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Closing the Global Bomb Radiocarbon Budget

This study focuses on simulating the global bomb 14C budget, addressing difficulties faced in the past and new developments since 2000. It explores the estimation of a biospheric bomb 14C inventory based on atmospheric and oceanic observations.

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Closing the Global Bomb Radiocarbon Budget

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  1. Closing the Global Bomb Radiocarbon Budget Tobias Naegler1,2, Vago Hesshaimer1, and Ingeborg Levin1 1Institut für Umweltphysik, Universität Heidelberg, Germany 2Laboratoire des Sciences du Climat et de l‘Environnement, Gif-Sur-Yvette, France

  2. The global bomb 14C cycle Stratosphere nuclear bombs nuclear bombs stratosphere-troposphere exchange (STE) Troposphere air-sea gas exchange carbon exchange biosphere-atmosphere Ocean Biosphere

  3. Transfer of bomb 14C from atmosphere to ocean and biosphere

  4. Transfer of bomb 14C from atmosphere to ocean and biosphere

  5. Transfer of bomb 14C from atmosphere to ocean and biosphere

  6. Transfer of bomb 14C from atmosphere to ocean and biosphere

  7. Transfer of bomb 14C from atmosphere to ocean and biosphere

  8. Why simulating the bomb 14C budget? • test of carbon cycle models • consistency check of observation-based bomb 14C inventory estimates

  9. Closing the global bomb 14C budget: difficulties to face (until ~2000) • bomb 14C production: large uncertainties • atmospheric models: not calibrated, • low resolution • observed bomb 14C inventories: • stratosphere (1955-1970) biased? • ocean (GEOSECS in 1970s) large spread • biosphere not available

  10. New developments since 2000: • new extensive bomb test compilation • (Yang 2000) • re-evaluation of stratospheric 14C observations • (Hesshaimer & Levin 2000, Naegler 2005) •  no or only small bias in stratospheric 14C observations • new ocean bomb 14C inventory estimates (GEOSECS, WOCE) • (Peacock 2004, Key et al. 2004) • Global RAdioCarbon Exploration Model (GRACE): data calibrated stratosphere-troposphere box model (Hesshaimer 1997, Naegler 2005)  Re-evaluation of the global bomb 14C budget now possible

  11. 30km ATMOSPHERE 21km 15km 9km 0km 90°S 60°S 30°S 0° 30°N 60°N 90°N BIOSPHERE OCEAN Leaves Twigs Wood Soil Setup of the GRACE model bomb 14C 14C from nuclear industry natural 14C Land use change CO2 Fossil fuel & cement production CO2

  12. Global bomb radiocarbon budget

  13. Question: Is it possible to estimate a biospheric bomb 14C inventory based on atmospheric and oceanic observations?

  14. YES! Basic assumptions: • bomb 14C production is known from GRACE • ocean bomb 14C inventories correct for 1975 and 1995 • shape of ocean bomb 14C inventory in GRACE is realistic  history of ocean bomb 14C inventory given by simulated shape and observed GEOSECS and WOCE inventories

  15. Observation-based bomb 14C inventories

  16. Conclusions I: • GRACE simulates bomb 14C inventories in good agreement with all available bomb 14C observations •  bomb radiocarbon budget closed • indirect, but data-based estimate of the biospheric bomb 14C inventory •  constraints for setup & parameterisation of biosphere models

  17. Conclusions II • ocean inventory estimates from Peacock (2004) and Key et al. (2004) confirmed • ocean inventory estimate from Broecker et al. (1985)/Wanninkhof (1992) is too high • re-evaluation of the bomb 14C constraints on air sea gas exchange necessary • see poster FF249 by Naegler, Ciais, Rodgers & Levin

  18. The End. Thank you.

  19. Bomb 14C observations in the different carbon reservoirs  information on carbon transfer rates between the reservoirs • stratosphere-troposphere exchange • air-sea gas exchange • biospheric turnover times

  20. Cumulative explosive force (Mt TNT) Bomb 14C production • cumulative explosive force: 350-600 Mt TNT • radiocarbon yield: 0.5 - 2.0 RCU/Mt TNT (1 RCU = 1 RadioCarbon Unit = 1026 atoms 14C)

  21. Calibration of the bomb 14C yield cumulated bomb radiocarbon production = cumulated explosive force · yield = observed stratospheric inventory + observed tropospheric inventory + observed ocean inventory + observed biospheric inventory observed stratospheric inventory + observed tropospheric inventory + modelledocean inventory + modelledbiospheric inventory

  22. Tropospheric 14CO2 observations in the 1960s data from Nydal & Lövseth, Manning et al., Levin et al. etc...

  23. Airborne observations of bomb 14CO2 from Telegadas, Hagemann

  24. Stratospheric 14CO2 concentrations Comparison model - observations

  25. D14C in the troposphere Comparison model - observations

  26. Ocean bomb radiocarbon inventory estimates 1 corrected for missing ocean areas, Naegler 2005

  27. Global bomb radiocarbon budget II bomb test compilation: Rath, biosphere: well-mixed

  28. Global bomb radiocarbon budget III bomb test compilation: Yang, biosphere: lagged-response

  29. NPP: D14CAtm RES: D14CPool Well-mixed Biosphere Model atmosphere: D14CAtm immediate response biospheric pool immediate mixing D14CPool

  30. NPP: D14CAtm RES: D14CDead dying biomass: D14CLiving Lagged-Response Biosphere Model atmosphere: D14CAtm lagged response living biomass D14CLiving dead biomass D14CDead

  31. Observed zonal profiles of ocean surface D14C data from Broecker et al., Key et al., Levin & Hesshaimer

  32. Ocean surface D14C zonal profile

  33. Modelled SF6: Comparison with data

  34. Modelled SF6 seasonality: Comparison with data

  35. Stratospheric data biased?

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