1. Theme 2 - Key Questions What are the effects of ocean acidification and related changes in seawater chemistry on marine organisms, what are the underlying mechanisms of the observed responses and the potential for adaptation, how are they modulated by other environmental stressors, and what are the consequences for marine ecosystems and ocean biogeochemical cycles?

2. CO 2 Theme 2: Ecosystem impacts, acclimation and adaptation WP5 WP8 Trophic interactions Climate relevant gases Nutrient availability Autotrophic processes WP6 Reproduction & growth WP4-8 Adaptation WP7 Microbial activity WP4 Biocalcification Ocean chemistry WP9 From process studies to ecosystem models Theme 2 Ecosystem impacts, acclimation and adaptation WP4 Sensitivity of calcification (D. Iglesias-Rodriguez) WP5 Sensitivity of autotrophic processes (U. Riebesell) WP6 Performance: reproduction and growth(H.-O. Pörtner) WP7 Microbial diversity and activity, in particular nitrogen cycling (J. Middelburg) WP8 Impact on trophic interactions (F. Thingstad) WP9 From process studies to ecosystem models (A. Oschlies)

3. WP 5 Sensitivity of autotrophic processes Objectives: Quantify effects of OA on photosynthetic carbon metabolism & nitrogen fixation Assess the consequences for elemental stoichiometry, partitioning of organic matter into dissolved & particulate phases, and vertical transport Search for changes in gene expression for selected genes relevant for nutrients and carbon metabolism Determine effects on the production of climate relevant biogases Assess effects on the speciation and bioavailability of major and trace nutrients (Fe, Zn) Partners: IFM-GEOMAR, AWI, PML, NIOZ, NOC, UiB, UC

4. WP 5 Sensitivity of autotrophic processes Description of Work: Determine community level responses to OA of photosynthetic carbon and nitrogen fixation, exudation, partitioning into dissolved and particulate organic matter, stoichiometry, and production of climate relevant biogases in off-shore mesocosm CO 2 perturbation experiments (IFM- GEOMAR, UiB, UC, AWI, PML, NIOZ, NOC) Pelagic mesocosm CO 2 enrichment experiment 380 720 550860 1040 1200 pCO 2 (µatm)

5. WP 5 Sensitivity of autotrophic processes Description of Work: CA activity centrifugation Mass spectrometer Photosynthesis CO 2 / HCO 3 - uptake 180 µmol photons m -2 s -1 15 °C 300 µmol Photonen m -2 s -1 361803601800 ppmv CO 2 Assess combined effects of acidification and changes in temperature, light, and nutrients on carbon and energy fluxes in key phytoplankton taxa (AWI, IFM-GEOMAR, PML, NIOZ ) Membrane inlet mass spectrometry Assess combined effects of acidification and changes in temperature, light, and nutrients on carbon and energy fluxes in key phytoplankton taxa (AWI, IFM-GEOMAR, PML, NIOZ ) Model carbon fluxes and energy allocation at the cellular level based on results obtained experimentally (AWI)

6. WP 5 Sensitivity of autotrophic processes Description of Work: Determine expression of selected genes for nutrients and carbon uptake, exudation, and carbonic anhydrase and the influence on gene diversity in (meta)genomic databases in laboratory and mesocosm experiments (IFM-GEOMAR, NIOZ) Determine changes in the speciation and bioavailability of major and trace nutrients (Fe, Zn) and related effects on photosynthesis and carbon metabolism (NIOZ, NOC)

7. WP 5 Sensitivity of autotrophic processes Deliverables in first 18 months: Standardized protocols (for experimental WPs 4, 5, 6, 7, 8) for ensuring internal consistency of the CO 2 system in CO 2 perturbation studies (month 3; R, PU) Methodologies applied in off-shore CO 2 perturbation studies, presented at “The Ocean in a high CO 2 world” meeting (month 9; O, PU) Workshop on protocols for CO 2 perturbation experiments (month 12; O, PP) Report on OA-related changes in nutrient and trace metal chemistry (month 12; R, PU) Comprehensive data sets on off-shore mesocosm CO 2 perturbation studies (months 18, O, CO)