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 GCRPFord Res. Labs

NDSEGFP

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

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

Ar/N2: 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

Ar/N2: 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

Ar/N2: 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

Ar/N2: 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…

The Ar/N2 source/sink

Atmosphere

Ar: 1O2: 22.5N2: 84

The Ar/N2 source/sink

Atmosphere

Ar: 1O2: 22.5N2: 84

Heat Fluxes

Ar/N2

The Ar/N2 source/sink

Atmosphere

Ar: 1O2: 22.5N2: 84

Heat Fluxes

Ar/N2

Ar/N2

O2/N2

(thermal)

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

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

Princeton Ar/N2 cooperative flask sampling network

Climatology ofAr/N2 seasonal

cycle

Monthly average

values shown

Multiple years (~3) stacked

Testing models with observations

Observed & modeled heat fluxes

Solubility equations

Atmospheric transport

model

Predicted Ar/N2

ECMWFor

MIT OGCM (NCEP/COADS)

TM2or

GCTM

Data-Model comparison

•Overall agreement

Data-Model comparison

•Overall agreement

•Phase problems

Syowa

Transportmatters

MacQuarie

Heat fluxesmatter

Cape Grim

Transportand

heat fluxesmatter

Data-Model comparison

•Overall agreement

•Phase problems

•SYO: Transport matters

•MAC: Heat fluxes matter

•CGT: Both terms matter

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

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

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 (?)

Correlated variability in Ar/N2 and O2/N2

Improving collection protocols

SST relaxation term in MIT OGCM