Build-up and decline of organic matter during PeECE III

Abstract

Abstract. Increasing atmospheric carbon dioxide (CO 2 ) concentrations due to anthropogenic fossil fuel combustion are currently changing the ocean's chemistry. Increasing oceanic [CO 2 ] and consequently decreasing seawater pH have the potential to significantly impact marine life. Here we describe and analyze the build-up and decline of a natural phytoplankton bloom initiated during the 2005 mesocosm Pelagic Ecosystem CO 2 Enrichment study (PeECE III). The draw-down of inorganic nutrients in the upper surface layer of the mesocosms was reflected by a concomitant increase of organic matter until day t 11 , the peak of the bloom. From then on, biomass standing stocks steadily decreased as more and more particulate organic matter was lost into the deeper layer of the mesocosms. We show that organic carbon export to the deeper layer was significantly enhanced at elevated CO 2 . This phenomenon might have impacted organic matter remineralization leading to decreased oxygen concentrations in the deeper layer of the high CO 2 mesocosms as indicated by deep water ammonium concentrations. This would have important implications for our understanding of pelagic ecosystem functioning and future carbon cycling.

Influence of changing carbonate chemistry on morphology and weight of coccoliths formed by <i>Emiliania huxleyi</i>

“…At this site, E. huxleyi usually blooms during late spring at typical surface water temperatures between 10-12 • C (compare Schulz et al, 2008). All experiments are generally similar in their design.…”

Influence of CO<sub>2</sub> and nitrogen limitation on the coccolith volume of <I>Emiliania huxleyi</I> (Haptophyta)

“…The extent of change in the canonical stoichiometry depends primarily on the C:N:P supply and the cellular growth rate (Klausmeier et al, 2008). However, experimental evidence from mesocosm and laboratory experiments indicate the importance of pCO 2 for the stoichiometry of E. huxleyi under projected ocean acidification/carbonation (Leonardos and Geider, 2005;Engel et al, 2005;Schulz et al, 2008).…”

Effects of CO<sub>2</sub> perturbation on phosphorus pool sizes and uptake in a mesocosm experiment during a low productive summer season in the northern Baltic Sea

“…The intensity of upwelling shaped the pattern of temperature not only in the fjord but also in the mesocosms varying from 7.8 to 15.9 • C. Such variations in temperature influence the phosphorus transformation and interleave with CO 2 effects. While nutrients were added in previous CO 2 enrichment experiments Schulz et al, 2008), no amendments were undertaken in this study in order to be close to natural conditions. Initial PO 4 concentrations of only 0.17 ± 0.01 µmol L −1 were measured, however, PO 4 was never exhausted (Figs.…”