MEPS 272:25-31 (2004)  -  doi:10.3354/meps272025

Chromophoric dissolved organic matter in experimental mesocosms maintained under different pCO2 levels

Emma Rochelle-Newall1,5,*, Bruno Delille2, Michel Frankignoulle2, Jean-Pierre Gattuso1, Stéphan Jacquet3, Ulf Riebesell4, Anja Terbruggen4, Ingrid Zondervan4

1Laboratoire d¹Océanographie, CNRS-Université de Paris 6, BP 28, 06234 Villefranche-sur-mer Cedex, France
2Unité d¹Océanographie Chimique, Université de Liege, 4000 Liège, Belgium
3UMR CARRTEL, Station INRA d¹Hydrobiologie Lacustre, 74203 Thonon les Bains Cedex, France
4Alfred Wegener Institute for Polar and Marine Research, 27515 Bremerhaven, Germany
5Present address: Centre IRD de Noumea, BP A5, 98848 Noumea Cedex, New Caledonia

ABSTRACT: Chromophoric dissolved organic matter (CDOM) represents the optically active fraction of the bulk dissolved organic matter (DOM) pool. Recent evidence pointed towards a microbial source of CDOM in the aquatic environment and led to the proposal that phytoplankton is not a direct source of CDOM, but that heterotrophic bacteria, through reprocessing of DOM of algal origin, are an important source of CDOM. In a recent experiment designed at looking at the effects of elevated pCO2 on blooms of the coccolithophorid alga Emiliania huxleyi, we found that despite the 3 different pCO2 levels tested (190, 414 and 714 ppm), no differences were observed in accumulation of CDOM over the 20 d of incubation. Unlike previous mesocosm experiments where relationships between CDOM accumulation and bacterial abundance have been observed, none was observed here. These results provide some new insights into the apparent lack of effect of pCO2 on CDOM accumulation in surface waters, and question the previously proposed mechanisms and rates of CDOM production in natural phytoplankton blooms.

KEY WORDS: CDOM · DOC · Mesocosms · Viruses · Cyanobacteria · Heterotrophic bacteria · CO2

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