Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements?

Methane is a strong greenhouse gas and large uncertainties exist concerning the future evolution of its atmospheric abundance. Analyzing methane atmospheric mixing and stable isotope ratios in air trapped in polar ice sheets helps in reconstructing the evolution of its sources and sinks in the past. This is important to improve predictions of atmospheric CH4 mixing ratios in the future under the influence of a changing climate. The aim of this study is to assess whether past atmospheric δ13C(CH4) variations can be reliably reconstructed from firn air measurements. Isotope reconstructions obtained with a state of the art firn model from different individual sites show unexpectedly large discrepancies and are mutually inconsistent. We show that small changes in the diffusivity profiles at individual sites lead to strong differences in the firn fractionation, which can explain a large part of these discrepancies. Using slightly modified diffusivities for some sites, and neglecting samples for which the firn fractionation signals are strongest, a combined multi-site inversion can be performed, which returns an isotope reconstruction that is consistent with firn data. However, the isotope trends are lower than what has been concluded from Southern Hemisphere (SH) archived air samples and high-accumulation ice core data. We conclude that with the current datasets and understanding of firn air transport, a high precision reconstruction of δ13C of CH4 from firn air samples is not possible, because reconstructed atmospheric trends over the last 50 yr of 0.3–1.5 ‰ are of the same magnitude as inherent uncertainties in the method, which are the firn fractionation correction (up to ~2 ‰ at individual sites), the Kr isobaric interference (up to ~0.8 ‰, system dependent), inter-laboratory calibration offsets (~0.2 ‰) and uncertainties in past CH4 levels (~0.5 ‰).

Improving accuracy and precision of ice core δD(CH4) analyses using methane pre-pyrolysis and hydrogen post-pyrolysis trapping and subsequent chromatographic separation

Firn and polar ice cores offer the only direct palaeoatmospheric archive. Analyses of past greenhouse gas concentrations and their isotopic compositions in air bubbles in the ice can help to constrain changes in global biogeochemical cycles in the past. For the analysis of the hydrogen isotopic composition of methane (δD(CH4) or δ2H(CH4)) 0.5 to 1.5 kg of ice was hitherto used. Here we present a method to improve precision and reduce the sample amount for δD(CH4) measurements in (ice core) air. Pre-concentrated methane is focused in front of a high temperature oven (pre-pyrolysis trapping), and molecular hydrogen formed by pyrolysis is trapped afterwards (post-pyrolysis trapping), both on a carbon-PLOT capillary at −196 °C. Argon, oxygen, nitrogen, carbon monoxide, unpyrolysed methane and krypton are trapped together with H2 and must be separated using a second short, cooled chromatographic column to ensure accurate results. Pre- and post-pyrolysis trapping largely removes the isotopic fractionation induced during chromatographic separation and results in a narrow peak in the mass spectrometer. Air standards can be measured with a precision better than 1‰. For polar ice samples from glacial periods, we estimate a precision of 2.3‰ for 350 g of ice (or roughly 30 mL – at standard temperature and pressure (STP) – of air) with 350 ppb of methane. This corresponds to recent tropospheric air samples (about 1900 ppb CH4) of about 6 mL (STP) or about 500 pmol of pure CH4.

On the interference of Kr during carbon isotope analysis of methane using continuous-flow combustion–isotope ratio mass spectrometry

Stable carbon isotope analysis of methane (delta C-13 of CH4) on atmospheric samples is one key method to constrain the current and past atmospheric CH4 budget. A frequently applied measurement technique is gas chromatography (GC) isotope ratio mass spectrometry (IRMS) coupled to a combustion-preconcentration unit. This report shows that the atmospheric trace gas krypton (Kr) can severely interfere during the mass spectrometric measurement, leading to significant biases in delta C-13 of CH4, if krypton is not sufficiently separated during the analysis. According to our experiments, the krypton interference is likely composed of two individual effects, with the lateral tailing of the doubly charged Kr-86 peak affecting the neighbouring m/z 44 and partially the m/z 45 Faraday cups. Additionally, a broad signal affecting m/z 45 and especially m/z 46 is assumed to result from scattered ions of singly charged krypton. The introduced bias in the measured isotope ratios is dependent on the chromatographic separation, the krypton-to-CH4 mixing ratio in the sample, the focusing of the mass spectrometer as well as the detector configuration and can amount to up to several per mil in delta C-13. Apart from technical solutions to avoid this interference, we present correction routines to a posteriori remove the bias.

Green Wireless-Energy Efficiency in Wireless Networks

Wireless networks have become more and more popular because of ease of installation, ease of access, and support of smart terminals and gadgets on the move. In the overall life cycle of providing green wireless technology, from production to operation and, finally, removal, this chapter focuses on the operation phase and summarizes insights in energy consumption of major technologies. The chapter also focuses on the edge of the network, comprising network access points (APs) and mobile user devices. It discusses particularities of most important wireless networking technologies: wireless access networks including 3G/LTE and wireless mesh networks (WMNs); wireless sensor networks (WSNs); and ad-hoc and opportunistic networks. Concerning energy efficiency, the chapter discusses challenges in access, wireless sensor, and ad-hoc and opportunistic networks.

From stellar nebula to planetesimals

Context. Solar and extrasolar comets and extrasolar planets are the subject of numerous studies in order to determine their chemical composition and internal structure. In the case of planetesimals, their compositions are important as they govern in part the composition of future planets. Aims. The present works aims at determining the chemical composition of icy planetesimals, believed to be similar to present day comets, formed in stellar systems of solar chemical composition. The main objective of this work is to provide valuable theoretical data on chemical composition for models of planetesimals and comets, and models of planet formation and evolution. Methods. We have developed a model that calculates the composition of ices formed during the cooling of the stellar nebula. Coupled with a model of refractory element formation, it allows us to determine the chemical composition and mass ratio of ices to rocks in icy planetesimals throughout in the protoplanetary disc. Results. We provide relationships for ice line positions (for different volatile species) in the disc, and chemical compositions and mass ratios of ice relative to rock for icy planetesimals in stellar systems of solar chemical composition. From an initial homogeneous composition of the nebula, a wide variety of chemical compositions of planetesimals were produced as a function of the mass of the disc and distance to the star. Ices incorporated in planetesimals are mainly composed of H2O, CO, CO2, CH3OH, and NH3. The ice/rock mass ratio is equal to 1 ± 0.5 in icy planetesimals following assumptions. This last value is in good agreement with observations of solar system comets, but remains lower than usual assumptions made in planet formation models, taking this ratio to be of 2–3.

Cyanide Compounds

Chapter 4, “Cyanide Compounds,” illustrates an explosively developing research theme in which the cyanide ligand is used as a linking agent for the designed assembly of polynuclear metal complexes. Syntheses of several basic building blocks, such as K3[Cr(CN)6],Cr(Me3tacn)(CN)3,K4[Mo(CN)8],Na[W(CO)5CN],K[CpFe(CO)(CN)2],[NEt4][Cp*Rh(CN)3],[Fe4(bpy)8(μ-CN)4][PF6]4,. are given here. These units may be used in several ways to construct polynuclear compounds. One approach involves a hexacyanometalate core decorated with peripheral metal centers, e.g., [{Cu(tpa)(CN)}6Fe][ClO4]8. or [Cr{CNNi(tetren)}6][ClO4]9. An octacyanometalate unit can lead to higher nuclearity condensed compounds, as in [Co{Co(MeOH)3}8(μ-CN)30{Mo(CN)3}6]. Alternatively, a cluster core may be substituted with cyano complexes as ligands, as in [PPh4]2[Fe4S4{NCW(CO)5}4]. If there are two cis cyano ligands on the building block, then quadrilateral or square structures often result, as in {CpFe(CO(μ-CN)2Cu(PCy3)}2 and [Fe2Cu2(bpy)6(μ-CN)4][PF6]4 However, if there are three adjacent cyano ligands, then cubic cages may be constructed as in [(CpCo)4(Cp*Rh)4(μ-CN)12][PF6]4.

Metamagnetic Copper(II) Diphosphonates with Layered Structures

Compounds [NH3(CH2)4NH3]Cu3(hedp)2·2H2O (1) and [NH3(CH2)3NH3]Cu3(hedp)2·3.5H2O (2), where hedp represents 1-hydroxyethylidenediphosphonate, exhibit two-dimensional structures closely related to each other. The anionic layers with composition {Cu3(hedp)2}n2n- contain four- and eight-membered rings assembled from vertex-sharing {CuO4} units and {CPO3} tetrahedra. The protonated diamines and lattice water fill the interlayer spaces. Crystal data for 2:  space group P1̄, a = 8.0315(4), b = 11.3713(6), c = 13.3117(7) Å, α = 97.122(1), β = 103.187(1), γ = 108.668(1)°, V = 1095.5(1) Å3, Z = 2. Magnetic properties of the two compounds have been investigated. Both show typical metamagnetic behaviors at low temperature. The critical field at which the antiferromagnetic ground-state switches to a ferrimagnetic state is ∼48 Oe for 1 and 185 Oe for 2 at about 2 K.

The stable carbon isotopic composition of Daphnia ephippia in small, temperate lakes reflects in-lake methane availability

Daphnia can ingest methane-oxidizing bacteria and incorporate methanogenic carbon into their biomass, leading to low stable carbon isotope ratios (expressed as δ13C values) of their tissue. Therefore, δ13C analysis of Daphnia resting eggs (ephippia) in lake sediment records can potentially be used to reconstruct past in-lake availability of methane (CH4). However, detailed multilake studies demonstrating that δ13C values of recently deposited Daphnia ephippia (δ13Cephippia) are systematically related to in-lake CH4 concentrations (CH4aq) are still missing. We measured δ13Cephippia from surface sediments of 15 small lakes in Europe, and compared these values with late-summer CH4aq. δ13Cephippia ranged from −51.6‰ to −25.9‰, and was strongly correlated with CH4aq in the surface water and above the sediment (r −0.73 and −0.77, respectively), whereas a negative rather than the expected positive correlation was found with δ13C values of carbon dioxide (CO2) (r −0.54), and no correlation was observed with CO2aq. At eight sites, offsets between δ13 CCO2 and δ13Cephippia exceeded offsets between δ13 CCO2 and δ13Calgae reported in literature. δ13Cephippia was positively correlated with δ13C values of sedimentary organic matter (r 0.54), but up to 20.7‰ lower in all except one of the lakes (average −6.1‰). We conclude that incorporation of methanogenic carbon prior to ephippia formation must have been widespread by Daphnia in our study lakes, especially those with high CH4aq. Our results suggest a systematic relationship between δ13Cephippia values and CH4aq in small temperate lakes, and that δ13Cephippia analysis on sediment records may provide insights into past changes in in-lake CH4aq.

Retrieving the paleoclimatic signal from the deeper part of the EPICA Dome C ice core

An important share of paleoclimatic information is buried within the lowermost layers of deep ice cores. Because improving our records further back in time is one of the main challenges in the near future, it is essential to judge how deep these records remain unaltered, since the proximity of the bedrock is likely to interfere both with the recorded temporal sequence and the ice properties. In this paper, we present a multiparametric study (δD-δ18Oice, δ18Oatm, total air content, CO2, CH4, N2O, dust, high-resolution chemistry, ice texture) of the bottom 60 m of the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core from central Antarctica. These bottom layers were subdivided into two distinct facies: the lower 12 m showing visible solid inclusions (basal dispersed ice facies) and the upper 48 m, which we will refer to as the "basal clean ice facies". Some of the data are consistent with a pristine paleoclimatic signal, others show clear anomalies. It is demonstrated that neither large-scale bottom refreezing of subglacial water, nor mixing (be it internal or with a local basal end term from a previous/initial ice sheet configuration) can explain the observed bottom-ice properties. We focus on the high-resolution chemical profiles and on the available remote sensing data on the subglacial topography of the site to propose a mechanism by which relative stretching of the bottom-ice sheet layers is made possible, due to the progressively confining effect of subglacial valley sides. This stress field change, combined with bottom-ice temperature close to the pressure melting point, induces accelerated migration recrystallization, which results in spatial chemical sorting of the impurities, depending on their state (dissolved vs. solid) and if they are involved or not in salt formation. This chemical sorting effect is responsible for the progressive build-up of the visible solid aggregates that therefore mainly originate "from within", and not from incorporation processes of debris from the ice sheet's substrate. We further discuss how the proposed mechanism is compatible with the other ice properties described. We conclude that the paleoclimatic signal is only marginally affected in terms of global ice properties at the bottom of EPICA Dome C, but that the timescale was considerably distorted by mechanical stretching of MIS20 due to the increasing influence of the subglacial topography, a process that might have started well above the bottom ice. A clear paleoclimatic signal can therefore not be inferred from the deeper part of the EPICA Dome C ice core. Our work suggests that the existence of a flat monotonic ice–bedrock interface, extending for several times the ice thickness, would be a crucial factor in choosing a future "oldest ice" drilling location in Antarctica.

An inter-regional assessment of concentrations and δ13C values of methane and dissolved inorganic carbon in small European lakes

Methane (CH4) and carbon dioxide emissions from lakes are relevant for assessing the greenhouse gas output of wetlands. However, only few standardized datasets describe concentrations of these gases in lakes across different geographical regions. We studied concentrations and stable carbon isotopic composition (δ13C) of CH4 and dissolved inorganic carbon (DIC) in 32 small lakes from Finland, Sweden, Germany, the Netherlands, and Switzerland in late summer. Higher concentrations and δ13C values of DIC were observed in calcareous lakes than in lakes on non-calcareous areas. In stratified lakes, δ13C values of DIC were generally lower in the hypolimnion due to the degradation of organic matter (OM). Unexpectedly, increased δ13C values of DIC were registered above the sediment in several lakes. This may reflect carbonate dissolution in calcareous lakes or methanogenesis in deepwater layers or in the sediments. Surface water CH4 concentrations were generally higher in western and central European lakes than in Fennoscandian lakes, possibly due to higher CH4 production in the littoral sediments and lateral transport, whereas CH4 concentrations in the hypolimnion did not differ significantly between the regions. The δ13C values of CH4 in the sediment suggest that δ13C values of biogenic CH4 are not necessarily linked to δ13C values of sedimentary OM but may be strongly influenced by OM quality and methanogenic pathway. Our study suggests that CH4 and DIC cycling in small lakes differ between geographical regions and that this should be taken into account when regional studies on greenhouse gas emissions are upscaled to inter-regional scales.

Evaluating atmospheric methane inversion model results for Pallas, northern Finland

A state-of-the-art inverse model, CarbonTracker Data Assimilation Shell (CTDAS), was used to optimize estimates of methane (CH4) surface fluxes using atmospheric observations of CH4 as a constraint. The model consists of the latest version of the TM5 atmospheric chemistry-transport model and an ensemble Kalman filter based data assimilation system. The model was constrained by atmospheric methane surface concentrations, obtained from the World Data Centre for Greenhouse Gases (WDCGG). Prior methane emissions were specified for five sources: biosphere, anthropogenic, fire, termites and ocean, of which bio-sphere and anthropogenic emissions were optimized. Atmospheric CH 4 mole fractions for 2007 from northern Finland calculated from prior and optimized emissions were compared with observations. It was found that the root mean squared errors of the posterior esti - mates were more than halved. Furthermore, inclusion of NOAA observations of CH 4 from weekly discrete air samples collected at Pallas improved agreement between posterior CH 4 mole fraction estimates and continuous observations, and resulted in reducing optimized biosphere emissions and their uncertainties in northern Finland.

Composition-dependent outgassing of comet 67P/Churyumov-Gerasimenko from ROSINA/DFMS

Context. Early measurements of Rosetta’s target comet, 67P/Churyumov-Gerasimenko (67P), showed a strongly heterogeneous coma in H2O, CO, and CO2. Aims. The purpose of this work is to further investigate the coma heterogeneity of 67P, and to provide predictions for the near-perihelion outgassing profile based on the proposed explanations. Methods. Measurements of various minor volatile species by ROSINA/DFMS on board Rosetta are examined. The analysis focuses on the currently poorly illuminated winter (southern) hemisphere of 67P. Results. Coma heterogeneity is not limited to the major outgassing species. Minor species show better correlation with either H2O or CO2. The molecule CH4 shows a different diurnal pattern from all other analyzed species. Such features have implications for nucleus heterogeneity and thermal processing. Conclusions. Future analysis of additional volatiles and modeling the heterogeneity are required to better understand the observed coma profile.

Decision strategies for policy decisions under uncertainties: The case of mitigation measures addressing methane emissions from ruminants

Decision strategies aim at enabling reasonable decisions in cases of uncertain policy decision problems which do not meet the conditions for applying standard decision theory. This paper focuses on decision strategies that account for uncertainties by deciding whether a proposed list of policy options should be accepted or revised (scope strategies) and whether to decide now or later (timing strategies). They can be used in participatory approaches to structure the decision process. As a basis, we propose to classify the broad range of uncertainties affecting policy decision problems along two dimensions, source of uncertainty (incomplete information, inherent indeterminacy and unreliable information) and location of uncertainty (information about policy options, outcomes and values). Decision strategies encompass multiple and vague criteria to be deliberated in application. As an example, we discuss which decision strategies may account for the uncertainties related to nutritive technologies that aim at reducing methane (CH4) emissions from ruminants as a means of mitigating climate change, limiting our discussion to published scientific information. These considerations not only speak in favour of revising rather than accepting the discussed list of options, but also in favour of active postponement or semi-closure of decision-making rather than closure or passive postponement.

Sensitivity and fragmentation calibration of the ROSINA double focusing mass spectrometer

The goal of this work has been to calibrate sensitivities and fragmentation pattern of various molecules as well as further characterize the lab model of the ROSINA Double Focusing Mass Spectrometer (DFMS) on board ESA’s Rosetta spacecraft bound to comet 67P/Churyumov-Gerasimenko. The detailed calibration and characterization of the instrument is key to understand and interpret the results in the coma of the comet. A static calibration was performed for the following species: Ne, Ar, Kr, Xe, H2O, N2, CO2, CH4, C2H6, C3H8, C4H10, and C2H4. The purpose of the calibration was to obtain sensitivities for all detectors and emissions, the fragmentation behavior of the ion source and to show the capabilities to measure isotopic ratios at the comet. The calibration included the recording of different correction factors to evaluate the data, including a detailed investigation of the detector gain. The quality of the calibration that could be tested for different gas mixtures including the calibration of the density inside the ion source when calibration gas from the gas calibration unit is introduced. In conclusion the calibration shows that DFMS meets the design requirements and that DFMS will be able to measure the D/H at the comet and help shed more light on the puzzle about the origin of water on Earth.

Mapping spectroscopic uncertainties into prospective methane retrieval errors from Sentinel-5 and its precursor

Sentinel-5 (S5) and its precursor (S5P) are future European satellite missions aiming at global monitoring of methane (CH4) column-average dry air mole fractions (XCH4). The spectrometers to be deployed onboard the satellites record spectra of sunlight backscattered from the Earth's surface and atmosphere. In particular, they exploit CH4 absorption in the shortwave infrared spectral range around 1.65 mu m (S5 only) and 2.35 mu m (both S5 and S5P) wavelength. Given an accuracy goal of better than 2% for XCH4 to be delivered on regional scales, assessment and reduction of potential sources of systematic error such as spectroscopic uncertainties is crucial. Here, we investigate how spectroscopic errors propagate into retrieval errors on the global scale. To this end, absorption spectra of a ground-based Fourier transform spectrometer (FTS) operating at very high spectral resolution serve as estimate for the quality of the spectroscopic parameters. Feeding the FTS fitting residuals as a perturbation into a global ensemble of simulated S5- and S5P-like spectra at relatively low spectral resolution, XCH4 retrieval errors exceed 0.6% in large parts of the world and show systematic correlations on regional scales, calling for improved spectroscopic parameters.