Methane stable isotope analysis, coupled with mole fraction measurement, has been used to link isotopic signature to methane emissions from landfill sites, coal mines and gas leaks in the United ...Kingdom. A mobile Picarro G2301 CRDS (Cavity Ring-Down Spectroscopy) analyser was installed on a vehicle, together with an anemometer and GPS receiver, to measure atmospheric methane mole fractions and their relative location while driving at speeds up to 80 kph. In targeted areas, when the methane plume was intercepted, air samples were collected in Tedlar bags, for δ13C–CH4 isotopic analysis by CF-GC-IRMS (Continuous Flow Gas Chromatography-Isotope Ratio Mass Spectrometry). This method provides high precision isotopic values, determining δ13C–CH4 to ±0.05 per mil. The bulk signature of the methane plume into the atmosphere from the whole source area was obtained by Keeling plot analysis, and a δ13C–CH4 signature, with the relative uncertainty, allocated to each methane source investigated. Both landfill and natural gas emissions in SE England have tightly constrained isotopic signatures. The averaged δ13C–CH4 for landfill sites is −58 ± 3‰. The δ13C–CH4 signature for gas leaks is also fairly constant around −36 ± 2‰, a value characteristic of homogenised North Sea supply. In contrast, signatures for coal mines in N. England and Wales fall in a range of −51.2 ± 0.3‰ to −30.9 ± 1.4‰, but can be tightly constrained by region. The study demonstrates that CRDS-based mobile methane measurement coupled with off-line high precision isotopic analysis of plume samples is an efficient way of characterising methane sources. It shows that isotopic measurements allow type identification, and possible location of previously unknown methane sources. In modelling studies this measurement provides an independent constraint to determine the contributions of different sources to the regional methane budget and in the verification of inventory source distribution.
•CH4 source plumes were located by a mobile Picarro analyser.•CH4 plumes from landfill sites, coal mines and gas leaks were sampled.•High precision isotopic analysis of air samples collected was carried out.•CH4 isotopic signatures were allocated to CH4 sources in UK.•The method provides an independent constraint to determine CH4 sources contribution.
European CH4 emissions are estimated for the period 2001–2006 using a four‐dimensional variational (4DVAR) inverse modeling system, based on the atmospheric zoom model TM5. Continuous observations ...are used from various European monitoring stations, complemented by European and global flask samples from the NOAA/ESRL network. The available observations mainly provide information on the emissions from northwest Europe (NWE), including the UK, Ireland, the BENELUX countries, France and Germany. The inverse modeling estimates for the total anthropogenic emissions from NWE are 21% higher compared to the EDGARv4.0 emission inventory and 40% higher than values reported to U.N. Framework Convention on Climate Change. Assuming overall uncertainties on the order of 30% for both bottom‐up and top‐down estimates, all three estimates can be still considered to be consistent with each other. However, the uncertainties in the uncertainty estimates prevent us from verifying (or falsifying) the bottom‐up inventories in a strict sense. Sensitivity studies show some dependence of the derived spatial emission patterns on the set of atmospheric monitoring stations used, but the total emissions for the NWE countries appear to be relatively robust. While the standard inversions include a priori information on the spatial and temporal emission patterns from bottom‐up inventories, a further sensitivity inversion without this a priori information results in very similar NWE country totals, demonstrating that the available observations provide significant constraints on the emissions from the NWE countries independent from bottom‐up inventories.
We find that summer methane (CH4) release from seabed sediments west of Svalbard substantially increases CH4 concentrations in the ocean but has limited influence on the atmospheric CH4 levels. Our ...conclusion stems from complementary measurements at the seafloor, in the ocean, and in the atmosphere from land‐based, ship and aircraft platforms during a summer campaign in 2014. We detected high concentrations of dissolved CH4 in the ocean above the seafloor with a sharp decrease above the pycnocline. Model approaches taking potential CH4 emissions from both dissolved and bubble‐released CH4 from a larger region into account reveal a maximum flux compatible with the observed atmospheric CH4 mixing ratios of 2.4–3.8 nmol m−2 s−1. This is too low to have an impact on the atmospheric summer CH4 budget in the year 2014. Long‐term ocean observatories may shed light on the complex variations of Arctic CH4 cycles throughout the year.
Key Points
Summer CH4 release from seabed sediments west of Svalbard substantially increases concentrations in the ocean, but not in the atmosphere
The modeled flux is constrained to a maximum of 2.4 to 3.8 nmol m−2 s−1, compatible with the observed atmospheric CH4 from 20 June to 1 August 2014
Any ocean‐atmosphere flux of the CH4 accumulated beneath the pycnocline may only occur if physical processes remove this dynamic barrier
Rising methane: is there a methane emergency? Nisbet, E G; Jones, A E; Pyle, J A ...
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
2022-Jan-24, Letnik:
380, Številka:
2215
Journal Article
ABSTRACT
The evolutionary history of oxygenesis is controversial. Form I of ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco) in oxygen‐tolerant organisms both enables them to carry out ...oxygenic extraction of carbon from air and enables the competitive process of photorespiration. Carbon isotopic evidence is presented from ~2.9 Ga stromatolites from Steep Rock, Ontario, Canada, ~2.9 Ga stromatolites from Mushandike, Zimbabwe, and ~2.7 Ga stromatolites in the Belingwe belt, Zimbabwe. The data imply that in all three localities the reef‐building autotrophs included organisms using Form I Rubisco. This inference, though not conclusive, is supported by other geochemical evidence that these stromatolites formed in oxic conditions. Collectively, the implication is that oxygenic photosynthesizers first appeared ~2.9 Ga ago, and were abundant 2.7–2.65 Ga ago.
Rubisco specificity (its preference for CO2 over O2) and compensation constraints (the limits on carbon fixation) may explain the paradox that despite the inferred evolution of oxygenesis 2.9 Ga ago, the Late Archaean air was anoxic. The atmospheric CO2:O2 ratio, and hence greenhouse warming, may reflect Form I Rubisco's specificity for CO2 over O2. The system may be bistable under the warming Sun, with liquid oceans occurring in either anoxic (H2O with abundant CH4 plus CO2) or oxic (H2O with more abundant CO2, but little CH4) greenhouse states. Transition between the two states would involve catastrophic remaking of the biosphere. Build‐up of a very high atmospheric inventory of CO2 in the 2.3 Ga glaciation may have allowed the atmosphere to move up the CO2 compensation line to reach stability in an oxygen‐rich system. Since then, Form I Rubisco specificity and consequent compensation limits may have maintained the long‐term atmospheric disproportion between O2 and CO2, which is now close to both CO2 and O2 compensation barriers.
The effects of several methane-inhibitors on rumen fermentation were compared during three 24
h consecutive batch cultures of ruminal microbes in the presence of nonlimiting amounts of hydrogen. ...After the initial incubation series, methane production was reduced greater than 92% from that of non-treated controls (25.8
±
8.1
μmol
ml
−1 incubation fluid) in cultures treated with nitroethane, sodium laurate, Lauricidin
® or a finely-ground product of the marine algae,
Chaetoceros (added at 1, 5, 5 and 10
mg
ml
−1, respectively) but not in cultures treated with sodium nitrate (1
mg
m1
−1). Methane production during two successive incubations was reduced greater than 98% from controls (22.5
±
3.2 and 23.5
±
7.9
μmol
ml
−1, respectively) by all treatments. Reductions in amounts of volatile fatty acids and ammonia produced and amounts of hexose fermented, when observed, were most severe in sodium laurate-treated cultures. These results demonstrate that all tested compounds inhibited ruminal methane production in our
in vitro system but their effects on fermentation differed.
Tropical methane sources are an important part of the global methane budget and include natural wetlands, rice agriculture, biomass burning, ruminants, fossil fuels, and waste. δ13CCH4 can provide ...strong constraints on methane source apportionment. For example, tropical wetlands in this study give δ13CCH4 values between −61.5 ± 2.9‰ and −53.0 ± 0.4‰ and in general are more enriched in 13C than temperate and boreal wetlands. However, thus far, relatively few measurements of δ13CCH4 in methane‐enriched air have been made in the tropics. In this study samples have been collected from tropical wetland, rice, ruminant, and biomass burning emissions to the atmosphere. Regional isotopic signatures vary greatly as different processes and source material affect methane signatures. Measurements were made to determine bulk source inputs to the atmosphere, rather than to study individual processes. These measurements provide inputs for regional methane budget models, to constrain emissions with better source apportionment.
Key Points
Methane δ13C isotopic signatures have been measured in the tropics for wetland, rice, ruminant, and biomass burning
Wetlands, rice, and ruminants are depleted in 13C, but it is difficult to distinguish between them; biomass burning values are enriched in 13C
Isotopic measurements are essential in determining the causes of methane growth
Plain Language Summary
Tropical methane sources are an important part of the global methane budget and include natural wetlands, rice agriculture, biomass burning, ruminants, fossil fuels, and waste. Carbon isotopes in methane can provide strong constraints on methane source apportionment. However, thus far, relatively few measurements of carbon isotopes in methane‐enriched air have been made in the tropics. In this study samples have been collected from tropical wetland, rice, ruminant, and biomass burning emissions to atmosphere. Regional isotopic signatures vary greatly as different processes and source material affect methane signatures. Measurements were made to determine bulk source inputs to the atmosphere, rather than to study individual processes, to provide inputs for regional methane budget models, and to constrain emissions with better source apportionment.
High-precision Pt–Re–Os and Sm–Nd isotope and highly siderophile element (HSE) and rare earth element (REE) abundance data are reported for two 2.7 b.y. old komatiite lava flows, Tony’s flow (TN) ...from the Belingwe greenstone belt, Zimbabwe, and the PH-II flow (PH) from Munro Township in the Abitibi greenstone belt, Canada. The emplaced lavas are calculated to have contained ∼25% (TN) and ∼28% (PH) MgO. These lavas were derived from mantle sources characterized by strong depletions in highly incompatible lithophile trace elements, such as light REE (Ce/Sm
N
=
0.64
±
0.02 (TN) and 0.52
±
0.01 (PH), ε
143Nd(T)
=
+2.9
±
0.2 in both sources).
190Pt–
186Os and
187Re–
187Os isochrons generated for each flow yield ages consistent with respective emplacement ages obtained using other chronometers. The calculated precise initial
186Os/
188Os
=
0.1198318
±
3 (TN) and 0.1198316
±
5 (PH) and
187Os/
188Os
=
0.10875
±
17 (TN) and 0.10873
±
15 (PH) require time-integrated
190Pt/
188Os and
187Re/
188Os of 0.00178
±
11 and 0.407
±
8 (TN) and 0.00174
±
18 and 0.415
±
5 (PH). These parameters, which by far represent the most precise and accurate estimates of time-integrated Pt/Os and Re/Os of the Archean mantle, are best matched by those of enstatite chondrites. The data also provide evidence for a remarkable similarity in the composition of the sources of these komatiites with respect to both REE and HSE. The calculated absolute HSE abundances in the TN and PH komatiite sources are within or slightly below the range of estimates for the terrestrial Primitive Upper Mantle (PUM). Assuming a chondritic composition of the bulk silicate Earth, the strong depletions in LREE, yet chondritic Re/Os in the komatiite sources are apparently problematic because early Earth processes capable of fractionating the LREE might also be expected to fractionate Re/Os. This apparent discrepancy could be reconciled via a two-stage model, whereby the moderate LREE depletion in the sources of the komatiites initially occurred within the first 100 Ma of Earth’s history as a result of either global magma ocean differentiation or extraction and subsequent long-term isolation of early crust, whereas HSE were largely added subsequently via late accretion. The komatiite formation, preceded by derivation of basaltic magmas, was a result of second-stage, large-degree dynamic melting in mantle plumes.
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