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Verhulst, KR, Karion A, Kim J, Salameh PK, Keeling RF, Newman S, Miller J, Sloop C, Pongetti T, Rao P, Wong C, Hopkins FM, Yadav V, Weiss RF, Duren RM, Miller CE.  2017.  Carbon dioxide and methane measurements from the Los Angeles Megacity Carbon Project - Part 1: calibration, urban enhancements, and uncertainty estimates. Atmospheric Chemistry and Physics. 17:8313-8341.   10.5194/acp-17-8313-2017   AbstractWebsite

We report continuous surface observations of carbon dioxide (CO2) and methane (CH4) from the Los Angeles (LA) Megacity Carbon Project during 2015. We devised a calibration strategy, methods for selection of background air masses, calculation of urban enhancements, and a detailed algorithm for estimating uncertainties in urban-scale CO2 and CH4 measurements. These methods are essential for understanding carbon fluxes from the LA megacity and other complex urban environments globally. We estimate background mole fractions entering LA using observations from four "extra-urban" sites including two "marine" sites located south of LA in La Jolla (LJO) and offshore on San Clemente Island (SCI), one "continental" site located in Victorville (VIC), in the high desert northeast of LA, and one "continental/mid-troposphere" site located on Mount Wilson (MWO) in the San Gabriel Mountains. We find that a local marine background can be established to within similar to 1 ppm CO2 and similar to 10 ppb CH4 using these local measurement sites. Overall, atmospheric carbon dioxide and methane levels are highly variable across Los Angeles. "Urban" and "suburban" sites show moderate to large CO2 and CH4 enhancements relative to a marine background estimate. The USC (University of Southern California) site near downtown LA exhibits median hourly enhancements of similar to 20 ppm CO2 and similar to 150 ppb CH4 during 2015 as well as similar to 15 ppm CO2 and similar to 80 ppb CH4 during mid-afternoon hours (12:00-16:00 LT, local time), which is the typical period of focus for flux inversions. The estimated measurement uncertainty is typically better than 0.1 ppm CO2 and 1 ppb CH4 based on the repeated standard gas measurements from the LA sites during the last 2 years, similar to Andrews et al. (2014). The largest component of the measurement uncertainty is due to the single-point calibration method; however, the uncertainty in the background mole fraction is much larger than the measurement uncertainty. The background uncertainty for the marine background estimate is similar to 10 and similar to 15% of the median mid-afternoon enhancement near downtown LA for CO2 and CH4, respectively. Overall, analytical and background uncertainties are small relative to the local CO2 and CH4 enhancements; however, our results suggest that reducing the uncertainty to less than 5% of the median mid-afternoon enhancement will require detailed assessment of the impact of meteorology on background conditions.

Keeling, RF, Garcia HE.  2002.  The change in oceanic O2 inventory associated with recent global warming. Proceedings of the National Academy of Sciences of the United States of America. 99:7848-7853.   10.1073/pnas.122154899   AbstractWebsite

Oceans general circulation models predict that global warming may cause a decrease in the oceanic O-2 inventory and an associated O-2 outgassing. An independent argument is presented here in support of this prediction based on observational evidence of the ocean's biogeochemical response to natural warming. On time scales from seasonal to centennial, natural O-2 flux/heat flux ratios are shown to occur in a range of 2 to 10 nmol of O-2 per joule of warming, with larger ratios typically occurring at higher latitudes and overlongertime scales. The ratios are several times larger than would be expected solely from the effect of heating on the O-2 solubility, indicating that most of the O-2 exchange is biologically mediated through links between heating and stratification. The change in oceanic O-2 inventory through the 1990s is estimated to be 0.3 +/- 0.4 X 10(14) mol of O-2 per year based on scaling the observed anomalous long-term ocean warming by natural O-2 flux/heating ratios and allowing for uncertainty due to decadal variability. Implications are discussed for carbon budgets based on observed changes in atmospheric O-2/N-2 ratio and based on observed changes in ocean dissolved inorganic carbon.

Tanhua, T, Keeling RF.  2012.  Changes in column inventories of carbon and oxygen in the Atlantic Ocean. Biogeosciences. 9:4819-4833.   10.5194/bg-9-4819-2012   AbstractWebsite

Increasing concentrations of dissolved inorganic carbon (DIC) in the interior ocean are expected as a direct consequence of increasing concentrations of CO2 in the atmosphere. This extra DIC is often referred to as anthropogenic carbon (C-ant), and its inventory, or increase rate, in the interior ocean has previously been estimated by a multitude of observational approaches. Each of these methods is associated with hard to test assumptions since C-ant cannot be directly observed. Results from a simpler concept with fewer assumptions applied to the Atlantic Ocean are reported on here using two large data collections of carbon relevant bottle data. The change in column inventory on decadal time scales, i.e. the storage rate, of DIC, respiration compensated DIC and oxygen is calculated for the Atlantic Ocean. We report storage rates and the confidence intervals of the mean trend at the 95% level (CI), reflecting the mean trend but not considering potential biasing effects of the spatial and temporal sampling. For the whole Atlantic Ocean the mean trends for DIC and oxygen are non-zero at the 95% confidence level: DIC: 0.86 (CI: 0.72-1.00) and oxygen: -0.24 (CI: -0.41-(-0.07)) mol m(-2) yr(-1). For oxygen, the whole Atlantic trend is dominated by the subpolar North Atlantic, whereas for other regions the O-2 trends are not significant. The storage rates are similar to changes found by other studies, although with large uncertainty. For the subpolar North Atlantic the storage rates show significant temporal and regional variation of all variables. This seems to be due to variations in the prevalence of subsurface water masses with different DIC and oxygen concentrations leading to sometimes different signs of storage rates for DIC compared to published C-ant estimates. This study suggest that accurate assessment of the uptake of CO2 by the oceans will require accounting not only for processes that influence C-ant but also additional processes that modify CO2 storage.

Rafelski, LE, Piper SC, Keeling RF.  2009.  Climate effects on atmospheric carbon dioxide over the last century. Tellus Series B-Chemical and Physical Meteorology. 61:718-731.   10.1111/j.1600-0889.2009.00439.x   AbstractWebsite

The buildup of atmospheric CO(2) since 1958 is surprisingly well explained by the simple premise that 57% of the industrial emissions (fossil fuel burning and cement manufacture) has remained airborne. This premise accounts well for the rise both before and after 1980 despite a decrease in the growth rate of fossil fuel CO(2) emissions, which occurred at that time, and by itself should have caused the airborne fraction to decrease. In contrast, the buildup prior to 1958 was not simply proportional to cumulative fossil fuel emissions, and notably included a period during the 1940s when CO(2) growth stalled despite continued fossil fuel emissions. Here we show that the constancy of the airborne fraction since 1958 can be in part explained by decadal variations in global land air temperature, which caused a warming-induced release of CO(2) from the land biosphere to the atmosphere. We also show that the 1940s plateau may be related to these decadal temperature variations. Furthermore, we show that there is a close connection between the phenomenology producing CO(2) variability on multidecadal and El Nino timescales.

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).

Lueker, TJ, Walker SJ, Vollmer MK, Keeling RF, Nevison CD, Weiss RF, Garcia HE.  2003.  Coastal upwelling air-sea fluxes revealed in atmospheric observations of O2/N2, CO2 and N2O. Geophysical Research Letters. 30   10.1029/2002gl016615   AbstractWebsite

[1] We capture water column ventilation resulting from coastal upwelling in continuous records of O-2/N-2, CO2, and N2O at Trinidad, California. Our records reveal the gas exchange response time of the ocean to the upwelling and ensuing biological production. Satellite and buoy wind data allow extrapolation of our records to assess coastal upwelling air-sea fluxes of O-2 and N2O. We improve on previous regional estimates of N2O flux in coastal and continental shelf region of the western U. S. We characterize the source of N2O as being predominately from nitrification based on the O-2/N2O emissions ratio observed in our atmospheric records.

Graven, HD, Xu X, Guilderson TP, Keeling RF, Trumbore SE, Tyler S.  2012.  Comparison of independent delta(co2)-c-14 records at Point Barrow, Alaska. Radiocarbon. 55:1541-1545.   10.2458/azu_js_rc.55.16220   AbstractWebsite

Two independent programs have collected and analyzed atmospheric CO2 samples from Point Barrow, Alaska, for radiocarbon content (Delta C-14) over the period 2003-2007. In one program, flask collection, stable isotope analysis, and CO2 extraction are performed by the Scripps Institution of Oceanography's CO2 Program and CO2 is graphitized and measured by accelerator mass spectrometry (AMS) at Lawrence Livermore National Laboratory. In the other program, the University of California, Irvine, performs flask collection, sample preparation, and AMS. Over 22 common sample dates spanning 5 yr, differences in measured Delta C-14 are consistent with the reported uncertainties and there is no significant bias between the programs.

Graven, H, Allison CE, Etheridge DM, Hammer S, Keeling RF, Levin I, Meijer HAJ, Rubino M, Tans PP, Trudinger CM, Vaughn BH, White JWC.  2017.  Compiled records of carbon isotopes in atmospheric CO2 for historical simulations in CMIP6. Geoscientific Model Development. 10:4405-4417.   10.5194/gmd-10-4405-2017   AbstractWebsite

The isotopic composition of carbon (Delta C-14 and delta C-13) in atmospheric CO2 and in oceanic and terrestrial carbon reservoirs is influenced by anthropogenic emissions and by natural carbon exchanges, which can respond to and drive changes in climate. Simulations of C-14 and C-13 in the ocean and terrestrial components of Earth system models (ESMs) present opportunities for model evaluation and for investigation of carbon cycling, including anthropogenic CO2 emissions and uptake. The use of carbon isotopes in novel evaluation of the ESMs' component ocean and terrestrial biosphere models and in new analyses of historical changes may improve predictions of future changes in the carbon cycle and climate system. We compile existing data to produce records of Delta C-14 and delta C-13 in atmospheric CO2 for the historical period 1850-2015. The primary motivation for this compilation is to provide the atmospheric boundary condition for historical simulations in the Coupled Model Intercomparison Project 6 (CMIP6) for models simulating carbon isotopes in the ocean or terrestrial biosphere. The data may also be useful for other carbon cycle modelling activities.

Resplandy, L, Keeling RF, Stephens BB, Bent JD, Jacobson A, Rodenbeck C, Khatiwala S.  2016.  Constraints on oceanic meridional heat transport from combined measurements of oxygen and carbon. Climate Dynamics. 47:3335-3357.   10.1007/s00382-016-3029-3   AbstractWebsite

Despite its importance to the climate system, the ocean meridional heat transport is still poorly quantified. We identify a strong link between the northern hemisphere deficit in atmospheric potential oxygen (APO = O + 1.1 CO) and the asymmetry in meridional heat transport between northern and southern hemispheres. The recent aircraft observations from the HIPPO campaign reveal a northern APO deficit in the tropospheric column of 10.4 1.0 per meg, double the value at the surface and more representative of large-scale air-sea fluxes. The global northward ocean heat transport asymmetry necessary to explain the observed APO deficit is about 0.7-1.1 PW, which corresponds to the upper range of estimates from hydrographic sections and atmospheric reanalyses.

Rafelski, LE, Paplawsky B, Keeling RF.  2015.  Continuous measurements of dissolved O-2 and oxygen isotopes in the Southern California coastal ocean. Marine Chemistry. 174:94-102.   10.1016/j.marchem.2015.05.011   AbstractWebsite

Dissolved O-2/N-2, O-2/Ar, O-2 saturation and delta O-18 were measured continuously near the surface ocean at the Scripps Institution of Oceanography pier in La Jolla, California, for five weeks. The data showed diurnal cycles, in O-2 and delta O-18, with amplitudes of 19 mmol m(-3) and 1.1%., respectively. The diurnal cycles are well described by a box model that includes photosynthesis, respiration, air-sea gas exchange, and mixing. The timing of the cycles can be explained using a photosynthesis rate proportional to photosynthetically active radiation, and the shapes of the cycles can be explained by mixing with a subsurface layer of water that is supersaturated in O-2. Based on the diurnal cycles in O-2 and delta O-18, the average maximum daily photosynthesis rate was 3.7-4.7 mmol O-2 m(-3) h(-1), which is supported by the light-saturated photosynthesis rate estimated from the measured chlorophyll concentration. In the future, these continuous measurement techniques could be used at different locations and depths to improve the understanding of variability in oceanic primary production. (C) 2015 Elsevier B.V. All rights reserved.