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Keeling, RF.  1993.  On the role of large bubbles in air-sea gas exchange and supersaturation in the ocean. Journal of Marine Research. 51:237-271.   10.1357/0022240933223800   AbstractWebsite

A parameterization of bubble-induced gas exchange is presented in which the bubble contribution to gas exchange is expressed in terms of separate transfer velocities for ingassing (K(b)in) and outgassing (K(b)out). The difference between the ingassing and outgassing velocities (K(b)in - K(b)out) is further separated into two components, the first caused by the injection of small bubbles into the water, the second caused by gas exchange across the surface of hydrostatically compressed larger bubbles. It is argued that both K(b)out and the exchange contribution to the difference K(b)in - K(b)out should be largely independent of the dissolved concentrations of the major gases N2 and O2. A simple model is presented which allows K(b)out and the exchange contribution to the difference K(b)in - K(b)out to be estimated. The model incorporates data from laboratory simulation experiments on the bubble production spectrum. The results indicate that bubbles larger than 0.05 cm in radius, which have often been assumed to play a negligible role, contribute significantly to bubble-induced gas exchange and supersaturation in the ocean. The model is used to explore the sensitivity of bubble-induced gas exchange to the overall air entrainment rate, size and depth distributions of the bubbles, and to the gas exchange rates across the surface of individual bubbles. The model suggests that bubbles may make an important contribution to overall gas exchange at windspeeds above 10 m sec-1. In this regime gas transfer velocities should depend, not just on diffusivity, but also on the solubility of the gases. It is suggested that K(b)(out) should scale roughly as alpha-0.3D0.35 where a is the solubility and D is the diffusivity. The model results, in combination with measurements on inert gas supersaturations, suggest that the global-mean supersaturation of CO2 induced by bubbles is not larger than 0.3% and most probably is around 0.08%. A major uncertainty results from a lack of information on production rates and distributions of large bubbles. Several possible experiments are proposed for improving estimates of bubble-induced gas exchange and supersaturation.

Manizza, M, Keeling RF, Nevison CD.  2012.  On the processes controlling the seasonal cycles of the air-sea fluxes of O2 and N2O: A modelling study. Tellus Series B-Chemical and Physical Meteorology. 64   10.3402/tellusb.v64i0.18429   AbstractWebsite

The seasonal dynamics of the air-sea gas flux of oxygen (O-2) are controlled by multiple processes occurring simultaneously. Previous studies showed how to separate the thermal component from the total O-2 flux to quantify the residual oxygen flux due to biological processes. However, this biological signal includes the effect of both net euphotic zone production (NEZP) and subsurface water ventilation. To help understand and separate these two components, we use a large-scale ocean general circulation model (OGCM), globally configured, and coupled to a biogeochemical model. The combined model implements not only the oceanic cycle of O-2 but also the cycles of nitrous oxide (N2O), argon (Ar) and nitrogen (N-2). For this study, we apply a technique to distinguish the fluxes of O-2 driven separately by thermal forcing, NEZP, and address the role of ocean ventilation by carrying separate O-2 components in the model driven by solubility, NEZP and ventilation. Model results show that the ventilation component can be neglected in summer compared to the production and thermal components polewards but not equatorward of 30 degrees in each hemisphere. This also implies that neglecting the role of ventilation in the subtropical areas would lead to overestimation of the component of O-2 flux due to NEZP by 20-30%. Model results also show that the ventilation components of air-sea O-2 and N2O fluxes are strongly anti-correlated in a ratio that reflects the subsurface tracer/tracer relationships (similar to 0.1 mmol N2O/mol O-2) as derived from observations. The results support the use of simple scaling relationships linking together the thermally driven fluxes of Ar, N-2 and O-2. Furthermore, our study also shows that for latitudes polewards of 30 degrees of both hemispheres, the Garcia and Keeling (2001) climatology, when compared to our model results, has a phasing error with the fluxes being too early by similar to 2-3 weeks.

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.

Keeling, RF, Visbeck M.  2011.  On the linkage between Antarctic surface water stratification and global deep-water temperature. Journal of Climate. 24:3545-3557.   10.1175/2011jcli3642.1   AbstractWebsite

The suggestion is advanced that the remarkably low static stability of Antarctic surface waters may arise from a feedback loop involving global deep-water temperatures. If deep-water temperatures are too warm, this promotes Antarctic convection, thereby strengthening the inflow of Antarctic Bottom Water into the ocean interior and cooling the deep ocean. If deep waters are too cold, this promotes Antarctic stratification allowing the deep ocean to warm because of the input of North Atlantic Deep Water. A steady-state deep-water temperature is achieved such that the Antarctic surface can barely undergo convection. A two-box model is used to illustrate this feedback loop in its simplest expression and to develop basic concepts, such as the bounds on the operation of this loop. The model illustrates the possible dominating influence of Antarctic upwelling rate and Antarctic freshwater balance on global deep-water temperatures.

Garcia, HE, Keeling RF.  2001.  On the global oxygen anomaly and air-sea flux. Journal of Geophysical Research-Oceans. 106:31155-31166.   10.1029/1999jc000200   AbstractWebsite

We present a new climatology of monthly air-sea oxygen fluxes throughout the ice-free surface global ocean. The climatology is based on weighted linear least squares regressions using heat flux monthly anomalies for spatial and temporal interpolation of historical O-2 data. The seasonal oceanic variations show that the tropical belt (20degreesS-20degreesN) is characterized by relatively small air-sea fluxes when compared to the middle to high latitudes (40degrees-70degrees). The largest and lowest seasonal fluxes occur during summer and winter in both hemispheres. By means of an atmospheric transport model we show that our climatology is in better agreement with the observed amplitude and phasing of the variations in atmospheric O-2/N-2 ratios because of seasonal air-sea exchanges at baseline stations in the Pacific Ocean than with previous air-sea O-2 climatologies. Our study indicates that the component of the air-sea O-2 flux that correlates with heat flux dominates the large-scale air-sea O-2 exchange on seasonal timescales. The contribution of each major oceanic basin to the atmospheric observations is described. The seasonal net thermal (SNOT) and biological (SNOB) outgassing components of the flux are examined in relation to latitudinal bands, basin-wide, and hemispheric contributions. The Southern Hemisphere's SNOB (similar to0.26 Pmol) and SNOT (similar to0.29 Pmol) values are larger than the Northern Hemisphere's SNOB (similar to0.15 Pmol) and SNOT (similar to0.16 Pmol) values (1 Pmol = 10(15) mol). We estimate a global extratropical carbon new production during the outgassing season of 3.7 Pg C (1 Pg = 10(15) g), lower than previous estimates with air-sea O-2 climatologies.

Keeling, RF.  2002.  On the freshwater forcing of the thermohaline circulation in the limit of low diapycnal mixing. Journal of Geophysical Research-Oceans. 107   10.1029/2000jc000685   AbstractWebsite

[1] A conjecture is offered on the stability characteristics of the thermohaline circulation in the limit of very low diapycnal mixing. In this limit the action of the winds on the Antarctic Circumpolar Current (ACC) can sustain a deep overturning pattern known as the "reconfigured conveyor,'' consisting of upwelling around Antarctica and sinking in the North Atlantic, as shown by the work of Toggweiler and others. It is conjectured that in this limit, northern sinking should be stabilized in an "on'' state because of the penetration of freshwater into the ocean interior via isopycnal layers that outcrop to the surface within and south of the ACC. This conjecture is supported by qualitative arguments and by a hydraulic model for the reconfigured conveyor. The hydraulic model takes into account the freshwater budgets of the Atlantic basin, Antarctic surface waters, and the remaining oceans. It also takes into account, in simple terms, wind-driven Antarctic upwelling, eddy transports and mixing within the ACC, changes in pycnocline depth, the role of temperature forcing, and advective feedbacks on salinity. The hydraulic model suggests that multiple "on/off'' states of the reconfigured conveyor are possible but only if the deep waters that form in the Northern Hemisphere are fresher than the intermediate waters that form in the vicinity of the ACC in the Southern Hemisphere, a condition that is not satisfied in the modern ocean.

Tans, PP, Berry JA, Keeling RF.  1993.  Oceanic 13C/12C observations: A new window on ocean CO2 uptake. Global Biogeochemical Cycles. 7:353-368.   10.1029/93gb00053   AbstractWebsite

Equations are developed describing the rate of change of carbon isotopic ratios in the atmosphere and oceans in terms of deltaC-13 quantities. The equations enable one to perform calculations directly with delta and epsilon quantities commonly reported in the literature. The main cause of the change occurring today is the combustion of fossil fuel carbon with lower deltaC-13 values. The course of this isotopic anomaly in atmosphere and oceans can provide new constraints on the carbon budgets of these reservoirs. Recently published deltaC-13 isotopic data of total inorganic carbon in the oceans [Quay et al., 1992] appear to lead to incompatible results with respect to the uptake of fossil fuel CO2 by the oceans if two different approaches Lo the data are taken. Consideration of the air-sea isotopic disequilibrium leads to an uptake estimate of only a few tenths of a gigaton C (Gt, for 10(15) g) per year, whereas the apparent change in the ocean deltaC-13 inventory leads to an estimate of more than 2 Gt C yr-1. Both results are very uncertain with presently available data. The isotopic ratio has the advantage that the signal-to-noise ratio for the measurement of the uptake of the isotopic signal by the oceans is better than for the uptake of total carbon. The drawback is that isotopic exchange with carbon reservoirs that are difficult to characterize introduces uncertainty into the isotopic budget. The accuracy requirements for the measurements are high, demanding careful standardization at all stages.

Hamme, RC, Keeling RF.  2008.  Ocean ventilation as a driver of interannual variability in atmospheric potential oxygen. Tellus Series B-Chemical and Physical Meteorology. 60:706-717.   10.1111/j.1600-0889.2008.00376.x   AbstractWebsite

We present observations of interannual variability on 2-5 yr timescales in atmospheric potential oxygen (APO approximate to O(2) + CO(2)) from the Scripps Institution of Oceanography global flask sampling network. Interannual variations in the tracer APO are expected to arise from air-sea fluxes alone, because APO is insensitive to exchanges with the terrestrial biosphere. These interannual variations are shown to be regionally coherent and robust to analytical artefacts. We focus on explaining a feature dominant in records from the Northern Hemisphere stations, marked by increasing APO in the late 1990s, followed by an abrupt drawdown in 2000-2001. The timing of the drawdown matches a renewal of deep convection in the North Atlantic, followed the next year by a severe winter in the western North Pacific that may have allowed ventilation of denser isopycnals than usual. We find a weak correlation between changes in the interhemispheric APO difference and El Nino indices, and the observations show no strong features of the 1997-98 El Nino. Comparisons with estimates of variations in ocean productivity and ocean heat content demonstrate that these processes are secondary influences at these timescales. We conclude that the evidence points to variability in ocean ventilation as the main driver of interannual variability in APO.

Keeling, RF, Kortzinger A, Gruber N.  2010.  Ocean deoxygenation in a warming world. Annual Review of Marine Science. 2:199-229., Palo Alto: Annual Reviews   10.1146/annurev.marine.010908.163855   Abstract

Ocean warming and increased stratification of the upper ocean caused by global climate change will likely lead to declines in dissolved O(2) in the ocean interior (ocean deoxygenation) with implications for ocean productivity, nutrient cycling, carbon cycling, and marine habitat. Ocean models predict declines of 1 to 7% in the global ocean O(2) inventory over the next century, with declines continuing for a thousand years or more into the future. An important consequence may be an expansion in the area and volume of so-called oxygen minimum zones, where O(2) levels are too low to support many macrofauna and profound changes in biogeochemical cycling occur. Significant deoxy enation has occurred over the past 50 years in the North Pacific and tropical oceans, suggesting larger changes are looming. The potential for larger O(2) declines in the future suggests the need for all improved observing system for tracking ocean O(2) changes.

Graven, HD, Guilderson TP, Keeling RF.  2012.  Observations of radiocarbon in CO2 at La Jolla, California, USA 1992-2007: Analysis of the long-term trend. Journal of Geophysical Research-Atmospheres. 117   10.1029/2011jd016533   AbstractWebsite

High precision measurements of Delta C-14 were performed on CO2 sampled at La Jolla, California, USA over 1992-2007. A decreasing trend in Delta C-14 was observed, which averaged -5.5 parts per thousand yr(-1) yet showed significant interannual variability. Contributions to the trend in global tropospheric Delta C-14 by exchanges with the ocean, terrestrial biosphere and stratosphere, by natural and anthropogenic C-14 production and by C-14-free fossil fuel CO2 emissions were estimated using simple models. Dilution by fossil fuel emissions made the strongest contribution to the Delta C-14 trend while oceanic C-14 uptake showed the most significant change between 1992 and 2007, weakening by 70%. Relatively steady positive influences from the stratosphere, terrestrial biosphere and C-14 production moderated the decreasing trend. The most prominent excursion from the average trend occurred when Delta C-14 decreased rapidly in 2000. The rapid decline in Delta C-14 was concurrent with a rapid decline in atmospheric O-2, suggesting a possible cause may be the anomalous ventilation of deep C-14-poor water in the North Pacific Ocean. We additionally find the presence of a 28-month period of oscillation in the Delta C-14 record at La Jolla.

Graven, HD, Guilderson TP, Keeling RF.  2012.  Observations of radiocarbon in CO2 at seven global sampling sites in the Scripps flask network: Analysis of spatial gradients and seasonal cycles. Journal of Geophysical Research-Atmospheres. 117   10.1029/2011jd016535   AbstractWebsite

High precision measurements of Delta C-14 were conducted for monthly samples of CO2 from seven global stations over 2- to 16-year periods ending in 2007. Mean Delta C-14 over 2005-07 in the Northern Hemisphere was 5 parts per thousand lower than Delta C-14 in the Southern Hemisphere, similar to recent observations from I. Levin. This is a significant shift from 1988-89 when Delta C-14 in the Northern Hemisphere was slightly higher than the South. The influence of fossil fuel CO2 emission and transport was simulated for each of the observation sites by the TM3 atmospheric transport model and compared to other models that participated in the Transcom 3 Experiment. The simulated interhemispheric gradient caused by fossil fuel CO2 emissions was nearly the same in both 1988-89 and 2005-07, due to compensating effects from rising emissions and decreasing sensitivity of Delta C-14 to fossil fuel CO2. The observed 5 parts per thousand shift must therefore have been caused by non-fossil influences, most likely due to changes in the air-sea C-14 flux in the Southern Ocean. Seasonal cycles with higher Delta C-14 in summer or fall were evident at most stations, with largest amplitudes observed at Point Barrow (71 degrees N) and La Jolla (32 degrees N). Fossil fuel emissions do not account for the seasonal cycles of Delta C-14 in either hemisphere, indicating strong contributions from non-fossil influences, most likely from stratosphere-troposphere exchange.

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/annurev.energy.23.1.207   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.

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.

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Keeling, RF, Visbeck M.  2005.  Northern ice discharges and Antarctic warming: could ocean eddies provide the link? Quaternary Science Reviews. 24:1809-1820.   10.1016/j.quascirev.2005.04.005   AbstractWebsite

A mechanism is advanced for explaining the Antarctic warm events from 90 to 30ka BP which involves meltwater-induced changes in the salinity gradient across the Antarctic Circumpolar Current (ACC) and consequent changes in the poleward heat transport by ocean eddies. Based on simple linear scale analysis, the mechanism is shown to yield warming in the Antarctic interior of roughly the magnitude seen in Antarctic ice-core records (similar to 2 degrees C) in response to ice discharges into the North Atlantic. Consistent with observations, the mechanism produces gradual Antarctic warming and cooling, as dictated by the time required for salinity anomalies to build up and dissipate across the ACC. The mechanism also allows the onset of warming or cooling to be tied to changes in Atlantic overturning, which is relevant here, not for influencing ocean heat transport directly, but for influencing the routing of meltwater from the North Atlantic into the Southern Ocean. The ideas presented here highlight the possibility that eddy processes in the ocean may play a first-order role in aspects of climate variability on millennial time scales. (c) 2005 Elsevier Ltd. All rights reserved.

Nevison, C, Munro D, Lovenduski N, Cassar N, Keeling R, Krummel P, Tjiputra J.  2018.  Net community production in the Southern Ocean: Insights from comparing atmospheric potential oxygen to satellite ocean color algorithms and ocean models. Geophysical Research Letters. 45:10549-10559.   10.1029/2018gl079575   AbstractWebsite

The contribution of oceanic net community production (NCP) to the observed seasonal cycle in atmospheric potential oxygen (APO) is estimated at Cape Grim, Tasmania. The resulting APO(NCP) signal is compared to satellite and ocean model-based estimates of POC export and NCP across the Southern Ocean. The satellite products underestimate the amplitude of the observed APONCP seasonal cycle by more than a factor of 2. Ocean models suggest two reasons for this underestimate: (1) Current satellite products substantially underestimate the magnitude of NCP in early spring. (2) Seasonal O-2 outgassing is supported in large part by storage of carbon in DOC and living biomass. More DOC observations are needed to help evaluate this latter model prediction. Satellite products could be improved by developing seasonally dependent relationships between remote sensing chlorophyll data and in situ NCP, recognizing that the former is a measure of mass, the latter of flux. Plain Language Summary Phytoplankton in the surface ocean transform carbon dioxide into organic carbon while also producing oxygen. A fraction of the carbon is exported into the deep ocean, while the oxygen is emitted to the atmosphere. The carbon export rate influences how much carbon dioxide the ocean can absorb. The rate is commonly estimated using satellite-based phytoplankton color measured in the surface ocean, but such estimates involve many uncertain steps and assumptions. Small but detectible seasonal cycles in atmospheric oxygen have been used as an independent method for evaluating satellite-based estimates of organic carbon export. In this study, we evaluate eight satellite-derived carbon export estimates based on their ability to reproduce the observed seasonal cycle of atmospheric oxygen measured at a southeastern Australia site. All underpredict the seasonal oxygen cycle by at least a factor of 2, in part because they fail to capture the carbon and oxygen produced in early springtime and also because they focus on large particles of carbon that are heavy enough to sink while neglecting the dissolved fraction of organic carbon. Our study suggests that satellite estimates could be improved by a better understanding of seasonal variations in the relationship between phytoplankton productivity and carbon export.

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Cui, YY, Vijayan A, Falk M, Hsu YK, Yin DZ, Chen XM, Zhao Z, Avise J, Chen YJ, Verhulst K, Duren R, Yadav V, Miller C, Weiss R, Keeling R, Kim J, Iraci LT, Tanaka T, Johnson MS, Kort EA, Bianco L, Fischer ML, Stroud K, Herner J, Croes B.  2019.  A multiplatform inversion estimation of statewide and regional methane emissions in California during 2014-2016. Environmental Science & Technology. 53:9636-9645.   10.1021/acs.est.9b01769   AbstractWebsite

California methane (CH4) emissions are quantified for three years from two tower networks and one aircraft campaign. We used backward trajectory simulations and a mesoscale Bayesian inverse model, Mbring ratios (VI ' initialized by three inventories, to achieve the emission quantification. Results show total statewide CH4 emissions of 2.05 +/- 0.26 (at 95% confidence) Tg/yr, which is 1.14 to 1.47 times greater than the anthropogenic emission estimates by California Air Resource Board (GARB). Some of differences could be biogenic emissions, superemitter point sources, and other episodic emissions which may not be completely included in the CARB inventory. San Joaquin Valley (SJV) has the largest CH4 emissions (0.94 +/- 0.18 Tg/yr), followed by the South Coast Air Basin, the Sacramento Valley, and the San Francisco Bay Area at 0.39 +/- 0.18, 0.21 +/- 0.04, and 0.16 +/- 0.05 Tg/yr, respectively. The dairy and oil/gas production sources in the SJV contribute 0.44 +/- 0.36 and 0.22 +/- 0.23 Tg CH4/yr, respectively. This study has important policy implications for regulatory programs, as it provides a thorough multiyear evaluation of the emissions inventory using independent atmospheric measurements and investigates the utility of a complementary multiplatform approach in understanding the spatial and temporal patterns of CH4 emissions in the state and identifies opportunities for the expansion and applications of the monitoring network.

Nottrott, A, Kleissl J, Keeling R.  2014.  Modeling passive scalar dispersion in the atmospheric boundary layer with WRF large-eddy simulation. Atmospheric Environment. 82:172-182.   10.1016/j.atmosenv.2013.10.026   AbstractWebsite

The ability of the Weather Research and Forecasting, large-eddy simulation model (WRF-LES) to model passive scalar dispersion from continuous sources in convective and neutral atmospheric boundary layers was investigated. WRF-LES accurately modeled mean plume trajectories and concentration fields. WRF-LES statistics of concentration fluctuations in the daytime convective boundary layer were similar to data obtained from laboratory experiments and other LES models. However, poor turbulence resolution near the surface in neutral boundary layer simulations caused under prediction of mean dispersion in the crosswind horizontal direction and over prediction of concentration variance in the neutral surface layer. A gradient in the intermittency factor for concentration fluctuations was observed near the surface, downwind of ground-level sources in the daytime boundary layer. That observation suggests that the intermittency factor is a promising metric for estimating source-sensor distance in source determination applications. (C) 2013 Elsevier Ltd. All rights reserved.

Manning, MR, Edmonds J, Emori S, Grubler A, Hibbard K, Joos F, Kainuma M, Keeling RF, Kram T, Manning AC, Meinshausen M, Moss R, Nakicenovic N, Riahi K, Rose SK, Smith S, Swart R, van Vuuren DP.  2010.  Misrepresentation of the IPCC CO2 emission scenarios. Nature Geoscience. 3:376-377.   10.1038/ngeo880   AbstractWebsite
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Keeling, RF, Manning AC, McEvoy EM, Shertz SR.  1998.  Methods for measuring changes in atmospheric O2 concentration and their application in southern hemisphere air. Journal of Geophysical Research-Atmospheres. 103:3381-3397.   10.1029/97jd02537   AbstractWebsite

Methods are described for measuring changes in atmospheric O-2 concentration with emphasis on gas handling procedures. Cryogenically dried air samples are collected in 5 L glass flasks at ambient pressure and analyzed against reference gases derived from high-pressure aluminum tanks. Fractionation effects are minimized by avoiding pressure and flow variations throughout the gas-handling system. The overall external reproducibility is approximately +/-3.3 per meg, with systematic errors associated with collecting samples and with storing them for 1 year reduced to the level of 3 per meg or smaller. The demonstrated short-term reproducibly of air delivered from high-presure tanks is +/-1.5 per meg, with the composition changing by at most 5 per meg by surface desorption reactions as the tank is depleted to below 3500 kPa. A 9-year survey of a suite of six reference gases showed no systematic long-term trends in relative O-2 concentrations to the level of 5 per meg. Results are presented from samples collected at Cape Grim (41 degrees S), Macquarie Island (54 degrees S) and the South Pole Station (90 degrees S). From measurements spanning 1991-1995 it is found that the O-2 concentrations at the South Pole are on average 3.6+/-1.2 per meg higher than at Cape Grim. This result runs contrary to the expectation that the air at high southern latitudes should be depleted in O-2 as a result of O-2 uptake from the Southern Ocean and may require the existence of unknown O-2 sources near Antarctica or unexpected atmospheric transport patterns.

Graven, HD, Guilderson TP, Keeling RF.  2007.  Methods for high-precision 14C AMS measurement of atmospheric CO2 at LLNL. Radiocarbon. 49:349-356. AbstractWebsite

Development of radiocarbon analysis with precision better than 2%omicron has the potential to expand the utility of (CO2)-C-14 measurements for carbon cycle investigations as atmospheric gradients currently approach the typical measurement precision of 2-5%omicron. The accelerator mass spectrometer at Lawrence Livermore National Laboratory (LLNL) produces high and stable beam currents that enable efficient acquisition times for large numbers of C-14 counts. One million C-14 atoms can be detected in approximately 25 min, suggesting that near 1%omicron counting precision is economically feasible at LLNL. The overall uncertainty in measured values is ultimately determined by the variation between measured ratios in several sputtering periods of the same sample and by the reproducibility of replicate samples. Experiments on the collection of 1 million counts on replicate samples of CO2 extracted from a whole air cylinder show a standard deviation of 1.7%omicron in 36 samples measured over several wheels. This precision may be limited by the reproducibility of oxalic acid I standard samples, which is considerably poorer. We outline the procedures for high-precision sample handling and analysis that have enabled reproducibility in the cylinder extraction samples at the <2%omicron level and describe future directions to continue increasing measurement precision at LLNL.

Keeling, RF.  1991.  Mechanisms for stabilization and destabilization of a simple biosphere: catastrophe on Daisyworld. Scientists on Gaia. ( Schneider S, Boston PJ, Eds.).:118-120., Cambridge, Mass.: MIT Press Abstract
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Keeling, RF.  1988.  Measuring correlations between atmospheric oxygen and carbon dioxide mole fractions: A preliminary study in urban air. Journal of Atmospheric Chemistry. 7:153-176.   10.1007/bf00048044   AbstractWebsite

On 25 and 26 October 1986 the air in Cambridge, Massachusetts was monitored for O2 and CO2 mole fraction. O2 concentrations were detected from changes in the relative refractivity of dried air between two lines of 198Hg at 2537.269 and 4359.562 Å using dual-wavelength interferometry. Changes in oxygen mole fraction were resolved with two-minute time resolution to a precision of ±2.0 ppm. Changes in O2 were shown to be strongly anticorrelated with changes in CO2 as expected for combustion processes. The demonstrated instrumental capabilities are appropriate for measuring changes in O2 mole fraction in background air which could be of importance to a broad range of biogeochemical studies.

Petrenko, VV, Severinghaus JP, Schaefer H, Smith AM, Kuhl T, Baggenstos D, Hua Q, Brook EJ, Rose P, Kulin R, Bauska T, Harth C, Buizert C, Orsi A, Emanuele G, Lee JE, Brailsford G, Keeling R, Weiss RF.  2016.  Measurements of 14C in ancient ice from Taylor Glacier, Antarctica constrain in situ cosmogenic 14CH4 and 14CO production rates. Geochimica et Cosmochimica Acta. 177:62-77.   10.1016/j.gca.2016.01.004   Abstract

Carbon-14 (14C) is incorporated into glacial ice by trapping of atmospheric gases as well as direct near-surface in situ cosmogenic production. 14C of trapped methane (14CH4) is a powerful tracer for past CH4 emissions from “old” carbon sources such as permafrost and marine CH4 clathrates. 14C in trapped carbon dioxide (14CO2) can be used for absolute dating of ice cores. In situ produced cosmogenic 14C in carbon monoxide (14CO) can potentially be used to reconstruct the past cosmic ray flux and past solar activity. Unfortunately, the trapped atmospheric and in situ cosmogenic components of 14C in glacial ice are difficult to disentangle and a thorough understanding of the in situ cosmogenic component is needed in order to extract useful information from ice core 14C. We analyzed very large (≈1000 kg) ice samples in the 2.26–19.53 m depth range from the ablation zone of Taylor Glacier, Antarctica, to study in situ cosmogenic production of 14CH4 and 14CO. All sampled ice is >50 ka in age, allowing for the assumption that most of the measured 14C originates from recent in situ cosmogenic production as ancient ice is brought to the surface via ablation. Our results place the first constraints on cosmogenic 14CH4 production rates and improve on prior estimates of 14CO production rates in ice. We find a constant 14CH4/14CO production ratio (0.0076 ± 0.0003) for samples deeper than 3 m, which allows the use of 14CO for correcting the 14CH4 signals for the in situ cosmogenic component. Our results also provide the first unambiguous confirmation of 14C production by fast muons in a natural setting (ice or rock) and suggest that the 14C production rates in ice commonly used in the literature may be too high.

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.

Keeling, RF, Blaine T, Paplawsky B, Katz L, Atwood C, Brockwell T.  2004.  Measurement of changes in atmospheric Ar/N2 ratio using a rapid-switching, single-capillary mass spectrometer system. Tellus Series B-Chemical and Physical Meteorology. 56:322-338.   10.1111/j.1600-0889.2004.00117.x   AbstractWebsite

The atmospheric Ar/N-2 ratio is expected to undergo very slight variations due to exchanges of Ar and N-2 across the air-sea interface, driven by ocean solubility changes. Observations of these variations may provide useful constraints on large-scale fluxes of heat across the air-sea interface. A mass spectrometer system is described that incorporates a magnet with a wide exit face, allowing a large mass spread, and incorporates an inlet with rapid (5 s) switching of sources gases through a single capillary, thus achieving high precision in the comparison of sample and reference gases. The system allows simultaneous measurement of Ar/N-2, O-2/N, and CO2/N-2 ratios. The system achieves a short-term precision in Ar/N-2 of 10 per meg for a 10 s integration, which can be averaged to achieve an internal precision of a few per meg in the comparison of reference gases. Results for Ar/N-2 are reported from flasks samples collected from nine stations in a north-to-south global network over about a 1 yr period. The imprecision on an individual flask, as estimated from replicate agreement, is 11 per meg. This imprecision is dominated by real variability between samples at the time of analysis. Seasonal cycles are marginally resolved at the extra-tropical stations with amplitudes of 5 to 15 per meg. Annual-mean values are constant between stations to within 5 per meg. The results are compared with a numerical simulation of the cycles and gradients in Ar/N-2 based on the TM2 tracer transport model in combination with air-sea Ar and N-2 fluxes derived from climatological air-sea heat fluxes. The possibility is suggested that Ar/N-2 ratios may be detectably enriched near the ground by gravimetric or thermal fractionation under conditions of strong surface inversions.