Effects of three oil spill dispersants on marine bacterial populations: I. Preliminary Study. Quantitative Evolution of Aerobes

The effects of three hydrocarbon dispersant agents (Corexit 9527, Hydrogamosol LT and OSR LT 126) on the bacterial flora of the marine environment are analysed in 20-square-metre basins filled with lagoon seawater.Four months after the first treatment, oil slicks were no longer visible, whereas the appearance of the untreated reference slick had hardly changed. The treatment of 10-litre crude-oil slicks causes an appreciable and long lasting increase in the bacterial population.     

Source, genesis, and timing of giant ignimbrite deposits associated with Ethiopian continental flood basalts

The Ethiopian continental flood basalt (CFB) province (∼30 Ma, > 3 × 10⁵ km³) was formed as the result of the impingement of the Afar mantle plume beneath the Ethiopian lithosphere. This province includes major sequences of rhyolitic ignimbrites generally found on top of the flood basalt sequence. Their volume is estimated to be at least 6 × 10⁴km³, which represents 20% of that of the trap basalts. Their phenocryst assemblage (alkali feldspar, quartz, aegyrine-augite, ilmenite ± Ti-magnetite, richterite, and eckermanite) suggests temperatures in the range of 740 to 900°C. Four units were recognized in the field (Wegel Tena, Jima, Lima Limo, and Debre Birhan areas), each with its own geochemical specificity. Zr/Nb ratios remain constant between basalt and rhyolite in each area, and rhyolites associated with high-Ti or low-Ti basalts are, respectively, enriched or depleted in titanium. Their trace element and isotope (Sr, Nd, O) signatures (high ¹⁴³Nd/¹⁴⁴Nd and low ⁸⁷Sr/⁸⁶Sr ratios, compared to those of rhyolites from other CFB provinces) are clearly different from those of typical crustal melts and indicate that the Ethiopian rhyolites are among the most isotopically primitive rhyolites. Their major and trace element patterns suggest that they are likely to be derived from fractional crystallization of basaltic magmas similar in composition to the exposed flood basalts with only limited crustal contribution. Since Ethiopian high-Ti basalts have been shown to form from melting of a mantle plume, it is likely that Ethiopian ignimbrites, at least those that are Ti-rich, also incorporated material from the deep mantle.Rb-Sr isochrons on whole rocks and mineral separates (30.1 ± 0.4 Ma for Wegel Tena and 30.5 ± 0.4 Ma for Jima ignimbrites) show that most of the silicic volcanism occurred within < 2 Ma during the Oligocene. Ignimbritic eruptions resumed in the Miocene during two episodes dated at 15.4 ± 0.2 Ma and 8.0 ± 0.2 Ma for the Debre Birhan area. The Rb-Sr isochron ages of ignimbrites (both Oligocene and Miocene rhyolites) are indistinguishable within uncertainties from the ⁴⁰Ar/³⁹Ar ages of the underlying flood basalts. The Oligocene ignimbrites and the underlying trap basalts are synchronous with a shift in the oxygen composition of foraminifera recorded in Indian and Atlantic Ocean cores. The temporal coincidence of Ethiopian Oligocene volcanism, which released immense volumes of S (> 1.4 × 10¹⁵ mol) and Cl (6.4 × 10¹⁵ mol) into the atmosphere over a short time span, with the global cooling event at 30.3 Ma suggests that this volcanism might have accelerated the climate change that was already underway.     

Oxygen isotopes in single micrometer-sized quartz grains: tracing the source of Saharan dust over long-distance atmospheric transport

Oxygen isotope compositions were measured by ion microprobe in individual micrometer-sized quartz grains extracted from one aerosol sample collected on the Cape Verde Islands and from four surface samples (three soils and one sediment) representing potential source regions of aerosols in Western and Central Africa (Morocco, Algeria, Niger, and Chad). A large range of δ¹⁸O values, from +6.2‰ to +39.3‰ is present within the aerosol quartz grains. The different size fractions of the quartz grains from the surface samples overlap nearly entirely this range but show significant differences in their δ¹⁸O distributions for the different size fractions of the grains (i.e., different modes, different proportions of grains with low or high δ¹⁸O, ...). These differences in δ¹⁸O distributions can be related to different geological formations (i.e., mantle-derived magmatic rocks, crustal magmatic rocks, or sedimentary rocks) outcropping in each region, thus giving a fingerprint of the source region. Quartz grains with unusually high δ¹⁸O values between +30‰ and +40‰ were attributed to lacustrine cherts formed in evaporitic environments (Chad basin).The existence of distinct δ¹⁸O distributions for the surface samples, which reflect regional geology but indicate some transport of the grains, enables the characterization of mixing processes during dust emission in the atmosphere. Particles are mixed at a regional scale in the dust reservoir, but injection of fine particles into the high troposphere occurs as a discrete and localized event with no mixing during the subsequent long-range transport by the easterlies. The comparison of the δ¹⁸O distribution of the quartz from the aerosol sample with the equivalent size fractions in surface samples shows that the Niger area is the more probable source region for the aerosol although the Moroccan source cannot be excluded. This method gives a valuable tool to trace the source region of dust into the atmosphere or into sediment samples, allowing the reconstruction of air mass circulations.     

Dynamic orbit determination and gravity field model improvement from GPS, DORIS and Laser measurements on TOPEX/POSEIDON satellite

Summary. In the framework of the GRIM series of gravity field models, the CNES/GRGS GINS precise orbit determination software has been adapted to dynamic GPS data processing. That is simultaneous processing of all available observables (i.e. GPS, DORIS, Laser) and all available satellite orbits (i.e. GPS, TOPEX/POSEIDON) can now be performed. The TOPEX/POSEIDON (T/P) mission satellite is equipped with a GPS receiver, a DORIS receiver and a laser reflector that represents an unprecedented opportunity to compare and combine these three tracking systems to estimate orbital parameters and gravity field coefficients. Different combinations including : GPS + DORIS, DORIS + LASER, GPS + DORIS + LASER, have been tested and have shown small but systematic improvement in T/P orbit accuracy when GPS and DORIS data were processed simultaneously. Five tuned gravity field models have been generated by accumulating different combinations of T/P normal equations associated to the GPS, DORIS and Laser data. GPS data have a greater dynamic impact on gravity field spherical harmonics coefficient determination than DORIS and Laser data. Furthermore, the results obtained with the solutions including and T/P normal equations suggest that indeed these different tracking systems are somehow complementary in a dynamic sense. Received 30 March 1995; Accepted 19 September 1996     

Long-wavelength global gravity field models: GRIM4-S4, GRIM4-C4

Summary.  GFZ Potsdam and GRGS Toulouse/Grasse jointly developed a new pair of global models of the Earth's gravity field to satisfy the requirements of the recent and future geodetic and altimeter satellite missions. A precise gravity model is a prerequisite for precise satellite orbit restitution, tracking station positioning and altimeter data reduction. According to different applications envisaged, the new model exists in two parallel versions: the first one being derived exclusively from satellite tracking data acquired on 34 satellites, the second one further incorporating satellite altimeter data over the oceans and terrestrial gravity data. The most recent “satellite-only” gravity model is labelled GRIM4-S4 and the “combined” gravity model GRIM4-C4. The models are solutions in spherical harmonics and have a resolution up to degree and order 60 plus a few resonance terms in the case of GRIM4-S4, and up to degree/order 72 in the case of GRIM4-C4, corresponding to a spatial resolution of 555 km at the Earth's surface. The gravitational coefficients were estimated in a rigorous least squares adjustment simultaneously with ocean tidal terms and tracking station position parameters, so that each gravity model is associated with a consistent ocean tide model and a terrestrial reference frame built up by over 300 optical, laser and Doppler tracking stations. Comprehensive quality tests with external data and models, and test arc computations over a wide range of satellites have demonstrated the state-of-the-art capabilities of both solutions in long-wavelength geoid representation and in precise orbit computation. Received 1 February 1996; Accepted 17 July 1996     

Primordial heavy noble gases in the pristine Paris carbonaceous chondrite

The Paris carbonaceous chondrite represents the most pristine carbonaceous chondrite, providing a unique opportunity to investigate the composition of early solar system materials prior to the onset of significant aqueous alteration. A dual origin (namely from the inner and outer solar system) has been demonstrated for water in the Paris meteorite parent body (Piani et al. 2018 ). Here, we aim to evaluate the contribution of outer solar system (cometary‐like) water ice to the inner solar system water ice using Xe isotopes. We report Ar, Kr, and high‐precision Xe isotopic measurements within bulk CM 2.9 and CM 2.7 fragments, as well as Ne, Ar, Kr, and Xe isotope compositions of the insoluble organic matter (IOM). Noble gas signatures are similar to chondritic phase Q with no evidence for a cometary‐like Xe component. Small excesses in the heavy Xe isotopes relative to phase Q within bulk samples are attributed to contributions from presolar materials. CM 2.7 fragments have lower Ar/Xe relative to more pristine CM 2.9 fragments, with no systematic difference in Xe contents. We conclude that Kr and Xe were little affected by aqueous alteration, in agreement with (1) minor degrees of alteration and (2) no significant differences in the chemical signature of organic matter in CM 2.7 and CM 2.9 areas (Vinogradoff et al. 2017 ). Xenon contents in the IOM are larger than previously published data of Xe in chondritic IOM, in line with the Xe component in Paris being pristine and preserved from Xe loss during aqueous alteration/thermal metamorphism.     

Magnetic Activity Associated With Radio Noise Storms

As it crossed the solar disk in May and June 1998, AR 8227 was tracked by TRACE, Yohkoh, SOHO, and many ground-based observatories. We have studied how the evolution of the magnetic field resulted in changes in activity in the corona. In particular, we examine how the evolving field may have led to the acceleration of electrons which emit noise storms observed by the Nançay Radio Heliograph between 30 May and 1 June 1998, in the absence of any flare. The magnetic changes were related to moving magnetic features (MMFs) in the vicinity of the leading spot and are related to the decay of this spot. Within the limits of the instrumental capabilities, the location in time and space of the radio emissions followed the changes observed in the photospheric magnetograms. We have extrapolated the photospheric magnetic field with a linear force-free approximation and find that the active region magnetic field was very close to being potential. These computations show a complex magnetic topology associated to the MMFs. The observed photospheric evolution is expected to drive magnetic reconnection in such complex magnetic topology. We therefore propose that the MMFs are at the origin of the observed metric noise-storms.     

Geochemical changes at the Bagni di Triponzo thermal spring during the Umbria-Marche 1997–1998 seismic sequence

After the earthquakes of September 26, 1997, that hit the Umbria-Marcheboundary (Apennine, Central Italy), with a maximum 6.0 M_w, aprogram of geochemical surveying together with a collection ofhydrogeological changes episodes was extended throughout theepicentre-area, taking the yearly period of the seismic sequence as a whole.After a first areal screening, the Bagni di Triponzo thermal spring wasselected for a discrete temporal monitoring (weekly and monthly basis),being the unique thermal spring throughout the epicentre area. This sitedeserves peculiar interest in deepening the knowledge about deep fluidscirculation changing during seismicity.Laboratory and on-field analyses included major, minor and trace elementsas well as dissolved gases (He, Ar, CH₄, CO₂, H₂S,²²²Rn, NH₄, As, Li, Fe, B, etc...) and selected isotopic ratios(C, H, O, He, Sr, Cl), meaningful from tectonic point of view.The chemistry and isotopic chemistry of the spring were fully outlined anddiscussed, pointing out the main process involving the thermal aquifer: thewater-rock interaction inside the Evaporite Triassic Basement (ETB),possibly involving also the Paleozoic Crystalline Basement. On theother hand, sudden and apparent geochemical and hydrogeologicalvariations during the seismic sequence ruled out an evolution in thewater-rock interaction processes. They occurred both at depth, i.e.,induced by fluid remobilization within the crust explained by the Coseismic Strain Model and by the Fault Valve Activity Model, and in the shallow part of the reservoir (i.e., meteoric watercontamination). A statistical multivariable analysis (Factor Analysis) wasaccomplished to better constrain the correlation between the paroxysmalphases of the seismic sequence and the observed trends and spike-likeanomalies. The groundwater variations was inferred to occur mainly insidethe ETB, from depth (1–2 km) up to surface, particularly in associationof the Sellano earthquake (14/10/1997) and of the seismic re-activationof the sequence at the end of March 1998 (Gualdo Tadino-Rigali andVerchiano areas). The lack of deeper input from below the ETB (slightsignature of PCB), as the lack of He mantle signature, during the seismicperiod as a whole, accounted for seismogenic fault segments rooted onlyin the crust. The results also provide useful information about theearthquake-related response mechanisms occurring at this site, thatrepresent the basic task for planning and managing the impendinghydro-geochemical network aimed at defining the relationships betweenseismic cycle, fluids and reliable earthquake forerunners.     

Unintended consequences: The spillover effects of common property regulations

The closure of the Hawaiian longline swordfish fishery over the period 2001–2004, which was motivated by the protection of endangered sea turtles, created the elements of a natural experiment that allows identification of the market transfer of catch (and sea turtle bycatch) to other regions. This paper exploits the fact that the vessels in the Hawaiian longline fishery sell their catch in the US fresh swordfish market to analyze the pattern of changes in US fresh and frozen swordfish consumption both before and after the closure regulation was imposed. The mechanisms by which any unintended consequences on endangered sea turtles in other fishery locations in the world are shown to take place through the US swordfish market. At the estimated annual market transfer, a bootstrap analysis of the probability distribution of bycatch rates indicates that the regulation led to an additional 2882 sea turtle interactions at the sample means.     

Adsorption of xenon ions onto defects in organic surfaces: Implications for the origin and the nature of organics in primitive meteorites

Noble gases trapped in primitive meteorites are quantitatively hosted by a poorly defined organic phase, labeled phase Q. Xenon is enriched in heavy isotopes by +1.30 ± 0.06% per atomic mass unit (amu, 1σ) in phase Q relative to solar. To understand the origin of this fractionation, we have performed adsorption experiments of xenon atoms and ions, ionized in a radiofrequency plasma. Within the reaction vessel, anthracite was heated and the resulting smoke deposited onto the walls of the vessel, resulting in carbon-rich films. Xenon was trapped in the carbon films either as ions in the ionization zone of the vessel, or as neutral atoms outside this zone. Xenon trapped as ionic Xe is tightly bound and is enriched by +1.36 ± 0.05%/amu (1σ) in heavy isotopes, reproducing the isotopic fractionation of xenon trapped in phase Q relative to solar. Neutral xenon is more loosely trapped, is in much lower concentration, and is not isotopically fractionated. Ionized conditions allow the constant xenon isotopic composition observed in meteorite during stepwise heating release to be reproduced. Furthermore, the trapping efficiency of Xe⁺ estimated from these experiments is consistent with the high xenon concentration measured in phase Q of primitives meteorites.Xenon was not trapped in the film by implantation because the energies of the incident Xe atoms and ions were far too low (<1 eV). From the difference of behavior between ionic and neutral forms, we propose that xenon ions were trapped via chemical bonding at the surface of the newly created C-rich film. The observed mass-dependent fractionation of xenon is unlikely to have occurred in the gas phase. It is more probably related to variations in chemical bonding strengths of Xe isotopes as chemical bonds involving heavy Xe isotopes are more stable than those involving light ones. For young stars, including the young Sun, photons emitted in the far UV energy range able to ionize noble gases (<100 nm) were orders of magnitude more abundant than for the Present-day Sun, allowing efficient ionization of gaseous species. A way to achieve Q-noble gas fractionation and trapping was UV irradiation by nearby young stars from O/B association of the surface of growing organic grains in the outer part of the solar system or by the young Sun at the edge of the disk.