Siderophile and chalcophile element abundances in shergottites: Implications for Martian core formation

Elemental abundances for volatile siderophile and chalcophile elements for Mars inform us about processes of accretion and core formation. Such data are few for Martian meteorites, and are often lacking in the growing number of desert finds. In this study, we employed laser ablation inductively coupled plasma–mass spectrometry (LA‐ICP‐MS) to analyze polished slabs of 15 Martian meteorites for the abundances of about 70 elements. This technique has high sensitivity, excellent precision, and is generally accurate as determined by comparisons of elements for which literature abundances are known. However, in some meteorites, the analyzed surface is not representative of the bulk composition due to the over‐ or underrepresentation of a key host mineral, e.g., phosphate for rare earth elements (REE). For other meteorites, the range of variation in bulk rastered analyses of REE is within the range of variation reported among bulk REE analyses in the literature. An unexpected benefit has been the determination of the abundances of Ir and Os with a precision and accuracy comparable to the isotope dilution technique. Overall, the speed and small sample consumption afforded by this technique makes it an important tool widely applicable to small or rare meteorites for which a polished sample was prepared. The new volatile siderophile and chalcophile element abundances have been employed to determine Ge and Sb abundances, and revise Zn, As, and Bi abundances for the Martian mantle. The new estimates of Martian mantle composition support core formation at intermediate pressures (14 ± 3 GPa) in a magma ocean on Mars.     

Defining and detecting undesirable disturbance in the context of marine eutrophication

An understanding of undesirable disturbance to the balance of organisms is needed to diagnose marine eutrophication as defined by EU Directives and OSPAR. This review summarizes the findings of the UK Defra-funded Undesirable Disturbance Study Team, which concluded that 'an undesirable disturbance is a perturbation of a marine ecosystem that appreciably degrades the health or threatens the sustainable human use of that ecosystem'. A methodology is proposed for detecting disturbance of temperate salt-water communities dominated by phytoplanktonic or phytobenthic primary producers. It relies on monitoring indicators of ecosystem structure and vigour, which are components of health. Undesirable disturbance can be diagnosed by accumulating evidence of ecohydrodynamic type-specific changes in: (i) bulk indicators; (ii) frequency statistics; (iii) flux measurements; (iv) structural indicators; and (v) indicator species. These are exemplified by (i) chlorophyll, transparency, dissolved oxygen, and opportunistic seaweed cover; (ii) HABs frequency; (iii) primary production; (iv) benthic and planktonic 'trophic indices'; (v) seagrasses and Nephrops norvegicus. Ecological Quality Objectives are proposed for some of these. Linking the diagnosis to eutrophication requires correlation of changes with nutrient enrichment. The methodology, which requires the development of a plankton community index and emphasizes the importance of primary production as an indicator of vigour, can be harmonized with the EU Water Framework Directive and OSPAR's Strategy to Combat Eutrophication.     

Glacial-isostatic Adjustment and the Viscosity Structure Underlying the Vatnajökull Ice Cap,Iceland

We examine the dependence of glacial-isostatic adjustment (GIA) due to changes in the Vatnajökull Ice Cap, Iceland, on the underlying viscosity structure. Iceland offers a unique case study for GIA research, with a thinner elastic lithosphere underlain by a low-viscosity zone or asthenosphere, as opposed to regions such as Fennoscandia or North America described by a thicker lithosphere, while not necessarily featuring an asthenosphere.A laterally homogeneous spherical earth model is used consisting of an elastic lithosphere, a viscoelastic asthenosphere, a viscoelastic upper and lower mantle and a fluid core. We examine the response of the earth model to three ice models with circular plans and cross-section profiles based on the assumption of perfectly plastic material, but with different load histories. These are: (1) A history where the ice cap grows from a AD 900 minimum to a maximum at 1890, followed by a uniform decrease until 1991, continuing to the present day at an average rate based on recent mass-balance measurements, (2) a history that is the same as the first, except for constant ice volumes prior to 1890, and (3) a history that is again the same as the first model, except that the post-1991 changes correspond to the measured mass-balance values. We first compare the response to each ice model using typical earth-model parameters for Iceland presented in the literature. We then undertake a parameter-space search, where we assess the importance of lithosphere thickness, asthenosphere viscosity and basal asthenosphere depth, to predicted vertical-displacement rates, and compare them to rates determined from GPS measurements obtained from campaigns conducted between 1991 and 1999.The earth-viscosity structure that provides the optimum predictions with respect to the GPS-derived vertical-displacement rates consists of an elastic lithosphere with a thickness of between 20 and 30 km, an asthenosphere viscosity between 1 and 2 × 10¹⁸ Pa s, and a basal asthenosphere depth between 250 km and possibly greater than 400 km. We find that the very low asthenosphere viscosity values of ca. 10¹⁷ Pa s sometimes suggested in the literature are not necessary to account for the rapid vertical-displacement rates observed, which are the result of the contemporary decrease in the mass of the ice cap not considered previously.     

Cumulative damage in strength-dominated collisions of rocky asteroids: Rubble piles and brick piles

Laboratory impact experiments were performed to investigate the conditions that produce large-scale damage in rock targets. Aluminum cylinders (6.3 mm diameter) impacted basalt cylinders (69 mm diameter) at speeds ranging from 0.7 to 2.0 km/s. Diagnostics included measurements of the largest fragment mass, velocities of the largest remnant and large fragments ejected from the periphery of the target, and X-ray computed tomography imaging to inspect some of the impacted targets for internal damage. Significant damage to the target occurred when the kinetic energy per unit target mass exceeded roughly of the energy required for catastrophic shattering (where the target is reduced to one-half its original mass). Scaling laws based on a rate-dependent strength were developed that provide a basis for extrapolating the results to larger strength-dominated collisions. The threshold specific energy for widespread damage was found to scale with event size in the same manner as that for catastrophic shattering. Therefore, the factor of four difference between the two thresholds observed in the lab also applies to larger collisions. The scaling laws showed that for a sequence of collisions that are similar in that they produce the same ratio of largest fragment mass to original target mass, the fragment velocities decrease with increasing event size. As a result, rocky asteroids a couple hundred meters in diameter should retain their large ejecta fragments in a jumbled rubble-pile state. For somewhat larger bodies, the ejection velocities are sufficiently low that large fragments are essentially retained in place, possibly forming ordered “brick-pile” structures.     

The Virtual Solar Observatory—A Resource for International Heliophysics Research

The Virtual Solar Observatory (VSO) has been developed to allow researchers, educators, and the general public to access data and images from the major sources of on-line solar data. The VSO substantially reduces the effort required to locate disparate data sets, and removes the need for the user to locate the data and learn multiple interfaces. The VSO provides a single interface to about 60 geographically distributed data sets including space- and ground-based sources. These data sets incorporate several physical variables including magnetic field, intensity, Doppler velocity, etc., and all wavelengths from X-ray to radio. All layers of the sun, from the interior to the corona, are included. In this paper we describe the system and present the interface that the user will encounter. We also discuss future enhancements planned for the system.     

The Meteoritical Bulletin,No. 96, September 2009

Abstract— The Meteoritical Bulletin No. 96 contains a total of 1590 newly approved meteorite names with their relevant data. These include 12 from specific locations within Africa, 76 from northwest Africa, 9 from the Americas, 13 from Asia, 1 from Australia, 2 from Europe, 950 from Antarctica recovered by the Chinese Antarctic Research Expedition (CHINARE), and 527 from the American Antarctic program (ANSMET). Among these meteorites are 4 falls, Almahata Sitta (Sudan), Sulagiri (India), Ash Creek (United States), and Maribo (Denmark). Almahata Sitta is an anomalous ureilite and is debris from asteroid 2008 TC3 and Maribo is a CM2 chondrite. Other highlights include a lunar meteorite, a CM1 chondrite, and an anomalous IVA iron.     

Travelling and hunting in a changing Arctic: assessing Inuit vulnerability to sea ice change in Igloolik, Nunavut

The observations of community members and instrumental records indicate changes in sea ice around the Inuit community of Igloolik, in the Canadian territory of Nunavut. This paper characterizes local vulnerability to these changes, identifying who is vulnerable, to what stresses, and why, focusing on local and regional use of sea ice for the harvesting of renewable resources and travel. This analysis is coupled with instrumental and sea ice data to evaluate changing temperature/wind/sea ice trends over time, to complement local observations. We demonstrate the relationships between changing sea ice conditions/dynamics and harvesting activities (i.e. dangers and accessibility), with specific emphasis on ringed seal and walrus seasonal hunting, to illustrate current sea ice exposures that hunters are facing. Community members are adapting to such changes, as they have done for generations. However, current adaptive capacity is both enabled, and constrained, by social, cultural, and economic factors that manifest within the modern northern Hamlet. Enabling factors include the ability of hunters to manage or share the risks associated with sea ice travel, as well as through their flexibility in resource use, as facilitated by sophisticated local knowledge and land/navigational skills. Constraining factors include the erosion of land-based knowledge and skills, altered sharing networks, as well as financial and temporal limitations on travel/harvesting. The differential ability of community members to balance enabling and constraining factors, in relation to current exposures, comprises their level of vulnerability to sea ice change.