Compositional constraints on the genesis of diogenites

Abstract– We have done bulk rock compositional analyses (INAA, ICP‐MS) and petrologic study of a suite of diogenite meteorites. Most contain orthopyroxenes with mg#s of 70.6–79.0. Meteorite Hills (MET) 00425 is magnesian (mg# of 83.9). Lewis Cliff (LEW) 88011 contains orthopyroxene grains of varying mg# (76.3–68.6). Queen Alexandra Range (QUE) 93009 (orthopyroxene mg# 70.6) contains coarse‐grained noritic clasts (plagioclase An_84.7–88.3), and is rich in incompatible trace elements. It has Eu/Eu* < 1, indicating that cumulate norites do not dominate its trace element inventory. Queen Alexandra Range 93009 may be transitional between diogenites and magnesian cumulate eucrites. Lewis Cliff 88679, a dimict breccia of harzburgite and orthopyroxenite, has anomalously low concentrations of highly incompatible elements (e.g., Nb, La, Ta, U) compared to other diogenites, but is similar to them in less highly incompatible elements (e.g., Y, Zr, Yb, Hf). It is unlikely that this characteristic reflects a low proportion of a trapped melt component. The highly incompatible elements were likely mobilized after impact mixing of the two parent lithologies. Graves Nunataks 98108 shows an extreme range in Eu/Eu* attributable to the heterogeneous distribution of plagioclase; one sample has the lowest Eu/Eu* among diogenites. We find no compelling evidence to support the hypothesis that diogenite parent magmas were contaminated by partial melts of the eucritic crust. We posit that subsolidus equilibration between orthopyroxene and minor/trace phases (including phosphates) resulted in preferential redistribution of Eu²⁺ relative to Eu³⁺ and other rare earth elements, and results in anomalously low Eu/Eu* in samples leached in acids that dissolve phosphates.     

Ordinary (mesostasis) and not‐so‐ordinary (symplectites) late‐stage assemblages in howardites

Abstract– Two categories of symplectites have been observed in howardites: three‐phase, composed of vermicular intergrowths of ferroan augite, fayalitic olivine, and silica, and two‐phase, composed of vermicular intergrowths of orthopyroxene and troilite. Three‐phase symplectites have been previously shown to represent the breakdown products of metastable pyroxene. In howardites, they appear to be genetically related to gabbroic eucrites. In some cases and under yet‐to‐be specified conditions, ferroan clinopyroxene in gabbroic eucrites may undergo only localized decomposition resulting in oriented exsolution‐like features. Breakdown phases in those cases are fayalitic olivine, silica, and—depending on the MgO content of the system—orthopyroxene. As opposed to three‐phase symplectites, two‐phase symplectites are most likely of diogenitic origin. They probably formed via impact‐induced localized melting of diogenitic orthopyroxene in the presence of troilite (grain boundary melting). Three‐phase symplectites in howardites occasionally contain accessory amounts of ilmenite, troilite, and/or kamacite and are exclusively associated with medium‐grained FeO‐rich pyroxene, silica, and plagioclase. All minerals involved are late‐stage crystallites or mesostasis phases. In general, highly evolved eucritic lithologies constitute only a minor fraction of howardites. However, considering that three‐phase symplectites are generated in a low‐pressure, i.e., near‐surface, environment, FeO‐ and CaO‐rich eucritic rocks may be exposed locally on Vesta’s surface. This, in turn, is highly relevant to the ongoing DAWN mission.     

Ocean/atmosphere interaction and Malthusian catastrophes on the northern fringe of the Asian summer monsoon region in China, 1368–1911

How and to what extent are human societies affected by climate change? There has been a growing body of research using big historical data and statistical analyses to provide scientific answers to this inter-disciplinary research question. However, quantitative analysis measuring the historical demographic impact of ocean/atmosphere interaction is still scanty. Here we use 544 years (1368–1911) of historical records to trace the demographic impact brought about by ocean/atmosphere interaction in Shaanxi, located on the northern fringe of the Asian summer monsoon region in China. Our results show that: (1) North Atlantic Oscillation (NAO) and El Niño Southern Oscillation (ENSO) caused Malthusian catastrophes mainly through drought at the inter-annual scale; (2) drought reinforced the synchrony of various Malthusian catastrophes at the inter-annual to multi-decadal scale; and (3) the unusual cycles of NAO drove drought and various Malthusian catastrophes in the cold 1550–1730 period at the multi-decadal scale. This study represents a pioneering attempt to quantitatively assess the demographic impact caused by the ocean/atmosphere in historical China. Our findings may help to conceptualise the climate–human nexus in those ecologically marginal regions that are impacted by ocean/atmosphere interaction, and to explain the synchrony of social crisis in Eurasia in the 17th century.     

Historic range of variability in geomorphic processes as a context for restoration: Rocky Mountain National Park,Colorado, USA

Evaluation of historic range of variability (HRV) is an effective tool for determining baseline conditions and providing context to researchers and land managers seeking to understand and enhance ecological function. Incorporating HRV into restoration planning acknowledges the dynamic quality of landscapes by allowing variability and disturbance at reasonable levels and permitting riverine landscapes to adapt to the physical processes of their watersheds. HRV analysis therefore represents a practical (though under‐utilized) method for quantifying process‐based restoration goals. We investigated HRV of aggradational processes in the subalpine Lulu City wetland in Rocky Mountain National Park to understand the impacts of two centuries of altered land use and to guide restoration planning following a human‐caused debris flow in 2003 that deposited up to 1 m of sand and gravel in the wetland. Historic aerial photograph interpretation, ground penetrating radar surveys, and trenching, coring, and radiocarbon dating of valley‐bottom sediments were used to map sediment deposits, quantify aggradation rates, and identify processes (in‐channel and overbank fluvial deposition, direct hillslope input, beaver pond filling, peat accumulation) creating alluvial fill within the wetland. Results indicate (i) the Lulu City wetland has been aggrading for several millennia, (ii) the aggradation rate of the past one to two centuries is approximately six times higher than long‐term pre‐settlement averages, (iii) during geomorphically active periods, short‐term aggradation rates during the pre‐settlement period were probably much higher than the long‐term average rate, and (iv) the processes of aggradation during the last two centuries are the same as historic processes of aggradation. Understanding the HRV of aggradation rates and processes can constrain management and restoration scenarios by quantifying the range of disturbance from which a landscape can recover without active restoration. Copyright © 2011 John Wiley & Sons, Ltd.     

A new formula describing the scaffold structure of spiral galaxies

We describe a new formula capable of quantitatively characterizing the Hubble sequence of spiral galaxies including grand design and barred spirals. Special shapes such as ring galaxies with inward and outward arms are also described by the analytic continuation of the same formula. The formula is   r (φ) = A /log [ B tan   (φ/2 N )]  . This function intrinsically generates a bar in a continuous, fixed relationship relative to an arm of arbitrary winding sweep. A is simply a scale parameter while B , together with N , determines the spiral pitch. Roughly, greater N results in tighter winding. Greater B results in greater arm sweep and smaller bar/bulge, while smaller B fits larger bar/bulge with a sharper bar/arm junction. Thus B controls the 'bar/bulge-to-arm' size, while N controls the tightness much like the Hubble scheme. The formula can be recast in a form dependent only on a unique point of turnover angle of pitch – essentially a one-parameter fit, aside from a scalefactor. The recast formula is remarkable and unique in that a single parameter can define a spiral shape with either constant or variable pitch capable of tightly fitting Hubble types from grand design spirals to late-type large barred galaxies. We compare the correlation of our pitch parameter to Hubble type with that of the traditional logarithmic spiral for 21 well-shaped galaxies. The pitch parameter of our formula produces a very tight correlation with ideal Hubble type suggesting it is a good discriminator compared to logarithmic pitch, which shows poor correlation here similar to previous works. Representative examples of fitted galaxies are shown.     

RAT J1953+1859: a dwarf nova discovered through high amplitude QPOs in quiescence

We report the discovery of an accreting binary, RAT J1953+1859, made during the RApid Temporal Survey (RATS) on the Isaac Newton Telescope. It showed high amplitude (0.3 mag) quasi-periodic oscillations on a time-scale of ∼20 min. Further observations made using the Nordic Optical Telescope showed it to be ∼4 mag brighter than in the discovery images. These photometric observations, together with radial velocity data taken using the William Herschel Telescope, point to an orbital period of ∼90 min. These data suggest that RAT J1953+1859 is a dwarf novae of the SU UMa type. What makes RAT J1953+1859 unusual is that it is the first such system to be discovered as a result of high amplitude QPOs during quiescence. This suggests that high-cadence wide-field surveys could be another means to discover cataclysmic variables as a result of their short period variability.     

Sharing the burden of financing adaptation to climate change

Climate change may cause most harm to countries that have historically contributed the least to greenhouse gas emissions and land-use change. This paper identifies consequentialist and non-consequentialist ethical principles to guide a fair international burden-sharing scheme of climate change adaptation costs. We use these ethical principles to derive political principles – historical responsibility and capacity to pay – that can be applied in assigning a share of the financial burden to individual countries. We then propose a hybrid ‘common but differentiated responsibilities and respective capabilities’ approach as a promising starting point for international negotiations on the design of burden-sharing schemes. A numerical assessment of seven scenarios shows that the countries of Annex I of the United Nations Framework Convention on Climate Change would bear the bulk of the costs of adaptation, but contributions differ substantially subject to the choice of a capacity to pay indicator. The contributions are less sensitive to choices related to responsibility calculations, apart from those associated with land-use-related emissions. Assuming costs of climate adaptation of USD 100 billion per year, the total financial contribution by the Annex I countries would be in the range of USD 65–70 billion per year. Expressed as a per capita basis, this gives a range of USD 43–82 per capita per year.     

Diagenetic crystallization and oxidation of siderite in red bed (Buntsandstein) sediments from the Central Iberian Chain,Spain

Compactional deformation facilitated replacement of dolomite and calcite by siderite and its subsequent oxidation in carbonate cemented red beds of the Triassic Buntsandstein in the Iberian Chain. Locally, the sedimentary clasts were cemented by carbonate that was derived from dissolution of locally exposed dolomite in the basement. Microstructures indicate that during sedimentation of the rocks, oxidizing conditions prevailed in the sediments and the basement was reddened by impregnation of hematite. Reducing conditions prevailed during deformation of the sediments. Ferric iron was reduced to Fe²⁺, that reacted with deformed dolomite and calcite cement to produce fine grained siderite. At a later stage, siderite crystallites were (partly) oxidized to form a secondary phase of brown ferric oxide (goethite). Locally, goethite transformed to fine grained hematite that caused secondary reddening of the sediments. The reactions are associated with a combined volume loss of the solid phases of c. 50% per reaction mol; this was accommodated by the formation of pores. Oxidation of siderite was associated with release of CO₂; localized dissolution took place of feldspar and concurrently growth of kaolinite occurred by acidifying condition during release of CO₂. The relation of redox reactions and deformation is comparable to those in red bed conglomerates in the region. Reductive dissolution occurred at sites of stress concentration, particularly at contact points of pebbles. Late stage precipitation of ferric oxides and pyrolusite took place at oxidizing conditions in association with uplift.     

Modelling phosphorus inputs from agricultural sources and urban areas in river basins

An area-differentiated model approach (MEPhos) for the quantification of mean annual P-inputs from point and diffuse sources is presented. The following pathways are considered: artificial drainage, wash-off, groundwater outflow, soil erosion, rainwater sewers, combined sewer overflows, municipal waste water treatment plants and industrial effluents. Two retention functions for rivers and reservoirs are included in order to model P-sinks within a river basin. This allows a complete record of P-loads in heterogeneous meso- and macroscale river basins and enables validation of modeling results with water quality data on a load basis. The model is applied to the River Ruhr basin (4,485 km²) in Germany, which includes contrasting natural conditions, land use patterns as well as population and industry densities. Based on validated modelling results sub-areas of high P-loads are localized and management options for the reduction of P-inputs to surface waters are proposed taking into account the site conditions of the sub-areas relevant for high P-inputs into surface waters.     

Analysis of the Spatial Coherence of Short-Period Acoustic-Gravity Waves in the Atmosphere

Summary The coherence of atmospheric acoustic-gravity waves has been measured in the period range 10–100 s at the Large Aperture Microbarograph Array in south-eastern Montana. The acoustic-gravity waves observed were signals generated by presumed nuclear explosions. The decrease of coherence with increasing distance between pairs of microbarographs is less rapid in the direction of wave propagation than transverse to it. Variation of direction of arrival over a small range of azimuth (±5°) explains the spatial behaviour of coherence in the direction normal to the wave propagation; variation of phase velocity of ±10 ms^-1 explains the behaviour along the direction of wave propagation. Both effects may be due to inhomogeneities in the atmosphere; the velocity variation may be due to the presence in the signal of several normal modes of acoustic- gravity waves, each travelling at a slightly different phase velocity in the range 300–330 ms^-1.