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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.

K
Keeling, RF, Manning AC, Paplawsky WJ, Cox AC.  2007.  On the long-term stability of reference gases for atmospheric O2/N2 and CO2 measurements. Tellus Series B-Chemical and Physical Meteorology. 59:3-14.   10.1111/j.1600-0889.2006.00228.x   AbstractWebsite

Measurements of changes in the atmospheric O-2/N-2 ratio have typically relied on compressed air derived from high-pressure tanks as the reference material against which atmospheric changes are assessed. The validity of this procedure is examined here in the context of the history of 18 O-2/N-2 reference tanks compared over a 12-yr time-frame. By considering differences in tank sizes, material types, and by performing additional tests, the long-term stability of the delivered gas is evaluated with respect to surface reactions, leakage, regulator effects, and thermal diffusion and gravimetric fractionation. Results are also reported for the stability of CO2 in these tanks. The results emphasize the importance of orienting tanks horizontally within a thermally insulated enclosure to reduce thermal and gravimetric fractionation of both O-2/N-2 and CO2 concentrations, and they emphasize the importance of avoiding elastomeric O-rings at the head-valve base. With the procedures documented here, the long-term drift in O-2/N-2 appears to be zero to within approximately +/- 0.4 per meg yr(-1), which projects to an uncertainty of +/- 0.16 Pg C yr(-1) (1 sigma) in O-2-based global carbon budgets.

M
Manning, AC, Keeling RF.  2006.  Global oceanic and land biotic carbon sinks from the Scripps atmospheric oxygen flask sampling network. Tellus Series B-Chemical and Physical Meteorology. 58:95-116.   10.1111/j.1600-0889.2006.00175.x   AbstractWebsite

Measurements of atmospheric O-2/N-2 ratio and CO2 concentration are presented over the period 1989-2003 from the Scripps Institution of Oceanography global flask sampling network. A formal framework is described for making optimal use of these data to estimate global oceanic and land biotic carbon sinks. For the 10-yr period from 1990 to 2000, the oceanic and land biotic sinks are estimated to be 1.9 +/- 0.6 and 1.2 +/- 0.8 Pg C yr(-1), respectively, while for the 10-yr period from 1993 to 2003, the sinks are estimated to be 2.2 +/- 0.6 and 0.5 +/- 0.7 Pg C yr(-1), respectively. These estimates, which are also compared with earlier results, make allowance for oceanic O-2 and N-2 outgassing based on observed changes in ocean heat content and estimates of the relative outgassing per unit warming. For example, for the 1993-2003 period we estimate outgassing of 0.45 x 10(14) mol O-2 yr(-1) and 0.20 x 10(14) mol N-2 yr(-1), which results in a correction of 0.5 Pg C yr(-1) on the oceanic and land biotic carbon sinks. The basis for this oceanic outgassing correction is reviewed in the context of recent model estimates. The main contributions to the uncertainty in the global sinks averages are from the estimates for oceanic outgassing and the estimates for fossil fuel combustion. The oceanic sink of 2.2 Pg C yr(-1) for 1993-2003 is consistent, within the uncertainties, with the integrated accumulation of anthropogenic CO2 in the ocean since 1800 as recently estimated from oceanic observations, assuming the oceanic sink varied over time as predicted by a box-diffusion model.

Manning, AC, Keeling RF, Severinghaus JP.  1999.  Precise atmospheric oxygen measurements with a paramagnetic oxygen analyzer. Global Biogeochemical Cycles. 13:1107-1115.   10.1029/1999gb900054   AbstractWebsite

A methodology has been developed for making continuous, high-precision measurements of atmospheric oxygen concentrations by modifying a commercially available paramagnetic oxygen analyzer. Incorporating several design improvements, an effective precision of 0.2 ppm O-2 from repeated measurements over a 1-hour interval was achieved. This is sufficient to detect background changes in atmospheric O-2 to a level that constrains various aspects of the global carbon cycle. The analyzer was used to measure atmospheric O-2 in a semicontinuous fashion from air sampled from the end of Scripps Pier, La Jolla, California, and data from a 1-week period in August 1996 are shown. The data exhibit strongly anticorrelated changes in O-2 and CO2 caused by local or regional combustion of fossil fuels. During periods of steady background CO2 concentrations, however, we see additional variability in O-2 concentrations, clearly not due to local combustion and presumably due to oceanic sources or sinks of O-2. This variability suggests that in contrast to CO2, higher O-2 sampling rates, such as those provided by continuous measurement programs, may be necessary to define an atmospheric O-2 background and thus aid in validating and interpreting other O-2 data from flask sampling programs. Our results have also demonstrated that this paramagnetic analyzer and gas handling design is well suited for making continuous measurements of atmospheric O-2 and is suitable for placement at remote background air monitoring sites.

S
Stephens, BB, Keeling RF, Paplawsky WJ.  2003.  Shipboard measurements of atmospheric oxygen using a vacuum-ultraviolet absorption technique. Tellus Series B-Chemical and Physical Meteorology. 55:857-878.   10.1046/j.1435-6935.2003.00075.x   AbstractWebsite

We have developed an instrument for making continuous, field-based, part-per-million (ppm) level measurements of atmospheric oxygen concentration, and have implemented it on research cruises in the equatorial Pacific and Southern Oceans. The instrument detects changes in oxygen by the absorption of vacuum ultraviolet (VUV) radiation as it passes through a flowing gas stream, and has a precision comparable to existing laboratory techniques. Here we describe the VUV instrument and present atmospheric O-2 and CO2 data collected from the NOAA ship Ka' imimoana in the equatorial Pacific during April and May of 1998, and from the NSF ship Lawrence M. Gould in the Southern Ocean during October 1998. These data represent the first field-based measurements of atmospheric O-2, and significant additions to the O-2 datasets in these regions. Our boreal-springtime equatorial measurements reveal significant short-term variations in atmospheric O-2, resulting from variations in atmospheric mixing relative to the strong interhemispheric gradient. Our austral-springtime Southern Ocean observations confirm the low O-2 concentrations seen in flask samples from this region, allow the separate identification of oceanic and industrial influences on CO2, and provide evidence of a Southern Ocean source for CO2 at this time of year. These shipboard VUV observations do not provide any evidence to support coupled ocean-atmosphere model predictions of a large decreasing atmospheric O-2 gradient between equatorial and high-southern latitudes.