Differential Impacts of Solar UV Radiation on Photosynthetic Carbon Fixation from the Coastal to Offshore Surface Waters in the South China Sea

Abstract

We carried out experiments during an expedition (14 August to 14 September, 2007) that covered up to 250,000 km(2) to investigate the effects of solar UV radiation (UVR, 280-400 nm) on the photosynthetic carbon fixation of tropical phytoplankton assemblages in surface seawater of the South China Sea. From coastal to pelagic surface seawaters, UV-B (280-315 nm) caused similar inhibition, while UV-A (315-400 nm) induced photosynthetic inhibition increased from coastal to offshore waters. UV-B resulted in an inhibition by up to 27% and UV-A by up to 29%. Under reduced levels of solar radiation with heavy overcast, UV-A resulted in enhanced photosynthetic carbon fixation by up to 25% in coastal waters where microplankton was abundant. However, such a positive impact was not observed in the offshore waters where piconanoplankton was more abundant. The daily integrated inhibition of UV-A reached 4.3% and 13.2%, and that of UV-B reached 16.5% and 13.5%, in the coastal and offshore waters, respectively.

Vertical Patterns of Early Summer Chlorophyll a Concentration in the Indian Ocean with Special Reference to the Variation of Deep Chlorophyll Maximum

“…Solar irradiation was known to be lower at the DCM with much more short-waveband blue light [35]; only larger phytoplankton cells can utilize short-waveband energy for photosynthesis [4,36]. Growth of smaller cells at this layer might thus be inferior to their larger counterparts, leading to a negative correlation of pico-cells in proportion to the DCM depth (r = −0.53, P < 0.01).…”

“…In surface oceans, a series of environmental factors are known to control the biomass and distribution of phytoplankton. Light intensity influences phytoplankton growth and productivity through driving or photoinhibiting photosynthesis [3,4], while vertical mixing affects carbon fixation ability by balancing the damage and repair at high or low light levels [5,6]. The available trace metals (e.g., copper and iron) also lead to variations in phytoplankton biomass or size communities [7][8][9].…”

Photosynthetic responses of &lt;i&gt;Emiliania huxleyi&lt;/i&gt; to UV radiation and elevated temperature: roles of calcified coccoliths

“…However, some differences might arise when considering the responses on more dense cultures (Guan and Gao, 2010) with shorter wavelengths of UVB causing more damage to photosynthesis than to calcification, and longer wavelengths of UVA resulting in a decrease of calcification; in general terms, large cell density affects the control of the carbonate system (Gattuso et al, 2010). The irradiance levels of PAR, UVA and UVB used by us in our experiments were respectively about 18.1, 43.6 and Sea where coccolithophores are abundant (Ho et al, 2010;Li et al, 2011). Previous studies (Guan and Gao, 2010) indicated that E. huxleyi response changed with the irradiance and this was the base to use BWFs with an exposure response model based on irradiance (Neale and Kieber, 2000).…”

Effects of the World’s Oceans on Global Climate Change

“…Very interesting consequences follow from the fact that different species of PP have differential sensitivity, that is, different ability to stand against UV-induced damages [11]. That means that during the periods of enhanced UV radiation some changes in structure of plank- ton communities take place.…”

“…Second, with similar PP concentration, the effects will be maximum in zone with maximum solar illumination, that is, in tropics. Third, effects of UV irradiation can considerably differ in coastal and open ocean due to difference in prevailing PP species (Li et al, 2011). The most important consequences of PP concentration and corresponding light penetration fluctuations for ocean and atmosphere circulation are analyzed by Gnanadesikan and Anderson [10] using a coupled climate model.…”