Carbon Isotope Fractionation

1. Review of carbon isotopic fractionation in Emiliania huxleyi under high pCO2 Can alkenones be used as a paleobarometer? Sollberger, S. (2009) Chemical Oceanographic Unit University of Liege

2. Background Experimental framework Calculation methods Results Discussion & Outlook References Contents 1 Background Carbon isotopic fractionation Alkenones Coccolithophorid 2 Experimental framework Batch cultures Mesocosms 3 Calculation methods Carbon isotopic composition Isotopic fractionation 4 Results Riebesell et al. (2000) Rost et al. (2002) Benthien et al. (2007) Environmental inﬂuences 5 Discussion & Outlook 2 / 17

3. Background Experimental framework Calculation methods Results Discussion & Outlook References Carbon isotopic fractionation Since 1968... Use of carbon isotopic fractionation Sediment tracer - alkenones 3 / 17

4. Background Experimental framework Calculation methods Results Discussion & Outlook References Carbon isotopic fractionation Since 1968... Correlation between [CO2(aq)] and p in marine phytoplankton (Degens et al., 1968) Use of carbon isotopic fractionation Sediment tracer - alkenones 3 / 17

5. Background Experimental framework Calculation methods Results Discussion & Outlook References Carbon isotopic fractionation Since 1968... Correlation between [CO2(aq)] and p in marine phytoplankton (Degens et al., 1968) Use of carbon isotopic fractionation Reconstruction of paleo-CO2 (Rau et al., 1989, 1991; Freeman and Hayes, 1992; Jasper et al., 1994) Sediment tracer - alkenones 3 / 17

6. Background Experimental framework Calculation methods Results Discussion & Outlook References Carbon isotopic fractionation Since 1968... Correlation between [CO2(aq)] and p in marine phytoplankton (Degens et al., 1968) Use of carbon isotopic fractionation Reconstruction of paleo-CO2 (Rau et al., 1989, 1991; Freeman and Hayes, 1992; Jasper et al., 1994) BIAIS: species-speciﬁc CIF, irradiance, growth rate, physical isolation (e.g. sea ice) etc. Sediment tracer - alkenones 3 / 17

7. Background Experimental framework Calculation methods Results Discussion & Outlook References Carbon isotopic fractionation Since 1968... Correlation between [CO2(aq)] and p in marine phytoplankton (Degens et al., 1968) Use of carbon isotopic fractionation Reconstruction of paleo-CO2 (Rau et al., 1989, 1991; Freeman and Hayes, 1992; Jasper et al., 1994) BIAIS: species-speciﬁc CIF, irradiance, growth rate, physical isolation (e.g. sea ice) etc. Sediment tracer - alkenones Speciﬁc to Haptophyta E. huxleyi (Riebesell et al., 2000; Rost et al., 2002; Benthien et al., 2007) 3 / 17

8. Background Experimental framework Calculation methods Results Discussion & Outlook References Alkenones Unsaturated ketones with unique structure Organic molecules uniquely traceable to speciﬁc organisms → biomarkers 5-10 % of total cellular carbon Resistant to diagenesis (up to 100 Myrs.) Cellular energy storage (excess photosynthate)? Remains under debate Visualized by gas chromatography 37-39 carbon atoms with 2 or 3 double bonds (unsaturation) e.g. C37:2 or C37:3 If T ↑ → then ↓ of multiple bonds 4 / 17

17. Background Experimental framework Calculation methods Results Discussion & Outlook References Emiliania huxleyi Main characteristics Large bloom former Major actor in the oceanic carbon export Calcifying organism (a) serc.carleton.edu (b) www.co2.ulg.ac.be/peace 5 / 17

18. Background Experimental framework Calculation methods Results Discussion & Outlook References Batch cultures Table 1 Set of the diﬀerent parameters tested on carbon isotopic fractionation and complementary information Riebesell et al. (2000) Rost et al. (2002) Methods HCl, NaOH, NaHCO3 HCl, NaOH [CO2] (µmol l-1 ) 1.1 → 53.5 5 → 34 PFD (µmol m-2 s-1 ) 150 15, 30, 80, 150 Light:Dark cycle 16:8 16:8, 24:0 Experimental run 2 2 Analyzer GC-IRMS IRMS Characteristics Addition of NaOH & HCl in order to modify [CO2] → changes in TA while DIC remains constant (1st run) Addition of NaHCO3 in order to modify [CO2] → changes in both TA and DIC (2nd run) Modern ocean concentration range: 8 − 25µmol l-1 6 / 17

19. Background Experimental framework Calculation methods Results Discussion & Outlook References A mesocosm bloom experiment Nine 11 m3 confined water environments (Bergen, 2001) Future conditions (meso. no 1,2,3) pCO2 fixed to ∼ 710 µatm Present conditions (meso. no 4,5,6) pCO2 fixed to ∼ 410 µatm Glacial conditions (meso. no 7,8,9) pCO2 fixed to ∼ 190 µatm 7 / 17

23. Background Experimental framework Calculation methods Results Discussion & Outlook References Carbon isotopic composition In a sample, relative to PeeDee belemnite standard (PDB) δ13CSample = (13C/12C)Sample (13C/12C)PDB − 1 × 1000 In CO2 δ13CCO2 = δ13CDIC + 23.644 − 9701.5 TK (Rau et al., 1996) Alkenone unsaturation index UK, 37 = [C37:2] [C37:2]+[C37:3] (Prahl and Wakeham, 1987) 8 / 17

27. Background Experimental framework Calculation methods Results Discussion & Outlook References Isotopic fractionation In POC POC = δ13CCO2aq +1000 δ13CPOC +1000 − 1 × 1000 (Freeman and Hayes, 1992) In alkenones Alk = δ13CCO2aq +1000 δ13C37:X +1000 − 1 × 1000 (Freeman and Hayes, 1992) 9 / 17

30. Background Experimental framework Calculation methods Results Discussion & Outlook References Batch cultures (Riebesell et al., 2000) Table 2 A few results from Riebesell et al. (2000): response of the growth rate, the C:N ratio and the alkenones content per cell under increasing [CO2] Run Growth rate C:N Alk 1st ⇑ ⇑ ⇑ 2nd ⇓ ⇓ ⇑ Discussion Differences between the runs are not clear → experimental context?? Increase in alkenones is less significant when normalized to POC Small effect of ∆ [CO2] on alkenones and Uk 37 is affected rather by POC than by ∆ [CO2] 10 / 17

31. Background Experimental framework Calculation methods Results Discussion & Outlook References Batch cultures (Rost et al., 2002) Table 3 A few results from Rost et al. (2002): response of the growth rate, POC and PIC under increasing [CO2] Run Growth rate POC PIC 1st ⇑ ⇑ ⇓ 2nd ⇑ ⇑ ⇓ Discussion Stronger eﬀect of light on growth rate → independence of µ to [CO2] PIC is enhanced under increasing light P is largely independent of the ambient [CO2] (∆ less than 2 ‰) Discrimination of 13 C is higher under high irradiance Values of at 16:8 cycle are lower than at continuous light 11 / 17

32. Background Experimental framework Calculation methods Results Discussion & Outlook References Mesocosms (Benthien et al., 2007) Results No notable effect of CO2 Differences in δ13CPOC → differences in δ13CCO2 at d0 ↓ δ13CPOC in present & future conditions ↓ POC during POC ↑ in present & past conditions Cellular alkenones concentration remains cst during exponential growth but ↑ when nutrient are exhausted Isotopic offset between treatments due to differences in δ13CCO2aq or δ13CDIC Discussion Variability between treatments must be < variability between one triplicate PEP and TEP are enriched in 13C 12 / 17

33. Background Experimental framework Calculation methods Results Discussion & Outlook References Mesocosms (Benthien et al., 2007) Results No notable effect of CO2 Differences in δ13CPOC → differences in δ13CCO2 at d0 ↓ δ13CPOC in present & future conditions ↓ POC during POC ↑ in present & past conditions Cellular alkenones concentration remains cst during exponential growth but ↑ when nutrient are exhausted Isotopic offset between treatments due to differences in δ13CCO2aq or δ13CDIC Discussion Variability between treatments must be < variability between one triplicate PEP and TEP are enriched in 13C 12 / 17

34. Background Experimental framework Calculation methods Results Discussion & Outlook References Environmental inﬂuences Table 3 Review of the major factors inﬂuencing alkenones unsaturation and POC within the actors Authors [CO2] Growth rate PFD Other Deuser et al. (1968) √ Popp et al. (1998) √ Burkhardt et al. (1999) √ Riebesell et al. (2000) √ √ Rost et al. (2002) √ √ Benthien et al. (2007) √ 13 / 17

35. Background Experimental framework Calculation methods Results Discussion & Outlook References Discussion & Outlook Experiments Use of alkenones as a paleobarometer can only be applied as a first approximation since the response is not proved in modern seawater [CO2] Effect of light intensity and irradiance cycle as strong or stronger than the effect of [CO2]. Need extensive knowledge of environmental conditions determining phytoplankton growth Varying nutrient conditions influence the CO2 signal Improvements Different experimental approaches lead to variations of the magnitude of the results No adaptation of E. huxleyi to increasing pCO2 during the experiments 14 / 17

36. Background Experimental framework Calculation methods Results Discussion & Outlook References Literature cited I Benthien, A., Zondervan, I., Engel, A., Hefter, J., Terbr´’uggen, A., and Riebesell, U. (2007). Carbon isotopic fractionation during a mesocosm bloom experiment dominated by Emiliania huxleyi: Eﬀects of CO2 concentration and primary production. Geochim. et Cosmochim. Acta, 71:1528–1541. Burkhardt, S., Riebesell, U., and Zondervan, I. (1999). Eﬀects of growth rate, CO2 concentration and cell size on the stable isotope fractionation in marine phytoplankton. Geochim. et Cosmochim. Acta, 63:3729–3741. Degens, E. T., Guillard, R. R. L., Sackett, W. M., and Hellebust, J. A. (1968). Metabolic fractionation of carbon isotopes in marine plankton. i. temperature and respiration experiments. Deep-Sea Res., 15:1–9. Deuser, W. G., Degens, E. T., and Guillard, R. R. L. (1968). Carbon isotope relationships between plankton and sea water. Geochim. Cosmochim. Acta, 32:657–660. Freeman, K. H. and Hayes, J. M. (1992). Fractionation of carbon isotopes by phytoplankton and estimates of ancient CO2 levels. Global Biogeochem. Cycles, 6:185–198. 15 / 17

37. Background Experimental framework Calculation methods Results Discussion & Outlook References Literature cited II Jasper, J. P., Hayes, J. M., Mix, A. C., and Prahl, F. G. (1994). Photosynthetic fractionation of 13 c and concentrations of dissolved CO2 in the central equatorial pacific during the last 255,000 years. Paleoceanography, 9:781–798. Popp, B. N., Laws, E. A., Bidigare, R. R., Dore, J. E., Hanson, K. L., and Wakeham, S. G. (1998). Effect of phytoplankton cell geometry on carbon isotopic fractionation. Geochim. Cosmochim. Acta, 62:69–77. Prahl, F. G. and Wakeham, S. G. (1987). Calibration of unsaturation patterns in long-chain ketone compositions for paleotemperature assessment. Nature, 330:367–369. Rau, G. H., Froelich, P. N., Takahashi, T., and Des Marais, D. J. (1991). Does sedimentary organic δ13 c record variations in quarternary ocean [CO2(aq)]? Paleoceanography, 6:335–347. Rau, G. H., Riebesell, U., and Wolf-Gladrow, D. (1996). A model of photosynthetic 13 c fractionation by marine phytoplankton based on diffusive molecular CO2 uptake. Mar. Ecol. Prog. Ser., 133:275–285. 16 / 17

38. Background Experimental framework Calculation methods Results Discussion & Outlook References Literature cited III Rau, G. H., Takahashi, T., and Des Marais, D. J. (1989). Latitudinal variations in plankton δ13 c: Implications for CO2 and productivity in past oceans. Nature, 341:516–518. Riebesell, U., Revill, A. T., Holdsworth, D. G., and Volkman, J. K. (2000). The eﬀects of varying CO2 concentration on lipid composition and carbon isotope fractionation in Emiliania huxleyi. Geochim. et Cosmochim. Acta, 64:4179–4192. Rost, B., Zondervan, I., and Riebesell, U. (2002). Light-dependent carbon isotope fractionation in the coccolithophorid Emiliania huxleyi. Limnol. Oceanogr., 47(1):120–128. 17 / 17

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