Export 10 results:
Sort by: Author [ Title  (Desc)] Type Year
A B C D E F G H I J K L [M] N O P Q R S T U V W X Y Z   [Show ALL]
Killworth, PD, Carmack EC, Weiss RF, Matear R.  1996.  Modeling deep-water renewal in Lake Baikal. Limnology and Oceanography. 41:1521-1538. AbstractWebsite

Temperature, dissolved oxygen, nutrients, and chlorofluorocarbon-12 data obtained from Lake Baikal are used to describe deep-water renewal in a deep, temperate-latitude lake. Observations are used to propose the physical mechanism governing convection and to formulate a model of deep ventilation. The key physical mechanism governing deep-water renewal is the so-called thermobaric instability. Because the temperature of maximum density decreases with depth, a lake can become conditionally unstable if the base of the cold mixed layer is displaced to a depth at which its temperature matches the local temperature of maximum density, thereby resulting in sinking plumes. An important consequence of this phenomenon is that deep temperate lakes such as Baikal do not completely mix twice yearly; instead, deep ventilation is episodic. A two-dimensional model of a wind- and buoyancy-driven lake shows many strong mixing events and a fairly realistic seasonal cycle, indicating that the hypothesis is physically realizable. A filling-box model is used to deduce the annually averaged fluxes necessary to produce a steady vertical distribution of tracers as observed. Good fits are obtained to oxygen and chlorofluorocarbon distributions by this model.

Chipperfield, MP, Liang Q, Rigby M, Hossaini R, Montzka SA, Dhomse S, Feng WH, Prinn RG, Weiss RF, Harth CM, Salameh PK, Muhle J, O'Doherty S, Young D, Simmonds PG, Krummel PB, Fraser PJ, Steele LP, Happell JD, Rhew RC, Butler J, Yvon-Lewis SA, Hall B, Nance D, Moore F, Miller BR, Elkins J, Harrison JJ, Boone CD, Atlas EL, Mahieu E.  2016.  Model sensitivity studies of the decrease in atmospheric carbon tetrachloride. Atmospheric Chemistry and Physics. 16:15741-15754.   10.5194/acp-16-15741-2016   AbstractWebsite

Carbon tetrachloride (CCl4) is an ozone-depleting substance, which is controlled by the Montreal Protocol and for which the atmospheric abundance is decreasing. However, the current observed rate of this decrease is known to be slower than expected based on reported CCl4 emissions and its estimated overall atmospheric lifetime. Here we use a three-dimensional (3-D) chemical transport model to investigate the impact on its predicted decay of uncertainties in the rates at which CCl4 is removed from the atmosphere by photolysis, by ocean uptake and by degradation in soils. The largest sink is atmospheric photolysis (74% of total), but a reported 10% uncertainty in its combined photolysis cross section and quantum yield has only a modest impact on the modelled rate of CCl4 decay. This is partly due to the limiting effect of the rate of transport of CCl4 from the main tropospheric reservoir to the stratosphere, where photolytic loss occurs. The model suggests large interannual variability in the magnitude of this stratospheric photolysis sink caused by variations in transport. The impact of uncertainty in the minor soil sink (9% of total) is also relatively small. In contrast, the model shows that uncertainty in ocean loss (17% of total) has the largest impact on modelled CCl4 decay due to its sizeable contribution to CCl4 loss and large lifetime uncertainty range (147 to 241 years). With an assumed CCl4 emission rate of 39 Gg year(-1), the reference simulation with the best estimate of loss processes still underestimates the observed CCl4 (overestimates the decay) over the past 2 decades but to a smaller extent than previous studies. Changes to the rate of CCl4 loss processes, in line with known uncertainties, could bring the model into agreement with in situ surface and remote-sensing measurements, as could an increase in emissions to around 47 Gg year(-1). Further progress in constraining the CCl4 budget is partly limited by systematic biases between observational datasets. For example, surface observations from the National Oceanic and Atmospheric Administration (NOAA) network are larger than from the Advanced Global Atmospheric Gases Experiment (AGAGE) network but have shown a steeper decreasing trend over the past 2 decades. These differences imply a difference in emissions which is significant relative to uncertainties in the magnitudes of the CCl4 sinks.

Penkett, SA, Butler JH, Kurylo MJ, Reeves CE, Rodriguez JM, Singh H, Toohey D, Weiss R.  1995.  Methyl bromide. Scientific assessment of ozone depletion: 1994 (World Meterological Organization, Global Ozone Research and Monitoring Report). ( World Meteorological O, Ed.).:26., Geneva, Switzerland; Nairobi, Kenya; Washington, DC, USA: World Meteorological Organization Abstract
Petrenko, VV, Etheridge DM, Weiss RF, Brook EJ, Schaefer H, Severinghaus JP, Smith AM, Lowe D, Hua QA, Riedel K.  2010.  Methane from the East Siberian Arctic Shelf. Science. 329:1146-1147.   10.1126/science.329.5996.1146-b   AbstractWebsite

In their Report “Extensive methane venting to the atmosphere from sediments of the East Siberian Arctic Shelf” (5 March, p. 1246), N. Shakhova et al. write that methane (CH4) release resulting from thawing Arctic permafrost “is a likely positive feedback to climate warming.” They add that the release of Arctic CH4 was implied in previous climate shifts as well as in the recently renewed rise in atmospheric CH4. These claims are not supported by all the literature they cite. Their reference 5 (1) presents measurements of emissions only of carbon dioxide, not CH4. Their reference 8 (2), a study we conducted, suggests that a very large (∼50%) increase in atmospheric CH4 concentration associated with an abrupt warming event ∼11,600 years ago was driven mainly by wetlands, without distinguishing between high and low latitudes. Their reference 9 (3) was published in 1993 and is not relevant to the renewed growth of atmospheric CH4 that started in 2007. Their reference 10 (4) does not imply Arctic CH4 releases in this renewed growth, and other recent work (5) also does not support sustained new emissions from the Arctic as the cause.

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.

Miller, BR, Weiss RF, Salameh PK, Tanhua T, Greally BR, Muhle J, Simmonds PG.  2008.  Medusa: A sample preconcentration and GC/MS detector system for in situ measurements of atmospheric trace halocarbons, hydrocarbons, and sulfur compounds. Analytical Chemistry. 80:1536-1545.   10.1021/ac702084k   AbstractWebsite

Significant changes have occurred in the anthropogenic emissions of many compounds related to the Kyoto and Montreal Protocols within the past 20 years and many of their atmospheric abundances have responded dramatically. Additionally, there are a number of related natural compounds with underdetermined source or sink budgets. A new instrument, Medusa, was developed to make the high frequency in situ measurements required for the determination of the atmospheric lifetimes and emissions of these compounds. This automated system measures a wide range of halocarbons, hydrocarbons, and sulfur compounds involved in ozone depletion and/or climate forcing, from the very volatile perfluorocarbons (PFCs, e.g., CF(4) and CF(3)CF(3)) and hydrofluorocarbons (HFCs, e.g., CH(3)CF(3)) to the higher-boiling point solvents (such as CH(3)CCl(3) and CCl(2)= CCl(2)) and CHBr(3). A network of Medusa systems worldwide provides 12 in situ ambient air measurements per day of more than 38 compounds of part per trillion mole fractions and precisions up to 0.1% RSD at the five remote field stations operated by the Advanced Global Atmospheric Gases Experiment (AGAGE). Ihis custom system couples gas chromatography/mass spectrometry (GC/MSD) with a novel scheme for cryogen-free low-temperature preconcentration (-165 degrees C) of analytes from 2 L samples in a two-trap process using HayeSep D adsorbent.

Petrenko, VV, Severinghaus JP, Schaefer H, Smith AM, Kuhl T, Baggenstos D, Hua Q, Brook EJ, Rose P, Kulin R, Bauska T, Harth C, Buizert C, Orsi A, Emanuele G, Lee JE, Brailsford G, Keeling R, Weiss RF.  2016.  Measurements of 14C in ancient ice from Taylor Glacier, Antarctica constrain in situ cosmogenic 14CH4 and 14CO production rates. Geochimica et Cosmochimica Acta. 177:62-77.   10.1016/j.gca.2016.01.004   Abstract

Carbon-14 (14C) is incorporated into glacial ice by trapping of atmospheric gases as well as direct near-surface in situ cosmogenic production. 14C of trapped methane (14CH4) is a powerful tracer for past CH4 emissions from “old” carbon sources such as permafrost and marine CH4 clathrates. 14C in trapped carbon dioxide (14CO2) can be used for absolute dating of ice cores. In situ produced cosmogenic 14C in carbon monoxide (14CO) can potentially be used to reconstruct the past cosmic ray flux and past solar activity. Unfortunately, the trapped atmospheric and in situ cosmogenic components of 14C in glacial ice are difficult to disentangle and a thorough understanding of the in situ cosmogenic component is needed in order to extract useful information from ice core 14C. We analyzed very large (≈1000 kg) ice samples in the 2.26–19.53 m depth range from the ablation zone of Taylor Glacier, Antarctica, to study in situ cosmogenic production of 14CH4 and 14CO. All sampled ice is >50 ka in age, allowing for the assumption that most of the measured 14C originates from recent in situ cosmogenic production as ancient ice is brought to the surface via ablation. Our results place the first constraints on cosmogenic 14CH4 production rates and improve on prior estimates of 14CO production rates in ice. We find a constant 14CH4/14CO production ratio (0.0076 ± 0.0003) for samples deeper than 3 m, which allows the use of 14CO for correcting the 14CH4 signals for the in situ cosmogenic component. Our results also provide the first unambiguous confirmation of 14C production by fast muons in a natural setting (ice or rock) and suggest that the 14C production rates in ice commonly used in the literature may be too high.

Lupton, JE, Weiss RF, Craig H.  1977.  Mantle helium in the Red Sea brines. Nature. 266:244-246.   10.1038/266244a0   AbstractWebsite

HELIUM isotope studies on terrestrial samples have revealed the existence of two helium components which are clearly distinct from atmospheric helium. The first of these, which we term ‘crustal helium’, was identified in 1946 in natural gas wells1. This crustal component is produced by radioactive decay of U and Th to 4He, with 3He production by (n, α) reactions on Li; the resulting helium is characterised by 3He/4He ≃ 10−7, one-tenth of the atmospheric ratio2. The second component, ‘mantle helium’, was discovered as ‘excess 3He’ in deep ocean water, attributed to a flux of primordial helium from the mantle3. Studies of the 3He/4He ratio in deep water on the East Pacific Rise4 and in helium trapped in submarine basalt glasses5,6 have shown that this mantle component is characterised by 3He/4He ≃ 10−5, about 10 times the atmospheric ratio and 100 times the ratio in crustal helium. Basalt glasses from the Western Pacific Lau Basin, the East Pacific Rise, and the Mid-Atlantic Ridge contain trapped helium with similar 3He/4He ratios, indicating that mantle helium in at least three areas in which new lithosphere is being formed has a unique and uniform isotopic signature.

Lupton, JE, Weiss RF, Craig H.  1977.  Mantle helium in hydrothermal plumes in the Galapagos Rift. Nature. 267:603-604.   10.1038/267603a0   AbstractWebsite

THE 3He/4He ratio in deep Pacific water is 20–30% higher than in atmospheric helium because of injection of primordial helium from the mantle1,2. The largest 3He enrichments in the Pacific have been found in water on the crest of the East Pacific Rise where the isotopic ratios indicate2 that the excess helium component has a 3He/4He ratio about ten times the atmospheric ratio, in agreement with the ratios measured in trapped helium in the glassy rims of oceanic tholeiites3,4. Recent measurements in this laboratory5 have shown that the hot brines in the axial rift of the Red Sea are very highly enriched in mantle helium. 3He and 4He are respectively 3300 and 380 times supersaturated relative to atmospheric solubility equilibrium in seawater, with a 3He/4He ratio of 1.2×10−5, or 8.6 times the ratio in atmospheric helium. Comparison of the enrichments of various elements in the Red Sea brines and in brines associated with salt domes6 shows that helium is the only component in the Red Sea brines which unequivocally requires derivation from hydrothermal circulation of seawater in basalts. The helium isotopes are thus an extremely powerful and sensitive tracer for the detection and mapping of hydrothermal systems in oceanic spreading centres.

Falkner, KK, Measures CI, Herbelin SE, Edmond JM, Weiss RF.  1991.  The major and minor element geochemistry of Lake Baikal. Limnology and Oceanography. 36:413-423. AbstractWebsite

A comprehensive, joint Soviet-American study of the chemistry of Lake Baikal, the world's deepest (1,632 m) lake, was carried out in July 1988. In this paper, we report the major, minor, and preliminary trace element concentrations for three profiles obtained at or near the deepest and central part of the three major basins of the lake. With the exception of Ba, the distributions of major and minor elements were homogeneous, displaying no variations greater than analytical uncertainties. Average concentrations in mu-mol kg-1 (1 SD) are titration alkalinity = 1,093(6), SO42- = 57.4(1.3), Cl = 12.3(0.7), Ca = 402(7), Mg = 126(1), Na = 155(4), and K = 24.1(1.0); and in nmol kg-1 are Sr = 1,350(30), Li = 296(12), Ba = 74.7(2.6), Rb = 7.10(0.23), and U = 1.77(0.12). Excluding K and Cl, these values compare favorably with previously published results. Although some hydrothermal activity is known to occur within the lake, it does not appear to significantly affect major ion cycling. The residence times of the major ions are 330 yr or the same as that of water in the basin and so are controlled predominantly by their riverine fluxes. There is not yet enough information to assess whether hydrothermal processes affect minor element cycles. Ba concentrations decrease with depth, showing abrupt decreases near the bottom at two stations. It appears to undergo some form of uptake at the sediments, but further study is required to discern the processes governing Ba distribution.