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

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

Transfer of bomb 14 C from atmosphere to ocean and biosphere

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

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

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

0°60°N30°N90°N30°S60°S90°S 9km 15km 21km 30km 0km ATMOSPHERE BIOSPHERE LeavesTwigsWood Soil OCEAN Fossil fuel & cement production CO 2 Land use change CO 2 natural 14 Cbomb 14 C 14 C from nuclear industry Setup of the GRACE model

Global bomb radiocarbon budget

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

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

Observation-based bomb 14 C inventories

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

re-evaluation of the bomb 14 C constraints on air sea gas exchange necessary  see poster FF249 by Naegler, Ciais, Rodgers & Levin 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

The End. Thank you.

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

Bomb 14 C production radiocarbon yield: RCU/Mt TNT cumulative explosive force: Mt TNT (1 RCU = 1 RadioCarbon Unit = atoms 14 C) Cumulative explosive force (Mt TNT)

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

Tropospheric 14 CO 2 observations in the 1960s data from Nydal & Lövseth, Manning et al., Levin et al. etc...

Airborne observations of bomb 14 CO 2 from Telegadas, Hagemann

Stratospheric 14 CO 2 concentrations Comparison model - observations

 14 C in the troposphere Comparison model - observations

Ocean bomb radiocarbon inventory estimates publicationMethodGEOSECS (1975) in RCU WOCE (1995) in RCU Broecker et al. 1980tritium314±30 Broecker et al. 1985tritium289 Lassey et al tritium,  14 C 303 Broecker et al. 1994not specified350 (~300) Hesshaimer et al. 1994box model225 (for 1974) Broecker et al. 1995silicate, tritium305±30 Lassey et al. 1996box model Jain et al. 1997upwelling-diffusion ocean327±33 Sweeney et al. 2004ocean inversion Peacock 2004corrected silicate264± ±15 1 Peacock 2004multitracer correlation245±60 1 Key et al. 2004potential alkalinity345± corrected for missing ocean areas, Naegler 2005

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

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

biospheric pool immediate mixing  14 C Pool Well-mixed Biosphere Model NPP:  14 C Atm RES:  14 C Pool atmosphere:  14 C Atm immediate response

Lagged-Response Biosphere Model NPP:  14 C Atm RES:  14 C Dead atmosphere:  14 C Atm lagged response living biomass  14 C Living dead biomass  14 C Dead dying biomass:  14 C Living

Observed zonal profiles of ocean surface  14 C data from Broecker et al., Key et al., Levin & Hesshaimer

Ocean surface  14 C zonal profile

Modelled SF 6 : Comparison with data

Modelled SF 6 seasonality: Comparison with data

Stratospheric data biased?