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Klatt, O, Roether W, Hoppema M, Bulsiewicz K, Fleischmann U, Rodehacke C, Fahrbach E, Weiss RF, Bullister JL.  2002.  Repeated CFC sections at the Greenwich Meridian in the Weddell Sea. Journal of Geophysical Research-Oceans. 107   10.1029/2000jc000731   AbstractWebsite

[1] Repeated observations of the tracer chlorofluorocarbon-11 (CFC-11) for a section along the Greenwich Meridian from Antarctica (70degreesS) to about 50 S are presented for the period 1984-1998. The CFC sections display a highly persistent pattern. A middepth CFC minimum in the central Weddell Sea is bounded laterally by elevated levels of dissolved CFCs at the southern margin of the Weddell Basin and by a column of elevated CFC concentrations around 55degreesS near to the northern margin. Part of the latter column covers waters of the Antarctic Circumpolar Current, which indicates that a moderate portion of these waters was ventilated in the Weddell Sea. Deep CFC maxima adjoining the southern and northern margins of the Weddell Basin indicate advective cores of recently ventilated waters. The southern core supports previous notions of deep water import into the Weddell Sea from the east. For all deep and bottom waters, the portions ventilated on the CFC timescale (similar to50 years) are small. Effective initial CFC saturations for these portions are estimated to be between 60 and 70%, using in part new data from off the Filchner-Ronne Ice Shelf. For various CFC features along the section (mostly advective cores), ventilated fractions and mean ages of these fractions were obtained (with error limits). The procedure was to fit an age distribution of a prescribed form to CFC-11 time series for these features, constructed from the various realizations of the CFC section. The ages are between 3 and 19 years, and the ventilated fractions range between 6 and 23%, indicating a rather limited ventilation of the interior Weddell Sea subsurface layer waters on the CFC timescale. It is shown that the concurrent CFC-12 data provide little additional information. The work demonstrates a high information content of repeated tracer observations and encourages similar approaches also in other ocean regions.

Rigby, M, Montzka SA, Prinn RG, White JWC, Young D, O’Doherty S, Lunt MF, Ganesan AL, Manning AJ, Simmonds PG, Salameh PK, Harth CM, Mühle J, Weiss RF, Fraser PJ, Steele PL, Krummel PB, McCulloch A, Park S.  2017.  Role of atmospheric oxidation in recent methane growth. Proceedings of the National Academy of Sciences.   10.1073/pnas.1616426114   Abstract

The growth in global methane (CH4) concentration, which had been ongoing since the industrial revolution, stalled around the year 2000 before resuming globally in 2007. We evaluate the role of the hydroxyl radical (OH), the major CH4 sink, in the recent CH4 growth. We also examine the influence of systematic uncertainties in OH concentrations on CH4 emissions inferred from atmospheric observations. We use observations of 1,1,1-trichloroethane (CH3CCl3), which is lost primarily through reaction with OH, to estimate OH levels as well as CH3CC3 emissions, which have uncertainty that previously limited the accuracy of OH estimates. We find a 64–70% probability that a decline in OH has contributed to the post-2007 methane rise. Our median solution suggests that CH4 emissions increased relatively steadily during the late 1990s and early 2000s, after which growth was more modest. This solution obviates the need for a sudden statistically significant change in total CH4 emissions around the year 2007 to explain the atmospheric observations and can explain some of the decline in the atmospheric 13CH4/12CH4 ratio and the recent growth in C2H6. Our approach indicates that significant OH-related uncertainties in the CH4 budget remain, and we find that it is not possible to implicate, with a high degree of confidence, rapid global CH4 emissions changes as the primary driver of recent trends when our inferred OH trends and these uncertainties are considered.

McNorton, J, Chipperfield MP, Gloor M, Wilson C, Feng WH, Hayman GD, Rigby M, Krummel PB, O'Doherty S, Prinn RG, Weiss RF, Young D, Dlugokencky E, Montzka SA.  2016.  Role of OH variability in the stalling of the global atmospheric CH4 growth rate from 1999 to 2006. Atmospheric Chemistry and Physics. 16:7943-7956.   10.5194/acp-16-7943-2016   AbstractWebsite

The growth in atmospheric methane (CH4) concentrations over the past 2 decades has shown large variability on a timescale of several years. Prior to 1999 the globally averaged CH4 concentration was increasing at a rate of 6.0aEuro-ppbaEuro-yr(-1), but during a stagnation period from 1999 to 2006 this growth rate slowed to 0.6aEuro-ppbaEuro-yr(-1). From 2007 to 2009 the growth rate again increased to 4.9aEuro-ppbaEuro-yr(-1). These changes in growth rate are usually ascribed to variations in CH4 emissions. We have used a 3-D global chemical transport model, driven by meteorological reanalyses and variations in global mean hydroxyl (OH) concentrations derived from CH3CCl3 observations from two independent networks, to investigate these CH4 growth variations. The model shows that between 1999 and 2006 changes in the CH4 atmospheric loss contributed significantly to the suppression in global CH4 concentrations relative to the pre-1999 trend. The largest factor in this is relatively small variations in global mean OH on a timescale of a few years, with minor contributions of atmospheric transport of CH4 to its sink region and of atmospheric temperature. Although changes in emissions may be important during the stagnation period, these results imply a smaller variation is required to explain the observed CH4 trends. The contribution of OH variations to the renewed CH4 growth after 2007 cannot be determined with data currently available.

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Weiss, RF, Jahnke RA, Keeling CD.  1982.  Seasonal effects of temperature and salinity on the partial pressure of CO2 in seawater. Nature. 300:511-513.   10.1038/300511a0   AbstractWebsite

The exchange of CO2 between the atmosphere and the sea is of major importance to our understanding of the climatic consequences of anthropogenic CO2. Because the solubility of CO2 and the dissociation of carbonic acid in seawater are modulated by temperature and salinity, the detection of long-term changes in the oceanic carbonate system, first requires that the comparatively large short-term variations in the partial pressure of CO2 should be characterized. We present here the first direct observations of seasonal variations in the partial pressure of CO2 in the subtropical gyres of the North and South Pacific Ocean. These variations compare well with the variations predicted from observed changes in temperature and salinity using empirical equations which do not require the determination of alkalinity or total inorganic carbon, and the agreement is improved by the inclusion of air–sea exchange in the model calculations. Thus we predict that specific alkalinity within the two gyres remains extremely constant, which is confirmed by carbonate equilibrium calculations based on our measurements of total inorganic carbon.

Kurylo, MJ, Rodriguez JM, Andreae MO, Atlas EL, Blake DR, Butler JH, Lal S, Lary DJ, Midgley PM, Montzka SA, Novelli PC, Reeves CE, Simmonds PG, Steele LP, Sturges WT, Weiss RF, Yokouchi Y.  1999.  Short-lived ozone-related compounds. Scientific assessment of ozone depletion, 1998 (World Meteorological Organization, Global Ozone Research and Monitoring Project Report 44). :56., Washington, DC: National Oceanic and Atmospheric Administration Abstract
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Rhew, RC, Miller BR, Vollmer MK, Weiss RF.  2001.  Shrubland fluxes of methyl bromide and methyl chloride. Journal of Geophysical Research-Atmospheres. 106:20875-20882.   10.1029/2001jd000413   AbstractWebsite

Flux measurements in coastal sage scrub, chamise chaparral, and creosote bush scrub environments show that methyl bromide (CH(3)Br) and methyl chloride (CH(3)Cl), compounds that are involved in stratospheric ozone depletion, are both produced and consumed by southern California shrubland ecosystems. CH(3)Br and CH(3)Cl are produced in association with a variety of plants and are consumed by the soils, although there is a large variability in the fluxes, depending on predominant vegetation and environmental conditions. At sites with a net uptake of both compounds the fluxes of CH(3)Cl and CH(3)Br show a strong correlation, with a molar ratio of roughly 40:1, pointing to a similar mechanism of consumption. In contrast, the net production rates of these compounds show no apparent correlation with each other. The average observed net CH(3)Br uptake rates are an order of magnitude smaller than the previously reported average soil consumption rates assigned to shrublands. Extrapolations from our field measurements suggest that shrublands globally have a maximum net consumption of <1 Gg yr(-1) for CH(3)Br and < 20 Gg yr(-1) for CH(3)Cl and may, in fact, be net sources for these compounds. Consequently, the measured net fluxes from shrubland ecosystems can account for part of the present imbalance in the CH(3)Br budget by adding a new source term and potentially reducing the soil sink term. These results also suggest that while shrubland soil consumption of CH(3)Cl may be small, soils in general may be a globally significant sink for CH(3)Cl.

Wells, KC, Millet DB, Bousserez N, Henze DK, Chaliyakunnel S, Griffis TJ, Luan Y, Dlugokencky EJ, Prinn RG, O'Doherty S, Weiss RF, Dutton GS, Elkins JW, Krummel PB, Langenfelds R, Steele LP, Kort EA, Wofsy SC, Umezawa T.  2015.  Simulation of atmospheric N2O with GEOS-Chem and its adjoint: evaluation of observational constraints. Geoscientific Model Development. 8:3179-3198.   10.5194/gmd-8-3179-2015   AbstractWebsite

We describe a new 4D-Var inversion framework for nitrous oxide (N2O) based on the GEOS-Chem chemical transport model and its adjoint, and apply it in a series of observing system simulation experiments to assess how well N2O sources and sinks can be constrained by the current global observing network. The employed measurement ensemble includes approximately weekly and quasicontinuous N2O measurements (hourly averages used) from several long-term monitoring networks, N2O measurements collected from discrete air samples onboard a commercial aircraft (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container; CARIBIC), and quasi-continuous measurements from the airborne HIAPER Pole-to-Pole Observations (HIPPO) campaigns. For a 2-year inversion, we find that the surface and HIPPO observations can accurately resolve a uniform bias in emissions during the first year; CARIBIC data provide a somewhat weaker constraint. Variable emission errors are much more difficult to resolve given the long lifetime of N2O, and major parts of the world lack significant constraints on the seasonal cycle of fluxes. Current observations can largely correct a global bias in the stratospheric sink of N2O if emissions are known, but do not provide information on the temporal and spatial distribution of the sink. However, for the more realistic scenario where source and sink are both uncertain, we find that simultaneously optimizing both would require unrealistically small errors in model transport. Regardless, a bias in the magnitude of the N2O sink would not affect the a posteriori N2O emissions for the 2-year timescale used here, given realistic initial conditions, due to the timescale required for stratosphere-troposphere exchange (STE). The same does not apply to model errors in the rate of STE itself, which we show exerts a larger influence on the tropospheric burden of N2O than does the chemical loss rate over short (< 3 year) timescales. We use a stochastic estimate of the inverse Hessian for the inversion to evaluate the spatial resolution of emission constraints provided by the observations, and find that significant, spatially explicit constraints can be achieved in locations near and immediately upwind of surface measurements and the HIPPO flight tracks; however, these are mostly confined to North America, Europe, and Australia. None of the current observing networks are able to provide significant spatial information on tropical N2O emissions. There, averaging kernels (describing the sensitivity of the inversion to emissions in each grid square) are highly smeared spatially and extend even to the midlatitudes, so that tropical emissions risk being conflated with those elsewhere. For global inversions, therefore, the current lack of constraints on the tropics also places an important limit on our ability to understand extratropical emissions. Based on the error reduction statistics from the inverse Hessian, we characterize the atmospheric distribution of unconstrained N2O, and identify regions in and downwind of South America, central Africa, and Southeast Asia where new surface or profile measurements would have the most value for reducing present uncertainty in the global N2O budget.

Vollmer, MK, Weiss RF.  2002.  Simultaneous determination of sulfur hexafluoride and three chlorofluorocarbons in water and air. Marine Chemistry. 78:137-148.   10.1016/s0304-4203(02)00015-4   AbstractWebsite

We have developed an analytical technique for the simultaneous measurement of the four trace gases sulfur hexafluoride (SF(6)) and the chlorofluorocarbons CCl(2)F(2) (CFC-12), CCl(3)F (CFC-11) and CCl(2)FCClF(2) (CFC-113) in water and air. Water samples are flame sealed into 350-ml glass ampoules which allow storage and sampling in locations where field measurements are not practical. For analysis, these ampoules are stripped of dissolved gases after their stems are cracked in an enclosed chamber such that the headspace fraction in the ampoule is included in the measurement. The extracted gases are then trapped cryogenically and are separated on packed columns. CFC-11 and CFC-113 are measured on one electron capture detector (ECD), while SF(6) and CFC-12 are cryofocussed on a second trap and analyzed on a second ECD. Detection limits for seawater samples are about 0.015 fmol kg(-1) for SF(6), 0.010 pmol kg(-1) for CFC-12, 0.014 pmol kg(-1) for CFC-11, and 0.024 pmol kg(-1) for CFC-113. This analytical technique also allows for analysis of air samples with low concentrations or at low pressures. Results from a profile in the northeastern Pacific Ocean show that SF6 partial pressure ages are consistent with those of CFC-11 and CFC-12 over the age range covered by this profile. From this, we infer that SF6 is useful for the dating of recently ventilated waters, thus complementing the dating of older waters using CFCs. Earlier reports of the degradation of CFC-113 in oxygenated water are supported by our results for samples stored in ampoules. (C) 2002 Elsevier Science B.V All rights reserved.

Warner, MJ, Weiss RF.  1985.  Solubilities of chlorofluorocarbons 11 and 12 in water and seawater. Deep-Sea Research Part a-Oceanographic Research Papers. 32:1485-1497.   10.1016/0198-0149(85)90099-8   AbstractWebsite

The solubilities of dilute mixtures of the chlorofluorocarbons CCl3F (CFC-11) and CCl2F2 (CFC-12) in pure water and seawater over the temperature range 0 to 40°C have been measured by gas chromatography. The data have been fitted to equations in temperature and salinity of the form used previously to fit the solubilities of other gases. The fitted values have an estimated accuracy of ∼1.5% and a relative precision of ∼0.7% for both chlorofluorocarbons. The nonideal behavior of these compounds in dilute air mixtures is discussed, and their solubilities from a water-saturated atmosphere are presented in parametric form.

Weiss, RF.  1971.  Solubility of helium and neon in water and seawater. Journal of Chemical and Engineering Data. 16:235-241.   10.1021/je60049a019   AbstractWebsite

Sulfur hexafluoride (SF6) has been measured at Cape Grim since 1978 via a combination of in situ and flask measurements, including measurements on the Cape Grim air archive. The long-term growth rate of SF6 as observed at Cape Grim has increased from 0.1 ppt yr-1 in the late 1970s to 0.24 ppt yr-1 in the mid-1990s. Since then the growth rate has remained relatively constant at 0.23±0.02 ppt yr-1, indicating relatively constant global emissions (±10 %) since 1995. Pollution episodes at Cape Grim have been used to estimate regional (Melbourne and environs) and Australian emissions of SF6 at 3±1.5 and 15±7.5 tonnes yr-1 during 2001-2003.

Weiss, RF, Kyser TK.  1978.  Solubility of krypton in water and seawater. Journal of Chemical and Engineering Data. 23:69-72.   10.1021/je60076a014   AbstractWebsite
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Weiss, RF.  1970.  The solubility of nitrogen, oxygen and argon in water and seawater. Deep-Sea Research. 17:721-735.   10.1016/0011-7471(70)90037-9   AbstractWebsite

Recent precise data on the solubilities of nitrogen, oxygen and argon in distilled water and seawater are fitted to thermodynamically consistent equations by the method of least squares. The temperature dependence of the Bunsen solubility coefficient is treated using the integrated van't Hoff equation. It is shown that the Setchénow relation gives an adequate representation of the salting-out effect. Equations expressing the solubilities of these gases, as a function of temperature and salinity, in units of the Bunsen coefficient, ml/l., and ml/kg are given along with solubility tables in each of these units.

Weiss, RF.  1993.  South Atlantic Ventilation Experiment : SIO chlorofluorocarbon measurements. Scripps Institution of Oceanography Reference Series. :466., La Jolla, CA: Scripps Institution of Oceanography, University of California, San Diego Abstract
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Nevison, CD, Keeling RF, Weiss RF, Popp BN, Jin X, Fraser PJ, Porter LW, Hess PG.  2005.  Southern Ocean ventilation inferred from seasonal cycles of atmospheric N2O and O2/N2 at Cape Grim, Tasmania. Tellus Series B-Chemical and Physical Meteorology. 57:218-229.   10.1111/j.1600-0889.2005.00143.x   AbstractWebsite

The seasonal cycle of atmospheric N(2)O is derived from a 10-yr observational record at Cape Grim, Tasmania (41 degrees S, 145 degrees E). After correcting for thermal and stratospheric influences, the observed atmospheric seasonal cycle is consistent with the seasonal outgassing of microbially produced N(2)O from the Southern Ocean, as predicted by an ocean biogeochemistry model coupled to an atmospheric transport model (ATM). The model-observation comparison suggests a Southern Ocean N(2)O source of similar to 0.9 Tg N yr(-1) and is the first study to reproduce observed atmospheric seasonal cycles in N(2)O using specified surface sources in forward ATM runs. However, these results are sensitive to the thermal and stratospheric corrections applied to the atmospheric N(2)O data. The correlation in subsurface waters between apparent oxygen utilization (AOU) and N(2)O production (approximated as the concentration in excess of atmospheric equilibrium Delta N(2)O) is exploited to infer the atmospheric seasonal cycle in O(2)/N(2) due to ventilation of O(2)-depleted subsurface waters. Subtracting this cycle from the observed, thermally corrected seasonal cycle in atmospheric O(2)/N(2) allows the residual O(2)/N(2) signal from surface net community production to be inferred. Because N(2)O is only produced in subsurface ocean waters, where it is correlated to O(2) consumption, atmospheric N(2)O observations provide a methodology for distinguishing the surface production and subsurface ventilation signals in atmospheric O(2)/N(2), which have previously been inseparable.

Yadav, V, Duren R, Mueller K, Verhulst KR, Nehrkorn T, Kim J, Weiss RF, Keeling R, Sander S, Fischer ML, Newman S, Falk M, Kuwayama T, Hopkins F, Rafiq T, Whetstone J, Miller C.  2019.  Spatio-temporally resolved methane fluxes from the Los Angeles megacity. Journal of Geophysical Research-Atmospheres. 124:5131-5148.   10.1029/2018jd030062   AbstractWebsite

We combine sustained observations from a network of atmospheric monitoring stations with inverse modeling to uniquely obtain spatiotemporal (3-km, 4-day) estimates of methane emissions from the Los Angeles megacity and the broader South Coast Air Basin for 2015-2016. Our inversions use customized and validated high-fidelity meteorological output from Weather Research Forecasting and Stochastic Time-Inverted Lagrangian model for South Coast Air Basin and innovatively employ a model resolution matrix-based metric to disentangle the spatiotemporal information content of observations as manifested through estimated fluxes. We partially track and constrain fluxes from the Aliso Canyon natural gas leak and detect closure of the Puente Hills landfill, with no prior information. Our annually aggregated fluxes and their uncertainty excluding the Aliso Canyon leak period lie within the uncertainty bounds of the fluxes reported by the previous studies. Spatially, major sources of CH4 emissions in the basin were correlated with CH4-emitting infrastructure. Temporally, our findings show large seasonal variations in CH4 fluxes with significantly higher fluxes in winter in comparison to summer months, which is consistent with natural gas demand and anticorrelated with air temperature. Overall, this is the first study that utilizes inversions to detect both enhancement (Aliso Canyon leak) and reduction (Puente Hills) in CH4 fluxes due to the unintended events and policy decisions and thereby demonstrates the utility of inverse modeling for identifying variations in fluxes at fine spatiotemporal resolution.

Alexander, B, Vollmer MK, Jackson T, Weiss RF, Thiemens MH.  2001.  Stratospheric CO2 isotopic anomalies and SF6 and CFC tracer concentrations in the Arctic polar vortex. Geophysical Research Letters. 28:4103-4106.   10.1029/2001gl013692   AbstractWebsite

Isotopic measurements (delta O-17 and delta O-18) Of CO2 along with concentration measurements of SF6, CC1(3)F (CFC-11), CC1(2)F(2) (CFC-12) and CC1(2)FCC1F(2) (CFC-113) in stratospheric samples collected within the Arctic polar vortex are reported. These are the first simultaneous measurements of the concentration of fluorinated compounds and the complete oxygen isotopic composition Of CO2 in the middle atmosphere. A mass-independent anomaly in the oxygen isotopic composition Of CO2 is observed that arises from isotopic exchange with stratospheric O(D-1) derived from O-3 photolysis. The data exhibit a strong anti-correlation between the Delta O-17 (the degree of the mass-independent anomaly) and molecular tracer concentrations. The potential ability of tl-ris isotopic proxy to trace mesospheric and stratospheric transport is discussed.

Nevison, CD, Kinnison DE, Weiss RF.  2004.  Stratospheric influences on the tropospheric seasonal cycles of nitrous oxide and chlorofluorocarbons. Geophysical Research Letters. 31   10.1029/2004gl020398   AbstractWebsite

The stratospheric influence on the tropospheric seasonal cycles of N2O, CFC-11 ( CCl3F), CFC-12 (CCl2F2) and CFC-113 (CCl2FCClF2) is investigated using observations from the AGAGE global trace gas monitoring network and the results of the Whole Atmosphere Community Climate Model (WACCM). WACCM provides the basis for a number of predictions about the relative amplitudes of N2O and CFC seasonal cycles and about the relative magnitude and phasing of seasonal cycles in the northern and southern hemispheres. These predictions are generally consistent with observations, suggesting that the stratosphere exerts a coherent influence on the tropospheric seasonal cycles of trace gases whose primary sinks are in the stratosphere. This stratospheric influence may complicate efforts to validate estimated source distributions of N2O, an important greenhouse gas, in atmospheric transport model studies.

Fraser, PJ, Porter LW, Baly SB, Krummel PB, Dunse BL, Steele LP, Derek N, Langenfelds RL, Levin I, Oram DE, Elkins JW, Vollmer MK, Weiss RF.  2004.  Sulfur hexafluoride at Cape Grim: Long term trends and regional emissions, Baseline 2001-2002. :18-23., Melbourne Abstract
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Muhle, J, Huang J, Weiss RF, Prinn RG, Miller BR, Salameh PK, Harth CM, Fraser PJ, Porter LW, Greally BR, O'Doherty S, Simmonds PG.  2009.  Sulfuryl fluoride in the global atmosphere. Journal of Geophysical Research-Atmospheres. 114   10.1029/2008jd011162   AbstractWebsite

The first calibrated high-frequency, high-precision, in situ atmospheric and archived air measurements of the fumigant sulfuryl fluoride (SO(2)F(2)) have been made as part of the Advanced Global Atmospheric Gas Experiment (AGAGE) program. The global tropospheric background concentration of SO(2)F(2) has increased by 5 +/- 1% per year from similar to 0.3 ppt (parts per trillion, dry air mol fraction) in 1978 to similar to 1.35 ppt in May 2007 in the Southern Hemisphere, and from similar to 1.08 ppt in 1999 to similar to 1.53 ppt in May 2007 in the Northern Hemisphere. The SO(2)F(2) interhemispheric concentration ratio was 1.13 +/- 0.02 from 1999 to 2007. Two-dimensional 12-box model inversions yield global total and global oceanic uptake atmospheric lifetimes of 36 +/- 11 and 40 +/- 13 years, respectively, with hydrolysis in the ocean being the dominant sink, in good agreement with 35 +/- 14 years from a simple oceanic uptake calculation using transfer velocity and solubility. Modeled SO2F2 emissions rose from similar to 0.6 Gg/a in 1978 to similar to 1.9 Gg/a in 2007, but estimated industrial production exceeds these modeled emissions by an average of similar to 50%. This discrepancy cannot be explained with a hypothetical land sink in the model, suggesting that only similar to 2/3 of the manufactured SO(2)F(2) is actually emitted into the atmosphere and that similar to 1/3 may be destroyed during fumigation. With mean SO(2)F(2) tropospheric mixing ratios of similar to 1.4 ppt, its radiative forcing is small and it is probably an insignificant sulfur source to the stratosphere. However, with a high global warming potential similar to CFC-11, and likely increases in its future use, continued atmospheric monitoring of SO(2)F(2) is warranted.

Weiss, RF, Van Woy FA, Salameh PK.  1992.  Surface water and atmospheric carbon dioxide and nitrous oxide observations by shipboard automated gas chromatography : results from expeditions between 1977 and 1990. Scripps Institution of Oceanography Reference Series. :144., La Jolla, Calif.: Scripps Institution of Oceanography, University of California, San Diego Abstract
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Deeds, DA, Kulongoski JT, Mühle J, Weiss RF.  2015.  Tectonic activity as a significant source of crustal tetrafluoromethane emissions to the atmosphere: Observations in groundwaters along the San Andreas Fault. Earth and Planetary Science Letters. 412:163-172.   10.1016/j.epsl.2014.12.016   AbstractWebsite

Tetrafluoromethane (CF4) concentrations were measured in 14 groundwater samples from the Cuyama Valley, Mil Potrero and Cuddy Valley aquifers along the Big Bend section of the San Andreas Fault System (SAFS) in California to assess whether tectonic activity in this region is a significant source of crustal CF4 to the atmosphere. Dissolved CF4 concentrations in all groundwater samples but one were elevated with respect to estimated recharge concentrations including entrainment of excess air during recharge ( C r e ; ∼30 fmol kg−1 H2O), indicating subsurface addition of CF4 to these groundwaters. Groundwaters in the Cuyama Valley contain small CF4 excesses (0.1–9 times C r e ), which may be attributed to an in situ release from weathering and a minor addition of deep crustal CF4 introduced to the shallow groundwater through nearby faults. CF4 excesses in groundwaters within 200 m of the SAFS are larger (10–980 times C r e ) and indicate the presence of a deep crustal flux of CF4 that is likely associated with the physical alteration of silicate minerals in the shear zone of the SAFS. Extrapolating CF4 flux rates observed in this study to the full extent of the SAFS (1300 km × 20–100 km) suggests that the SAFS potentially emits ( 0.3 – 1 ) × 10 − 1 kg CF4 yr−1 to the Earth's surface. For comparison, the chemical weathering of ∼ 7.5 × 10 4 km 2 of granitic rock in California is estimated to release ( 0.019 – 3.2 ) × 10 − 1 kg CF4 yr−1. Tectonic activity is likely an important, and potentially the dominant, driver of natural emissions of CF4 to the atmosphere. Variations in preindustrial atmospheric CF4 as observed in paleo-archives such as ice cores may therefore represent changes in both continental weathering and tectonic activity, including changes driven by variations in continental ice cover during glacial–interglacial transitions.

Weiss, RF.  1981.  The temporal and spatial distribution of tropospheric nitrous oxide. Journal of Geophysical Research-Oceans and Atmospheres. 86:7185-7195.   10.1029/JC086iC08p07185   AbstractWebsite

The concentration of nitrous oxide has been measured in air samples collected between 1976 and 1980 at several monitoring stations and aboard Oceanographic vessels in the major world oceans. These measurements demonstrate that the tropospheric nitrous oxide concentration is increasing at ∼0.2% per year, thus confirming earlier observations of the increase based on stored samples. The measurements also show that the concentration of nitrous oxide in the northern hemisphere is higher than in the southern hemisphere, the average difference during the sampling interval having been about 0.8 parts per billion (ppb), compared to a January 1, 1978 northern hemisphere dry air mole fraction of 300.2 ppb. The data are well represented by a simple box model which relates the tropospheric rate of increase to an exponentially increasing source function. The observed increase may be explained by combustion of fossil fuels and agricultural activity, with a total source strength of ∼11 × 1010 mol/yr as of January 1, 1978. A substantial fraction of this production is explained by combustion, and agricultural production is therefore considerably less than has been previously estimated. The concentration of nitrous oxide in the preindustrial unperturbed troposphere is estimated to have been between 281 and 291 ppb, depending upon the rate of increase of the mean anthropogenic source function, and the preindustrial latitudinal distribution is estimated to have been nearly uniform. According to the model projections, the concentration of tropospheric nitrous oxide in the year 2000 will be 5 to 7% above present values. The observed rate of tropospheric increase directly affects the production of stratospheric nitric oxide, and plays a significant role in the earth's radiation balance, conservatively estimated as 10–15% of the effect due to increasing carbon dioxide.

Deeds, DA, Muhle J, Weiss RF.  2008.  Tetrafluoromethane in the deep North Pacific Ocean. Geophysical Research Letters. 35   10.1029/2008gl034355   AbstractWebsite

Dissolved tetrafluoromethane (CF(4)) has been measured for the first time in the North Pacific Ocean. Surface water collected during calm weather is near equilibrium with the modern atmosphere. Deep water, isolated from atmospheric exchange for centuries, is near equilibrium with the preindustrial atmosphere, after accounting for an expected 5% addition of this low-solubility gas due to air injection during high-latitude deep-water formation. These results strongly suggest that dissolved CF(4) is conservative in seawater and that the oceanic imprint of anthropogenic increases in atmospheric CF(4) can be used as a time-dependent tracer of ocean ventilation and subsurface circulation processes. Although the continental lithosphere is a source of natural atmospheric CF(4), we find no evidence of an oceanic lithospheric CF(4) input into deep Pacific waters. The estimated upper limit of a potential oceanic lithospheric CF(4) flux to the global atmosphere is on the order of 4% of that from the continental lithosphere.

Gordon, AL, Weiss RF, Smethie WM, Warner MJ.  1992.  Thermocline and intermediate water communication between the south Atlantic and Indian oceans. Journal of Geophysical Research-Oceans. 97:7223-7240.   10.1029/92jc00485   AbstractWebsite

A conductivity-temperature-depth and tracer chemistry section in the southeast South Atlantic in December 1989 and January 1990 presents strong evidence that there is a significant interocean exchange of thermocline and intermediate water between the South Atlantic and Indian oceans. Eastward flowing water at 10-degrees-W composed of South Atlantic Central (thermocline) Water is too enriched with chlorofluoromethanes 11 and 12 and oxygen to be the sole source of similar theta-S water within the northward flowing Benguela Current. About two thirds of the Benguela Current thermocline transport is drawn from the Indian Ocean; the rest is South Atlantic water that has folded into the Benguela Current in association with the Agulhas eddy-shedding process. South Atlantic Central water passes in the Indian Ocean by a route to the south of the Agulhas Return Current. The South Atlantic water loops back to the Atlantic within the Indian Ocean, perhaps mostly within the Agulhas recirculation cell of the southwest Indian Ocean. Linkage of Atlantic and Indian Ocean water diminishes with increasing depth; it extends through the lower thermocline into the Antarctic Intermediate Water (AAIW) (about 50% is derived from the Indian Ocean) but not into the deep water. While much of the interocean exchange remains on an approximate horizontal "isopycnal" plane, as much as 10 x 10(6) m3 s-1 of Indian Ocean water within the 25 x 10(6) m3 s-1 Benguela Current, mostly derived from the lower thermocline and AAIW, may balance deeper Atlantic export of North Atlantic Deep Water (NADW). The addition of salt water from the evaporative Indian Ocean into the South Atlantic Ocean thermocline and AAIW levels may precondition the Atlantic for NADW formation. While AAIW seems to be the chief feed for NADW, the bulk of it enters the subtropical South Atlantic, spiked with Indian Ocean salt, within the Benguela Current rather than along the western boundary of the South Atlantic.

Kirschke, S, Bousquet P, Ciais P, Saunois M, Canadell JG, Dlugokencky EJ, Bergamaschi P, Bergmann D, Blake DR, Bruhwiler L, Cameron-Smith P, Castaldi S, Chevallier F, Feng L, Fraser A, Heimann M, Hodson EL, Houweling S, Josse B, Fraser PJ, Krummel PB, Lamarque JF, Langenfelds RL, Le Quere C, Naik V, O'Doherty S, Palmer PI, Pison I, Plummer D, Poulter B, Prinn RG, Rigby M, Ringeval B, Santini M, Schmidt M, Shindell DT, Simpson IJ, Spahni R, Steele LP, Strode SA, Sudo K, Szopa S, van der Werf GR, Voulgarakis A, van Weele M, Weiss RF, Williams JE, Zeng G.  2013.  Three decades of global methane sources and sinks. Nature Geoscience. 6:813-823.   10.1038/ngeo1955   AbstractWebsite

Methane is an important greenhouse gas, responsible for about 20% of the warming induced by long-lived greenhouse gases since pre-industrial times. By reacting with hydroxyl radicals, methane reduces the oxidizing capacity of the atmosphere and generates ozone in the troposphere. Although most sources and sinks of methane have been identified, their relative contributions to atmospheric methane levels are highly uncertain. As such, the factors responsible for the observed stabilization of atmospheric methane levels in the early 2000s, and the renewed rise after 2006, remain unclear. Here, we construct decadal budgets for methane sources and sinks between 1980 and 2010, using a combination of atmospheric measurements and results from chemical transport models, ecosystem models, climate chemistry models and inventories of anthropogenic emissions. The resultant budgets suggest that data-driven approaches and ecosystem models overestimate total natural emissions. We build three contrasting emission scenarios - which differ in fossil fuel and microbial emissions - to explain the decadal variability in atmospheric methane levels detected, here and in previous studies, since 1985. Although uncertainties in emission trends do not allow definitive conclusions to be drawn, we show that the observed stabilization of methane levels between 1999 and 2006 can potentially be explained by decreasing-to-stable fossil fuel emissions, combined with stable-to-increasing microbial emissions. We show that a rise in natural wetland emissions and fossil fuel emissions probably accounts for the renewed increase in global methane levels after 2006, although the relative contribution of these two sources remains uncertain.