Export 217 results:
Sort by: Author Title Type [ Year  (Desc)]
Forster, P, Ramaswamy V, Artaxo P, Berntsen J, Betts R, Fahey DW, Haywood J, Lean J, Lowe DC, Myhre G, Nganga J, Prinn R, Raga G, Schulz M, van Dorland R, Bodeker G, Boucher O, Collins WD, Conway TJ, Dlugokencky E, Elkins JW, Etheridge D, Foukal P, Fraser P, Geller M, Joos F, Keeling CD, Keeling R, Kinne S, Lassey K, Lohmann U, Manning AC, Montzka SA, Oram D, O'Shaughnessy K, Piper SC, Plattner GK, Ponater M, Ramankutty N, Reid GC, Rind D, Rosenlof KH, Sausen R, Schwarzkopf D, Solanki SK, Stenchikov G, Stuber N, Takemura T, Textor C, Wang R, Weiss R, Whorf T.  2007.  Changes in atmospheric constituents and in radiative forcing. Climate Change 2007 : The Physical Science Basis : Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. ( Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt K, Tignor M, Miller H, Eds.).:129-234., Cambridge; New York: Cambridge University Press Abstract

For policymakers -- Technical summary -- Historical overview of climate change science -- Changes in atmospheric constituents and radiative forcing -- Observations: atmospheric surface and climate change -- Observations: changes in snow, ice, and frozen ground -- Observations: ocean climate change and sea level -- Paleoclimate -- Coupling between changes in the climate system and biogeochemistry -- Climate models and their evaluation -- Understanding and attributing climate change -- Global climate projections -- Regional climate projections -- Annex I: Glossary -- Annex II: Contributors to the IPCC WGI Fourth Assessment Report -- Annex III: Reviewers of the IPCC WGI Fourth Assessment Report -- Annex IV: Acronyms.

Clerbaux, C, Cunnold DM, Anderson J, Engel AEJ, Fraser PJ, Mahieu E, Manning A, Miller J, Montzka SA, Nassar R, Prinn R, Reimann S, Rinsland CP, Simmonds P, Verdonik D, Weiss R, Wuebbles D, Yokouchi K.  2007.  Long-lived compounds. Scientific assessment of ozone depletion, 2006 (World Meteorological Organization, Global Ozone Research and Monitoring Project, Report 50). :83., Geneva, Switzerland: World Meteorological Organization Abstract
Simmonds, PG, Manning AJ, Cunnold DM, McCulloch A, O'Doherty S, Derwent RG, Krummel PB, Fraser PJ, Dunse B, Porter LW, Wang RHJ, Greally BR, Miller BR, Salameh P, Weiss RF, Prinn RG.  2006.  Global trends, seasonal cycles, and European emissions of dichloromethane, trichloroethene, and tetrachloroethene from the AGAGE observations at Mace Head, Ireland, and Cape Grim, Tasmania. Journal of Geophysical Research-Atmospheres. 111   10.1029/2006jd007082   AbstractWebsite

[1] In situ observations ( every 4 hours) of dichloromethane (CH(2)Cl(2)) from April 1995 to December 2004 and trichloroethene (C(2)HCl(3)) and tetrachloroethene (C(2)Cl(4)) from September 2000 to December 2004 are reported for the Advanced Global Atmospheric Gases Experiment (AGAGE) station at Mace Head, Ireland. At a second AGAGE station at Cape Grim, Tasmania, CH(2)Cl(2) and C(2)Cl(4) data collection commenced in 1998 and 2000, respectively. C(2)HCl(3) is below the limit of detection at Cape Grim except during pollution episodes. At Mace Head CH(2)Cl(2) shows a downward trend from 1995 to 2004 of 0.7 +/- 0.2 ppt yr(-1) ( ppt: expressed as dry mole fractions in 10(12)), although from 1998 to 2004 the decrease has been only 0.3 +/- 0.1ppt yr(-1). Conversely, there has been a small but significant growth of 0.05 +/- 0.01 ppt yr(-1) in CH(2)Cl(2) at Cape Grim. The time series for C(2)HCl(3) and C(2)Cl(4) are relatively short for accurate trend analyses; however, we observe a small but significant decline in C(2)Cl(4) (0.18 +/- 0.05 ppt yr(-1)) at Mace Head. European emissions inferred from AGAGE measurements are compared to recent estimates from industry data and show general agreement for C(2)HCl(3). Emissions estimated from observations are lower than industry emission estimates for C(2)Cl(4) and much lower in the case of CH(2)Cl(2). A study of wildfires in Tasmania, uncontaminated by urban emissions, suggests that the biomass burning source of CH(2)Cl(2) may have been previously overestimated. All three solvents have distinct annual cycles, with the phases and amplitudes reflecting their different chemical reactivity with OH as the primary sink.

Vollmer, MK, Bootsma HA, Hecky RE, Patterson G, Halfman JD, Edmond JM, Eccles DH, Weiss RF.  2005.  Deep-water warming trend in Lake Malawi, East Africa. Limnology and Oceanography. 50:727-732. AbstractWebsite

We use historic water temperature measurements to define a deep-water warming trend in Lake Malawi, East Africa. Over the past six decades, the temperature of the deep water below 300 m has increased by similar to 0.7 degrees C. The warming trend is due mainly to the reduction of cold-water deep convection over this period, which is associated with milder winters in the region. Despite deep-water warming, density stratification was maintained at depths below 100 in. The observed warming trend was interrupted at least twice by abyssal cooling events that were associated with the wettest years on record. We propose that rainfall and cool river inflow are critical factors that control thermal structure and the rate of deep-water recharge in this deep, tropical lake.

Li, JL, Cunnold DM, Wang HJ, Weiss RF, Miller BR, Harth C, Salameh P, Harris JM.  2005.  Halocarbon emissions estimated from advanced global atmospheric gases experiment measured pollution events at Trinidad Head, California. Journal of Geophysical Research-Atmospheres. 110   10.1029/2004jd005739   AbstractWebsite

The emissions of halogenated gases from the West Coast region of the United States are estimated from measurements from 1995 to 2003 at the Advanced Global Atmospheric Gases Experiment site at Trinidad Head, California. The emissions estimation procedure uses pollution events combined with population densities integrated along back trajectories, and the estimates are constrained by independent estimates of CH4 and N2O emissions from the U. S. West Coast region. The best fit, average emissions of CH4 and N2O and the average chloroform emissions in California, Oregon, and Washington combined from 1996 to 2002 are 44, 3.7, and 0.07 kg person(-1) yr(-1), respectively. The emissions per person of CFC-11 (CCl3F), CFC-2 (CCl2F2), CFC-113 (CCl2FCClF2), and methyl chloroform (CH3CCl3) from California in 1996-1998 are calculated to be factors of approximately 2.2, 1.3, 0.7, and 1.6, respectively, less (more for CFC-113) than those reported for the northeastern United States by Barnes et al. (2003). The emission per person of all these gases in the U. S. West Coast region decreased from 1998 to 1999 by a factor of 2 or more, but from 1999 to 2002 the estimated emissions of all four gases have remained fairly constant and are 0.016, 0.048, 0.002, and 0.006 kg person(-1) yr(-1), respectively. The methyl chloroform estimates suggest a delay of up to 1 year in the decline of the emissions from 1996 to 1998, but otherwise, and in 1999-2000, in contrast to the Millet and Goldstein (2004) results, they are in agreement with the average methyl chloroform emissions per person for the United States based on the UNEP country by country consumption figures (A. McCulloch, private communication, 2004). Averaging the Trinidad Head and the Barnes et al. (2003) per person estimates and multiplying by the U. S. population suggests average methyl chloroform emissions in the United States of 18 Gg yr(-1) in 1996 to 1998. In 2001-2002, if the ratio of the emissions per person in these two regions was the same as in 1996-1998, we estimate U. S. emissions of 2.2 Gg yr(-1), which is one half of the Millet and Goldstein (2004) estimate.

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.

Reimann, S, Manning AJ, Simmonds PG, Cunnold DM, Wang RHJ, Li JL, McCulloch A, Prinn RG, Huang J, Weiss RF, Fraser PJ, O'Doherty S, Greally BR, Stemmler K, Hill M, Folini D.  2005.  Low European methyl chloroform emissions inferred from long-term atmospheric measurements. Nature. 433:506-508.   10.1038/nature03220   AbstractWebsite

Methyl chloroform (CH3CCl3, 1,1,1,-trichloroethane) was used widely as a solvent before it was recognized to be an ozone-depleting substance and its phase-out was introduced under the Montreal Protocol(1). Subsequently, its atmospheric concentration has declined steadily(2-4) and recent European methyl chloroform consumption and emissions were estimated to be less than 0.1 gigagrams per year(1,5). However, data from a short-term tropospheric measurement campaign ( EXPORT) indicated that European methyl chloroform emissions could have been over 20 gigagrams in 2000 (ref. 6), almost doubling previously estimated global emissions(1,4). Such enhanced emissions would significantly affect results from the CH3CCl3 method of deriving global abundances of hydroxyl radicals ( OH) (refs 7 - 12) - the dominant reactive atmospheric chemical for removing trace gases related to air pollution, ozone depletion and the greenhouse effect. Here we use long-term, high-frequency data from MaceHead, Ireland and Jungfraujoch, Switzerland, to infer European methyl chloroform emissions. We find that European emission estimates declined from about 60 gigagrams per year in the mid-1990s to 0.3 - 1.4 and 1.9 - 3.4 gigagrams per year in 2000 - 03, based on Mace Head and Jungfraujoch data, respectively. Our European methyl chloroform emission estimates are therefore higher than calculated from consumption data(1,5), but are considerably lower than those derived from the EXPORT campaign in 2000 ( ref. 6).

Prinn, RG, Huang J, Weiss RF, Cunnold DM, Fraser PJ, Simmonds PG, McCulloch A, Harth C, Reimann S, Salameh P, O'Doherty S, Wang RHJ, Porter LW, Miller BR, Krummel PB.  2005.  Evidence for variability of atmospheric hydroxyl radicals over the past quarter century. Geophysical Research Letters. 32   10.1029/2004gl022228   AbstractWebsite

The hydroxyl free radical (OH) is the major oxidizing chemical in the atmosphere, destroying about 3.7 petagrams (Pg) of trace gases each year, including many gases involved in ozone depletion, the greenhouse effect and urban air pollution. Measurements of 1,1,1-trichloroethane (methyl chloroform, CH3CCl3), which reacts with OH, provide the most accurate method currently utilized for determining the global behavior of OH. We report that CH3CCl3 levels rose steadily from 1978 to reach a maximum in 1992 and have since decreased rapidly to levels in 2004 about 30% of the levels when measurements began in 1978. Analysis of these observations shows that global average OH levels had a small maximum around 1989 and a larger minimum around 1998, with OH concentrations in 2003 being comparable to those in 1979. This post-1998 recovery of OH reported here contrasts with the situation 4 years ago when reported OH was decreasing. The 1997-1999 OH minimum coincides with, and is likely caused by, major global wildfires and an intense El Nino event at this time.

Greally, BR, Simmonds PG, O'Doherty S, McCulloch A, Miller BR, Salameh PK, Muhle J, Tanhua T, Harth C, Weiss RF, Fraser PJ, Krummel PB, Dunse BL, Porter LW, Prinn RG.  2005.  Improved continuous in situ measurements of C1–C3 PFCs, HFCs, HCFCs, CFCs and SF6 in Europe and Australia. Environmental Sciences. 2:253-261.   10.1080/15693430500402614   Abstract

Improved monitoring of non-CO2 greenhouse gases in air samples is presented, achieved using a new analytical system based on preconcentration, gas-chromatography and mass spectrometry. In addition to the major HFCs, HCFCs and CFCs, the new observations include the first in situ time series of the C1–C3 PFCs (CF4, C2F6 and C3F8) and the more volatile of the HFCs (CHF3, CH2F2, CH3CF3) alongside SF6, all of which are now monitored routinely as part of the Advanced Global Atmospheric Gases Experiment (AGAGE). Observed trends in newly monitored species are shown, obtained from 1–2 years continuous in situ air analyses at remote monitoring sites at Mace Head (Ireland) and Cape Grim (Australia). Observed deviations in the air background for these gas species are linked to modelled trajectories of air masses arriving at the monitoring stations to indicate potential source regions for emissions in Europe and Australia. In addition, preliminary estimates of 2004 mixing ratio growth rates of compounds are deduced from the observations, which highlight the importance of continuous atmospheric monitoring for verification of consumption-based emission estimates of non-CO2 greenhouse gases.

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.

Simmonds, PG, Derwent RG, Manning AJ, Fraser PJ, Krummel PB, O'Doherty S, Prinn RG, Cunnold DM, Miller BR, Wang HJ, Ryall DB, Porter LW, Weiss RF, Salameh PK.  2004.  AGAGE observations of methyl bromide and methyl chloride at Mace Head, Ireland, and Cape Grim, Tasmania, 1998-2001. Journal of Atmospheric Chemistry. 47:243-269.   10.1023/B:JOCH.0000021136.52340.9c   AbstractWebsite

In situ AGAGE GC-MS measurements of methyl bromide (CH3Br) and methyl chloride (CH3Cl) at Mace Head, Ireland and Cape Grim, Tasmania (1998-2001) reveal a complex pattern of sources. At Mace Head both gases have well-defined seasonal cycles with similar average annual decreases of 3.0% yr(-1) (CH3Br) and 2.6% yr(-1) (CH3Cl), and mean northern hemisphere baseline mole fractions of 10.37 +/- 0.05 ppt and 535.7 +/- 2.2 ppt, respectively. We have used a Lagrangian dispersion model and local meteorological data to segregate the Mace Head observations into different source regions, and interpret the results in terms of the known sources and sinks of these two key halocarbons. At Cape Grim CH3Br and CH3Cl also show annual decreases in their baseline mixing ratios of 2.5% yr(-1) and 1.5% yr(-1), respectively. Mean baseline mole fractions were 7.94 +/- 0.03 ppt (CH3Br) and 541.3 +/- 1.1 ppt (CH3Cl). Although CH3Cl has a strong seasonal cycle there is no well-defined seasonal cycle in the Cape Grim CH3Br record. The fact that both gases are steadily decreasing in the atmosphere at both locations implies that a change has occurred which is affecting a common, major source of both gases (possibly biomass burning) and/or their major sink process (destruction by hydroxyl radical).

O'Doherty, S, Cunnold DM, Manning A, Miller BR, Wang RHJ, Krummel PB, Fraser PJ, Simmonds PG, McCulloch A, Weiss RF, Salameh P, Porter LW, Prinn RG, Huang J, Sturrock G, Ryall D, Derwent RG, Montzka SA.  2004.  Rapid growth of hydrofluorocarbon 134a and hydrochlorofluorocarbons 141b, 142b, and 22 from Advanced Global Atmospheric Gases Experiment (AGAGE) observations at Cape Grim, Tasmania, and Mace Head, Ireland. Journal of Geophysical Research-Atmospheres. 109   10.1029/2003jd004277   AbstractWebsite

[1] An update of in situ Advanced Global Atmospheric Gases Experiment (AGAGE) hydrofluorocarbon (HFC)/hydrochlorofluorocarbon ( HCFC) measurements made at Mace Head, Ireland, and Cape Grim, Tasmania, from 1998 to 2002 are reported. HCFC-142b, HCFC-141b, HCFC-22 and HFC-134a show continued rapid growth in the atmosphere at mean rates of 1.1, 1.6, 6.0, and 3.4 ppt/year, respectively. Emissions inferred from measurements are compared to recent estimates from consumption data. Minor updates to the industry estimates of emissions are reported together with a discussion of how to best determine OH concentrations from these trace gas measurements. In addition, AGAGE measurements and derived emissions are compared to those deduced from NOAA-Climate Monitoring and Diagnostics Laboratory flask measurements ( which are mostly made at different locations). European emission estimates obtained from Mace Head pollution events using the Nuclear Accident Model ( NAME) dispersion model and the best fit algorithm ( known as simulated annealing) are presented as 3-year rolling average emissions over Europe for the period 1999-2001. Finally, the measurements of HCFC-141b, HCFC-142b, and HCFC-22 discussed in this paper have been combined with the Atmospheric Lifetime Experiment (ALE)/Global Atmospheric Gases Experiment (GAGE)/AGAGE measurements of CFC-11, CFC-12, CFC-113, CCl4, and CH3CCl3 to produce the evolution of tropospheric chlorine loading.

Nevison, CD, Lueker TJ, Weiss RF.  2004.  Quantifying the nitrous oxide source from coastal upwelling. Global Biogeochemical Cycles. 18   10.1029/2003gb002110   AbstractWebsite

A continuous record of atmospheric N2O measured from a tower in northern California captures strong pulses of N2O released by coastal upwelling events. The atmospheric record offers a unique, observation-based method for quantifying the coastal N2O source. A coastal upwelling model is developed and compared to the constraints imposed by the atmospheric record in the Pacific Northwest coastal region. The upwelling model is based on Ekman theory and driven by high-resolution wind and SST data and by relationships between subsurface N2O and temperature. A simplified version of the upwelling model is extended to the world's major eastern boundary regions to estimate a total coastal upwelling source of similar to0.2 +/- >70% Tg N2O-N/yr. This flux represents similar to5% of the total ocean source, estimated here at similar to4 Tg N2O-N/yr using traditional gas-transfer methods, and is probably largely neglected in current N2O budgets.

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
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.

Montzka, SA, Fraser PJ, Butler JH, Connell PS, Cunnold DM, Daniel JS, Derwent RG, Lal S, McCulloch A, Oram D, Reeves CE, Sanhueza E, Steele LP, Velders GJM, Weiss RF, Zander R.  2003.  Controlled substances and other source gases. Scientific assessment of ozone depletion, 2002 (World Meteorological Organization, Global Ozone Research and Monitoring Project, Report 47). :83., Washington, DC: National Oceanic and Atmospheric Administration Abstract
Rhew, RC, Miller BR, Bill M, Goldstein AH, Weiss RF.  2002.  Environmental and biological controls on methyl halide emissions from southern California coastal salt marshes. Biogeochemistry. 60:141-161.   10.1023/a:1019812006560   AbstractWebsite

Methyl bromide (CH3Br) and methyl chloride (CH3Cl) emission rates from southern California coastal salt marshes show large spatial and temporal variabilities that are strongly linked to biological and environmental factors. Here we discuss biogeochemical lines of evidence pointing to vegetation as the primary source of CH3Br and CH3Cl emissions from salt marshes. Sediments and macroalgae do not appear to be major producers of these compounds, based on observations that the highest fluxes are not inhibited by soil inundation; their emissions are not correlated with those of certain gases produced in soils; and emissions from mudflat- and macroalgae-dominated sites are relatively small. In contrast, the seasonal and spatial variabilities of methyl halide fluxes in these salt marshes are consistent with the production of these compounds by vascular plants, although the possibility of production by microflora or fungi associated with the salt marsh vegetation is not ruled out. Flux chamber measurements of emission rates are largely correlated to the overall plant biomass enclosed in the chamber, but appear also to be highly dependent on the predominant plant species. Emission rates follow a diurnal trend similar to the trends of ambient air temperature and photosynthetically active radiation, but not surface soil temperature. Diurnal variabilities in the carbon isotope compositions of CH3Cl and CH3Br and their relative ratios of emissions are consistent with simultaneously competing mechanisms of uptake and production.

Min, DH, Bullister JL, Weiss RF.  2002.  Anomalous chlorofluorocarbons in the Southern California Borderland Basins. Geophysical Research Letters. 29   10.1029/2002gl015408   AbstractWebsite

During the past two decades, unexpectedly high concentrations of chlorofluorocarbons (CFCs) have been observed in the bottom waters of the Southern California Borderland Basins (SCBB), with relatively constant spatial distribution patterns. In contrast to offshore waters in this region, CFC concentrations below the oxygen minimum layer (OML) in the deep SCBB increase with depth. The uniformity of the bottom-enhanced CFC signals and the near-zero levels of tritium suggest that this feature is likely maintained by release of CFCs from sediments and vertical mixing, and not by dumped CFC-bearing materials or an intrusion of recently ventilated waters. We hypothesize that CFC scavenging processes, either on particulate organic matter or hydrocarbon residues from the adjacent natural seeps, occur in these high-productivity near-surface coastal waters. The subsequent release of CFCs at the bottom boundary layer during the degradation of particulate material may cause the anomalous CFC distributions in the SCBB.

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.

Cunnold, DM, Steele LP, Fraser PJ, Simmonds PG, Prinn RG, Weiss RF, Porter LW, O'Doherty S, Langenfelds RL, Krummel PB, Wang HJ, Emmons L, Tie XX, Dlugokencky EJ.  2002.  In situ measurements of atmospheric methane at GAGE/AGAGE sites during 1985-2000 and resulting source inferences. Journal of Geophysical Research-Atmospheres. 107   10.1029/2001jd001226   AbstractWebsite

[1] Continuous measurements of methane since 1986 at the Global Atmospherics Gases Experiment/Advanced Global Atmospherics Gases Experiment (GAGE/AGAGE) surface sites are described. The precisions range from approximately 10 ppb at Mace Head, Ireland, during GAGE to better than 2 ppb at Cape Grim, Tasmania, during AGAGE (i.e., since 1993). The measurements exhibit good agreement with coincident measurements of air samples from the same locations analyzed by Climate Monitoring and Diagnostics Laboratory (CMDL) except for differences of approximately 5 ppb before 1989 (GAGE lower) and about 4 ppb from 1991 to 1995 (GAGE higher). These results are obtained before applying a factor of 1.0119 to the GAGE/AGAGE values to place them on the Tohoku University scale. The measurements combined with a 12-box atmospheric model and an assumed atmospheric lifetime of 9.1 years indicates net annual emissions (emissions minus soil sinks) of 545 Tg CH4 with a variability of only +/-20 Tg from 1985 to 1997 but an increase in the emissions in 1998 of 37 +/- 10 Tg. The effect of OH changes inferred by Prinn et al. [2001] is to increase the estimated methane emissions by approximately 20 Tg in the mid-1980s and to reduce them by 20 Tg in 1997 and by more thereafter. Using a two-dimensional (2-D), 12-box model with transport constrained by the GAGE/AGAGE chlorofluorocarbon measurements, we calculate that the proportion of the emissions coming from the Northern Hemisphere is between 73 and 81%, depending on the OH distribution used. However, this result includes an adjustment of 5% derived from a simulation of the 2-D estimation procedure using the 3-D MOZART model. This adjustment is needed because of the very different spatial emission distributions of the chlorofluorocarbons and methane which makes chlorofluorocarbons derived transport rates inaccurate for the 2-D simulation of methane. The 2-D model combined with the annual cycle in OH from Spivakovsky et al. [2000] provide an acceptable fit to the observed 12-month cycles in methane. The trend in the amplitude of the annual cycle of methane at Cape Grim is used to infer a trend in OH in 30degrees-90degreesS of 0 +/- 5% per decade from 1985 to 2000, in qualitative agreement with Prinn et al. [2001] for the Southern Hemisphere.

Bill, M, Rhew RC, Weiss RF, Goldstein AH.  2002.  Carbon isotope ratios of methyl bromide and methyl chloride emitted from a coastal salt marsh. Geophysical Research Letters. 29   10.1029/2001gl012946   AbstractWebsite

[1] Methyl bromide (CH3Br) and methyl chloride (CH3Cl) play important roles in stratospheric ozone depletion, but their atmospheric budgets have large uncertainties. The analysis of stable isotope composition of methyl halides may provide useful independent information for further constraining their budgets. Here we report the first measurements of CH3Br and CH3Cl stable carbon isotope ratios emitted from a biogenic source under in situ conditions. CH3Br and CH3Cl emissions from the salt marsh plant Batis maritima showed a strong diurnal variation in delta(13)C, from -65parts per thousand during the daytime to --12parts per thousand at night. The minimum delta(13)C values were observed at midday, coinciding with the time of greatest emissions and ambient temperature. At night, when the emissions were much smaller, the stable carbon isotopic ratios of CH3Br and CH3Cl became enriched in C-13. The daily mean delta(13)C of CH3Br and CH3Cl emissions, weighted by emission rate, were -43parts per thousand and -62parts per thousand respectively.

Rhein, M, Fischer J, Smethie WM, Smythe-Wright D, Weiss RF, Mertens C, Min DH, Fleischmann U, Putzka A.  2002.  Labrador Sea Water: pathways, CFC inventory, and formation rates. Journal of Physical Oceanography. 32:648-665.   10.1175/1520-0485(2002)032<0648:lswpci>;2   AbstractWebsite

In 1997, a unique hydrographic and chlorofluorocarbon (CFC: component CFC-11) dataset was obtained in the subpolar North Atlantic. To estimate the synopticity of the 1997 data, the recent temporal evolution of the CFC and Labrador Sea Water (LSW) thickness fields are examined. In the western Atlantic north of 50degreesN, the LSW thickness decreased considerably from 1994-97, while the mean CFC concentrations did not change much. South of 50degreesN and in the eastern Atlantic, the CFC concentration increased with little or no change in the LSW thickness. On shorter timescales, local anomalies due to the presence of eddies are observed, but for space scales larger than the eddies the dataset can be treated as being synoptic over the 1997 observation period. The spreading of LSW in the subpolar North Atlantic is described in detail using gridded CFC and LSW thickness fields combined with Profiling Autonomous Lagrangian Circulation Explorer (PALACE) float trajectories. The gridded fields are also used to calculate the CFC-11 inventory in the LSW from 40degrees to 65degreesN, and from 10degrees to 60degreesW. In total, 2300 +/- 250 tons of CFC-11 (equivalent to 16.6 million moles) were brought into the LSW by deep convection. In 1997, 28% of the inventory was still found in the Labrador Sea west of 45degreesW and 31% of the inventory was located in the eastern Atlantic. The CFC inventory in the LSW was used to estimate the lower limits of LSW formation rates. At a constant formation rate, a value of 4.4-5.6 Sv (Sv = 10(6) m(3) s(-1)) is obtained. If the denser modes of LSW are ventilated only in periods with intense convection, the minimum formation rate of LSW in 1988-94 is 8.1-10.8 Sv, and 1.8-2.4 Sv in 1995-97.

Vollmer, MK, Weiss RF, Williams RT, Falkner KK, Qiu X, Ralph EA, Romanovsky VV.  2002.  Physical and chemical properties of the waters of saline lakes and their importance for deep-water renewal: Lake Issyk-Kul, Kyrgyzstan. Geochimica Et Cosmochimica Acta. 66:4235-4246.   10.1016/s0016-7037(02)01052-9   AbstractWebsite

The relationships between electrical conductivity, temperature, salinity, and density are studied for brackish Lake Issyk-Kul. These studies are based on a newly determined major ion composition, which for the open lake shows a mean absolute salinity of 6.06 g kg(-1). The conductivity-temperature relationship of the lake water was determined experimentally showing that the lake water is about 1.25 times less conductive than seawater diluted to the same absolute salinity as that of the lake water. Based on these results, an algorithm is presented to calculate salinity from in-situ conductivity measurements. Applied to the field data, this shows small but important vertical salinity variations in the lake with a salinity maximum at 200 m and a freshening of the surface water with increasing proximity to the shores. The algorithm we adopt to calculate density agrees well with earlier measurements and shows that at 20degreesC and I atm Lake Issyk-Kul water is about 530 g m(-3) denser than seawater at the same salinity. The temperature of maximum density at I atm is about 0.15degreesC lower than that for seawater diluted to the same salinity. Despite its small variations, salinity plays an important role, together with temperature changes, in the static stability and in the production of deep-water in this lake. Changes in salinity may have had important consequences on the mixing regime and the fate of inflowing river water over geological time. Uncharged silicic acid is negligible for the stability of the water column except near an similar to15 m thick nepheloid layer observed at the bottom of the deep basin. Copyright (C) 2002 Elsevier Science Ltd.

Waugh, DW, Vollmer MK, Weiss RF, Haine TWN, Hall TM.  2002.  Transit time distributions in Lake Issyk-Kul. Geophysical Research Letters. 29   10.1029/2002gl016201   AbstractWebsite

[1] Measurements of sulfur hexafluoride (SF6)and chlorofluorocarbons (CFCs) are used to constrain the timescales for deep-water renewal in Lake Issyk-Kul. As these tracers have different tropospheric histories their combination provides more transport information than one tracer alone. In particular, from these measurements the mean, Gamma, and standard deviation, sigma, of the distributions of transit times since water made last contact with the surface can be tightly constrained. Gamma is older than the age determined from SF6 and younger than the ages from the CFCs, and increases from around 4 yrs at 200 m to around 10.5 yrs at the deepest location (655 m). sigma also increases with depth and equals around 0.7 to 0.8 Gamma, which corresponds to large ranges of transit times, and implies mixing processes play a major role in the transport. The approach used can also be applied to similar tracer measurements in the oceans and groundwaters to constrain transport in these geophysical systems.

Vollmer, MK, Weiss RF, Schlosser P, Williams RT.  2002.  Deep-water renewal in Lake Issyk-Kul. Geophysical Research Letters. 29   10.1029/2002gl014763   AbstractWebsite

[1] The deep-water renewal rates of Lake Issyk-Kul are studied using the time-dependent anthropogenically produced tracers sulfur hexafluoride (SF6), chlorofluorocarbons (CFCs) and tritium-helium-3. SF6 and the CFCs are used to calibrate a mixing model from which the vertical age distribution is calculated and found to be comparable to the SF6 apparent ages. Based on this model, the mean age of the water below 100 m depth is 6.1 yrs. The mean oxygen consumption rate for the same depth range is 6.4 m mol kg(-1) yr(-1) and the mean remineralization rates for nitrate, phosphate and silicate are 0.53, 0.003 and 0.67 m mol kg(-1) yr(-1), respectively.