Final Activity Report Summary - UVPHYTOMAA (UV photochemical bleaching of phytoplankton and coloured dissolved organic matter and the interactive effects on the inhibition of photosynthesis ...) The objective of the present project was to determine the impact of Ultra-Violet (UV) radiation on phytoplankton photosynthesis and photo-protection mechanisms (e.g. production of mycosporine-like amino-acids or MAAs) and coloured dissolved organic matter (CDOM) photo-degradation, in situ over contrasting biomes and seasons and in the laboratory on phytoplankton cultures.The interactive effect of UV on phytoplankton and CDOM have been poorly addressed in previous studies, but is critical for estimating the impact of stratospheric ozone depletion on ocean carbon cycling and the associated increase in surface UV-B radiation over mid- and high latitudes. These effects were examined; i) in situ, both at a coastal UK time-series site off Plymouth (L4 site) and in the Southern Ocean as part of an international study (SAZ-Sense), and ii) in the laboratory, on cultures of phytoplankton species representative of UK and Sub-Antarctic waters. The SAZ-Sense study was conducted in austral mid-summer (17 Jan to 20 Feb) 2007 to examine microbial ecosystem structure and biogeochemical processes in Sub-Antarctic Zone waters, west and east of Tasmania, and in the Polar Frontal Zone (55 degrees south).The project brought together research teams from Australasia, Europe, and North America. As part of the EIF, we examined the biochemical, photo-physiological, and bio-optical responses of phytoplankton and CDOM to variable UV irradiance. Kinetics experiments were conducted by incubating surface water samples over 1 to 2 days. In parallel, the spectral optical properties of the water column were characterised and water samples were taken for the determination of phytoplankton photosynthetic parameters, pigments composition and the concentration of UV photo-protective compounds (MAAs). These field studies showed contrasting responses of phytoplankton and CDOM to different UV scenarios as a result of changes in phytoplankton assemblage composition, water column optical properties (UV and visible) and environmental conditions (e.g. vertical mixing conditions, temperature and nutrient availability).
