratosphere). Only a fraction of UV-B reaches the ground through
the stratosphere and the upper troposphere. With little attenuation by the atmosphere
and ozone, most UV-A and visible light reach the ground. Since the mid of the last
century, the ozone layer has been destroyed with increasing accumulation of
anthropogenic CFCs (chlorofluorocarbons) and chlorinated organic compounds.
The ozone decreased in the stratosphere and ozone holes were discovered in the
atmosphere above Antarctica resulting in increased UV-B radiation at the ground,
to a different extent at different latitudes. Since the Montreal Protocol was enforced,
the amount of released CFCs has been reduced; however, the destroyed ozone layer
has not yet recovered due to the long lifetimes of CFCs in the atmosphere (Bais
et al. 2015). Additionally, several new gases destructive to the ozone layer are rapidly accumulating in the atmosphere (Laube et al. 2014). Ozone holes have also
been discovered over the Arctic (Manney et al. 2011). Therefore, more attention
should be given to the increased UV-B and other global environmental change drivers
(Häder and Gao 2015).
At the same time increased ocean temperature results in the shoaling of the
upper mixed layer, which increases the exposure of the plankton in this layer to UV
radiation. In addition, this temperature-dependent increased stratification reduces
the amount of nutrients transported upward through the thermocline into the UML
(Gao et al. 2012a).
In marine environments, seawater itself and particles (including phytoplankton)
and dissolved matters absorb and scatter solar radiation. The degree of absorption
and scattering depends on the wavelength. The solar radiation transmitted into the
water undergoes exponential attenuation (Piazena and Häder 1997). The energy
ratio of light with different wavelengths to the total light energy varies with depth
(Hargreaves 2003). In estuary and coastal ecosystems, particulate organic matters
K. Gao and D.-P. Häder