The remarkable Re–Os chronometer in molybdenite: how and why it works

The Re–Os (rhenium–osmium) chronometer applied to molybdenite (MoS₂) is now demonstrated to be remarkably robust, surviving intense deformation and high‐grade thermal metamorphism. Successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite, unique to each sample, such that recognized spatial decoupling of ¹⁸⁷Re parent and ¹⁸⁷Os daughter within individual molybdenite crystals is overcome. Highly precise, accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry (ID‐NTIMS). Spatial decoupling of parent–daughter precludes use of the laser ablation ICP‐MS microanalytical technique for Re–Os dating of molybdenite. The use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons. The Rb–Sr, K–Ar and ⁴⁰Ar/³⁹Ar chronometers are susceptible to chemical and thermal disturbance, particularly in terranes that have experienced subsequent episodes of hydrothermal/magmatic activity, and therefore should not be used as a basis for establishing accuracy in Re–Os dating of molybdenite, as has been done in the past. Re–Os ages for molybdenite are almost always in agreement with observed geological relationships and, when available, with zircon and titanite U–Pb ages. For terranes experiencing multiple episodes of metamorphism and deformation, molybdenite is not complicated by overgrowths as is common for some minerals used in U–Pb dating (e.g. zircon, monazite, xenotime), nor are Re and Os mobilized beyond the margins of individual crystals during solid‐state recrystallization. Moreover, inheritance of older molybdenite cores, incorporation of common Os, and radiogenic Os loss are exceedingly rare, whereas inheritance, common Pb and Pb loss are common complications in U–Pb dating techniques. Therefore, molybdenite ages may serve as point‐in‐time markers for age comparisons.     

Deuterium chemistry and airglow in the jovian thermosphere

We present a detailed study of the distribution of key deuterated species (viz., atomic D and HD) and the associated deuterium Lyman-α airglow in the jovian thermosphere. The reactions that appear to govern the abundances of these deuterated species are used in conjunction with C₂-chemistry in a 1-D photochemical-diffusion model. While the D abundance is mainly sensitive to H densities and the vibrational temperature profile, the D vertical distribution also depends on other parameters such as eddy mixing and the uncertain values of some of the reaction rate constants. We consider different scenarios by varying several parameters controlling the D distribution in the thermosphere. A radiative transfer model with coupling of the H and D Lyman-α lines is employed to obtain line profiles and total intensities at disk center for these scenarios. This allows a comparison of the impact of various parameters on the jovian D Lyman-α emission. A consequence of these chemical processes in the jovian thermosphere is the formation of CH₂D, CH₃D, and C₂H₅D, and other deuterated species. We also discuss the source of these deuterated hydrocarbons and their abundance. We find that HD vibrational chemistry impacts D in the thermosphere, CH₃D and C₂H₅D are vibrationally enhanced in the thermosphere, and variations in abundance of CH₃D and C₂H₅D in the thermosphere may reflect dynamical activity (i.e., Kh) in the jovian upper atmosphere. An observing program dedicated to providing such measurements of these testable phenomena would provide further insight into the synergistic coupling between chemistry, energetics and airglow in the jovian upper atmosphere.     

EUV observations of the chromospheric network

Extreme ultraviolet observations of a quiet region of the Sun on August 18, 1969, with the Harvard spectroheliometer on OSO 6 indicate that the chromospheric network can be observed in lines of the chromosphere and transition region (T = 8.4 × 10⁵ K) with almost identical structure. At coronal heights, the network changes but some residual structure can still be discerned in Mgx and perhaps Sixii (T = 2.3 × 10⁶ K), although there is little or no evidence remaining in Fexvi (T = = 3.5 × 10⁶ K).     

Geoconservation and geoscience in England: a mutually beneficial relationship

Geoconservation in England, as in Great Britain more widely, is very well established. Sites of national or international scientific importance, as determined by a systematic site assessment and selection exercise, can be protected by designation as Sites of Special Scientific Interest. Sites of local importance e.g. Local Geological Sites may also be taken into account when planning decisions are made that could have an impact on them. As a whole, the network of conserved geosites represents the key elements of our current understanding of the geology and geomorphology of England. Site selection and safeguard and management of this network are dependent on geoscience information, and in return continued geoscience fieldwork is dependent on having conserved sites available for study. Here, we review the relationship between geoconservation and geoscience, and how it has developed since the first geoconservation legislation nearly 70 years ago. We discuss the achievements, challenges and where and how this relationship needs to strengthen further to meet future needs of both geoscience and nature conservation. In a changing world, there will continue to be a need for innovative geoscience supported by effective geoconservation. Those interested in conserving England’s geological heritage will need to engage the wider geoscience community more than ever to deliver a shared vision for the natural environment.     

Knowledge gaps in our perceptual model of Great Britain's hydrology

There is a no lack of significant open questions in the field of hydrology. How will hydrological connectivity between freshwater bodies be altered by future human alterations to the hydrological cycle? Where does water go when it rains? Or what is the future space–time variability of flood and drought events? However, the answers to these questions will vary with location due to the specific and often poorly understood local boundary conditions and system properties that control the functional behaviour of a catchment or any other hydrologic control volume. We suggest that an open, shared and evolving perceptual model of a region's hydrology is critical to tailor our science questions, as it would be for any other study domain from the plot to the continental scale. In this opinion piece, we begin to discuss the elements of and point out some knowledge gaps in the perceptual model of the terrestrial water cycle of Great Britain. We discuss six major knowledge gaps and propose four key ways to reduce them. While the specific knowledge gaps in our perceptual model do not necessarily transfer to other places, we believe that the development of such perceptual models should be at the core of the debate for all hydrologic communities, and we encourage others to have a similar debate for their hydrologic domain.     

Spatial variability of precipitation regimes over Turkey

Abstract

This study aims to predict the daily precipitation from meteorological data from Turkey using the wavelet—neural network method, which combines two methods: discrete wavelet transform (DWT) and artificial neural networks (ANN). The wavelet—ANN model provides a good fit with the observed data, in particular for zero precipitation in the summer months, and for the peaks in the testing period. The results indicate that wavelet—ANN model estimations are significantly superior to those obtained by either a conventional ANN model or a multi linear regression model. In particular, the improvement provided by the new approach in estimating the peak values had a noticeably high positive effect on the performance evaluation criteria. Inclusion of the summed sub-series in the ANN input layer brings a new perspective to the discussions related to the physics involved in the ANN structure.     

Mainstreaming adaptation to climate change in Least Developed Countries (LDCs)

Abstract

The Least Developed Countries (LDCs) are a group of 49 of the world's poorest countries. They have contributed least to the emission of greenhouse gases (GHGs) but they are most vulnerable to the effects of climate change. This is due to their location in some of the most vulnerable regions of the world and their low capacities to adapt to these changes. Adaptation to climate change has become an important policy priority in the international negotiations on climate change in recent years. However, it has yet to become a major policy issue within developing countries, especially the LDCs. This article focuses on two LDCs, namely Bangladesh and Mali, where progress has been made regarding identifying potential adaptation options. For example, Bangladesh already has effective disaster response systems, and strategies to deal with reduced freshwater availability, and Mali has a well-developed programme for providing agro-hydro-meteorological assistance to communities in times of drought. However, much remains to be done in terms of mainstreaming adaptation to climate change within the national policymaking processes of these countries. Policymakers need targeting and, to facilitate this, scientific research must be translated into appropriate language and timescales.     

Tourist behaviour,local values,and interpretation at Ulu<Emphasis Type="Underline">r</Emphasis>u: ‘The sacred deed at Australia’s mighty heart’

This paper explores issues relating to multiple and changing values and uses of desert landscapes in the context of tourism at Uluru-Kata Tjuta National Park (UKTNP), co-managed by Aboriginal people and the Australian Government agency Parks Australia. More than 400,000 people visit the park each year, drawn mostly by the massive red monolith. To the local Aboriginal people, Anangu, this rock is Uluru, a complex of places with great spiritual importance. Since co-management, UKTNP has become a symbol of the reconciliation process between Aboriginal and settler Australians. Climbing the rock is a popular activity. Aboriginal co-managers ask visitors not to climb Uluru but rather to learn about their culture and home through their eyes. Park management aims to discourage climbing. This research investigated how visitors respond to the Anangu request not to climb, and why some climb while others do not. We argue that spatial and experiential aspects of the park support climbing at the expense of participation in other activities more attuned to Aboriginal understandings of landscape at Uluru.     

Effects of habitat complexity on cannibalism rates in European green crabs (Carcinus maenas Linnaeus, 1758)

The habitat in which predator–prey interactions take place may have a profound influence on the outcome of those interactions. Cannibalism is an intriguing form of predation whereby foraging by predators may contribute to the regulation of their own populations.This is particularly interesting in the case of invasive species, like the widely distributed European green crab (Carcinus maenas). This study explores how habitat complexity influences cannibalism rates in green crab populations of Prince Edward Island, Atlantic Canada. Both laboratory and field experiments were conducted to measure feeding rates by individual adult green crabs on a standard number of smaller conspecifics. In the laboratory, experimental treatments mimicked unstructured to increasingly structured habitats: water, sandy bottom, oyster shells, mussel shells, oyster shells with sandy bottom and mussel shells with sandy bottom. In those trials, adult green crabs consumed several times more juveniles on unstructured habitats than on the most structured ones, with a gradual decrease in predation rates across increasingly complex habitats. Field inclusion experiments used the same approach and were conducted in sandy bottoms, sandy bottoms with a layer of oyster shells and sandy bottoms with a layer of mussel shells. These trials showed similar patterns of decreasing feeding rates across increasingly complex habitats, but differences among treatments were not significant. These results support the idea that complex habitats have the potential to mediate predator–prey interactions, including adult–juvenile cannibalism in green crabs.