title: Effects of ocean acidification on marine dissolved organic matter are not detectable over the succession of phytoplankton blooms.
abstract: Marine dissolved organic matter (DOM) is one of the largest active organic carbon reservoirs on Earth, and changes in its pool size or composition could have a major impact on the global carbon cycle. Ocean acidification is a potential driver for these changes because it influences marine primary production and heterotrophic respiration. We simulated ocean acidification as expected for a "business-as-usual" emission scenario in the year 2100 in an unprecedented long-term mesocosm study. The large-scale experiments (50 m(3) each) covered a full seasonal cycle of marine production in a Swedish Fjord. Five mesocosms were artificially enriched in CO2 to the partial pressure expected in the year 2100 (900 μatm), and five more served as controls (400 μatm). We applied ultrahigh-resolution mass spectrometry to monitor the succession of 7360 distinct DOM formulae over the course of the experiment. Plankton blooms had a clear effect on DOM concentration and molecular composition. This succession was reproducible across all 10 mesocosms, independent of CO2 treatment. In contrast to the temporal trend, there were no significant differences in DOM concentration and composition between present-day and year 2100 CO2 levels at any time point of the experiment. On the basis of our results, ocean acidification alone is unlikely to affect the seasonal accumulation of DOM in productive coastal environments.
authors.affiliation: Institute for Chemistry and Biology of the Marine Environment (ICBM), Research Group for Marine Geochemistry (ICBM-MPI Bridging Group), Carl von Ossietzky University of Oldenburg, Carl-von-Ossietzky-Straße 9-11, 26129 Oldenburg, Germany.
authors.forename: Maren
authors.initials: M
authors.lastname: Zark
authors.affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors.forename: Ulf
authors.initials: U
authors.lastname: Riebesell
authors.affiliation: Institute for Chemistry and Biology of the Marine Environment (ICBM), Research Group for Marine Geochemistry (ICBM-MPI Bridging Group), Carl von Ossietzky University of Oldenburg, Carl-von-Ossietzky-Straße 9-11, 26129 Oldenburg, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Dittmar
keywords: FT-ICR-MS; dissolved organic matter; marine geochemistry; mesocosm study; ocean acidification; ultrahigh resolution mass spectrometry