Time-series of Phytoplankton Photosynthesis and Dynamics using PHYTO-PAM and Autonomous Underwater Vehicle
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- Institutt for biologi 
This MSc thesis comprises PHYTO-PAM measurements of phytoplankton photosynthesis, measured as electron transfer rates in order to study photosynthetic dynamics. Time-series of photosynthesis from two phytoplankton bloom scenarios were conducted, one during Arctic ice-edge bloom and one during low biomass post-bloom condition in mid-Norwegian temperate conditions (Hopavågen in Trøndelag). An Autonomous Underwater Vehicle (AUV) was used to provide a spatial scale of key environmental variables (temperature, salinity) from the sampling sites. In Hopavågen, a culture incubated in situ was used as a reference for the PAM data of natural community. Both case studies can be used for future interpretation of AUV measured salinity, temperature and fluorescence and represent future steps to estimate primary production from fluorometers on AUVs. In Mid-Norway the phytoplankton biomass was <0.5 µg Chl a /L primarily due to zooplankton grazing and possible nutrient limitation. In contrast, the photosynthesis and biomass measurements of the ice-edge bloom in the Arctic gave Chl a of 20 µg Chl a/L and correspondingly high photosynthetic rates. PAM data indicated that there were both Ek dependent and Ek independent changes in mid-Norway. The community in mid-Norway responded to irradiances by adjustments of photosynthesis, seen as photochemical quenching of fluorescence (PQ) and non-photochemical quenching (NPQ). These responses were seen as changes in α, Pmax and Ek. The culture showed a negative response in α with increasing irradiance. Pmax co varied with α resulting in no change in Ek (Ek-independent change). In the Arctic, PAM data indicate mixing of water masses, because there were no significant changes in α, Pmax or Ek. ΦPSII_max was also discussed in relation to ΦPSII and rETR at in situ irradiance. Both natural assemblage of phytoplankton and culture showed a decrease in ΦPSII_max at supra saturating irradiances. In the Arctic ΦPSII decreased at surface in contrast to deeper waters, indicating that there was PQ in the surface. High Performance Liquid Chromatography revealed different pigments groups of phytoplankton and light microscopy was used to identify dominant classes. The community in Mid-Norway was dominated by small Chl b containing algae. The ice-edge bloom was dominated by fucoxanthin and Chl c 1+2-containing Bacillariophyceae comprising Thalassiosira spp., Chaetoceros spp., Pseudo-Nitzschia spp. and Navicula spp.