title: Phytoplankton Productivity in an Arctic Fjord (West Greenland): Estimating Electron Requirements for Carbon Fixation and Oxygen Production.
abstract: Accurate quantification of pelagic primary production is essential for quantifying the marine carbon turnover and the energy supply to the food web. Knowing the electron requirement (Κ) for carbon (C) fixation (ΚC) and oxygen (O2) production (ΚO2), variable fluorescence has the potential to quantify primary production in microalgae, and hereby increasing spatial and temporal resolution of measurements compared to traditional methods. Here we quantify ΚC and ΚO2 through measures of Pulse Amplitude Modulated (PAM) fluorometry, C fixation and O2 production in an Arctic fjord (Godthåbsfjorden, W Greenland). Through short- (2h) and long-term (24h) experiments, rates of electron transfer (ETRPSII), C fixation and/or O2 production were quantified and compared. Absolute rates of ETR were derived by accounting for Photosystem II light absorption and spectral light composition. Two-hour incubations revealed a linear relationship between ETRPSII and gross 14C fixation (R2 = 0.81) during light-limited photosynthesis, giving a ΚC of 7.6 ± 0.6 (mean ± S.E.) mol é (mol C)-1. Diel net rates also demonstrated a linear relationship between ETRPSII and C fixation giving a ΚC of 11.2 ± 1.3 mol é (mol C)-1 (R2 = 0.86). For net O2 production the electron requirement was lower than for net C fixation giving 6.5 ± 0.9 mol é (mol O2)-1 (R2 = 0.94). This, however, still is an electron requirement 1.6 times higher than the theoretical minimum for O2 production [i.e. 4 mol é (mol O2)-1]. The discrepancy is explained by respiratory activity and non-photochemical electron requirements and the variability is discussed. In conclusion, the bio-optical method and derived electron requirement support conversion of ETR to units of C or O2, paving the road for improved spatial and temporal resolution of primary production estimates.
authors.affiliation: Nordic Center for Earth Evolution (NordCEE), Department of Biology, University of Southern Denmark, Odense, Denmark; Greenland Climate Research Centre, Greenland Institute of Natural Resources, Nuuk, Greenland.
authors.forename: Kasper
authors.initials: K
authors.lastname: Hancke
authors.affiliation: Arctic Research Center, Aarhus University, Aarhus, Denmark.
authors.forename: Tage
authors.initials: T
authors.lastname: Dalsgaard
authors.affiliation: Greenland Climate Research Centre, Greenland Institute of Natural Resources, Nuuk, Greenland; Arctic Research Center, Aarhus University, Aarhus, Denmark.
authors.forename: Mikael Kristian
authors.initials: MK
authors.lastname: Sejr
authors.affiliation: Institute for Bioscience, Aarhus University, Aarhus, Denmark.
authors.forename: Stiig
authors.initials: S
authors.lastname: Markager
authors.affiliation: Nordic Center for Earth Evolution (NordCEE), Department of Biology, University of Southern Denmark, Odense, Denmark; Greenland Climate Research Centre, Greenland Institute of Natural Resources, Nuuk, Greenland; Arctic Research Center, Aarhus University, Aarhus, Denmark; Scottish Association for Marine Science, Scottish Marine Institute, Oban, United Kingdom.
authors.forename: Ronnie Nøhr
authors.initials: RN
authors.lastname: Glud
mesh_terms: D001110:Arctic Regions; D044822:Biodiversity; D057486:Carbon Cycle; D004579:Electron Transport; D005453:Fluorescence; D005470:Fluorometry / Q000379:methods; D006116:Greenland; D008027:Light; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010839:Phytoplankton / Q000378:metabolism*
chemical_list: D045332:Photosystem II Protein Complex; D010100:Oxygen