Marine ecosystem community carbon and nutrient uptake stoichiometry under varying ocean acidification during the PeECE III experiment

Abstract

Abstract. Changes to seawater inorganic carbon and nutrient concentrations in response to the deliberate CO 2 perturbation of natural plankton assemblages were studied during the 2005 Pelagic Ecosystem CO 2 Enrichment (PeECE III) experiment. Inverse analysis of the temporal inorganic carbon dioxide system and nutrient variations was used to determine the net community stoichiometric uptake characteristics of a natural pelagic ecosystem perturbed over a range of pCO 2 scenarios (350, 700 and 1050 µatm). Nutrient uptake showed no sensitivity to CO 2 treatment. There was enhanced carbon production relative to nutrient consumption in the higher CO 2 treatments which was positively correlated with the initial CO 2 concentration. There was no significant calcification response to changing CO 2 in Emiliania huxleyi by the peak of the bloom and all treatments exhibited low particulate inorganic carbon production (∼15 µmol kg −1 ). With insignificant air-sea CO 2 exchange across the treatments, the enhanced carbon uptake was due to increase organic carbon production. The inferred cumulative C:N:P stoichiometry of organic production increased with CO 2 treatment from 1:6.3:121 to 1:7.1:144 to 1:8.25:168 at the height of the bloom. This study discusses how ocean acidification may incur modification to the stoichiometry of pelagic production and have consequences for ocean biogeochemical cycling.

Build-up and decline of organic matter during PeECE III

“…The draw-down of the major nutrients nitrate, phosphate and silicate in the upper surface layer during the bloom phase of the experiment followed the same temporal pattern in all mesocosms, irrespective of pCO 2 (for details see Bellerby et al, 2007). The same was observed for the concomitant build-up of Chl-a and particulate organic matter (POC,PON and POP).…”

Long-term culture at elevated atmospheric CO2fails to evoke specific adaptation in seven freshwater phytoplankton species

“…CO 2 concentrations in the medium, however, were at treatment levels during the initial phase of growth and were consistently different, representative of the high versus low CO 2 conditions we sought to establish in our cultures throughout the growth cycle (figure 2; Anabaena in regime 2 is an exception). Comparable falls in CO 2 concentrations have been reported in large-scale marine mesocosm studies, with CO 2 concentration in elevated CO 2 mesocosms falling to half the treatment concentration of 1000 ppm [30]. In natural marine systems under current CO 2 concentrations, algal blooms can reduce CO 2 concentration by over 90 ppm [31].…”

Mesocosm CO<sub>2</sub> perturbation studies: from organism to community level

“…It can not be ruled out that the pervasive response of the plankton community to the nutrient addition has masked possible effects caused by the CO 2 perturbations. In fact, no significant differences between CO 2 treatments were observed for PeECE II+III -concentrations of POM and DOM (Engel et al, 2004;Rochelle-Newall et al, 2004;Riebesell et al, 2007) PeECE III -phytoplankton composition and cell cycle during bloom development -inorganic nutrient utilization, nutrient stoichiometry Bellerby et al, 2007; and nutrient turnover (Tanaka et al, 2008) -biogenic calcification -bacterial abundance, diversity of attached bacteria, 14 C-leucine based bacterial production, bacteriaphytoplankton coupling -micro-zooplankton grazing -calcite loss due to microzooplankton grazing Fig. 2.…”

“…-biogenic calcification and carbon loss -stoichiometry of carbon to nutrient uptake and organic matter production (Engel et al, 2005) PeECE II -bacterial production and ectoenzymatic activities (Grossart et al, 2006) -particle sitze distribution and phytoplankton community structure (Engel et al, 2008) PeECE III -carbon drawdown, C:N:P stoichiometry of community production and carbon loss Bellerby et al, 2007) -cumulative 14 C primary production (Egge et al, 2007) -diversity of free bacteria -viral abundance and diversity -copepod nauplii recruitment (Carotenuto et al, 2007) -DMS/DMSP concentrations Wingenter et al, 2007) -chloriodomethane production (Wingenter et al, 2007) -iron availability (E. Breitbarth, unpublished data)…”