243
(POM) and chromophoric dissolved organic matter (CDOM) are the main factors
resulting in the attenuation of solar irradiances. In offshore waters, due to high
transparency, the attenuation of solar radiation mainly depends on the biomass density or degradation of the phytoplankton and the intake and excretion of inorganic/
organic matter of zooplankton (Häder et al. 2011). The transmission depth varies
greatly for light with different wavelengths in different waters. For example, in the
Atlantic, UV-B (310 nm) can reach 30 m, 100 m for UV-A (380 nm), over 190 m for
blue light (450–500 nm) and 20 m for other visible light wavelengths (600–700 nm)
(Piazena et al. 2002). In the offshore waters of the South China Sea, the visible light
can penetrate deeper than 80 m (the depth of the euphotic zone), 50 m for UV-A and
38 m for UV-B which accounts for 62% and 47% of the depth of the euphotic zone,
respectively (Li et al. 2009). In the coastal waters of Shantou with large quantities
of suspended particles, the visible light can only penetrate less than 10 m in the
waters adjacent to the aquaculture area; UV-A and UV-B can only transmit less than
5 m and 3 m, respectively, accounting for 50% and 30% of the depth of the euphotic
zone (Gao et al. 2007a; Li and Gao 2012). In the estuary of Jiulong River of Fujian
Province, visible light penetrates even less (0.47–5 m), only 0.25–1.8 m for UV-A
and 0.21–1.7 m for UV-B which accounts for 36–75% and 46–56% of the depth of the
euphotic zone, respectively, of the transmission depth of visible light (Li et al. 2011b).
Recently, it has been suggested that intensity and transmission depth of UV will
also change with global ocean changes (Zepp et al. 2007; Häder et al. 2011). By
affecting the phytoplankton biomass of the euphotic zone, global change will indirectly influence the attenuation of visible light and UV in the water column, which
may increase the intensity and the transmission depth of UV (Zepp et al. 2007). On
the other hand, dissolved organic carbon (DOC) and particulate organic carbon
(POC) are the main factors attenuating UV-A and UV-B, respectively. Increased
temperatures will accelerate bacterial decay and photodegradation of CDOM and
increase the transmission depth of UV (Tzortziou et al. 2007; Zhang et al. 2009).
Exposure to solar ultraviolet radiation is fluctuating due to vertical mixing within the
epilimnion. Therefore, increased solar UVR (as a result of a shallower epilimnion and
more frequent circulation near the surface), fluctuating irradiances (as a result of
stronger vertical mixing due to increased wind stress), and attenuation of solar radiation in the water column will have a compound effect (Helbling et al. 2015). This new
scenario for oceanic phytoplankton requires further studies.
UV-B irradiance at the earth surface also changes with latitude, ozone content
in the stratosphere, and suspended particles in the atmosphere. Thus, the effect of
UV on photosynthetic carbon fixation varies with different areas, waters, and
depths. In the past, many marine in situ carbon sequestration studies and investigations have been carried out in ordinary transparent containers (glass or PC culture
bottles) which block most of the UV radiation. As a result, the effects of UV radiation on carbon fixation and other biological processes have been ignored in many
studies and investigations. A large number of reports have given insight into the
effect of UV radiation on phytoplankton (see reviews Häder et al. 2014; Häder and
Gao 2015).
12 Effects of Ocean Acidification and UV Radiation on Marine Photosynthetic…
(POM) and chromophoric dissolved organic matter (CDOM) are the main factors
resulting in the attenuation of solar irradiances. In offshore waters, due to high
transparency, the attenuation of solar radiation mainly depends on the biomass density or degradation of the phytoplankton and the intake and excretion of inorganic/
organic matter of zooplankton (Häder et al. 2011). The transmission depth varies
greatly for light with different wavelengths in different waters. For example, in the
Atlantic, UV-B (310 nm) can reach 30 m, 100 m for UV-A (380 nm), over 190 m for
blue light (450–500 nm) and 20 m for other visible light wavelengths (600–700 nm)
(Piazena et al. 2002). In the offshore waters of the South China Sea, the visible light
can penetrate deeper than 80 m (the depth of the euphotic zone), 50 m for UV-A and
38 m for UV-B which accounts for 62% and 47% of the depth of the euphotic zone,
respectively (Li et al. 2009). In the coastal waters of Shantou with large quantities
of suspended particles, the visible light can only penetrate less than 10 m in the
waters adjacent to the aquaculture area; UV-A and UV-B can only transmit less than
5 m and 3 m, respectively, accounting for 50% and 30% of the depth of the euphotic
zone (Gao et al. 2007a; Li and Gao 2012). In the estuary of Jiulong River of Fujian
Province, visible light penetrates even less (0.47–5 m), only 0.25–1.8 m for UV-A
and 0.21–1.7 m for UV-B which accounts for 36–75% and 46–56% of the depth of the
euphotic zone, respectively, of the transmission depth of visible light (Li et al. 2011b).
Recently, it has been suggested that intensity and transmission depth of UV will
also change with global ocean changes (Zepp et al. 2007; Häder et al. 2011). By
affecting the phytoplankton biomass of the euphotic zone, global change will indirectly influence the attenuation of visible light and UV in the water column, which
may increase the intensity and the transmission depth of UV (Zepp et al. 2007). On
the other hand, dissolved organic carbon (DOC) and particulate organic carbon
(POC) are the main factors attenuating UV-A and UV-B, respectively. Increased
temperatures will accelerate bacterial decay and photodegradation of CDOM and
increase the transmission depth of UV (Tzortziou et al. 2007; Zhang et al. 2009).
Exposure to solar ultraviolet radiation is fluctuating due to vertical mixing within the
epilimnion. Therefore, increased solar UVR (as a result of a shallower epilimnion and
more frequent circulation near the surface), fluctuating irradiances (as a result of
stronger vertical mixing due to increased wind stress), and attenuation of solar radiation in the water column will have a compound effect (Helbling et al. 2015). This new
scenario for oceanic phytoplankton requires further studies.
UV-B irradiance at the earth surface also changes with latitude, ozone content
in the stratosphere, and suspended particles in the atmosphere. Thus, the effect of
UV on photosynthetic carbon fixation varies with different areas, waters, and
depths. In the past, many marine in situ carbon sequestration studies and investigations have been carried out in ordinary transparent containers (glass or PC culture
bottles) which block most of the UV radiation. As a result, the effects of UV radiation on carbon fixation and other biological processes have been ignored in many
studies and investigations. A large number of reports have given insight into the
effect of UV radiation on phytoplankton (see reviews Häder et al. 2014; Häder and
Gao 2015).
12 Effects of Ocean Acidification and UV Radiation on Marine Photosynthetic…