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Graven, H, Fischer ML, Lueker T, Jeong S, Guilderson TP, Keeling RF, Bambha R, Brophy K, Callahan W, Cui X, Frankenberg C, Gurney KR, LaFranchi BW, Lehman SJ, Michelsen H, Miller JB, Newman S, Paplawsky W, Parazoo NC, Sloop C, Walker SJ.  2018.  Assessing fossil fuel CO2 emissions in California using atmospheric observations and models. Environmental Research Letters. 13   10.1088/1748-9326/aabd43   AbstractWebsite

Analysis systems incorporating atmospheric observations could provide a powerful tool for validating fossil fuel CO2 (ffCO(2)) emissions reported for individual regions, provided that fossil fuel sources can be separated from other CO2 sources or sinks and atmospheric transport can be accurately accounted for. We quantified ffCO(2) by measuring radiocarbon (C-14) in CO2, an accurate fossil-carbon tracer, at nine observation sites in California for three months in 2014-15. There is strong agreement between the measurements and ffCO(2) simulated using a high-resolution atmospheric model and a spatiotemporally-resolved fossil fuel flux estimate. Inverse estimates of total in-state ffCO(2) emissions are consistent with the California Air Resources Board's reported ffCO(2) emissions, providing tentative validation of California's reported ffCO(2) emissions in 2014-15. Continuing this prototype analysis system could provide critical independent evaluation of reported ffCO(2) emissions and emissions reductions in California, and the system could be expanded to other, more data-poor regions.

Fischer, ML, Parazoo N, Brophy K, Cui XG, Jeong S, Liu JJ, Keeling R, Taylor TE, Gurney K, Oda T, Graven H.  2017.  Simulating estimation of California fossil fuel and biosphere carbon dioxide exchanges combining in situ tower and satellite column observations. Journal of Geophysical Research-Atmospheres. 122:3653-3671.   10.1002/2016jd025617   AbstractWebsite

We report simulation experiments estimating the uncertainties in California regional fossil fuel and biosphere CO2 exchanges that might be obtained by using an atmospheric inverse modeling system driven by the combination of ground-based observations of radiocarbon and total CO2, together with column-mean CO2 observations from NASA's Orbiting Carbon Observatory (OCO-2). The work includes an initial examination of statistical uncertainties in prior models for CO2 exchange, in radiocarbon-based fossil fuel CO2 measurements, in OCO-2 measurements, and in a regional atmospheric transport modeling system. Using these nominal assumptions for measurement and model uncertainties, we find that flask measurements of radiocarbon and total CO2 at 10 towers can be used to distinguish between different fossil fuel emission data products for major urban regions of California. We then show that the combination of flask and OCO-2 observations yields posterior uncertainties in monthly-mean fossil fuel emissions of similar to 5-10%, levels likely useful for policy relevant evaluation of bottom-up fossil fuel emission estimates. Similarly, we find that inversions yield uncertainties in monthly biosphere CO2 exchange of similar to 6%-12%, depending on season, providing useful information on net carbon uptake in California's forests and agricultural lands. Finally, initial sensitivity analysis suggests that obtaining the above results requires control of systematic biases below approximately 0.5ppm, placing requirements on accuracy of the atmospheric measurements, background subtraction, and atmospheric transport modeling.

Welp, LR, Keeling RF, Meijer HAJ, Bollenbacher AF, Piper SC, Yoshimura K, Francey RJ, Allison CE, Wahlen M.  2011.  Interannual variability in the oxygen isotopes of atmospheric CO2 driven by El Nino. Nature. 477:579-582.   10.1038/nature10421   AbstractWebsite

The stable isotope ratios of atmospheric CO2 (O-18/O-16 and C-13/C-12) have been monitored since 1977 to improve our understanding of the global carbon cycle, because biosphere-atmosphere exchange fluxes affect the different atomic masses in a measurable way(1). Interpreting the O-18/O-16 variability has proved difficult, however, because oxygen isotopes in CO2 are influenced by both the carbon cycle and the water cycle(2). Previous attention focused on the decreasing O-18/O-16 ratio in the 1990s, observed by the global Cooperative Air Sampling Network of the US National Oceanic and Atmospheric Administration Earth System Research Laboratory. This decrease was attributed variously to a number of processes including an increase in Northern Hemisphere soil respiration(3); a global increase in C-4 crops at the expense of C-3 forests(4); and environmental conditions, such as atmospheric turbulence(5) and solar radiation(6), that affect CO2 exchange between leaves and the atmosphere. Here we present 30 years' worth of data on O-18/O-16 in CO2 from the Scripps Institution of Oceanography global flask network and show that the interannual variability is strongly related to the El Nino/Southern Oscillation. We suggest that the redistribution of moisture and rainfall in the tropics during an El Nino increases the O-18/O-16 ratio of precipitation and plant water, and that this signal is then passed on to atmospheric CO2 by biosphere-atmosphere gas exchange. We show how the decay time of the El Nino anomaly in this data set can be useful in constraining global gross primary production. Our analysis shows a rapid recovery from El Nino events, implying a shorter cycling time of CO2 with respect to the terrestrial biosphere and oceans than previously estimated. Our analysis suggests that current estimates of global gross primary production, of 120 petagrams of carbon per year(7), may be too low, and that a best guess of 150-175 petagrams of carbon per year better reflects the observed rapid cycling of CO2. Although still tentative, such a revision would present a new benchmark by which to evaluate global biospheric carbon cycling models.

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.

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.