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The insoluble organic material (IOM) in primitive chondritic meteorites is very enriched in D (up to δD ≈ 3500‰ in bulk). Based largely on a series of electron paramagnetic resonance (EPR) studies of IOM from three meteorites (Orgueil, Murchison and Tagish Lake), it has been suggested that these enrichments are the result of exchange with H2D+ in the solar nebula and that exchange with radicals in the IOM was particularly facile so that they are enormously enriched in D (δD ≥ 95000‰). To try to test whether radicals are largely responsible for the D enrichments in IOM, we have used EPR to measure the radical concentrations (spins/g) and g-factors of 18 IOM separates from C1-2 chondrites of varying petrologic type and chemical group that have a much wider range of H isotopic compositions (δD ≈ 600–3500‰) than in previous studies. We confirm the previous studies findings that IOM exhibits non-Curie law behavior and that it does not completely saturate even at microwave excitation powers of 200 mW. We also have obtained similar g-factor values. However, our IOM samples typically exhibit a lower and more limited range of spin concentrations, and smaller deviations from Curie law behavior than in previous studies. Nor do we observe correlations between bulk δD and either spins/g or non-Curie law behavior that would be expected if exchange between H2D+ and radicals, as previously proposed, was the cause of the D-enrichments in IOM. Indeed, in general the radical concentrations and the degree of non-Curie law behavior do not seem to correlate with any of the measured IOM properties, with chondrite group or parent body history (e.g., degree of aqueous alteration). The only exceptions are the IOM in four Tagish Lake lithologies whose spin concentrations increase with increasing degree of thermal processing as indicated by decreasing H/C and δD, and increasing aromaticity.

This article explores discursive struggles between ideologies of nature development and nature conservation in the context of the Murchison Falls Conservation Area (MFCA) in Uganda. Based on the concepts of critical discourse moments and discourse coalitions, the article offers a nuanced perspective on nature policy in a specific, though not unique, context. The purpose of studying tensions between different positions in nature policy from a critical discourse perspective is to increase the awareness of the role of language use in the struggles. Moreover, the study aims at enhancing the understanding of different interests and thus reducing the conflict potential regarding the MFCA. This article explores discursive struggles between ideologies of nature development and nature conservation discourses in the context of the Murchison Falls Conservation Area (MFCA) in Uganda. Based on the concepts of critical discourse moments and discourse coalitions, the article offers a nuanced perspective on nature policy in a specific, though not unique, context. The purpose of studying tensions between different positions in nature policy from a critical discourse perspective is to increase the awareness of the role of discourse coalitions in the struggles. Thus, the study aims at enhancing the understanding of different interests by creating awareness about the conflict potential regarding the MFCA.

International audience; The origin of volatile element depletion in terrestrial planets and meteorites relative to a solar composition represented by CI carbonaceous chondrites remains an unsolved problem. The isotope compositions of moderately volatile elements may offer the possibility to distinguish between the various processes that may have caused this depletion (e.g., partial condensation or partial evaporation). We report high precision Sn isotope measurements in carbonaceous chondrites and ordinary chondrites and the results are reported as δ124/116Sn. Four carbonaceous chondrites (Orgueil CI, Murchison CM2, NWA 5240 CV3 and Allende CV3) show a limited range in δ124/116Sn (-0.02‰ to 0.11‰) with an average value of 0.04 ± 0.11‰ (2 s.d.) for a wide range of Sn concentrations (0.63 ppm to 1.57 ppm). The absence of Sn isotope fractionation among carbonaceous chondrites suggests that volatile depletion may have taken place under thermodynamic equilibrium conditions between solid and vapor in the Solar Nebula. Alternatively, the mixing of two components, a volatile-free component containing no or little Sn and a volatile-rich component could explain this trend. This latter hypothesis is consistent with the overall trace element pattern found in carbonaceous chondrites, showing a constant relative abundance when normalized to CI chondrites for the most volatile elements. In contrast with carbonaceous chondrites, ordinary chondrites exhibit a larger range of Sn isotope compositions (δ124/116Sn from -2.02‰ to 0.64‰), but neither the degree of metamorphism (3-6) nor the group (H, L, LL) is correlated with Sn isotopic variations, or with the Sn contents (range 0.20 to 1.44 ppm). Nineteen out of twenty-one ordinary chondrites are enriched in light Sn isotopes compared with carbonaceous chondrites and the bulk silicate Earth. The trace element patterns of volatile elements in ordinary chondrites suggest that equilibrated ordinary chondrites have been disturbed by parent body processes related to metamorphic or shock overprinting but also inherited isotope fractionation found in unequilibrated ordinary chondrites. Last, the isotope composition of the bulk silicate Earth (BSE) indicates that the volatile element depletion observed in the Earth took place in conditions perhaps similar to those of carbonaceous chondrites, as a simple model describing the effect of Earth's core formation on Sn isotopes shows that the Sn isotope composition of the bulk Earth is identical to that of the BSE and of carbonaceous chondrites.

A series of experiments was performed to constrain the chemical and isotopic evolution of insoluble organic material (IOM) during hydrothermal alteration at temperatures ranging from 250 °C to 450 °C at 50 MPa. Experiments involved IOM that was extracted from the Murchison (CM2) meteorite or synthesized by aqueous carbonization of dextrose. Flash (dry) pyrolysis experiments at 400 – 1000 °C were also conducted with Murchison IOM to distinguish between the effects of hydrothermal and thermal degradation. Extended reaction times (up to 3905 h) were employed to establish D/H equilibria between IOM and H2O. The H isotope compositions of the H2O used in the experiments ranged from δD = −447‰ to 3259‰. Results revealed that the extent of the IOM H isotope evolution strongly depends on the δD composition of the coexisting H2O with minimal temperature effects. The empirical relationship that describes the isotope exchange between IOM and H2O is as follows: δDIOM (‰) = 0.643 (±0.007) * δDH2O (‰) – 86 (±8) Based on this empirical relationship, two models are proposed for the H2O-IOM H exchange. The first assumes that all H in IOM is exchangeable and that the redistribution of H-bearing moieties with temperature results in an “apparent” eorganics-H2O = −357‰. The second model considers a higher eorganics-H2O (−131‰), in accordance with theoretical studies, and assumes the presence of two H reservoirs, one that undergoes H isotope exchange with H2O and one that does not. In this case, 74% of the H in IOM is exchangeable with H2O. In our experiments, the hydrothermally altered Murchison IOM lost labile 15N enriched N-H moieties. Experiments that included 15N-labelled NH3(aq) found that there was only minor N exchange with IOM. Furthermore, the experimental data show that the extent of H and N loss is temperature and process dependent. This results in the decoupling of N/C and H/C atomic ratio systematics between hydrothermal alteration and flash (dry) pyrolysis, with much more limited changes in H/C and N/C after flash pyrolysis. In the light of the experiments, two models for the range of bulk and IOM H isotope compositions of the aqueously altered CI, CM, and CR chondrites are explored. The very D-rich IOM compositions, relative to the bulk compositions, cannot be explained by a fully exchangeable IOM with a reasonable value for eorganics-H2O (i.e.

A close relationship between CM and CO chondrites has been suggested by previous petrologic and isotopic studies, leading to the suggestion that they may originate from similar precursor materials or even a common parent body. In this study, we evaluate the genetic relationship between CM and CO chondrites using Ti, Cr, and O isotopes. We first provide additional constraints on the ranges of ε50Ti and ε54Cr values of bulk CM and CO chondrites by reporting the isotopic compositions of CM2 chondrites Murchison, Murray, and Aguas Zarcas and the CO3.8 chondrite Isna. We then report the ε50Ti and ε54Cr values for several ungrouped and anomalous carbonaceous chondrites that have been previously reported to exhibit similarities to the CM and CO chondrite groups, including Elephant Moraine (EET) 83226, EET 83355, Grosvenor Mountains (GRO) 95566, MacAlpine Hills (MAC) 87300, MAC 87301, MAC 88107, and Northwest Africa (NWA) 5958, and the oxygen isotope compositions of a subset of these samples. We additionally report the ε50Ti, ε54Cr, and O isotopic compositions of additional ungrouped chondrites LaPaz Ice Field (LAP) 04757, LAP 04773, Lewis Cliff (LEW) 85332, and Coolidge to assess their potential relationships with known carbonaceous and ordinary chondrite groups. LAP 04757 and LAP 04773 exhibit isotopic compositions indicating they are low-FeO ordinary chondrites. The isotopic compositions of Murchison, Murray, Aguas Zarcas, and Isna extend the compositional ranges defined by the CM and CO chondrites in ε50Ti versus ε54Cr space. The majority of the ungrouped carbonaceous chondrites with documented similarities to the CM and/or CO chondrites plot outside the CM and CO group fields in plots of ε50Ti versus ε54Cr,Δ17O versus ε50Ti, and Δ17O versus ε54Cr. Therefore, based on differences in their Ti, Cr, and O-isotopic compositions, we conclude that the CM, CO, and ungrouped carbonaceous chondrites likely represent samples of multiple distinct parent bodies. We also infer that these parent bodies formed from precursor materials that shared similar isotopic compositions, which may indicate formation in regions of the protoplanetary disk that were in close proximity to each other.

A técnica de espectroscopia Raman tem sido cada vez mais utilizada na caracterização de rochas terrestres e meteoritos em geral. No entanto, a literatura em língua portuguesa com informações sobre como se distinguir os minerais constituintes de rochas, sejam terrestres ou extraterrestres, são escassos e quase inexistentes. Dessa forma, o objetivo deste trabalho é apresentar como é possível determinar a presença de olivinas e identificar qual tipo de mineral do grupo especificamente se encontra na mostra de maneira rápida, sucinta e acessível. Vale salientar que o grupo das olivinas é caracterizado pelos seus membros finais, a faialita (Fe2SiO4) e a forsterita (Mg2SiO4). A identificação dos espectros foi realizada a partir de espectros de minerais puros alocados no banco de dados RRUFF e comparados com espectros obtidos dos meteoritos carbonáceos (Allende e Murchison) e o meteorito marciano NWA 7397. Por fim, este trabalho não possui o propósito de ter um aprofundamento detalhado de análises e as especificidades maiores do Raman, o qual poderá ser adquirido pelos leitores através de materiais complementares e com assistências de técnicos mais especializados no equipamento e na técnica de Raman.

Anurans inhabiting Australia’s semi-arid and arid zones display eruptive breeding patterns. They emerge in large numbers to reproduce after significant rainfall before burrowing deep underground, where they remain concealed for extensive periods until favourable conditions return. This cryptic life history hinders documentation of the natural history and ecology of arid adapted amphibians of Australia. Fundamental information for some species such as geographic distribution thus remains uncertain. Here, we report range extensions for two species of Cyclorana. Cyclorana are a genus of 14 burrowing frog species that occupy arid, semi-arid and monsoonal regions of Australia. We document a 188 km southerly range extension of Cyclorana cryptotis, and an 88 km northerly extension for Cyclorana maini; both within the Davenport Murchison Ranges bioregion of the Northern Territory. Our observation of C. cryptotis is significant as it is the first record of the species in the Davenport Murchison Ranges bioregion.

This paper presents processing and analysis results of ASTER and Landsat 8 scenes to aid in geological mapping of Murchison Greenstone Belt region of Limpopo Province, South Africa. Images of ASTER acquired in 2005 and 2006 and Landsat 8 acquired in 2019 were downloaded and subset covering 5 mapping sheets was extracted. Images of different band ratios and band combinations were experimented using ENVI and SNAP software to identify suitable band/band ratio combinations to produce FCCs that enabled discrimination of lithology, structural features, lineaments, alteration and iron oxides, land/water, surface features, vegetation cover and healthy vegetation etc. Using DEM data, slope and shaded relief were also prepared that enabled the identification of the extent of protruded outcrops, some structural features and lineaments using different FCC displays. These datasets prepared in ENVI file format were later exported to GeoTiff/Imagine file for display in ArcMap by the mapping geologists. FCCs made in various band combinations, ratio combination and also with slope are useful in discriminating geology, structural features and protruded outcrops including dykes that are not so visible in a true colour image of the same resolution. This study could illustrate the usefulness of remote sensing analysis to aid in geological mapping using freely available ASTER and Landsat 8 data.

The water quality in Murchison Bay of Lake Victoria, the Africa’s largest fresh water lake, is on decline due to rapid urban sprawl, decrease in vegetative surface and increase in impervious surface of the drainage area resulting in eutrophication of the lake. The objectives of our study are 1) to analyze the nutrient and metal concentrations in the Murchison Bay; 2) to identify and map the long-term landscape changes in Murchison Bay Watershed (MBW); 3) to analyze the impact of the landscape changes on the water quality of Murchison Bay. Water samples were collected from Miami Beach (MB), Ggaba Beach (GB) and Mulungo Beach (MuB), along the Murchison Bay and analyzed for various metal and nutrient concentrations. Landsat satellite imagery, sampled over three decades (1995-2019) of the MBW were analyzed for the land cover changes. The chemical analysis of the water samples showed that the P concentrations were above the critical limits while the As and Pb concentrations were higher but remained below the critical limits in water. The remote sensing analysis reveal that the impervious surface in the MBW increased by about 21.9% while the vegetative surface decreased by 4.2% during the period of 1995 to 2019. The Chlorophyll a concentration in the Murchison Bay increased over the period of time resulting in deterioration of water quality. Integration of environmental chemical analysis along with geospatial data aids in understanding the impact of land scape changes on the Murchison Bay water quality and to identify the areas vulnerable to change. https://doi.org/10.23953/cloud.ijarsg.474

Acetaldehyde (CH3 CHO) is ubiquitous throughout the interstellar medium and has been observed in cold molecular clouds, star forming regions, and in meteorites such as Murchison. As the simplest methyl-bearing aldehyde, acetaldehyde constitutes a critical precursor to prebiotic molecules such as the sugar deoxyribose and amino acids via the Strecker synthesis. In this study, we reveal the first laboratory detection of 2,3-butanedione (diacetyl, CH3 COCOCH3 ) - a butter and popcorn flavorant - synthesized within acetaldehyde-based interstellar analog ices exposed to ionizing radiation at 5 K. Detailed isotopic substitution experiments combined with tunable vacuum ultraviolet (VUV) photoionization of the subliming molecules demonstrate that 2,3-butanedione is formed predominantly via the barrier-less radical-radical reaction of two acetyl radicals (CH3 ĊO). These processes are of fundamental importance for a detailed understanding of how complex organic molecules (COMs) are synthesized in deep space thus constraining the molecular structures and complexity of molecules forming in extraterrestrial ices containing acetaldehyde through a vigorous galactic cosmic ray driven non-equilibrium chemistry.

Preservation bias may significantly impact the application of detrital zircon geochronology in reconstructing Earth surface processes. Here we compare detrital zircons from the actively eroding Murchison River channel in Western Australia with Ordovician fluvial sediments that have drained similar source rocks along the western margin of the West Australian Craton. In addition to standard analysis of detrital zircon age spectra we apply multivariate statistics to test the relation between 3-D grain shape, U-content and U–Pb ages, with the objective to quantify differences between both sample groups and track preservation along the transport pathway of the Murchison River. Our results show that zircon grains in modern river sands display an upstream trend toward larger surface areas, volume equivalent diameters and grain widths, as well as toward higher U-contents and lower apparent grain densities. 3-D grain shape, size and age spectra of Murchison River zircons evolve consistently downstream, but even at the river outlet remain distinct from the Ordovician samples, as a less mature representation of source. We interpret Ordovician river zircons to represent a significantly depleted subset from which up to 22% of the zircon population may have been lost compared to the actively transported detrital load. This discrepancy between the characteristics of detrital zircons in modern active rivers and ancient fluvial Ordovician sandstones demonstrates a bias that could be relevant for other source-sink detrital transport systems throughout Earth history. Keywords: X-ray tomography, Detrital, Zircon, Grain shape, Preservation, Fluvial

Machiite (IMA 2016-067), Al2Ti3O9, is a new mineral that occurs as a single euhedral crystal, 4.4 μm in size, in contact with an euhedral corundum grain, 12 μm in size, in a matrix of the Murchison CM2 carbonaceous chondrite. The mean chemical composition of holotype machiite by electron probe microanalysis is (wt%) TiO2 59.75, Al2O3 15.97, Sc2O3 10.29, ZrO2 9.18, Y2O3 2.86, FeO 1.09, CaO 0.44, SiO2 0.20, MgO 0.10, total 99.87, giving rise to an empirical formula (based on 9 oxygen atoms pfu) of (Al1.17Sc0.56Y0.10Ti0.084+Fe0.06Ca0.03Mg0.01)(Ti2.714+Zr0.28Si0.01)O9. The general formula is (Al,Sc)2(Ti4+,Zr)3O9. The end-member formula is Al2Ti3O9. Machiite has the C2/c schreyerite-type structure with a = 17.10 Å, b = 5.03 Å, c = 7.06 Å, β = 107°, V = 581 Å3, and Z = 4, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 4.27 g/cm3. The machiite crystal is highly 16O-depleted relative to the coexisting corundum grain (Δ17O = –0.2 ± 2.4‰ and –24.1 ± 2.6‰, respectively; where Δ17O = δ17O – 0.52 × δ18O). Machiite is a new member of the schreyerite (V2Ti3O9) group and a new Sc,Zr-rich ultrarefractory phase formed in the solar nebula, either by gas-solid condensation or as a result of crystallization from a Ca,Al-rich melt having solar-like oxygen isotopic composition (Δ17O~ –25‰) under high-temperature (~1400–1500 °C) and low-pressure (~10-4–10-5 bar) conditions in the CAI-forming region near the protosun. The currently observed disequilibrium oxygen isotopic composition between machiite and corundum may indicate that machiite subsequently experienced oxygen isotopic exchange with a planetary-like 16O-poor gaseous reservoir either in the solar nebula or on the CM chondrite parent body. The name machiite is in honor of Chi Ma, mineralogist at California Institute of Technology, for his contributions to meteorite mineralogy and discovery of many new minerals representing extreme conditions of formation.

We obtained mid-infrared spectra of chondrules, matrix, CAIs and bulk material from primitive type 1–4 chondrites in order to compare them with the dust material in young, forming Solar Systems and around comets. Our aim is to investigate whether there are similarities between the first processed materials in our early Solar System and protoplanetary disks currently forming around other stars. Comparison between the laboratory infrared data and astronomical spectra indicate a general similarity between processed Solar System materials and circumstellar dust. This includes fine-grained matrix material, but also processed component like chondrules and or impact shock processed CM like material. Comets investigated in this study also have spectral features that could allow contents of chondrules or impact shock processed matrix material. Chondrule spectra can be divided into two groups: (1) chondrules dominated by olivine features at ∼11.3 μm and ∼10.0 μm and (2) mesostasis rich chondrules that show main features at ∼10 μm. Bulk ordinary chondrites show similar features to both groups. Fine-grained matrix is divided into three groups: (1) phyllosilicate-rich with a main band at ∼10 μm, (2) olivine-rich with bands at 11.3 μm and ∼10 μm, and (3) pyroxene-rich with several peaks between 9.3 μm and 11.2 μm. Impact shock-processed matrix from Murchison (CM2) shows features from phyllosilicate-rich, amorphous and olivine-rich material. CAIs show melilite/spinel-rich features between 10.2 μm and 12.5 μm. Astronomical spectra are divided into four groups based on their spectral characteristics – amorphous (group 1), pyroxene-rich (group 2), olivine-rich (group 3) and ‘complex’ (group 4). Group 2 is similar to enstatite-rich fine grained material like e.g. Kakangari (K3) matrix. Groups 3 and 4 can be explained by a combination of varying concentrations of olivine and mesostasis-rich chondrules and fine-grained matrix, but also show very good agreement with shock processed material. Comparison of band ratios confirms the similarity with chondritic material e.g. for HD100546, while the inner disk of HD142527 show no sign of chondrule material. For some systems, though, we find that other amorphous materials such as IDP/GEMS have to be taken into account to fully fit their spectra.

We present the status of cosmic-ray detection activities at the Murchison Radio-astronomy Observatory. Using 128 antennas of the Murchison Widefield Array radio telescope in its extended configuration, we detect the radio emission from extensive air showers in the 122--154 MHz range at a rate of slightly less than once per hour, each with an approximate energy of 10$^{17}$ eV. We have developed a bespoke filter inversion to obtain high-time-resolution data from this general-purpose astronomy instrument, and directly capture the radio signal. Our future plans include the implementation of a particle-triggered mode, and expanded operations with the low-frequency component of the Square Kilometre Array, which will have ~100,000 antennas deployed on the same site.

CM2 chondrites experienced widespread aqueous and short term thermal alteration on their parent bodies. Whilst previous Raman spectroscopic investigations have investigated insoluble organic matter (IOM), they have not taken into account the binary nature of IOM. Studies employing mass spectrometry have indicated that IOM also known as macromolecular organic matter (MOM) is in fact composed of two distinct fractions: labile organic matter (LOM) and refractory organic matter (ROM). The ROM component represents the aromatic rich and heteroatom poor component of IOM/MOM, whilst the LOM fraction represents a more heteroatom and aliphatic rich component. Here we report Raman 2D maps and spectroscopic data for Murchison and Mighei, both before and after chemical degradation, which attacks and liberates LOM. The removal of LOM simulates the effects of aqueous alteration, where ester and ether bonds are broken and is thought to release some components to the soluble organic matter (SOM) fraction, also known as the free organic matter fraction (FOM). Raman spectroscopy can be used to reveal the nature of bonding (sp2 and sp3) within carbonaceous materials such as meteoritic organic matter, through evaluation of the D and G band peak centres and FWHM values from the recorded data. The presence of sp3 orbitals indicates that the organic materials contain aliphatic linkages and/or heteroatoms. Statistical analysis of the Raman parameters obtained here indicates that the organic matter originating the Raman response is indistinguishable between the bulk (chemically untreated) and chemically degraded (treated with KOH and HI) samples. Such an observation indicates that the ROM fraction is the major contributor to the Raman response of meteoritic organic matter and thus Raman spectroscopy is unlikely to record any aqueous alteration processes that have affected meteoritic organic matter. Therefore, studies which use Raman to probe the IOM are investigating just one of the components of IOM and not the entire fraction. Studies that aim to investigate the effects of aqueous alteration on meteoritic organic matter should use alternate techniques to Raman spectroscopy. Furthermore, the indistinguishable nature of the Raman response of ROM from Murchison and Mighei suggests these meteorites inherited a ROM component that is chemically similar, reflecting either a common process for the formation of CM2 meteoritic ROM and/or that these meteorites probed the same ROM reservoir.

Nereid, Neptune's third largest satellite, lies in an irregular orbit and is the only outer satellite in the system (apart from Triton) that can be spectroscopically characterized with the current generation of Earth-based telescopes. We report our results on spectral characterization of Nereid using its reflectance spectrum from 0.8-2.4 $\mu m$, providing the first measurements over the range of 0.8-1.4 $\mu m$. We detect spectral absorption features of crystalline water ice in close agreement with previous measurements. We show that model fits of simple intimate mixtures including water ice do not provide simultaneous matches to absorption band depths at 1.5 and 2.0 $\mu m$ when accounting for the spectral continuum. Possible solutions include invoking a more complex continuum, including both crystalline and amorphous water ice, and allowing for sub-micron sized grains. We show that mixtures including magnetite and the CM2 chondrite Murchison provide a flexible framework for interpreting spectral variation of bodies with neutral-sloped spectra like that of Nereid. Magnetite in particular provides a good match to the spectral continuum without requiring the presence of Tholin-like organics. We note that carbonaceous chondrites and their components may be useful analogs for the non-ice components of outer solar system bodies, consistent with recent findings by Fraser et al. (2019). Comparison to spectra of large TNOs and satellites of Uranus show that Nereid's low albedo, deep water bands, and neutral color is distinct from many other icy objects, but such comparisons are limited by incomplete understanding of spectral variability among $\sim$100km-sized icy bodies., Comment: 11 pages, 2 tables, 7 figures, accepted in PSJ

The naming of the Permian by Roderick Murchison in 1841 is well known. This is partly because he ‘completed’ the stratigraphic column at the system level, but also because of the exotic aspects of his extended fieldwork in remote parts of Russia and his reputed character. Here, we explore several debated and controversial aspects of this act, benefiting from access to documents and reports from Russian sources. Murchison or Sedgwick could have provided a name for the unnamed lower New Red Sandstone in 1835 based on British successions or those in Germany, so perhaps the imperial aim of naming time from British geology was not the urgent task some have assumed. Murchison has been painted as arrogant and imperialistic, which was doubtless true, but at the time many saw him as a great leader, even an attractive individual. Others suggest he succeeded because he stood on the shoulders of local geologists; however, his abilities of brilliant and rapid geological synthesis are undoubted. Two unexpected consequences of his work are that this arch-conservative is revered in Russia as a hero of geological endeavours and, for all his bombast, his ‘Permian’ was not widely accepted until 100 years after its naming. Supplementary material: Original text and English-language translations of five of the key papers (Murchison 1841d; Helmersen 1872; Shafranovsky 1964; Chuvashov 2010; Malakhova 2012) are available at: https://doi.org/10.6084/m9.figshare.c.5412079

International audience; utrophication of Lake Victoria led to changes in its phytoplankton communities. However, different levels of eutrophication exist in the open lake and the bays, and between embayments. This study utilized spatial and temporal sampling of Napoleon Gulf and Murchison Bay, exhibiting different trophic conditions. Over one year, we investigated phytoplankton biomass, richness, diversity and dissimilarity, and related the dynamics of the dominant species to the limnological and climatic conditions. The results confirmed that Napoleon Gulf and Murchison Bay showed large differences in eutrophication status, with lower nutrient concentrations in Napoleon Gulf than in Murchison Bay, where a strong gradient was observed from inshore to offshore areas. These nutrient dynamics resulted in a 4 to 10 fold higher chlorophyll-a in Murchison Bay than in Napoleon Gulf. From the embayments, 135 phytoplankton taxa were recorded with no significant differences in alpha diversity. However, high dissimilarity in community structure was observed in beta diversity, mostly due to a turnover among the dominant toxigenic species. Thus, from a similar species pool, there was a shift in the dominant toxigenic cyanobacteria from Microcystis flos-aquae and M. aeruginosa in Murchison Bay, Dolichospermum circinale and Planktolyngbya circumcreta in Napoleon Gulf to D. circinale in the offshore stations. These cyanobacteria are toxigenic taxa with known health hazards. Using partial least square models, we showed that both climatic variables (e.g. wind, solar radiation) and levels of inorganic dissolved nutrients (e.g. SRP, NO3-, and NH4+) are the main drivers of differences and dominance in cyanobacteria communities in northern Lake Victoria.

Spectroscopic signatures of water and hydroxyl radicals have been observed on the surfaces of asteroids1–3. As the lifetime of the exposed water ice is on the order of 104 to 106 yr in the inner asteroid belt4, there must be mechanisms to replenish the water in the absence of recent ice-exposing processes. However, such regenerative water-ice sources on asteroids are still elusive. Here we perform laboratory experiments by exposing the samples of the Murchison meteorite to energetic electrons and laser irradiation, simulating, respectively, the secondary electrons generated by the solar wind as well as galactic cosmic ray particles and the micrometeorites impacting on an asteroid. We find that a single simulated space-weathering component is insufficient and both are needed to regenerate water at low temperatures at the desired timescales. We propose that two main mechanisms can be the source of surface water on asteroids: low-temperature oxidation of organics and mineral dehydration. Water ice on the surfaces of asteroids can survive only up to 106 years. Laboratory experiments show that space weathering by energetic particles and micrometeorites can regenerate enough water by oxidizing organics and dehydrating minerals to explain the spectral features of hydration observed on asteroid surfaces.