1. Etude de la dissolution de la silice biogénique des agrégats. Utilisation dans la reconstruction des flux de sédimentation de la silice biogénique et du carbone dans la colonne deau. Brivaëla MORICEAU Supervised by Olivier RAGUENEAU

2. Introduction

3. Carbon cycle Introduction Deforestation Combustion Before the industrial era The carbon cycle was balanced Then: intense human activity Increase of C in the atmosphere (Berner and Berner 1996, Kump et al. 1999) www.ggl.ulaval.ca/personnel/bourque/s3/cycles.biogeochimiques.html Atmosphere Lithosphere PhotosynthesisRespiration Absorption Respiration Limestone and silicate alteration Precipitation Volcanicity Buried Biosphere Hydrosphere 770 GtC 610 GtC 39 000 GtC 55 000 000 GtC

4. Introduction Role of the ocean in the carbon cycle Sources Sinks Carbon exchanges T Surface exchange Physical pH alcalinity Chemical Photosynthesis Respiration Biological The global ocean retards the increase of carbon in the atmosphere "Les Humeurs de l'Océan" magazine Pour la Science, 1998

5. Diatoms Introduction Biological pump of carbon 40-45% of the PP (Mann 1999) aggregates and fecal pellets (Turner, 2002; Thornton 2002) Basis of an efficient food web (Silver et al., 1978) Important role of diatoms in the biological pump of carbon Diatoms awi-potsdam.de/Carbon/calcif-d.html

6. Si + C Influence of aggregation on biogenic silica (BSiO 2 ) dissolution? DSi Si + C Preservation Mesopelagic zone 50% DSi ? Depth of BSiO 2 recycling? Deep ocean Euphotic zone 0 m 100 m 1000 m several months several years 10-100 years Geological time scale

7. Organic carbon fluxes ORFOIS Dissolution parameters of BSiO 2 Parameterisation of global models + sedimentation rates of the sinking particles Reconstruction of BSiO 2 fluxes Theoretical water column Reconstruction of BSiO 2 fluxes In situ Laboratory experiments Mechanistic model Impact of aggregation on BSiO 2 dissolution? Impact of aggregation on the depth of the BSiO 2 recycling? Role of diatoms in the Biological pump? (Si/C) z = (Si/C) 0 z 0.41 Aggregat e Data base sediment trap Framework of the PhD Ragueneau et al. 2002 Which processes are involved? Validity of the experimental measurements? Semi-mechanistic model Mechanistic model

8. AWI Bremerhaven Uta Passow and Michael Garvey Organic carbon fluxes Dissolution parameters of the BSiO 2 + sedimentation rates of the sinking particles Reconstruction of the BSiO 2 fluxes Theoritical water column Reconstruction of the BSiO 2 fluxes In situ Laboratory experiments Mecanistic model Impact of aggregation on BSiO 2 dissolution? Impact of aggregation on the depth of the BSiO 2 recycling? Role of diatoms in the Biological pump? (Si/C) z = (Si/C) 0 z 0.41 Aggregate Data base sediment trap Ragueneau et al. 2002 Which processes are involved? Validity of the experimental measurements? Impact of aggregation on BSiO 2 dissolution?

9. 2- Cohesion - TEP (Transparent Exopolymer Particles) 1- Collision - High cell density - Differential sinking velocity GLUE How to make aggregates? Measurement of the BSiO 2 dissolution rate in aggregate: methods Shanks and Edmondson 1989 1 2 Skeletonema costatum 3 Chaetoceros decipiens Talassiosira weissflogii

10. Settling during 24-48 h Step 2 4 1 Aggregate treatment Free cell treatment Step 1 Dissolution 13°C Dark roller table Incubation without aggregation 13°C Dark shaker table Manual transfer of aggregates into artificial seawater (no nutrients) 1 Cell poor medium artificial seawater (no nutrients) 13°C Dark shaker table 2 Experiments Measurement of the BSiO 2 dissolution rate in aggregate: methods aggregation

11. Dissolution Experiment BSiO 2 TEP 100 Aggregates Free cells Parallel measurements Parameters that could possibly influence the BSiO 2 dissolution BSiO 2 dissolution rate : Si(OH) 4 = f(t) Initial dissolution rate (Greenwood 2001) Measurement of the BSiO 2 dissolution rate in aggregate: methods number of bacteria diatom viability Moriceau et al. in revision

12. 5 1 3 2 2 5 5 13 13 experiments on aggregates 5 experiments on freely suspended diatoms 3 diatom species Statistical t-test Significant decrease of the BSiO 2 dissolution rate x 2 0.054 d -1 0.026 d -1 Measurement of the BSiO 2 dissolution rate in aggregate: results and discussion From Moriceau et al., in revision

13. (1) The viability of the cells Free cells aggregates Which parameters could provoke a decrease of the BSiO 2 dissolution rate? Measurement of the BSiO 2 dissolution rate in aggregate: results and discussion Nelson et co-workers (1976) Evolution of the diatoms viability coupled dissolution experiment on T. weissflogii aggregates Free cells Number of cells alive Total number of cells R BSiO2 for cells alive ~ 0 Viability could explain the decrease of the BSiO 2 dissolution rate in aggregates Moriceau et al., in revision

14. From Moriceau et al. in revision Organic coating BSiO 2 Internal organic matter (2) Bacteria number Patrick and Holding (1985) Bidle and Azam (1999) Role of bacteria in the BSiO 2 dissolution Measurement of the bacterial number / diatom cell No possible differentiation between attached and free bacteria BUT Bacteria/diatom The number of bacteria per diatom could explain the decrease of the BSiO 2 dissolution rate in aggregates Measurement of the BSiO 2 dissolution rate in aggregate: results and discussion

15. (3) DSi concentration outside aggregates: 5 to 40 µM inside aggregates: 80 to 250 µM Van Cappellen and Qiu, 1997b Solubility of BSiO 2 between 4°C and 25°C: 500 - 1800µM (Hurd and Teyer 1975, Kamatani and Riley 1979, Van Cappellen and Qiu 1997a,b) Brzezinski and co-workers 1997 DSi inside natural aggregates: 300 µM DSi inside aggregates could explain the decrease of the BSiO 2 dissolution rate in aggregates DSi concentrations in the ocean = 0-200µM and average 70µM (NODC, www.nodc.noaa.gov/OC5/WOA01F) (Tréguer et al., 1995)www.nodc.noaa.gov/OC5/WOA01F Measurement of the BSiO 2 dissolution rate in aggregate: results and discussion

16. DSi time BSiO 2 or DSi Concentration Solubility (1200µM at 13°C) Dissolution rate measured = DissolutionDiffusion + DSi Aggregate 3 phases Free cell 2 phases Decrease 0 0.02 0.04 0.06 0.08 0.1 Average BSiO 2 dissolution rate d -1 free cells aggregates MODEL Experimental measurement of the BSiO 2 dissolution rate Measurement of the BSiO 2 dissolution rate in aggregate: results and discussion

17. University of Utrecht Philippe Van Cappellen and Goulven Laruelle Organic carbon fluxes Dissolution parameters of BSiO 2 + sedimentation rates of the sinking particles Reconstruction of BSiO 2 fluxes Theoritical water column Reconstruction of BSiO 2 fluxes In situ Laboratory experiments Mecanistic model Impact of aggregation on BSiO 2 dissolution? Impact of aggregation on the depth of the BSiO 2 recycling? Role of diatoms in the Biological pump? (Si/C) z = (Si/C) 0 z 0.41 Aggregate Data base sediment trap Ragueneau et al. 2002 Which processes are involved? Validity of the experimental measurements? Modelling the BSiO2 dissolution in an aggregate

18. R BSiO2 = K dis f(viability,DSi agg ) Modelling an aggregate Aggregate = sphere Modelling an aggregate: model description r DSi Decrease of the DSi diffusion solely Decrease of the DSi diffusion + BSiO 2 dissolution Dissolution Diffusion Viability = 0 no cell alive R BSiO2 DSi agg = DSi ext Decrease of the BSiO 2 dissolution solely ?

19. Moriceau et al. to be submitted a Model Output Internal DSi concenration External DSi concentration Modelling an aggregate: model description DSi agg (r = r agg ) = DSi ext R BSiO2 viability = 0 ; DSi agg = DSi ext 0.4 Freely suspended cells :10 nmol g -1 BSiO2 s -1 Decrease of the dissolution rate Decrease of the DSi diffusion Moriceau et al. to be submitted a k dis = 4 nmol g -1 BSiO2 s -1 and f ret = 150 k dis = 5 nmol g -1 BSiO2 s -1 and f ret = 125

20. WHY? Modelling an aggregate: Diffusion TEP Complex composition Chemical binding Geometry of the aggregate Dachs and Bayona 1998 Decrease of the diffusion of O 2 from the outside to the inside of the aggregate DSi f ret = 150 realistic ?? Brzezinski et al. 1997 f ret = 20-200 Calculation using Ficks Law f ret = 33-600 YES Moriceau et al. in revision

21. BSiO 2 dissolution rate inside an aggregate Dissolution coefficient Solubility of the BSiO 2 Porosity of an aggregate Molecular weight of the BSiO 2 Number of living cells Total number of cells BSiO 2 concentration DSi concentration Modelling an aggregate: decrease of the BSiO 2 dissolution 2- R BSiO2 varies with the DSi concentration inside the aggregate 3- R BSiO2 varies with the DSi concentration inside the aggregate and depends on the viability of the aggregated cells Impact of the high DSi agg and of the high viability of the aggregated cells

22. f viable = 0 variable m = 0.5-2 variable f viable = 0.4 1- DSi concentration inside the aggregate K dis = 6 nmol g -1 BSiO2 s -1 and f ret = 150 2- viability of the cells inside the aggregate K dis = 8-10 nmol g -1 BSiO2 s -1 and f ret = 200-150 Modelling an aggregate: decrease of the BSiO 2 dissolution rate 33-66 % of the decrease of the BSiO 2 dissolution rate is explained by the viability 16-33 % of the decrease of the BSiO 2 dissolution rate is explained by the high DSi concentration inside the aggregate From Moriceau et al. to be submitted a

23. Impact of aggregation on the depth of the BSiO2 recycling? Organic carbon fluxes Dissolution parameters of BSiO 2 + sedimentation rates of the sinking particles Reconstruction of BSiO 2 fluxes Theoritical water column Reconstruction of BSiO 2 fluxes In situ Laboratory experiments Mecanistic model Impact of aggregation on BSiO 2 dissolution? Impact of aggregation on the depth of the BSiO 2 recycling? Role of diatoms in the Biological pump? (Si/C) z = (Si/C) 0 z 0.41 Aggregate Data base sediment trap Ragueneau et al. 2002 Which processes are involved? Validity of the experimental measurements? Return to the LEMAR Olivier RAGUENEAU Validity of the experimental measurements?

24. Impact of the decrease of the BSiO2 dissolution rate in aggregates Aggregates s = 100 m d -1 R = 0.026 d -1 Freely suspended cells s = 1 m d -1 Smayda 1970 R = 0.054 d -1 Measured in this study for FC Aggregates s = 100 m d -1 Alldredge and Gotschalk 1988 R = 0.054 d -1 Measured in this study for FC 25% 50% BSiO 2 flux in the water column: methods Implication for paleoceanography Implication for primary production Aggregates form the majority of the sedimentation flux s Important impact of the decrease of the BSiO2 dissolution rate in aggregates Alldredge and Gotschalk 1988 Measured in this study for aggregate

25. From Turner 2002 Composition of the sedimentation flux BSiO 2 flux in the water column: methods Ragueneau et al., to be submitted 2 groups of particles to reconstruct the BSiO2 fluxes: Large particles (LP) Free cells (FC)

26. Which sites? Our reconstruction implies a known BSiO 2 production BSiO 2 flux in the water column: methods Weight % BSiO 2 in sediments : 8000 data points Annual BSiO 2 and C org fluxes in the water column: 200 data points PAP SACC APFP NACCPOOZ APFA BATS OSP EqPac Reasonable estimates of annual BSiO 2 production : 9 data points SINOPS www.Pangaea.de

27. Moriceau et al., to be submitted b Model output K dis fixed BSiO 2 flux in the water column: results and discussion 18% 700 large particles 82%5free cell % BSiO 2 S m d -1 36% 60 large particles 64% 2 free cell % BSiO 2 S m d -1 41% 700 large particles 59%0.5free cell % BSiO 2 S m d -1 s consistent with the literature K dis can be used in models Repartition can be obtained from the model not from in situ measurements Moriceau et al., to be submitted b PAP SACC APFP NACC POOZAPFA BATS OSP EqPac

28. Moriceau et al., to be submitted Sensibility tests Robustness of the model BSiO 2 flux in the water column: results Moriceau et al., to be submitted PAP SACC APFP NACC POOZAPFA BATS OSP EqPac With the same BSiO2 Production rate Different ratios of BSiO2 preserved in sediments Importance of particle dynamics

29. Sedimentation flux intensity depends on the ability of cells to enter into large particles Recycling or DSi availability depends on the amount of cells that can stay freely suspended Sedimentation flux Particle dynamics winter mixed layer = 200 m maximum amount of BSiO 2 integrated into large particles BSiO 2 flux in the water column: results Moriceau et al., to be submitted b

30. Role of the diatoms in the biological pump? Still in the LEMAR Still working with Olivier RAGUENEAU Organic carbon fluxes Dissolution parameters of BSiO 2 + sedimentation rates of the sinking particles Reconstruction of BSiO 2 fluxes Theoritical water column Reconstruction of BSiO 2 fluxes In situ Laboratory experiments Mecanistic model Impact of aggregation on BSiO 2 dissolution? Impact of aggregation on the depth of the BSiO 2 recycling? Role of diatoms in the Biological pump? (Si/C) z = (Si/C) 0 z 0.41 Aggregate Data base sediment trap Ragueneau et al. 2002 Which processes are involved? Validity of the experimental measurements?

31. Antia et al. (2001) Suess (1980) Betzer et al. (1984) Pace et al. (1987) Berger et al. (1987) Antia et al. (2001) Antia and co-workers, 2001 Different methods used to determine the carbon flux High variability between methods From BSiO 2 fluxes to C fluxes in the water column

32. How to evaluate the ratio of carbon that could reach the maximum depth of the Wind Mixed Layer (WML)? Is it possible to reconstruct the carbon flux from the BSiO 2 fluxes? Actual calculation of carbon fluxes problems YES Ragueneau et al., 2002 (Si/C) z = (Si/C) 0. z 0.41 From BSiO 2 fluxes to C fluxes in the water column

33. ZOOM BSiO 2 fluxes different types of particles Good reconstruction of the C fluxes Reconstruction of the carbon sedimentation fluxes From BSiO 2 fluxes to C fluxes in the water column Ragueneau et al., to be submitted (Si/C) z = (Si/C) 0 z 0.41 Moriceau et al., to be submitted b Ragueneau et al., to be submitted PAP SACC APFP NACC POOZAPFA BATS OSP EqPac

34. Comparison with other methods of calculation Our method: Lower estimation of the carbon flux From BSiO 2 fluxes to C fluxes in the water column Ragueneau et al., to be submitted PAP SACC APFP NACC POOZAPFA BATS OSP EqPac

35. Suess 1980 This study Betzer et al., 1984 Schlitzer et al., 2002 calculated at 133 m e 100m decreases with PP e 100m increases with PP e 100m is constant A trend between e WWML and PP still exists in our study From BSiO 2 fluxes to C fluxes in the water column Ragueneau et al., to be submitted

36. Importance of the seasonality SI = 6 – number of months necessary to reach half of the anual PP Berger and Wefer, 1990 1 2 3 4 5 6 PP months Constant PP SI ~0 Pulsed PP SI ~ 5 Pulsed PP export more than constant PP 50% of annual PP From BSiO 2 fluxes to C fluxes in the water column

37. Export ratio depends on the seasonality index Aggregation is a seasonal process Need to study the sedimentation flux in a seasonal time scale Importance of the seasonality From BSiO 2 fluxes to C fluxes in the water column Ragueneau et al., to be submitted

38. Conclusions et perspectives

39. Organic carbon fluxes Reconstruction of BSiO 2 fluxes Impact of aggregation on BSiO 2 dissolution? Impact of aggregation on the depth of the BSiO 2 recycling? Role of diatoms in the Biological pump? Dissolution parameters of BSiO 2 in the Aggregat e Which processes are involved? Validity of the experimental measurements?

40. Organic carbon fluxes Reconstruction of BSiO 2 fluxes Impact of aggregation on BSiO 2 dissolution? Impact of aggregation on the depth of the BSiO 2 recycling? Role of diatoms in the Biological pump? Dissolution parameters of BSiO 2 in the Aggregat e Which processes are involved? Validity of the experimental measurements? The BSiO 2 dissolution rate is decreased by a factor of 2 for aggregated diatoms The decrease of the DSi diffusion coefficient by a factor of 150 The high viability of aggregated cells The high DSi concentration inside aggregates The low number of bacteria per diatom

41. Organic carbon fluxes Reconstruction of BSiO 2 fluxes aggregation decrease the BSiO 2 dissolution by a factor of 2 Impact of aggregation on the depth of the BSiO 2 recycling? Role of diatoms in the Biological pump? Dissolution of BSiO 2 in the Aggregat e Validity of the experimental measurements? The BSiO 2 dissolution depth depends on the capacity of the cells to aggregate or to stay free Aggregation influences the depth of the BSiO 2 recycling due to aggregate sinking and dissolution rates YES The experimental measurements are accurate and can be used in a global model Importance of particle dynamics

42. Organic carbon fluxes Reconstruction of BSiO 2 fluxes Experimental measurement are accurate Role of diatoms in the Biological Pump? Capacity of diatoms to transport carbon Capacity of diatoms to Protect their carbon aggregation decrease the BSiO 2 dissolution by a factor of 2 Dissolution of BSiO 2 in the Aggregat e Aggregation influences the depth of the BSiO 2 recycling due to the sinking and dissolution rates Importance of the seasonality Post Doc CARBALIS Construction of a semi-mechanistic model Construction of a mechanistic model

43. Post Doc CARBALIS Carbon and Ballasts Interactions during Sinking: an Experimental and Modelling Approach The overall objective of CARBALIS is to improve our understanding of POC and ballasts interactions during sinking throughout the mesopelagic and deep layers of the ocean Experimental phase Modelling phase A 3 years Marie Curie Fellowship Supervised by O. Ragueneau At Stony Brook University (New York) + At the IUEM

44. The role of bacteria in the recycling of BSiO 2 during sedimentation Collaboration with C. Tamburini Coupled experiments: BSiO 2 dissolution + C degradation Collaboration with C. Lee, M. Goutx, U. Passow CARBALIS Construction of a mechanistic model Collaboration with R. Armstrong Use of the mechanistic model in 1D model Collaboration with P. Pondaven, K. Soetaert External carbon – BSiO 2 Internal carbon – BSiO 2 Modelling

45. Thank You!! Olivier Ragueneau Uta Passow Karline Soetaert Madeleine Goutx Catherine Jeandel Marion Laurent Memery Morgane gallinari Michael Sorcha Joëlle Jonathan Pierro Pierre U Matthieu Aude Leynaert Sophie Sabine Gwen Géraldine Eva Marie Tristan Le LEMAR LAWI Gerald Anja (les 2) Ma mère Ma sœur Béatrice Ma famille Loïc Danielle, Alain et Suzanne LIFREMER dArgenton Léquipe de BIOZAIR Christian Tamburini Cathy Léquipe de marseille Philippe Van Cappellen Goulven Laruelle Jim greenwood Léquipe de Si-Web Les microbios et les poissons Monique Bob Raoul Julien Ben Jacques Mathieu Hélène Anne Annick Rudolph Pascal Morin Pierre Lecorre Sandrine Stephane Martial Philippe Christophe Aurore Schumina Michaela Et bien dautres…

46. Diatoms aggregates The dissolution rate of the BSiO 2 is 2 times lower in aggregates The diffusion coefficient of the DSi is decreased by 150 in aggregates Validity of the experimental measurements Conclusion How does aggregation influence the BSiO 2 dissolution?

47. Impact of aggregation on the depth of the BSiO2 recycling? The depth of the BSiO 2 recycling depends on the amount of diatoms that aggregate or stay free In a model: Importance of the particle dynamics Importance of the particle dissolution kinetic In aggregate BSiO 2 dissolution is 2 times lower Optimum wind mixed layer maximum depth for the formation of large particles: 200 m Conclusion

48. Reconstruction of the C fluxes from BSiO2 fluxes Construction of a semi-mechanistic model We are able to evaluate the C flux at each depths We are able to evaluate the export efficiency down to the mixing zone Conclusion

49. C-Si interactions during degradation Intracellular carbon degrades after BSi dissolution?? or with the BSi?? Marker Lipids Extracellular C-BSi interaction: NSF-CNRS collaboration MedFlux Organic coating BSi Internal organic matter Particular lipids DSi Collect during 16hCollect during 48h Madeleine GOUTX Catherine GUIGUE

50. Plan Introduction Etude de la dissolution de la BSiO2 dans les agrégats de diatomées –Expérimentations –Modèle Impact sur les flux de silice Impact sur les flux de carbone Conclusion et Perspectives

51. Recent studies using a consequent data base demonstrated the better efficiency of coccoliths to transport carbon to the deep sea Coccolithophorids are more efficient The carbon attached to diatoms could be more labile Ragueneau et al, 2002

52. TE with EP from Laws TE with EP from Schlitzer CaCO 3 fluxBSiO 2 flux Latitude Coccolithophorids are more efficient Diatoms are more efficient The respective role of diatoms and coccolithophorids in the transfer efficiency depend on how the export production is estimated

53. DSi Shaking DSi + number of cells Aggregates and cell size