1. Measurements and Models of the Atmospheric Ar/N 2 ratio Mark Battle (Bowdoin College) Michael Bender (Princeton) Melissa B. Hendricks (Princeton) David T. Ho (Princeton/ Columbia) Robert Mika (Princeton) Galen McKinley (MIT/INE Mexico) Song-Miao Fan (Princeton) Tegan Blaine (Scripps) Ralph Keeling (Scripps) 2002 Fall AGU 12/09/02 Funding from: NSF NOAA GCRP Ford Res. Labs NDSEGFP

2. On the agenda: What makes a good tracer Why Ar/N 2 How (and where) we measure Ar/N 2 What we observe Comparison with models Conclusions and future prospects

3. The ideal tracer (one experimentalist’s perspective) Conservative Known sources and sinks, globally distributed Seasonally varying over land and ocean Measurable with great signal to noise

4. Ar/N 2 : The almost ideal tracer (one experimentalist’s perspective) Conservative Known sources and sinks, globally distributed Seasonally varying over land and ocean Measurable with great signal to noise chemically and biologically inert

5. Ar/N 2 : The almost ideal tracer (one experimentalist’s perspective) Conservative Known sources and sinks, globally distributed Seasonally varying over land and ocean Measurable with great signal to noise chemically and biologically inert oceanic sources driven by heat fluxes

6. Ar/N 2 : The almost ideal tracer (one experimentalist’s perspective) Conservative Known sources and sinks, globally distributed Seasonally varying over land and ocean Measurable with great signal to noise chemically and biologically inert oceanic sources driven by heat fluxes seasonal, but ocean only

7. Ar/N 2 : The almost ideal tracer (one experimentalist’s perspective) Conservative Known sources and sinks, globally distributed Seasonally varying over land and ocean Measurable with great signal to noise chemically and biologically inert oceanic sources driven by heat fluxes seasonal, but ocean only well, maybe not great…

8. The Ar/N 2 source/sink Atmosphere Ar: 1 O 2 : 22.5 N 2 : 84

9. The Ar/N 2 source/sink Atmosphere Ar: 1 O 2 : 22.5 N 2 : 84 Heat Fluxes   Ar/N 2

10. The Ar/N 2 source/sink Atmosphere Ar: 1 O 2 : 22.5 N 2 : 84 Heat Fluxes   Ar/N 2   O 2 /N 2 (thermal)

11. A quick word on units: Ar/N 2 changes are small  Ar/N 2 per meg  (Ar/N 2sa – Ar/N 2st )/(Ar/N 2st ) x10 6 1 per meg = 0.001 per mil

12. Our measurement technique: Paired 2-l glass flasks IRMS (Finnigan Delta+XL) 40/28 and 32/28 Custom dual-inlet system Standards: High pressure Al cylinder For more details: Sunday afternoon poster Ho et al. GC72B-0230

13. Princeton Ar/N 2 cooperative flask sampling network

14. Climatology of Ar/N 2 seasonal cycle Monthly average values shown Multiple years (~3) stacked

15. Testing models with observations Observed & modeled heat fluxes  Solubility equations  Atmospheric transport model  Predicted Ar/N 2 ECMWF or MIT OGCM (NCEP/COADS) TM2 or GCTM

16. Data-Model comparison Overall agreement

17. Data-Model comparison Overall agreement Phase problems

18. Syowa Transport matters

19. MacQuarie Heat fluxes matter

20. Cape Grim Transport and heat fluxes matter

21. Data-Model comparison Overall agreement Phase problems SYO: Transport matters MAC: Heat fluxes matter CGT: Both terms matter

22. Conclusions and the future… Ar/N 2 a promising “new” tracer General data-model agreement Better observations to come Need Ar/N 2 as active tracer in OGCMs Ready for Ar/N 2 in more atmospheric models

23. Odds and Ends Interannual variability in the seasonal cycle (perhaps primarily atmospheric) Secular trend: Tiny (~0.2 per meg/yr) Size of O 2 /N 2 thermal cycle: 13-34% of total Intersite gradients: A problem

24. Uncertainties All fitting techniques equivalent Std error on monthly avg. shown in plots Std error reflects: –Limited IRMS precision (  4.0) –Fractionation during transfer from flask to IRMS (  8.6) –Uncorrelated fractionation of flasks during collection (  2.6) –Correlated fractionation of flasks during collection (?) –Real variability within month (?)

25. Correlated variability in Ar/N 2 and O 2 /N 2

26. Improving collection protocols

27. SST relaxation term in MIT OGCM