In this thesis I described antioxidant responses of marine microalgae to excess irradiance
including ultraviolet radiation (UVR). Marine microalgae, including phytoplankton,
comprise an essential group of organisms: first of all they form the basis of open ocean
food chains and secondly they are able to withdraw (anthropogenic) carbon dioxide from
the atmosphere. Many studies have already described the effects of excess irradiance
including ultraviolet radiation (UVR) on photosynthesis, judging from a wealth of in situ
incubation studies showing inhibition of primary production in sunlit surface waters. In
addition, incident PAR levels may induce excess irradiance responses for example by de
novo synthesis of photoprotective pigments (xanthophylls). Ultraviolet radiation (280 – 400
nm) has been shown to substantially reduce primary production in most marine systems,
with natural UVAR (315 – 400 nm) and UVBR (280-315 nm) often having similar relative
proportions of inhibition. As a result of climate change phytoplankton irradiance exposure
(intensity and spectral composition) may change significantly. For example, since
stratification traps phytoplankton in the upper water layer, excess irradiance exposure (PAR,
UVAR, UVBR) may increase in those systems where stratification becomes more intense.
This applies to areas characterized by reduced average wind speeds or increased melt water
input. In contrast, other regions (s.a. Antarctic Circumpolar Vortex) may become more
deeply mixed by increased average wind speeds, thereby reducing irradiance intensities and
exposure durations, but increasing irradiance dynamics.