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Oxygen photolysis in the Mauritanian upwelling: Implications for net community production
Author(s) -
Kitidis Vassilis,
Tilstone Gavin H.,
Serret Pablo,
Smyth Timothy J.,
Torres Ricardo,
Robinson Carol
Publication year - 2014
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2014.59.2.0299
Subject(s) - colored dissolved organic matter , upwelling , chemistry , photic zone , dissolved organic carbon , absorbance , oxygen , photodissociation , chlorophyll a , photosynthetically active radiation , analytical chemistry (journal) , environmental chemistry , phytoplankton , photochemistry , photosynthesis , oceanography , geology , nutrient , chromatography , biochemistry , organic chemistry
We carried out 16 photochemical experiments of filtered surface water in a custom‐built solar simulator and concomitant measurements of in vitro gross primary production (GPP) and respiration (R) in the Mauritanian upwelling during a Lagrangian study following three sulfur hexafluoride—labeled patches of upwelled water (P1 to P3). Oxygen photolysis rates were correlated with the absorbance of chromophoric dissolved organic matter (CDOM) at 300 nm, suggesting first‐order kinetics with respect to CDOM. An exponential fit was used to calculate the apparent quantum yield (AQY) for oxygen photolysis, giving an average AQY of 0.00053 µmol O 2 (mole photons m −2 s −1 ) −1 at 280 nm and slope of 0.0012 nm −1 . Modeled photochemical oxygen demand (POD) at the surface (3–16 mmol m −3 d −1 ) occasionally exceeded R and was dominated by ultraviolet radiation (71–79%). Euphotic‐layer integrated GPP decreased with time during both P‐1 and P‐3, whereas R remained relatively constant and POD increased during P‐1 and decreased during P‐3. On Day 4 of P‐3, GPP and POD maxima coincided with high CDOM absorbance, suggesting “new” CDOM production. Omitting POD may lead to an underestimation of net community production (NCP), both through in vitro and geochemical methods (here by 2–22%). We propose that oxygen‐based NCP estimates should be revised upward. For the Mauritanian upwelling, the POD‐corrected NCP was strongly correlated with standard NCP with a slope of 1.0066 ± 0.0244 and intercept of 46.51 ± 13.15 mmol m −2 d −1 .