Constraints on the petrogenesis of Martian meteorites from the Rb-Sr and Sm-Nd isotopic systematics of the lherzolitic shergottites ALH77005 and LEW88516

Detailed Rb-Sr and Sm-Nd isotopic analyses have been completed on the lherzolitic shergottites ALH77005 and LEW88516. ALH77005 yields a Rb-Sr age of 185 ± 11 Ma and a Sm-Nd age of 173 ± 6 Ma, whereas the Rb-Sr and Sm-Nd ages of LEW88516 are 183 ± 10 and 166 ± 16 Ma, respectively. The initial Sr isotopic composition of ALH77005 is 0.71026 ± 4, and the initial ε_Nd value is +11.1 ± 0.2. These values are distinct from those of LEW88516, which has an initial Sr isotopic composition of 0.71052 ± 4 and an initial ε_Nd value of +8.2 ± 0.6. Several of the mineral and whole rock leachates lie off the Rb-Sr and Sm-Nd isochrons, indicating that the isotopic systematics of the meteorites have been disturbed. The Sm-Nd isotopic compositions of the leachates appear to be mixtures of primary igneous phosphates and an alteration component with a low ¹⁴³Nd/¹⁴⁴Nd ratio that was probably added to the meteorites on Mars. Tie lines between leachate-residue pairs from LEW88516 mineral fractions and whole rocks have nearly identical slopes that correspond to Rb-Sr ages of 90 ± 1 Ma. This age may record a major shock event that fractionated Rb/Sr from lattice sites located on mineral grain boundaries. On the other hand, the leachates could contain secondary alteration products, and the parallel slopes of the tie lines could be coincidental.Nearly identical mineral modes, compositions, and ages suggest that these meteorites are very closely related. Nevertheless, their initial Sr and Nd isotopic compositions differ outside analytical uncertainty, requiring derivation from unique sources. Assimilation-fractional-crystallization models indicate that these two lherzolitic meteorites can only be related to a common parental magma, if the assimilant has a Sr/Nd ratio near 1 and a radiogenic Sr isotopic composition. Further constraints placed on the evolved component by the geochemical and isotopic systematics of the shergottite meteorite suite suggest that it (a) formed at ∼4.5 Ga, (b) has a high La/Yb ratio, (c) is an oxidant, and (d) is basaltic in composition or is strongly enriched in incompatible elements. The composition and isotopic systematics of the evolved component are unlike any evolved lunar or terrestrial igneous rocks. Its unusual geochemical and isotopic characteristics could reflect hydrous alteration of an evolved Martian crustal component or hydrous metasomatism within the Martian mantle.     

杂食性鱼类对浅水水体底栖—浮游生境耦合作用的影响:微综述

浅水水体存在着强烈的底栖—浮游生境耦合作用,耦合的结果决定着水生态系统关键特征.在缺少大型水生植物的浅水系统中,底栖藻类和浮游藻类对光照和营养盐的竞争是底栖—浮游生境耦合最为重要的生态过程之一,但该过程受到杂食性鱼类的影响.本文以浅水水体的底栖—浮游生境耦合作用为切入点,综述了杂食性鱼类对浅水水体底栖—浮游生境耦合作用...     

Evolving geographies of innovation: existing paradigms,critiques and possible alternatives

ABSTRACT

Theory development on the geographies of innovation has been very successful in incorporating the changing patterns of knowledge dynamics due to globalization, lifting the gaze beyond processes of localized learning and increasingly acknowledging the multilevel, multiscalar governance of innovation. Arguably less attention has been directed to the changing qualities and impacts of innovation as a result of globalization, notably in view of social polarization and climate change. The aim of the article is to provide suggestions for how research on the geography of innovation can be improved by engaging with a more capacious understanding of innovation and territorial development. The authors explore how socio-ecological innovation can be introduced in contemporary discussions and practices of place-based smart specialization policy. They conclude by suggesting that future research should address and interrogate (1) the rise of the foundational economy as an expression of place-based innovation, which entails new forms of co-governance, and (2) the challenge of experimentalism in the public sector, a sector that looms large in lagging regions and the places that were deemed not to matter until they took their revenge on the mainstream political system.     

Development of a long-term wellbore sealing concept based on numerical simulations and in situ-testing in the Altmark natural gas field

This paper presents an innovative well abandonment concept developed for the long-term containment of CO₂ in depleted Rotliegend gas reservoirs. The new concept aims at amending the conventional standard well abandonment procedure, taking advantage of the natural creeping ability of the thick, homogeneous Zechstein rock salt formation located around 3,000?m in depth (Altmark area) and consists of four main sealing units: (1) a standard sealing element with cement from the reservoir to the impermeable caprock, (2) a salt plug created in the formerly reamed section of casing within the plastic Zechstein (Upper Permian) rock salt formation, (3) two bridge plugs at the bottom and top of the salt plug and (4) a standard sealing element with cement from the top bridge plug until the ground surface. This site-specific study mainly lays emphasis on the development and field testing of the naturally created salt plug, as a key component of the long-term wellbore sealing concept. Comprehensive numerical simulations conducted prior to and during the field test in 2010 and 2011 successfully predicted the evolution of convergence using downhole measurement data. Preliminary results comprise (1) proven convergence of the rock salt formation, (2) a successful coring and (3) restored integrity of Zechstein salt formation, as proven by the formation integrity test. Based on these results, the new long-term sealing concept has been successfully tested at the Altmark natural gas field and successful application of the concept on other sites with similar geological conditions is foreseen to be likely.     

A Similitude Theory for Bucket Foundations Under Monotonic Horizontal Load in Dense Sand

This paper aims at finding force-displacement relationships to be employed in the design of bucket foundations for offshore wind turbine. This is accomplished by combining small-scale tests and element tests within a theoretical framework. A similitude theory, regarding the lateral displacement of bucket foundations under horizontal load, is put forward. A constitutive law of the soil and a load-displacement relationship for the bucket foundation are theoretically obtained. Triaxial tests of sand, and small-scale tests of bucket foundation, are respectively employed to corroborate the theory. Attention is given to the different behaviour shown during the compressive and dilative phases of the soil. Some analogy between triaxial tests and tests of bucket foundation are pointed out. A theoretically derived power law is found capable to represent the dimensionless horizontal load-displacement curves of experimental results. In accordance with the theory, the exponent of the power law slightly varies between tests with considerably different features. The non-dimensional moment-rotation relationship is represented by a power law as well. The approach is considered valid for fatigue design. The study may be an interesting source for further researches on long-term cyclic horizontal loading.     

Calibration of an M L scale for South Africa using tectonic earthquake data recorded by the South African National Seismograph Network: 2006 to 2009

A relation to determine local magnitude (M _L) based on the original Richter definition is empirically derived from synthetic Wood–Anderson seismograms recorded by the South African National Seismograph Network. In total, 263 earthquakes in the distance range 10 to 1,000 km, representing 1,681 trace amplitudes measured in nanometers from synthesized Wood–Anderson records on the vertical channel were considered to derive an attenuation relation appropriate for South Africa through multiple regression analysis. Additionally, station corrections were determined for 26 stations during the regression analysis resulting in values ranging between ?0.31 and 0.50. The most appropriate M _L scale for South Africa from this study satisfies the equation: $$ {M_{{{\bf L}}}} = {\text{lo}}{{\text{g}}_{{10}}}(A) + 1.149\;{\text{lo}}{{\text{g}}_{{10}}}(R) + 0.00063R + 2.04 - S $$ The anelastic attenuation term derived from this study indicates that ground motion attenuation is significantly different from Southern California but comparable with stable continental regions.     

Neoendemic ground beetles and private tree haplotypes: two independent proxies attest a moderate last glacial maximum summer temperature depression of 3–4 °C for the southern Tibetan Plateau

Previous findings regarding the Last Glacial Maximum LGM summer temperature depression (maxΔT in July) on the Tibetan Plateau varied over a large range (between 0 and 9 °C). Geologic proxies usually provided higher values than palynological data. Because of this wide temperature range, it was hitherto impossible to reconstruct the glacial environment of the Tibetan Plateau. Here, we present for the first time data indicating that local neoendemics of modern species groups are promising proxies for assessing the LGM temperature depression in Tibet. We used biogeographical and phylogenetic data from small, wingless edaphous ground beetles of the genus Trechus, and from private juniper tree haplotypes. The derived values of the maxΔT in July ranged between 3 and 4 °C. Our data support previous findings that were based on palynological data. At the same time, our data are spatially more specific as they are not bound to specific archives. Our study shows that the use of modern endemics enables a detailed mapping of local LGM conditions in High Asia. A prerequisite for this is an extensive biogeographical and phylogenetic exploration of the area and the inclusion of additional endemic taxa and evolutionary lines.     

Identification of linear relationships from noisy data using errors-in-variables models??relevance for reconstruction of past climate from tree-ring and other proxy information

Reliable paleoclimate reconstructions are needed to assess if the recent climatic changes are unusual compared to pre-industrial climate variability. Here, we focus on one important problem in climate reconstructions: Transfer functions relating proxies (predictors) and target climatic quantities (predictands) can be seriously biased when predictand and predictor noise is not adequately accounted for, resulting in biased amplitudes of reconstructed climatic time series. We argue for errors-in-variables models (EVM) for unbiased identification of linear structural relationships between noisy proxies and target climatic quantities by (1) introducing underlying statistical concepts and (2) demonstrating the potential biases of using the EVM approach, the most commonly used direct ordinary least squares (OLS) regression, inverse OLS regression, or the reduced major axis method (??variance matching??) with a simulation example of artificial noise-disturbed sinusoidal time series. We then develop an alternative strategy for paleoclimate reconstruction from tree-ring and other proxy data, explicitly accounting for the identified problem.     

Advances towards improved low-frequency tree-ring reconstructions, using an updated Pinus sylvestris L. MXD network from the Scandinavian Mountains

The dendrochronological use of the parameter maximum density (MXD) in Pinus Sylvestris L., at high latitudes, has provided valuable insights into past summer temperature variations. Few long MXD chronologies, from climatically coherent regions, exist today, with the exception being in northern Europe. Five, 500-year-long, Fennoscandian, MXD chronologies were compared with regard to their common variability and climate sensitivity. They were used to test Signal-free standardization techniques, to improve inferences of low-frequency temperature variations. Climate analysis showed that, in accordance with previous studies on MXD in Fennoscandia, the summer temperature signal is robust (R ²?>?50 %) and reliable over this climatically coherent region. A combination of Individual standardization and regional curve standardization is recommended to refine long-term variability from these MXD chronologies and relieve problems arising from low replication and standardization end-effects.