Measurements and Models of the Atmospheric Ar/N2 ratio

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Measurements and Models of the Atmospheric Ar/N2
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
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On the agenda

• What makes a good tracer
• Why Ar/N2
• How (and where) we measure Ar/N2
• What we observe
• Comparison with models
• Conclusions and future prospects

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The ideal tracer(one experimentalists
perspective)

• Conservative
• Known sources and sinks, globally distributed
• Seasonally varying over land and ocean
• Measurable with great signal to noise

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Ar/N2 The almost ideal tracer(one
experimentalists perspective)

• Conservative
• Known sources and sinks, globally distributed
• Seasonally varying over land and ocean
• Measurable with great signal to noise

chemically and biologically inert
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Ar/N2 The almost ideal tracer(one
experimentalists 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
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Ar/N2 The almost ideal tracer(one
experimentalists 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
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Ar/N2 The almost ideal tracer(one
experimentalists 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
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The Ar/N2 source/sink
Atmosphere Ar 1 O2 22.5 N2 84
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The Ar/N2 source/sink
Atmosphere Ar 1 O2 22.5 N2 84
Heat Fluxes ? ?Ar/N2
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The Ar/N2 source/sink
Atmosphere Ar 1 O2 22.5 N2 84
Heat Fluxes ? ?Ar/N2
?Ar/N2 ? ?O2/N2 (thermal)
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A quick word on units
Ar/N2 changes are small ?Ar/N2 per meg ?
(Ar/N2sa Ar/N2st)/(Ar/N2st) x106 1 per meg
0.001 per mil
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Our measurement technique

• Paired 2-l glass flasks
• IRMS (Finnigan DeltaXL) 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
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Princeton Ar/N2 cooperative flask sampling network
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Climatology of Ar/N2 seasonal cycle

• Monthly average
• values shown
• Multiple years (3) stacked

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Testing models with observations
Observed modeled heat fluxes ? Solubility
equations ? Atmospheric transport
model ? Predicted Ar/N2
ECMWF or MIT OGCM (NCEP/COADS)
TM2 or GCTM
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Data-Model comparison

• Overall agreement

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Data-Model comparison

• Overall agreement
• Phase problems

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Syowa
Transport matters
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MacQuarie
Heat fluxes matter
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Cape Grim
Transport and heat fluxes matter
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Data-Model comparison

• Overall agreement
• Phase problems
• SYO Transport matters
• MAC Heat fluxes matter
• CGT Both terms matter

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Conclusions and the future

• Ar/N2 a promising new tracer
• General data-model agreement
• Better observations to come
• Need Ar/N2 as active tracer in OGCMs
• Ready for Ar/N2 in more atmospheric models

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Odds and Ends

• Interannual variability in the seasonal cycle
  (perhaps primarily atmospheric)
• Secular trend Tiny (0.2 per meg/yr)
• Size of O2/N2 thermal cycle 13-34 of total
• Intersite gradients A problem

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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 (?)

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Correlated variability in Ar/N2 and O2/N2
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Improving collection protocols
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SST relaxation term in MIT OGCM