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Takahashi, T, Weiss RF, Culberson CH, Edmond JM, Hammond DE, Wong CS, Li Y-hui, Bainbridge AE.  1970.  A carbonate chemistry profile at the 1969 GEOSECS intercalibration station in the eastern Pacific Ocean. Journal of Geophysical Research. 75:7648-7666., Washington, DC, United States (USA): American Geophysical Union, Washington, DC   10.1029/JC075i036p07648   AbstractWebsite

To compare and evaluate measurements made by the various laboratories participating in the Geochemical Ocean Section Study (Geosecs), four carbonate chemistry parameters, pH, pCO2, alkalinity, and total dissolved CO2, as well as temperature and salinity were measured for samples collected at the Geosecs intercalibration station, 28°20′±07′N and 121°41′±02′W. The methods for measurement include the glass-calomel electrode pair for pH, the pH and the potentiometric acid titration methods for alkalinity, gas chromatographic, infrared and potentiometric acid titration method for total CO2, and the gas equilibrator-infrared method for pCO2. The alkalinity values measured by the pH method agree with the values measured by the potentiometric acid titration method within 1%, and the total CO2 values measured by the chromatographic method agree with the values measured by the potentiometric acid titration method within 2%. The observed 3 to 5% difference between the total CO2 values measured by the chromatographic and infrared methods is attributed to the biological alteration of the unpoisoned samples used for the infrared methods. When two of the four measured carbonate parameters were used to calculate the remaining two parameters, the calculated values are found to differ systematically from the measured values for those two parameters. Such a discrepancy can be eliminated if a 30% error in the second apparent dissociation constant for carbonic acid (K2′) is assumed.

Takahashi, T, Feely RA, Weiss RF, Wanninkhof RH, Chipman DW, Sutherland SC, Takahashi TT.  1997.  Global air-sea flux of CO2: An estimate based on measurements of sea-air pCO2 difference. Proceedings of the National Academy of Sciences of the United States of America. 94:8292-8299.   10.1073/pnas.94.16.8292   AbstractWebsite

Approximately 250,000 measurements made for the pCO(2) difference between surface water and the marine atmosphere, Delta pCO(2), have been assembled for the global oceans. Observations made in the equatorial Pacific during El Nine events have been excluded from the data set, These observations are mapped on the global 4 degrees x 5 degrees grid for a single virtual calendar year (chosen arbitrarily to be 1990) representing a non-El Nino year. Monthly global distributions of Delta pCO(2) have been constructed using an interpolation method based on a lateral advection-diffusion transport equation. The net flux of CO2 across the sea surface has been computed using Delta pCO(2) distributions and CO2 gas transfer coefficients across sea surface. The annual net uptake flux of CO2 by the global oceans thus estimated ranges from 0.60 to 1.34 Gt-C.yr(-1) depending on different formulations used for wind speed dependence on the gas transfer coefficient, These estimates;Ire subject to an error of up to 75% resulting from the numerical interpolation method used to estimate the distribution of Delta pCO(2) over the global oceans, Temperate and polar oceans of the both hemispheres are the major sinks for atmospheric CO2, whereas the equatorial oceans are the major sources for CO2. The Atlantic Ocean is the most important CO2 sink, providing about 60% of the global ocean uptake, while the Pacific Ocean is neutral because of its equatorial source flux being balanced by the sink flux of the temperate oceans, The Indian and Southern Oceans take up about 20% each.

Thompson, RL, Dlugokencky E, Chevallier F, Ciais P, Dutton G, Elkins JW, Langenfelds RL, Prinn RG, Weiss RF, Tohjima Y, O'Doherty S, Krummel PB, Fraser P, Steele LP.  2013.  Interannual variability in tropospheric nitrous oxide. Geophysical Research Letters. 40:4426-4431.   10.1002/grl.50721   AbstractWebsite

Observations of tropospheric N2O mixing ratio show significant variability on interannual timescales (0.2ppb, 1 standard deviation). We found that interannual variability in N2O is weakly correlated with that in CFC-12 and SF6 for the northern extratropics and more strongly correlated for the southern extratropics, suggesting that interannual variability in all these species is influenced by large-scale atmospheric circulation changes and, for SF6 in particular, interhemispheric transport. N2O interannual variability was not, however, correlated with polar lower stratospheric temperature, which is used as a proxy for stratosphere-to-troposphere transport in the extratropics. This suggests that stratosphere-to-troposphere transport is not a dominant factor in year-to-year variations in N2O growth rate. Instead, we found strong correlations of N2O interannual variability with the Multivariate ENSO Index. The climate variables, precipitation, soil moisture, and temperature were also found to be significantly correlated with N2O interannual variability, suggesting that climate-driven changes in soil N2O flux may be important for variations in N2O growth rate.

Thompson, RL, Stohl A, Zhou LX, Dlugokencky E, Fukuyama Y, Tohjima Y, Kim SY, Lee H, Nisbet EG, Fisher RE, Lowry D, Weiss RF, Prinn RG, O'Doherty S, Young D, White JWC.  2015.  Methane emissions in East Asia for 2000-2011 estimated using an atmospheric Bayesian inversion. Journal of Geophysical Research-Atmospheres. 120:4352-4369.   10.1002/2014jd022394   AbstractWebsite

We present methane (CH4) emissions for East Asia from a Bayesian inversion of CH4 mole fraction and stable isotope (C-13-CH4) measurements. Emissions were estimated at monthly resolution from 2000 to 2011. A posteriori, the total emission for East Asia increased from 434 to 594Tgyr(-1) between 2000 and 2011, owing largely to the increase in emissions from China, from 394 to 544Tgyr(-1), while emissions in other East Asian countries remained relatively stable. For China, South Korea, and Japan, the total emissions were smaller than the prior estimates (i.e., Emission Database for Global Atmospheric Research 4.2 FT2010 for anthropogenic emissions) by an average of 29%, 20%, and 23%, respectively. For Mongolia, Taiwan, and North Korea, the total emission was less than 2Tgyr(-1) and was not significantly different from the prior. The largest reductions in emissions, compared to the prior, occurred in summer in regions important for rice agriculture suggesting that this source is overestimated in the prior. Furthermore, an analysis of the isotope data suggests that the prior underestimates emissions from landfills and ruminant animals for winter 2010 to spring 2011 (no data available for other times). The inversion also found a lower average emission trend for China, 1.2Tgyr(-1) compared to 2.8Tgyr(-1) in the prior. This trend was not constant, however, and increased significantly after 2005, up to 2.0Tgyr(-1). Overall, the changes in emissions from China explain up to 40% of the increase in global emissions in the 2000s.

Thompson, RL, Chevallier F, Crotwell AM, Dutton G, Langenfelds RL, Prinn RG, Weiss RF, Tohjima Y, Nakazawa T, Krummel PB, Steele LP, Fraser P, O'Doherty S, Ishijima K, Aoki S.  2014.  Nitrous oxide emissions 1999 to 2009 from a global atmospheric inversion. Atmospheric Chemistry and Physics. 14:1801-1817.   10.5194/acp-14-1801-2014   AbstractWebsite

N2O surface fluxes were estimated for 1999 to 2009 using a time-dependent Bayesian inversion technique. Observations were drawn from 5 different networks, incorporating 59 surface sites and a number of ship-based measurement series. To avoid biases in the inverted fluxes, the data were adjusted to a common scale and scale offsets were included in the optimization problem. The fluxes were calculated at the same resolution as the transport model (3.75 degrees longitude x 2.5 degrees latitude) and at monthly time resolution. Over the 11-year period, the global total N2O source varied from 17.5 to 20.1 Tg a(-1) N. Tropical and subtropical land regions were found to consistently have the highest N2O emissions, in particular in South Asia (20 +/- 3% of global total), South America (13 +/- 4 %) and Africa (19 +/- 3 %), while emissions from temperate regions were smaller: Europe (6 +/- 1 %) and North America (7 +/- 2 %). A significant multi-annual trend in N2O emissions (0.045 Tg a(-2) N) from South Asia was found and confirms inventory estimates of this trend. Considerable interannual variability in the global N2O source was observed (0.8 Tg a(-1) N, 1 standard deviation, SD) and was largely driven by variability in tropical and subtropical soil fluxes, in particular in South America (0.3 Tg a(-1) N, 1 SD) and Africa (0.3 Tg a(-1) N, 1 SD). Notable variability was also found for N2O fluxes in the tropical and southern oceans (0.15 and 0.2 Tg a(-1) N, 1 SD, respectively). Interannual variability in the N2O source shows some correlation with the El Nino-Southern Oscillation (ENSO), where El Nino conditions are associated with lower N2O fluxes from soils and from the ocean and vice versa for La Nina conditions.

Thompson, RL, Patra PK, Ishijima K, Saikawa E, Corazza M, Karstens U, Wilson C, Bergamaschi P, Dlugokencky E, Sweeney C, Prinn RG, Weiss RF, O'Doherty S, Fraser PJ, Steele LP, Krummel PB, Saunois M, Chipperfield M, Bousquet P.  2014.  TransCom N2O model inter-comparison - Part 1: Assessing the influence of transport and surface fluxes on tropospheric N2O variability. Atmospheric Chemistry and Physics. 14:4349-4368.   10.5194/acp-14-4349-2014   AbstractWebsite

We present a comparison of chemistry-transport models (TransCom-N2O) to examine the importance of atmospheric transport and surface fluxes on the variability of N2O mixing ratios in the troposphere. Six different models and two model variants participated in the inter-comparison and simulations were made for the period 2006 to 2009. In addition to N2O, simulations of CFC-12 and SF6 were made by a subset of four of the models to provide information on the models' proficiency in stratosphere-troposphere exchange (STE) and meridional transport, respectively. The same prior emissions were used by all models to restrict differences among models to transport and chemistry alone. Four different N2O flux scenarios totalling between 14 and 17 TgN yr(-1) (for 2005) globally were also compared. The modelled N2O mixing ratios were assessed against observations from in situ stations, discrete air sampling networks and aircraft. All models adequately captured the large-scale patterns of N2O and the vertical gradient from the troposphere to the stratosphere and most models also adequately captured the N2O tropospheric growth rate. However, all models underestimated the inter-hemispheric N2O gradient by at least 0.33 parts per billion (ppb), equivalent to 1.5 TgN, which, even after accounting for an overestimate of emissions in the Southern Ocean of circa 1.0 TgN, points to a likely underestimate of the Northern Hemisphere source by up to 0.5 TgN and/or an overestimate of STE in the Northern Hemisphere. Comparison with aircraft data reveal that the models over-estimate the amplitude of the N2O seasonal cycle at Hawaii (21 degrees N, 158 degrees W) below circa 6000 m, suggesting an overestimate of the importance of stratosphere to troposphere transport in the lower troposphere at this latitude. In the Northern Hemisphere, most of the models that provided CFC-12 simulations captured the phase of the CFC-12, seasonal cycle, indicating a reasonable representation of the timing of STE. However, for N2O all models simulated a too early minimum by 2 to 3 months owing to errors in the seasonal cycle in the prior soil emissions, which was not adequately represented by the terrestrial biosphere model. In the Southern Hemisphere, most models failed to capture the N2O and CFC-12 seasonality at Cape Grim, Tasmania, and all failed at the South Pole, whereas for SF6, all models could capture the seasonality at all sites, suggesting that there are large errors in modelled vertical transport in high southern latitudes.

Thompson, RL, Ishijima K, Saikawa E, Corazza M, Karstens U, Patra PK, Bergamaschi P, Chevallier F, Dlugokencky E, Prinn RG, Weiss RF, O'Doherty S, Fraser PJ, Steele LP, Krummel PB, Vermeulen A, Tohjima Y, Jordan A, Haszpra L, Steinbacher M, Van der Laan S, Aalto T, Meinhardt F, Popa ME, Moncrieff J, Bousquet P.  2014.  TransCom N2O model inter-comparison - Part 2: Atmospheric inversion estimates of N2O emissions. Atmospheric Chemistry and Physics. 14:6177-6194.   10.5194/acp-14-6177-2014   AbstractWebsite

This study examines N2O emission estimates from five different atmospheric inversion frameworks based on chemistry transport models (CTMs). The five frameworks differ in the choice of CTM, meteorological data, prior uncertainties and inversion method but use the same prior emissions and observation data set. The posterior modelled atmospheric N2O mole fractions are compared to observations to assess the performance of the inversions and to help diagnose problems in the modelled transport. Additionally, the mean emissions for 2006 to 2008 are compared in terms of the spatial distribution and seasonality. Overall, there is a good agreement among the inversions for the mean global total emission, which ranges from 16.1 to 18.7 TgN yr(-1) and is consistent with previous estimates. Ocean emissions represent between 31 and 38% of the global total compared to widely varying previous estimates of 24 to 38%. Emissions from the northern mid- to high latitudes are likely to be more important, with a consistent shift in emissions from the tropics and subtropics to the mid- to high latitudes in the Northern Hemisphere; the emission ratio for 0-30A degrees N to 30-90A degrees N ranges from 1.5 to 1.9 compared with 2.9 to 3.0 in previous estimates. The largest discrepancies across inversions are seen for the regions of South and East Asia and for tropical and South America owing to the poor observational constraint for these areas and to considerable differences in the modelled transport, especially inter-hemispheric exchange rates and tropical convective mixing. Estimates of the seasonal cycle in N2O emissions are also sensitive to errors in modelled stratosphere-to-troposphere transport in the tropics and southern extratropics. Overall, the results show a convergence in the global and regional emissions compared to previous independent studies.