Literature
Collapsing glaciers threaten Asia's water supplies
Authors: Jing Gao, Tandong Yao, Valérie Masson-Delmotte, Hans Christian Steen-Larsen & Weicai Wang

Abstract: The ‘third pole’ is the planet’s largest reservoir of ice and snow after the Arctic and Antarctic. It encompasses the Himalaya–Hindu Kush mountain ranges and the Tibetan Plateau. The region hosts the world’s 14 highest mountains and about 100,000 square kilometres of glaciers (an area the size of Iceland). Meltwater feeds ten great rivers, including the Indus, Brahmaputra, Ganges, Yellow and Yangtze, on which almost one-fifth of the world’s population depends.
Climate change threatens this vast frozen reservoir (see ‘Third pole warming’). For the past 50 years, glaciers in the Himalayas and Tibetan Plateau have been shrinking. Those in the Tian Shan mountains to the north have lost one-quarter of their mass, and might lose as much as half by mid-century. Their meltwater is expanding lakes. River flows at the start of summer peak earlier than they did 30 years ago. And weather patterns are shifting. A weaker Indian monsoon is reducing precipitation in the Himalayas and southern Tibetan Plateau; snow and rain are increasing in the northwestern Tibetan Plateau and Pamir Mountains. Original text link
Carbonate formation in salt dome cap rocks by microbial anaerobic oxidation of methane
Authors: K. H. Caesar, J. R. Kyle, T. W. Lyons, A. Tripati & S. J. Loyd

Abstract: Major hydrocarbon accumulations occur in traps associated with salt domes. Whereas some of these hydrocarbons remain to be extracted for economic use, significant amounts have degraded in the subsurface, yielding mineral precipitates as byproducts. Salt domes of the Gulf of Mexico Basin typically exhibit extensive deposits of carbonate that form as cap rock atop salt structures. Despite previous efforts to model cap rock formation, the details of subsurface reactions (including the role of microorganisms) remain largely unknown. Here we show that cap rock mineral precipitation occurred via closed-system sulfate reduction, as indicated by new sulfur isotope data. 13C-depleted carbonate carbon isotope compositions and low clumped isotope-derived carbonate formation temperatures indicate that microbial, sulfate-dependent, anaerobic oxidation of methane (AOM) contributed to carbonate formation. These findings suggest that AOM serves as an unrecognized methane sink that reduces methane emissions in salt dome settings perhaps associated with an extensive, deep subsurface biosphere. Original text link
Validation of ammonia diffusive and pumped samplers in a controlled atmosphere test facility using traceable Primary Standard Gas Mixtures
Authors: Nicholas A.Martin,Valerio Ferracci,Nathan Cassidy,Josh Hook,Ross M.Battersby,Elena Amico di Meane,Yuk S.Tang,Amy C.M.Stephens,Sarah R.Leeson,Matthew R.Jones,Christine F.Braban,Linda Gates,Markus Hangartner,Jean-Marc Stoll,Paolo Saccoe,Diego Pagani,John A.Hoffnagle,Eva Seitler

Abstract: We report the determination of ammonia (NH3) diffusive sampling rates for six different designs of commercial diffusive samplers (CEH ALPHA sampler, Gradko diffusion tube, Gradko DIFRAM-400, Passam ammonia sampler, and ICS Maugeri Radiello radial sampler (blue and white turbulence barriers)), together with the validation test results for a pumped sampler (CEH DELTA denuder). The devices were all exposed in the UK's National Physical Laboratory's (NPL) controlled atmosphere test facility (CATFAC). For each of the seven diffusive sampler exposure tests there were traceable concentrations of ammonia (in the range 3–25 μg m−3) generated under well-defined conditions of temperature, relative humidity and wind speed, which are applicable to a variety of ambient monitoring environments. The sampler exposure time at each concentration was 28 days, except for the radial devices, which were exposed for 14 days. The work relied on the dilution of newly developed stable Primary Standard Gas Mixtures (PSMs) prepared by gravimetry in passivated gas cylinders as a method of improving the metrological traceability of ammonia measurements. The exposed diffusive samplers were sent blind to the participants for analysis and the reported NH3 concentrations were then compared against the known reference concentration. From the results for each sampler type a diffusive sampling rate was calculated and compared against the rate used routinely by the participants. Some measurement results were in good agreement with the known traceable reference concentration (particularly for one diffusive sampler design (ALPHA)), while other devices exhibited over-reading and under-reading (each with a clear bias). The new diffusive sampling rates determined in the laboratory study were then applied to measurements in a field comparison campaign, and this was found to deliver an improvement in agreement between the different devices deployed. Original text link
A global database of water vapor isotopes measured with high temporal resolution infrared laser spectroscopy
Authors: Zhongwang Wei, Xuhui Lee, Franziska Aemisegger, Marion Benetti, Max Berkelhammer, Mathieu Casado, Kelly Caylor, Emanuel Christner, Christoph Dyroff, Omaira García, Yenny González, Timothy Griffis, Naoyuki Kurita, Jie Liang, Mao-Chang Liang, Guanghui Lin, David Noone, Konstantin Gribanov, Niels C. Munksgaard, Matthias Schneider, François Ritter, Hans Christian Steen-Larsen, Christine Vallet-Coulomb, Xuefa Wen, Jonathon S. Wright, Wei Xiao & Kei Yoshimura- Show fewer authors

Abstract: The isotopic composition of water vapour provides integrated perspectives on the hydrological histories of air masses and has been widely used for tracing physical processes in hydrological and climatic studies. Over the last two decades, the infrared laser spectroscopy technique has been used to measure the isotopic composition of water vapour near the Earth’s surface. Here, we have assembled a global database of high temporal resolution stable water vapour isotope ratios (δ18O and δD) observed using this measurement technique. As of March 2018, the database includes data collected at 35 sites in 15 Köppen climate zones from the years 2004 to 2017. The key variables in each dataset are hourly values of δ18O and δD in atmospheric water vapour. To support interpretation of the isotopologue data, synchronized time series of standard meteorological variables from in situ observations and ERA5 reanalyses are also provided. This database is intended to serve as a centralized platform allowing researchers to share their vapour isotope datasets, thus facilitating investigations that transcend disciplinary and geographic boundaries. Original text link
First observation of direct methane emission to the atmosphere from the subglacial domain of the Greenland Ice Sheet
Authors: Jesper Riis Christiansen & Christian Juncher Jørgensen

Abstract: During a 2016 field expedition to the West Greenland Ice Sheet, a striking observation of significantly elevated CH4 concentrations of up to 15 times the background atmospheric concentration were measured directly in the air expelled with meltwater at a subglacial discharge point from the Greenland Ice Sheet. The range of hourly subglacial CH4 flux rate through the discharge point was estimated to be 3.1 to 134 g CH4 hr−1. These measurements are the first observations of direct emissions of CH4 from the subglacial environment under the Greenlandic Ice Sheet to the atmosphere and indicate a novel emission pathway of CH4 that is currently a non-quantified component of the Arctic CH4 budget. Original text link
Automated measurements of greenhouse gases fluxes from tree stems and soils: magnitudes, patterns and drivers
Authors: Josep Barba, Rafael Poyatos & Rodrigo Vargas

Abstract: Tree stems exchange CO2, CH4 and N2O with the atmosphere but the magnitudes, patterns and drivers of these greenhouse gas (GHG) fluxes remain poorly understood. Our understanding mainly comes from static-manual measurements, which provide limited information on the temporal variability and magnitude of these fluxes. We measured hourly CO2, CH4 and N2O fluxes at two stem heights and adjacent soils within an upland temperate forest. We analyzed diurnal and seasonal variability of fluxes and biophysical drivers (i.e., temperature, soil moisture, sap flux). Tree stems were a net source of CO2 (3.80 ± 0.18 µmol m−2 s−1; mean ± 95% CI) and CH4 (0.37 ± 0.18 nmol m−2 s−1), but a sink for N2O (−0.016 ± 0.008 nmol m−2 s−1). Time series analysis showed diurnal temporal correlations between these gases with temperature or sap flux for certain days. CO2 and CH4 showed a clear seasonal pattern explained by temperature, soil water content and sap flux. Relationships between stem, soil fluxes and their drivers suggest that CH4 for stem emissions could be partially produced belowground. High-frequency measurements demonstrate that: a) tree stems exchange GHGs with the atmosphere at multiple time scales; and b) are needed to better estimate fluxes magnitudes and understand underlying mechanisms of GHG stem emissions. Original text link
Assessment of carbon dioxide and other trace gases emissions from fossil fuel combustion over Sacramento
Authors: J. C. Turnb0ull, A. Karion, M. L. Fischer, I. Faloona, T. Guilderson, S. J. Lehman, B. R. Miller, J. B. Miller, S. Montzka, T. Sherwood, S. Saripalli, C. Sweeney, and P. P. Tans

Abstract: Stable isotope analysis of hydrogen (δ2H) and oxygen (δ18O) can well indicate the source of water in beverages, but traditional isotope analysis only focuses on pure water or extracted water. The isotope composition of the extracted beverage water was determined by infrared spectroscopy (IRIS) and isotope mass spectrometry (IRMS). The samples of beer, soda, fruit juice and milk (without water extraction) were also analyzed by IRIS. For the IRIS analyzer, four needles were injected into each sample, and memory effects were corrected by three methods: (a) 1-4 needle data, (b) 2-4 needle data, and (c) 3-4 needle data. The results show that the values of δ2H and δ18O calculated by the three methods are much different from those of pure water. The memory effect was the smallest when only 3-4 needles were used. Except for fruit juice, the values of δ2H and δ18O of other beverage water conform to the atmospheric precipitation line. Comparing the results of IRIS and IRMS, except for the difference of δ2H in soda water and fruit juice, the difference of δ18O in beer is not significant. The correlation coefficients of δ2H and δ18O values of beer, soda, juice and milk extracts and complex beverages are 0.998 and 0.997 respectively, which are suitable for 1:1 line. Our conclusion is that IRIS can be used directly for the analysis of complex beverages without water extraction, but caution must be taken because the beverage contains sugar, which may clog syringes and increase memory effects. Alcohol in beverages can also interfere with spectral analysis.
Direct quantitative determination of carbon dioxide (CO2ff) from chemical fuel combustion can be used to assess carbon cycle and air quality. In the spring of 2009, we flew two times over Sacramento, California, to measure CO2, CO and CH4 in the boundary layer and troposphere in situ, while collecting samples in sample bottles. Samples in sample bottles are used to analyze 14CO2 and CO2 to determine the recently increased molar fraction of CO2. At the same time, a series of greenhouse gases and trace gases, including hydrocarbons and halogens, were determined with the sample. We observed a strong correlation between CO2 FF and many trace gases in urban emissions. Based on the correlation, we estimate the emission rates of CO2 FF and these trace gases and compare them with the previous emission rates. Carbon monoxide (CO) and benzene emission rates at county level obtained from the California Air Resources Committee's CEPAM database in recent years are in good agreement with our measurements, but previous emissions seem to have overestimated one or two indicators. For most other trace gases, our measurements are quite different from previous estimates (200-500%). On the first flight, we combined the emission rate of CO:CO 2 of 14±2 ppb CO/ppm CO 2 monitored on-line in situ to obtain the estimated value of the molar fraction of CO 2 ff. The carbon dioxide mixing ratio (CO2 bio) of the biosphere is estimated from the difference between total carbon dioxide emissions and fossil combustion emissions. The results show that CO2 bio varies greatly in different places. From the urban area up to 8 + 2 ppm to -6±1 ppm of ambient boundary layer air. Finally, based on the above molar fraction of CO2 ff, the total CO2 emissions from fossil combustion in Sacramento area are calculated by mass balance method. There are one or two uncertainties in the emission calculated by this method: the uncertainties of wind speed and boundary layer height. However, this attempt to use atmospheric radiocarbon to estimate urban-scale CO2 FF emissions shows that the CO2ff can be used to validate and improve previously estimated anthropogenic errors, respectively, in the biosphere, and that if transport uncertainty decreases, CO2ff emissions may be limited. Original text link
Steady Isotope Evidence of Water Vapor Source and Surface Runoff Composition in Heihe Source Area
Authors: Z. LiangJu, Y. Li, X. HongLang, C. GuoDong, Z. MaoXian, Y. YongGang, L. CaiZhi, Z. Jian

Abstract: Based on the determination of stable hydrogen (δD) and oxygen (δ18O) isotope ratios and the calculation of excess deuterium (d-excess) in different water bodies in the source area of Heihe River, combined with the reanalysis data of the American Center for Environmental Forecasting and the National Center for Atmospheric Research (NECP/NCAR), the source of atmospheric water vapor and the composition of surface runoff in the study area were preliminarily studied. The results show that the consistency of seasonal variation of precipitation δ18O in Heihe Source Area indicates that its water vapor source is the same; in summer, the values of δ18O and δD in Biniugou precipitation are positive while the values of d-excess are low; in winter, the values of δ18O and δD in precipitation are negative while the d-excess increases. The seasonal variation characteristics are similar to those of Urumqi precipitation isotopes, indicating that summer precipitation in this area mainly comes from westerly transport. In addition to westerly winds, winter precipitation is also affected by polar air masses. The high d-excess value of Biniugou indicates that the inner circulation characteristics of different water bodies in Heihe source area are very obvious because it is located in the northwest inland arid area. The time variations of δD, δ18O and d-excess of different water bodies in the source area of Heihe River indicate that the contribution of different potential water sources to surface runoff in the source area of Heihe River is different. For example, the consistency of the variation of δD, δ18O and d-excess of precipitation and river water in May-September, spring water and river water in December-February, seasonal variation law of precipitation similar to Mountain Runoff and significant difference between melt water and river water in September all indicate that the main contribution period of precipitation to surface runoff is from June to mid-September in Heihe source region, and in winter, it is mainly in the form of base flow (spring water). The recharge river water is mainly, but the discharge is low. Original text link
Study on Hydrogen and Oxygen Stable Isotope Ratio of Beverage Water by Spectroscopy without Water Extraction/Extraction
Authors: Lesley A. Chesson, Gabriel J. Bowen and James R. Ehleringer

Abstract: Stable isotope analysis of hydrogen (δ2H) and oxygen (δ18O) can well indicate the source of water in beverages, but traditional isotope analysis only focuses on pure water or extracted water. The isotope composition of the extracted beverage water was determined by infrared spectroscopy (IRIS) and isotope mass spectrometry (IRMS). The samples of beer, soda, fruit juice and milk (without water extraction) were also analyzed by IRIS. For the IRIS analyzer, four needles were injected into each sample, and memory effects were corrected by three methods: (a) 1-4 needle data, (b) 2-4 needle data, and (c) 3-4 needle data. The results show that the values of δ2H and δ18O calculated by the three methods are much different from those of pure water. The memory effect was the smallest when only 3-4 needles were used. Except for fruit juice, the values of δ2H and δ18O of other beverage water conform to the atmospheric precipitation line. Comparing the results of IRIS and IRMS, except for the difference of δ2H in soda water and fruit juice, the difference of δ18O in beer is not significant. The correlation coefficients of δ2H and δ18O values of beer, soda, juice and milk extracts and complex beverages are 0.998 and 0.997 respectively, which are suitable for 1:1 line. Our conclusion is that IRIS can be used directly for the analysis of complex beverages without water extraction, but caution must be taken because the beverage contains sugar, which may clog syringes and increase memory effects. Alcohol in beverages can also interfere with spectral analysis. Original text link