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Severinghaus, JP, Bender ML, Keeling RF, Broecker WS.  1996.  Fractionation of soil gases by diffusion of water vapor, gravitational settling, and thermal diffusion. Geochimica Et Cosmochimica Acta. 60:1005-1018.   10.1016/0016-7037(96)00011-7   AbstractWebsite

Air sampled from the moist unsaturated zone in a sand dune exhibits depletion in the heavy isotopes of N-2 and O-2. We propose that the depletion is caused by a diffusive flux of water vapor out of the dune, which sweeps out the other gases, forcing them to diffuse back into the dune. The heavy isotopes of N-2 and O-2 diffuse back more slowly, resulting in a steady-state depletion of the heavy isotopes in the dune interior. We predict the effect's magnitude with molecular diffusion theory and reproduce it in a laboratory simulation, finding good agreement between field, theory, and lab. The magnitude of the effect is governed by the ratio of the binary diffusivities against water vapor of a pair of gases, and increases similar to linearly with the difference between the water vapor mole fraction of the site and the advectively mixed reservoir with which it is in diffusive contact (in most cases the atmosphere). The steady-state effect is given by delta(i) = [i/j/i(0)/j(0) - 1] 10(3) parts per thousand congruent to [(1 - x(H2O)/1 - x(H2O0))((Dj-H2O/Di-H2O)-1) -1] 10(3) parts per thousand, where delta(i) is the fractional deviation in permil of the gas i/gas j ratio from the advectively mixed reservoir, x(H2O) and x(H2O0) are respectively the mole fractions of water vapor at the site and in the advectively mixed reservoir, and D-i-H2O is the binary diffusion coefficient of gas i with water vapor. The effect is independent of scale at steady state, but approaches steady state with the time constant of diffusion set by the length scale. Exploiting the mechanism, we make an experimental estimate of the relative diffusivities of O-2 and N-2 against water vapor, finding that O-2 diffuses 3.6 +/- 0.3% faster than N-2 despite its greater mass. We also confirm in the study dune the presence of two additional known processes: gravitational fractionation, heretofore seen only in the unconsolidated firn of polar ice sheets, and thermal diffusion, well described in laboratory studies but not seen previously in nature. We predict that soil gases in general will exhibit the three effects described here, the water vapor flux fractionation effect, gravitational fractionation, and thermal diffusion. However, our analysis neglects Knudsen diffusion and thus may be inapplicable to fine-grained soils.

Severinghaus, JP, Keeling RF, Miller BR, Weiss RF, Deck B, Broecker WS.  1997.  Feasibility of using sand dunes as archives of old air. Journal of Geophysical Research-Atmospheres. 102:16783-16792.   10.1029/97jd00525   AbstractWebsite

Large unaltered samples of the atmosphere covering the past century would complement the history of atmospheric gases obtained from bubbles in ice cores, enabling measurement of geochemically important species such as O-2, (CH4)-C-14, and (CO)-C-14. Sand dunes are a porous media with interstitial air in diffusive contact with the atmosphere, somewhat analogous to the unconsolidated layer of firn atop glaciers. Recent studies have demonstrated the value of firn as an archive of old air [Battle et al., 1996; Bender et al., 1994a]. Unlike firn, sand dunes are incompressible and so remain permeable to greater depths and may extend the firn record into the past century. To evaluate the feasibility of using sand dunes as archives of old air, we drilled 60 m deep test holes in the Algodones Dunes, Imperial Valley, California. The main objective was to see if the air in a sand dune is as old as predicted by a diffusion model, or if the dune is rapidly flushed by advective pumping during windstorms and barometric pressure changes. We dated the air with chlorofluorocarbons and krypton-85, anthropogenic tracers whose atmospheric concentrations are known and have been increasing rapidly in the past half century. These tracer data match the pure diffusion model well, showing that advection in this dune is negligible compared to diffusion as a transport mechanism and that the mean age of the air at 61 m depth is similar to 10 years. Dunes therefore do contain old air. However, dunes appear to suffer from two serious drawbacks as archives. Microbial metabolism is evident in elevated CO2 and N2O and depressed CH4 and O-2 concentrations in this dune, corrupting the signals of interest in this and probably most dunes. Second, isotopic analyses of N-2 and O-2 from the dune show that fractionation of the gases occurs due to diffusion of water vapor, complicating the interpretation of the O-2 signal beyond the point of viability for an air archive. Sand dunes may be useful for relatively inert gases with large atmospheric concentration changes such as chlorofluorocarbons.

Staudigel, H, Albarede F, Blichert-Toft J, Edmond J, McDonough B, Jacobsen SB, Keeling R, Langmuir CH, Nielsen RL, Plank T, Rudnick R, Shaw HF, Shirey S, Veizer J, White W.  1998.  Geochemical Earth Reference Model (GERM): description of the initiative. Chemical Geology. 145:153-159.   10.1016/S0009-2541(97)00141-1   Abstract

The Geochemical Earth Reference Model (GERM) initiative is a grass root effort with the goals of establishing a community consensus on a chemical characterization of the Earth, its major reservoirs, and the flu?;es between them. The GERM initiative will provide a review of available scientific constraints for: (1) the composition of all major chemical reservoirs of the present-day Earth, from core to atmosphere; (2) present-day fluxes between reservoirs; (3) the Earth's chemical and isotopic evolution since accretion; and (4) the chemical and isotopic evolution of seawater as a record of global tectonics and climate, Even though most of the constraints for the GERM will be drawn from chemical data sets, some data will have to come from other disciplines, such as geophysics, nuclear physics, and cosmochemistry. GERM also includes a diverse chemical and physical data base and computer codes that are useful for our understanding of how the Earth works as a dynamic chemical and physical system. The GERM initiative is developed in an open community discussion on the World Wide Web ( that is moderated by editors with responsibilities for different reservoirs, fluxes, data bases, and other scientific or technical aspects. These editors have agreed to lay out an initial, strawman GERM for their respective sections and to moderate community discussions leading to a first, preliminary consensus. The development of the GERM began with an initial workshop in Lyon, France in March, 1996. Since then, the GERM has continued to be developed on the Internet, punctuated by workshops and special sessions at professional meetings. A second GERM workshop will be held in La Jolla, CA USA on March 10-13, 1998. (C) 1998 Elsevier Science B.V. All nights reserved.

Stephens, BB, Long MC, Keeling RF, Kort EA, Sweeney C, Apel EC, Atlas EL, Beaton S, Bent JD, Blake NJ, Bresch JF, Casey J, Daube BC, Diao MH, Diaz E, Dierssen H, Donets V, Gao BC, Gierach M, Green R, Haag J, Hayman M, Hills AJ, Hoecker-Martinez MS, Honomichl SB, Hornbrook RS, Jensen JB, Li RR, McCubbin I, McKain K, Morgan EJ, Nolte S, Powers JG, Rainwater B, Randolph K, Reeves M, Schauffler SM, Smith K, Smith M, Stith J, Stossmeister G, Toohey DW, Watt AS.  2018.  The O-2/N-2 Ratio and CO2 Airborne Southern Ocean Study. Bulletin of the American Meteorological Society. 99:381-402.   10.1175/bams-d-16-0206.1   AbstractWebsite

The Southern Ocean plays a critical role in the global climate system by mediating atmosphere-ocean partitioning of heat and carbon dioxide. However, Earth system models are demonstrably deficient in the Southern Ocean, leading to large uncertainties in future air-sea CO2 flux projections under climate warming and incomplete interpretations of natural variability on interannual to geologic time scales. Here, we describe a recent aircraft observational campaign, the O-2/N-2 Ratio and CO2 Airborne Southern Ocean (ORCAS) study, which collected measurements over the Southern Ocean during January and February 2016. The primary research objective of the ORCAS campaign was to improve observational constraints on the seasonal exchange of atmospheric carbon dioxide and oxygen with the Southern Ocean. The campaign also included measurements of anthropogenic and marine biogenic reactive gases; high-resolution, hyperspectral ocean color imaging of the ocean surface; and microphysical data relevant for understanding and modeling cloud processes. In each of these components of the ORCAS project, the campaign has significantly expanded the amount of observational data available for this remote region. Ongoing research based on these observations will contribute to advancing our understanding of this climatically important system across a range of topics including carbon cycling, atmospheric chemistry and transport, and cloud physics. This article presents an overview of the scientific and methodological aspects of the ORCAS project and highlights early findings.

Stephens, BB, Wofsy SC, Keeling RF, Tans PP.  2000.  The CO2 budget and rectification airborne study. Inverse methods in global biogeochemical cycles. ( Kasibhatla P, Ed.).:311-324., Washington, DC: American Geophysical Union Abstract

The CD-ROM contains the code and data files for the Exercises outlined in the paper by Rayner, et at., (p. 81-106).

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.

Stephens, BB, Keeling RF, Heimann M, Six KD, Murnane R, Caldeira K.  1998.  Testing global ocean carbon cycle models using measurements of atmospheric O2 and CO2 concentration. Global Biogeochemical Cycles. 12:213-230.   10.1029/97gb03500   AbstractWebsite

We present a method for testing the performance of global ocean carbon cycle models using measurements of atmospheric O-2 and CO2 concentration. We combine these measurements to define a tracer, atmospheric potential oxygen (APO approximate to O-2 + CO2), which is conservative with respect to terrestrial photosynthesis and respiration. We then compare observations of APO to the simulations of an atmospheric transport model which uses ocean-model air-sea fluxes and fossil fuel combustion estimates as lower boundary conditions. We present observations of the annual-average concentrations of CO2, O-2, and APO at 10 stations in a north-south transect. The observations of APO show a significant interhemispheric gradient decreasing towards the north. We use air-sea CO2, O-2, and N-2 fluxes from the Princeton ocean biogeochemistry model, the Hamburg model of the ocean carbon cycle, and the Lawrence Livermore ocean biogeochemistry model to drive the TM2 atmospheric transport model. The latitudinal variations in annual-average APO predicted by the combined models are distinctly different from the observations. All three models significantly underestimate the interhemispheric difference in APO, suggesting that they underestimate the net southward transport of the sum of O-2 and CO2 in the oceans. Uncertainties in the model-observation comparisons include uncertainties associated with the atmospheric measurements, the atmospheric transport model, and the physical and biological components of the ocean models. Potential deficiencies in the physical components of the ocean models, which have previously been suggested as causes for anomalously large heat fluxes out of the Southern Ocean, may contribute to the discrepancies with the APO observations. These deficiencies include the inadequate parameterization of subgrid-scale isopycnal eddy mixing, a lack of subgrid-scale vertical convection, too much Antarctic sea-ice formation, and an overestimation of vertical diffusivities in the main thermocline.

Stephens, BB, Keeling RF.  2000.  The influence of Antarctic sea ice on glacial-interglacial CO2 variations. Nature. 404:171-174.   10.1038/35004556   AbstractWebsite

Ice-core measurements indicate that atmospheric CO(2) concentrations during glacial periods were consistently about 80 parts per million lower than during interglacial periods(1). Previous explanations for this observation(2-9) have typically had difficulty accounting for either the estimated glacial O(2) concentrations in the deep sea, (13)C/(12)C ratios in Antarctic surface waters, or the depth of calcite saturation; also lacking is an explanation for the strong link between atmospheric CO(2) and Antarctic air temperature(1). There is growing evidence that the amount of deep water upwelling at low latitudes is significantly overestimated in most ocean general circulation models(10,11) and simpler box models previously used to investigate this problem. Here we use a box model with deep-water upwelling confined to south of 55 degrees S to investigate the glacial-interglacial linkages between Antarctic air temperature and atmospheric CO(2) variations. We suggest that low glacial atmospheric CO(2) levels might result from reduced deep-water ventilation associated with either year-round Antarctic sea-ice coverage, or wintertime coverage combined with ice-induced stratification during the summer. The model presented here reproduces 67 parts per million of the observed glacial-interglacial CO(2) difference, as a result of reduced air-sea gas exchange in the Antarctic region, and is generally consistent with the additional observational constraints.

Sundquist, ET, Keeling RF.  2009.  The Mauna Loa carbon dioxide record: lessons for long-term earth observations. Carbon sequestration and its role in the global carbon cycle. ( McPherson BJ, Sundquist ET, Eds.).:27-35., Washington, DC: American Geophysical Union Abstract

"For carbon sequestration, the issues of monitoring, assessment and verification of carbon content and storage efficacy are perhaps the most uncertain yet most critical issues facing the broader context of climate change in relation to carbon sequestration. As a result, this book presents current perspectives and research that combine four major areas: verification and assessment of global carbon sources and sinks; potential capacity and temporal/spatial scales of terrestrial, oceanic, and geologic carbon storage; assessing risks and benefits associated with terrestrial, oceanic, and geologic carbon storage; and predicting, monitoring, and verifying effectiveness of terrestrial, oceanic and geologic carbon storage. This volume is based on a Chapman conference and will appeal to the rapidly growing group of scientists and engineers in examining methods for deliberate carbon sequestration through storage in plants, soils, the oceans, and geological repositories."--Publisher's description.