Major, minor, and lithophile trace element abundances and Nd and Hf isotope systematics are reported for two sets of remarkably fresh, by Archean standards, samples of komatiitic lavas from the ...3.48Ga Komati and the 3.27Ga Weltevreden Formations of the Barberton Greenstone Belt (BGB) in South Africa. These data are used to place new constraints on the thermal history of the early Archean mantle, on the timing of its differentiation, and on the origin and chemical nature of early mantle reservoirs and their evolution through time.
Projected moderate to strong depletions of highly incompatible lithophile trace elements and water in the mantle sources of both komatiite systems, combined with the partitioning behavior of V during lava differentiation, are consistent with anhydrous conditions during generation of the komatiite magmas. Komati and Weltevreden lavas are inferred to have erupted with temperatures of ∼1600°C, and, thus, represent the hottest known lavas on Earth. The calculated mantle potential temperatures of ∼1800°C for both komatiite systems are 150–200°C higher than those of contemporary ambient mantle. Combined, these observations are consistent with the origin of these BGB komatiite magmas in mantle plumes in the lower mantle.
New Sm–Nd and Lu–Hf isotopic data allow precise determination of initial ε143Nd=+0.46±0.10 and +0.50±0.11 and initial ε176Hf=+1.9±0.3 and +4.7±0.8 for the Komati and the Weltevreden system komatiites, respectively. These positive initial values reflect prior fractionation of Sm/Nd and Lu/Hf in the mantle early in Earth history. Conversely, μ142Nd values are 0.0±2.4 and +2.2±4.1 for the Komati and the Weltevreden systems, respectively. These values overlap, within uncertainties, those of modern terrestrial rocks, thus, limiting the magnitudes of possible Sm/Nd fractionations generated by early Earth processes in the sources of these rocks. Combined 142,143Nd and Hf isotope and lithophile trace element systematics are consistent with formation and long-term isolation of deep-seated mantle domains with fractionated Sm/Nd and Lu/Hf at ca. 4400Ma. These domains were likely generated as a result of crystallization of a primordial magma ocean, with Mg-perovskite and minor Ca-perovskite acting as fractionating phases. The inferred mantle domains were evidently mixed away by 2.7Ga on the scale of mantle reservoirs sampled by late Archean komatiite lavas emplaced worldwide.
Cyathostomins are ubiquitous nematodes of horses. Once ingested, they can spend a substantial time as encysted larvae in the intestinal wall. The larvae can comprise up to 90% of the total burden, ...with up to several million worms reported in individuals. These stages can emerge in large numbers to cause life-threatening colitis. Direct methods for detection of encysted larval burdens in live horses do not exist. Previously, two antigen complexes were identified as promising markers for infection. A component of these, cyathostomin gut associated larval antigen-1 (Cy-GALA-1), was identified following immunoscreening of a complementary DNA library. Serum immunoglobulin G(T) (IgG(T)) responses to Cy-GALA-1 were shown to inform on larval infection. Sequence analysis of polymerase chain reaction products amplified from individual worms indicated that Cy-GALA-1 was derived from Cyathostomum pateratum. As cyathostomin infections always comprise multiple species, a diagnostic test must account for this. Here, segments of the Cy-gala gene were isolated from four common species, Cyathostomum catinatum, Cylicocyclus ashworthi, Cylicostephanus goldi and Cylicostephanus longibursatus, and the associated proteins expressed in recombinant form. The specificity and immunogenicity of each protein was confirmed. Each protein was assessed by enzyme linked immuno sorbent assay (ELISA) for its ability for informing on the presence of encysted larval infection and the level of burden.
Atmospheric CO at Egham in SE England has shown a marked and progressive decline since 1997, following adoption of strict controls on emissions. The Egham site is uniquely positioned to allow both ...assessment and comparison of 'clean Atlantic background' air and CO-enriched air downwind from the London conurbation. The decline is strongest (approximately 50 ppb per year) in the 1997-2003 period but continues post 2003. A 'local CO increment' can be identified as the residual after subtraction of contemporary background Atlantic CO mixing ratios from measured values at Egham. This increment, which is primarily from regional sources (during anticyclonic or northerly winds) or from the European continent (with easterly air mass origins), has significant seasonality, but overall has declined steadily since 1997. On many days of the year CO measured at Egham is now not far above Atlantic background levels measured at Mace Head (Ireland). The results are consistent with MOPITT satellite observations and 'bottom-up' inventory results. Comparison with urban and regional background CO mixing ratios in Hong Kong demonstrates the importance of regional, as opposed to local reduction of CO emission. The Egham record implies that controls on emissions subsequent to legislation have been extremely successful in the UK.
Strategies are sought to reduce economic and environmental costs associated with ruminant methane emissions. The effect of oral nitroethane or 2-nitropropanol administration on ruminal ...methane-producing activity and volatile fatty acid production was evaluated in mature ewes. Daily administration of 24 and 72
mg nitroethane/kg body weight reduced (
P
<
0.05) methane-producing activity by as much as 45% and 69% respectively, when compared to control animals given no nitroethane. A daily dose of 120
mg 2-nitropropanol/kg body weight was needed to reduce (
P
<
0.05) methane-producing activity by 37% from that of untreated control animals. Reductions in methane-producing activity may have been diminished by the last day (day 5) of treatment, presumably due to ruminal adaptation. Oral administration of nitroethane or 2-nitropropanol had little or no effect on accumulations or molar proportions of volatile fatty acids in ruminal contents collected from the sheep. These results demonstrate that nitroethane was superior to 2-nitropropanol as a methane inhibitor and that both nitrocompounds reduced ruminal methanogenesis in vivo without redirecting the flow of reductant generated during fermentation to propionate and butyrate.
Ascension Island is a remote South Atlantic equatorial site, ideal for monitoring tropical background CH4. In September 2014 and July 2015, octocopters were used to collect air samples in Tedlar bags ...from different heights above and below the well‐defined Trade Wind Inversion (TWI), sampling a maximum altitude of 2700 m above mean sea level. Sampling captured both remote air in the marine boundary layer below the TWI and also air masses above the TWI that had been lofted by convective systems in the African tropics. Air above the TWI was characterized by higher CH4, but no distinct shift in δ13C was observed compared to the air below. Back trajectories indicate that lofted CH4 emissions from Southern Hemisphere Africa have bulk δ13CCH4 signatures similar to background, suggesting mixed emissions from wetlands, agriculture, and biomass burning. The campaigns illustrate the usefulness of unmanned aerial system sampling and Ascension's value for atmospheric measurement in an understudied region.
Key Points
Methane mole fraction and δ13C have been measured from samples collected by UASs on Ascension Island over two campaigns
CH4 mole fraction increases above the TWI, but isotopes have no consistent signal indicating input from Africa is close to background
The campaigns illustrate the usefulness of UAS sampling and Ascension's value for atmospheric measurement in an understudied region
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