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Battle, M, Fletcher SEM, Bender ML, Keeling RF, Manning AC, Gruber N, Tans PP, Hendricks MB, Ho DT, Simonds C, Mika R, Paplawsky B.  2006.  Atmospheric potential oxygen: New observations and their implications for some atmospheric and oceanic models. Global Biogeochemical Cycles. 20   10.1029/2005gb002534   AbstractWebsite

[ 1] Measurements of atmospheric O(2)/N(2) ratios and CO(2) concentrations can be combined into a tracer known as atmospheric potential oxygen (APO approximate to O(2)/N(2) + CO(2)) that is conservative with respect to terrestrial biological activity. Consequently, APO reflects primarily ocean biogeochemistry and atmospheric circulation. Building on the work of Stephens et al. ( 1998), we present a set of APO observations for the years 1996 - 2003 with unprecedented spatial coverage. Combining data from the Princeton and Scripps air sampling programs, the data set includes new observations collected from ships in the low-latitude Pacific. The data show a smaller interhemispheric APO gradient than was observed in past studies, and different structure within the hemispheres. These differences appear to be due primarily to real changes in the APO field over time. The data also show a significant maximum in APO near the equator. Following the approach of Gruber et al. ( 2001), we compare these observations with predictions of APO generated from ocean O(2) and CO(2) flux fields and forward models of atmospheric transport. Our model predictions differ from those of earlier modeling studies, reflecting primarily the choice of atmospheric transport model (TM3 in this study). The model predictions show generally good agreement with the observations, matching the size of the interhemispheric gradient, the approximate amplitude and extent of the equatorial maximum, and the amplitude and phasing of the seasonal APO cycle at most stations. Room for improvement remains. The agreement in the interhemispheric gradient appears to be coincidental; over the last decade, the true APO gradient has evolved to a value that is consistent with our time-independent model. In addition, the equatorial maximum is somewhat more pronounced in the data than the model. This may be due to overly vigorous model transport, or insufficient spatial resolution in the air-sea fluxes used in our modeling effort. Finally, the seasonal cycles predicted by the model of atmospheric transport show evidence of an excessive seasonal rectifier in the Aleutian Islands and smaller problems elsewhere.

Battle, M, Bender M, Hendricks MB, Ho DT, Mika R, McKinley G, Fan SM, Blaine T, Keeling RF.  2003.  Measurements and models of the atmospheric Ar/N2 ratio. Geophysical Research Letters. 30   10.1029/2003gl017411   AbstractWebsite

[1] The Ar/N-2 ratio of air measured at 6 globally distributed sites shows annual cycles with amplitudes of 12 to 37 parts in 10(6). Summertime maxima reflect the atmospheric Ar enrichment driven by seasonal warming and degassing of the oceans. Paired models of air-sea heat fluxes and atmospheric tracer transport predict seasonal cycles in the Ar/N-2 ratio that agree with observations, within uncertainties.

Bender, ML, Battle M, Keeling RF.  1998.  The O2 balance of the atmosphere: A tool for studying the fate of fossil-fuel CO2. Annual Review of Energy and the Environment. 23:207-223.   10.1146/   AbstractWebsite

Carbon dioxide is a radiatively active gas whose atmospheric concentration increase is likely to affect Earth's climate. CO2 is added to the atmosphere by biomass burning and the combustion of fossil fuels. Some added CO2 remains in the atmosphere. However, substantial amounts are taken up by the oceans and land biosphere, attenuating the atmospheric increase. Atmospheric O-2 measurements provide one constraint for partitioning uptake rates between the ocean and the land biosphere. Here we review studies of atmospheric O-2 concentration variations and discuss their implications for CO2 uptake by the ocean and the land biosphere. We compare estimates of anthropogenic carbon fluxes from O-2 studies with estimates from other approaches and examine the contribution of natural ocean carbon fluxes to atmospheric O-2 variations.

Betts, RA, Jones CD, Knight JR, Keeling RF, Kennedy JJ, Wiltshire AJ, Andrew RM, Aragao L.  2018.  A successful prediction of the record CO2 rise associated with the 2015/2016 El Nino. Philosophical Transactions of the Royal Society B-Biological Sciences. 373   10.1098/rstb.2017.0301   AbstractWebsite

In early 2016, we predicted that the annual rise in carbon dioxide concentration at Mauna Loa would be the largest on record. Our forecast used a statistical relationship between observed and forecast sea surface temperatures in the Nino 3.4 region and the annual CO2 rise. Here, we provide a formal verification of that forecast. The observed rise of 3.4 ppm relative to 2015 was within the forecast range of 3.15 +/- 0.53 ppm, so the prediction was successful. A global terrestrial biosphere model supports the expectation that the El Nino weakened the tropical land carbon sink. We estimate that the El Nino contributed approximately 25% to the record rise in CO2, with 75% due to anthropogenic emissions. The 2015/2016 CO2 rise was greater than that following the previous large El Nino in 1997/1998, because anthropogenic emissions had increased. We had also correctly predicted that 2016 would be the first year with monthly mean CO2 above 400 ppm all year round. We now estimate that atmospheric CO2 at Mauna Loa would have remained above 400 ppm all year round in 2016 even if the El Nino had not occurred, contrary to our previous expectations based on a simple extrapolation of previous trends. This article is part of a discussion meeting issue 'The impact of the 2015/2016 El Nino on the terrestrial tropical carbon cycle: patterns, mechanisms and implications'.

Blaine, TW, Keeling RF, Paplawsky WJ.  2006.  An improved inlet for precisely measuring the atmospheric Ar/N2 ratio. Atmospheric Chemistry and Physics. 6:1181-1184. AbstractWebsite

The atmospheric Ar/N-2 ratio is expected to be useful as a tracer of air-sea heat exchange, but this application has been hindered in part due to sampling artifacts. Here we show that the variability in delta(Ar/N-2) due to thermal fractionation at the inlet can be on the order of 40 - 80 per meg, and we introduce the use of an aspirated solar shield that successfully minimizes such fractionation. The data collected using this new inlet have a mean diurnal cycle of 1.0 per meg or less, suggesting that any residual thermal fractionation effect is reduced to this level.