The Meteoritical Bulletin,No. 102

Meteoritical Bulletin 102 contains 3141 meteorites including 12 falls (Boumdeid (2003), Boumdeid (2011), Braunschweig, Chelyabinsk, Dongyang, Draveil, Heyetang, Indian Butte, Katol, Ladkee, Ouadangou, Xining), with 2611 ordinary chondrites, 264 HED achondrites, 124 carbonaceous chondrites, 30 ureilites, 20 Martian meteorites, 16 primitive achondrites, 16 Rumuruti chondrites, 15 mesosiderites, 12 iron meteorites, 10 lunar meteorites, 9 enstatite chondrites, 4 enstatite achondrites, 4 Pallasites, 4 ungrouped achondrites, and 2 angrites, and with 1708 from Antarctica, 956 from Africa, 294 from South America, 126 from Asia, 47 from North America, 6 from Europe (including Russia), and 4 from Oceania. Information about approved meteorites can be obtained from the Meteoritical Bulletin Database (MBD) available on line at http://www.lpi.usra.edu/meteor/ .     

Estimating phytolith influx in lake sediments

So far, no phytolith extraction protocols have been tested for accuracy and repeatability. Here we aim to display a phytolith extraction method combining the strengths of two widely used protocols, supplemented with silica microspheres as exogenous markers for quantifying phytolith concentrations. Phytolith concentrations were estimated for samples from two sedimentary sequences in which numerical age–depth models make it possible to calculate phytolith influxes (phytolith numbers per cm²per yr). Analysis of replicates confirmed the statistical robustness, the repeatability and the very few biases of our extraction technique for small phytoliths, since the relationship between grass silica short cells and microspheres was kept stable. Furthermore, we demonstrated that silica microspheres are robust exogenous markers for estimating phytolith concentrations. The minimum number of items (i.e., phytoliths plus silica microspheres) that must be counted to estimate phytolith concentrations and thus influxes depends on the ratio of phytoliths to microspheres (R) and is minimized when R = 1. Nevertheless, we recommend using ratios R ≤ 1 in order to avoid having the counting process become excessively time-consuming, because microspheres are easier to identify and count than phytoliths.     

An assessment of the mixed layer salinity budget in the tropical Pacific Ocean. Observations and modelling (1990–2009)

This paper investigates mechanisms controlling the mixed-layer salinity (MLS) in the tropical Pacific during 1990–2009. We use monthly 1°?×?1° gridded observations of salinity, horizontal current and fresh water flux, and a validated ocean general circulation model with no direct MLS relaxation in both its full resolution (0.25° and 5 days) and re-sampled as the observation time/space grid resolution. The present study shows that the mean spatial distribution of MLS results from a subtle balance between surface forcing (E???P, evaporation minus precipitation), horizontal advection (at low and high frequencies) and subsurface forcing (entrainment and mixing), all terms being of analogous importance. Large-scale seasonal MLS variability is found mainly in the Intertropical and South Pacific Convergence Zones due to changes in their meridional location (and related heavy P), in the North Equatorial Counter Currents, and partly in the subsurface forcing. Maximum interannual variability is found in the western Pacific warm pool and in both convergence zones, in relation to El Niño Southern Oscillation (ENSO) events. In the equatorial band, this later variability is due chiefly to the horizontal advection of low salinity waters from the western to the central-eastern basin during El Niño (and vice versa during La Niña), with contrasted evolution for the Eastern and Central Pacific ENSO types. Our findings reveal that all terms of the MLS equation, including high-frequency (<1 month) salinity advection, have to be considered to close the salinity budget, ruling out the use of MLS (or sea surface salinity) only to directly infer the mean, seasonal and/or interannual fresh water fluxes.     

The age of SNC meteorites and the antiquity of the Martian surface

We report new Sm-Nd, Lu-Hf, and Pb-Pb mineral and whole-rock isotope data for the basaltic shergottite Zagami, as well as Pb-Pb whole-rock isotope data for the basaltic shergottite Los Angeles, the lherzolitic shergottite Dar-al-Gani 476 (DaG 476), and the clinopyroxenite Nakhla. In agreement with previous findings, our new Sm-Nd and Lu-Hf mineral ages on the Martian meteorite Zagami are young (155 and 185 Ma, respectively). The ²⁰⁷Pb/²⁰⁶Pb-²⁰⁴Pb/²⁰⁶Pb compositions of the insoluble fractions of shergottites (Zagami, Los Angeles, and literature data for Shergotty and EETA79001) form an excellent alignment indicative of a 4.0 Ga crystallization age. The range of Pb isotope compositions observed in the leachates of these samples attests to negligible contamination of the shergottites by terrestrial Pb and argues against mixing relationships. The age of 4.048 ± 0.017 Ga (MSWD = 1.5) provided by the Pb isotope compositions of the Zagami whole-rock and residues is therefore taken to date the crystallization of this rock, which, so far, was believed to be only ∼ 180 Ma old. Based on this result, we argue that the lithosphere of Mars is extremely old and that most mineral ages were reset recently by acidic aqueous solutions percolating through the Martian surface. This interpretation is consistent with photographic interpretations of erosional features on Mars. It also relieves the constraint imposed by the presence of anomalies of ¹⁴²Nd and ¹⁸²W (both products of extinct radioactive nuclides) that the Martian mantle should have preserved primordial isotopic heterogeneities, thus allowing for the planet interior to be actively convecting.     

Coloring the Field: Gender, “Race,” and the Politics of Fieldwork

My experiences combining research and activism within the Japanese-Canadian community reflect a growing concern among feminist and anti-racist scholars with the politics of work among people marginalized by racism and sexism. This concern arises within a context where “other voices” are being heard, but the legitimacy of one individual or group to represent another is being challenged. Such challenges require that essentialism and naturalism be addressed politically and theoretically, a difficult irony given the need to utilize essentialist categories to address the oppressive conditions under which they emerged. To do so, a critical theory of political construction is required.     

Oil Spills and Community Resilience: Uneven Impacts and Protection in Historical Perspective

Louisiana's coastal residents have endured centuries of hurricanes and decades of oil spills. Locally based, inherent resilient practices have enabled them to persist in place. This paper documents the evolution of actions taken by Louisiana's coastal residents that constitute effective resilient activities in the aftermath of disruptive events. It compares the efforts that arose from coastal communities that were rooted in local environmental knowledge with generic external programs designed to enable hazard mitigation, emergency response, and recovery form damaging hurricanes and oil spills. Additionally, it will identify points of opportunity to fortify resilience by integrating inherent and formal resilience.     

The Meteoritical Bulletin,no. 108

Meteoritical Bulletin 108 contains 2141 meteorites including 12 falls (Aguas Zarcas, Benenitra, Jalangi, Komaki, Ksar El Goraane, Mhabes el Hamra, Natun Balijan, Oued Sfayat, Shidian, Taqtaq‐e Rasoul, Tocache, Viñales), with 1640 ordinary chondrites, 149 carbonaceous chondrites, 134 HED achondrites, 45 lunar meteorites, 38 ureilites, 27 iron meteorites, 23 Martian meteorites, 22 primitive achondrites, 19 Rumuruti chondrites, 15 mesosiderites, 10 enstatite chondrites, 7 ungrouped achondrites, 4 pallasites, 4 ungrouped chondrites, and 4 angrites. Nine hundred and nine meteorites are from Africa, 747 from Antarctica, 279 from South America, 148 from Asia, 29 from North America, 18 from Oceania, 6 from Europe (including 2 from Russia), and 5 from unknown locations.     

Raman spectroscopy of shocked enstatite-rich meteorites

We present Raman patterns of enstatite in different classes of enstatite-rich chondrites and achondrites of various shock levels as previously reported from petrographic observations and X-ray diffraction analyses. Thin sections or mineral separates of four enstatite chondrites (LaPaz Icefield [LAP] 02225, MacAlpine Hills [MAC] 02837, Pecora Escarpment [PCA] 91020, and Itqiy), three aubrites (Larkman Nunatak [LAR] 04316, Khor Temiki, and Allan Hills [ALH] 84008), and a ureilite (Sayh al Uhaymir [SaU] 559) were examined by laser Raman spectroscopy. We find that the frequencies of fundamental Raman peaks of enstatites from the chondrites and aubrites deviate by ≤2 cm⁻¹ from the values for unshocked enstatite. This small difference implies a negligible effect of shock metamorphism on peak positions. Significant differences (<6 cm⁻¹) for peak positions are found for the pyroxenes of SaU 559 and may be attributed to minor substitution of Fe and Ca for Mg. Linear regressions of peak widths of enstatite chondrites against their established shock stages show a strong positive correlation for each mode (r² > 0.94). From this linear relationship, the 343 and 1014 cm⁻¹ peaks of the aubrites coincide with S4 determined from petrography. For Itqiy, we find S4–5, while the shock levels of SaU 559 exceed the petrologic scheme (S1–6), suggesting that the ureilite might have sustained multiple shock events or have been deformed in a high-pressure environment. Alternatively, for Itqiy (peak 343 cm⁻¹) and SaU 559 (all peaks) enstatites, minor substitutions of Fe and Ca for Mg may have further broadened their peak widths.     

The Meteoritical Bulletin,No. 103

Meteoritical Bulletin 103 contains 2582 meteorites including 10 falls (Ardón, Demsa, Jinju, Kri?evci, Kuresoi, Novato, Tinajdad, Tirhert, Vicência, Wolcott), with 2174 ordinary chondrites, 130 HED achondrites, 113 carbonaceous chondrites, 41 ureilites, 27 lunar meteorites, 24 enstatite chondrites, 21 iron meteorites, 15 primitive achondrites, 11 mesosiderites, 10 Martian meteorites, 6 Rumuruti chondrites, 5 ungrouped achondrites, 2 enstatite achondrites, 1 relict meteorite, 1 pallasite, and 1 angrite, and with 1511 from Antarctica, 588 from Africa, 361 from Asia, 86 from South America, 28 from North America, and 6 from Europe. Note: 1 meteorite from Russia was counted as European. The complete contents of this bulletin (244 pages) are available on line. Information about approved meteorites can be obtained from the Meteoritical Bulletin Database (MBD) available on line at http://www.lpi.usra.edu/meteor/ .