1. Phytoplankton in a high-CO 2 world: biological responses and their biogeochemical implications Ulf Riebesell Leibniz-Institut für Meereswissenschaften (IFM-GEOMAR) Kiel University, Germany

2. Potential drivers in a high-CO 2 world Atmospheric CO 2 Mixing,stratificationCirculation LightNutrients Carbon sinks & sources Oceanic CO 2 Carbonatechemistry Global warming Surface ocean temperature Nutrient utilization efficiency Atmospheric dust (Fe) Precipitation Ocean biota Windstress Rain ratio (CaCO 3 /C org ) Stoichiometry(Si/C/N/P/Fe)

3. Criteria for evaluating the biogeochemical relevance of feedbacks Sign of change positive feedback amplifies initial perturbation negative feedbackdampens initial perturbation Sensitivity level of perturbation needed to trigger a feedback Capacity strength of feedback compared to initial perturbation Longevity relevant time-scales: permanent vs. transient

4. Todays world pCO 2 : 280-380 ppmV High-CO 2 world pCO 2 : 580-720 ppmV Emiliania huxleyi Gephyrocapsa oceanica Calcidiscus leptoporus CO 2 -Calcification feedback

5. Calcite content (pg per cell) pCO 2 (µatm) Coccolithus pelagicus BUT ! CO 2 -Calcification feedback

6. 10m S=31.3 S=29.8 S=31.3 Sediment Trap pump CO 2 regulation 95% PAR 190 ppmV 370 ppmV 700 ppmV 190 370 700 pCO 2 (ppmv) Large Scale Facilities, Bergen, Norway Plankton development under past, present and future CO 2 (Mesocosm experiments in 2000 and 2003) 5m

7. Chlorophyll a pCO 2 (normalized) ppmV µg L -1 Year 2100 Present LGM Mesocosm experiment Bergen 2000 Emiliania huxleyi Initial nutrient concentrations: NO 3 - 15.5 mmol m -3 NO 3 - 15.5 mmol m -3 PO 4 3- 0.51 mmol m -3 PO 4 3- 0.51 mmol m -3 Si(OH) 4 ~0 Si(OH) 4 ~0 NO 3 - and PO 4 3- exhausted on day 13 B. Delille et al., in prep.

8. Primary production and calcification during a bloom of Emiliania huxleyi Calcification Production Dissolution Respiration B. Delille et al. in prep. CO 2 -Calcification feedback 10 20 30

9. Year 2100 (700 ppmV) Present (370 ppmV) LGM (190 ppmV) Calcification Production Respir. Dissol. -10 10 20 30 d11 d13 d15 d17 d19 d21 d2 d9 (µmolC.kg.d ) (µmolC.kg-1.d-1) B. Delille et al. in prep.

10. Year 2100 (700 ppmV) Present (370 ppmV) LGM (190 ppmV) Calcification Production Respir. Dissol. -10 10 20 30 d11 d13 d15 d17 d19 d21 d2 d9 (µmolC.kg.d ) (µmolC.kg-1.d-1) B. Delille et al. in prep. Increasing pCO 2 from 190 ppmV to 700 ppmV caused 24-48 h delay in the 24-48 h delay in the onset of calcification 40% decrease in 40% decrease in CaCO 3 production

11. Atmospheric CO 2 Ecosystem pH, Ca CO 3 Rain ratio Bio-calcificationFunctionalgroups Environment Biogeochemistry Surface ocean alkalinity Loop with even number of negative influences: positive feedback odd number of negative influences: negative feedback odd number of negative influences: negative feedback CO 2 -Calcification feedback negative influence positive influence Sign of change negative feedback (dampens initial perturbation) Sensitivity high Capacity low (6-30 Gt C until 2100 for 20-40% decrease) Longevity permanent vs. transient ?

12. Chlorophyll a ppmV µg L -1 Year 2100 Present LGM pCO 2 (normalized) Chlorophyll a Initial nutrient concentrations: NO 3 - 8.0 mmol m -3 NO 3 - 8.0 mmol m -3 PO 4 3- 0.5 mmol m -3 PO 4 3- 0.5 mmol m -3 Si(OH) 4 12.0 mmol m -3 Si(OH) 4 12.0 mmol m -3 NO 3 - exhausted on day 12 NO 3 - exhausted on day 12 Mesocosm experiment Bergen 2003 Year 2100: Diatoms > Dinophyceae (> Coccolithophores) Present: Coccolithophores > Diatoms (> Dinophyceae > Chlorophyceae) LGM: Diatoms (> Dinophyceae > Coccolithophores) B. Delille, unpubl.

13. R. Bellerby et al., unpubl. biological carbon fixation 0 2 4 6 8 10 12 14 16 18 20 Day DIC (µmol kg -1 ) Dissolved inorganic carbon Year 2100 Present LGM Carbon over-production feedback

14. Year 2100 Present LGM Day Carbon loss (µmol kg -1 ) Carbon loss = DIC - TPC - DOC Carbon over-production feedback

15. Transparent Exopolymer Particles Dissolved Polysaccharides Cell density Day DOC Low CO 2 High CO 2 DOC TEP Marine snow Export Exsudation Sign of change negative feedback Sensitivity ? Capacity high Longevity permanent vs. transient ? Carbon over-production feedback Engel et al. 2004 Nature 428, 929

16. FACE (Free Air CO 2 Enrichment) Program - with worldwide 33 experimental sites - 16 sites in Europe

17. Research needs: Observational studies on combined CO 2 and T-effects - assess biological responses - unravel biogeochemical processes and potential feedbacks through a suite of perturbation studies - laboratory experiments - mesocosm studies - open ocean CO 2 fertilization experiment