De-A-steroids in immature marine shales

Three series of de-A-diasterenes have been observed in a variety of immature marine shales. Two of them have been identified by comparison with authentic standards and the structures of the third assigned by extrapolation. The greater complexity in the number of series compared with diasterenes indicates that the ring A degradation occurred to differing extents. The rate of C-20 diagenetic isomerisation in the de-A-diasterenes proceeds at a similar rate to that in diasterenes. Two series of B-ring monoaromatic de-A-steroid hydrocarbons have also been found. Comparison with the B-ring monoaromatic anthrasteroids indicates that the de-A-compounds are 14α(H) and 14β(H) isomers. Diagenetic isomerisation of the 14α(H) isomers to the more stable 14β(H) isomers occurs at a rate similar to that in the B-ring monoaromatic anthrasteroid series.     

Climate change and journalistic norms: A case-study of US mass-media coverage

The Intergovernmental Panel on Climate Change – comprised of top climate scientists from around the globe – has reached consensus that human activities have contributed significantly to global climate change. However, over time, the United States has refused to join concerted international efforts – such as the Kyoto Protocol – to curb human activities contributing to climate change. US newspaper and television media constitute key influences among a set of complex dynamics shaping information dissemination in this politicized environment. Mass-media coverage of climate change is not simply a random amalgam of newspaper articles and television segments; rather, it is a social relationship between scientists, policy actors and the public that is mediated by such news packages. This paper demonstrates that consistent adherence to interacting journalistic norms has contributed to impediments in the coverage of anthropogenic climate change science. Through analysis of US newspaper and television coverage of human contributions to climate change from 1988 through 2004, this paper finds that adherence to first-order journalistic norms – personalization, dramatization, and novelty – significantly influence the employment of second-order norms – authority-order and balance – and that this has led to informationally deficient mass-media coverage of this crucial issue. By critically scrutinizing US print and television media as a ‘public arena,’ we improve understanding of how journalistic activities have shaped interactions at the interface with climate science, policy and the public.     

Investigation of the Ablation Behaviour of Andradite-Grossular Garnets and Rutile with Implications for U-Pb Geochronology

U-Pb dating of andradite-grossular garnet (grandite) and rutile by LA-ICP-MS can be used to constrain various metamorphic, metasomatic and igneous geological processes. In this study, we examine and compare the impact of different analytical conditions (fluence, pulse width, laser beam size and ablation frequency) on the ablation crater morphology, ablation rates, down-hole fractionation and U-Pb ages of grandite and rutile samples of different compositions. The shapes of grandite ablation craters suggest the mineral ablates by classical evaporation with significant melting that cannot be eliminated even at fluences just above the ablation threshold. Grandite garnets with higher andradite proportions have faster ablation rates. The overall low U contents of grandite require using large laser beam sizes to obtain acceptable precision of U-Pb ages. At such conditions and crater depths < 10 μm, fluences of 2.1 and 3.5 J cm^-2, laser pulse width of 5 ns and 20 ns, and ablation frequencies between 3.5 and 6.5 Hz, obtain similar and reproducible ages when the proportion of grossular is < 35%. Rutile ablation crater morphology shows evidence of melt splashing and thermal stress cracking. They have significant crater bottom features, which increase in relief with lower fluences and a higher number of laser shots, indicating the features are probably energy-related and making higher fluences, such as 5 J cm^-2, necessary for uniform ablation when using 193 nm excimer lasers. The slow ablation rate at low fluences and then steep increase at around 2.0 J cm^-2 suggests a transition in the ablation mechanism from exfoliation to classical vaporisation. Crater bottom features and other ablation behaviour vary between samples, which could be related to their difference in colour. Although the down-hole fractionation patterns of the samples are similar at 5 J cm^-2, the U-Pb ages of some samples vary significantly with different analytical conditions and/or measurement sessions, particularly when using laser beam sizes of 30 μm, suggesting differences in mass bias and more variable ablation behaviour. A laser beam size of at least 60 μm is recommended for reproducible U-Pb dating of rutile.     

Water Table Depth Estimates over the Contiguous United States Using a Random Forest Model

Water table depth (WTD) has a substantial impact on the connection between groundwater dynamics and land surface processes. Due to the scarcity of WTD observations, physically-based groundwater models are growing in their ability to map WTD at large scales; however, they are still challenged to represent simulated WTD compared to well observations. In this study, we develop a purely data-driven approach to estimating WTD at continental scale. We apply a random forest (RF) model to estimate WTD over most of the contiguous United States (CONUS) based on available WTD observations. The estimated WTD are in good agreement with well observations, with a Pearson correlation coefficient (r) of 0.96 (0.81 during testing), a Nash-Sutcliffe efficiency (NSE) of 0.93 (0.65 during testing), and a root mean square error (RMSE) of 6.87 m (15.31 m during testing). The location of each grid cell is rated as the most important feature in estimating WTD over most of the CONUS, which might be a surrogate for spatial information. In addition, the uncertainty of the RF model is quantified using quantile regression forests. High uncertainties are generally associated with locations having a shallow WTD. Our study demonstrates that the RF model can produce reasonable WTD estimates over most of the CONUS, providing an alternative to physics-based modeling for modeling large-scale freshwater resources. Since the CONUS covers many different hydrologic regimes, the RF model trained for the CONUS may be transferrable to other regions with a similar hydrologic regime and limited observations.     

Continental Scale Hydrostratigraphy: Comparing Geologically Informed Data Products to Analytical Solutions

This study synthesizes two different methods for estimating hydraulic conductivity (K) at large scales. We derive analytical approaches that estimate K and apply them to the contiguous United States. We then compare these analytical approaches to three-dimensional, national gridded K data products and three transmissivity (T) data products developed from publicly available sources. We evaluate these data products using multiple approaches: comparing their statistics qualitatively and quantitatively and with hydrologic model simulations. Some of these datasets were used as inputs for an integrated hydrologic model of the Upper Colorado River Basin and the comparison of the results with observations was used to further evaluate the K data products. Simulated average daily streamflow was compared to daily flow data from 10 USGS stream gages in the domain, and annually averaged simulated groundwater depths are compared to observations from nearly 2000 monitoring wells. We find streamflow predictions from analytically informed simulations to be similar in relative bias and Spearman's rho to the geologically informed simulations. R-squared values for groundwater depth predictions are close between the best performing analytically and geologically informed simulations at 0.68 and 0.70 respectively, with RMSE values under 10 m. We also show that the analytical approach derived by this study produces estimates of K that are similar in spatial distribution, standard deviation, mean value, and modeling performance to geologically-informed estimates. The results of this work are used to inform a follow-on study that tests additional data-driven approaches in multiple basins within the contiguous United States.     

Patterns and dynamics of river–aquifer exchange with variably-saturated flow using a fully-coupled model

The parallel physically-based surface–subsurface model PARFLOW was used to investigate the spatial patterns and temporal dynamics of river–aquifer exchange in a heterogeneous alluvial river–aquifer system with deep water table. Aquifer heterogeneity at two scales was incorporated into the model. The architecture of the alluvial hydrofacies was represented based on conditioned geostatistical indicator simulations. Subscale variability of hydraulic conductivities (K) within hydrofacies bodies was created with a parallel Gaussian simulation. The effects of subscale heterogeneity were investigated in a Monte Carlo framework. Dynamics and patterns of river–aquifer exchange were simulated for a 30-day flow event. Simulation results show the rapid formation of saturated connections between the river channel and the deep water table at preferential flow zones that are characterized by high conductivity hydrofacies. Where the river intersects low conductivity hydrofacies shallow perched saturated zones immediately below the river form, but seepage to the deep water table remains unsaturated and seepage rates are low. Preferential flow zones, although only taking up around 50% of the river channel, account for more than 98% of total seepage. Groundwater recharge is most efficiently realized through these zones. Subscale variability of K_sat slightly increased seepage volumes, but did not change the general seepage patterns (preferential flow zones versus perched zones). Overall it is concluded that typical alluvial heterogeneity (hydrofacies architecture) is an important control of river–aquifer exchange in rivers overlying deep water tables. Simulated patterns and dynamics are in line with field observations and results from previous modeling studies using simpler models. Alluvial heterogeneity results in distinct patterns and dynamics of river–aquifer exchange with implications for groundwater recharge and the management of riparian zones (e.g. river channel-floodplain connectivity via saturated zones).     

Integrated Hydrologic Modeling to Untangle the Impacts of Water Management During Drought

Over the past century, groundwater levels in California's San Joaquin Valley have dropped by more than 30 m in some areas mostly due to excessive groundwater extraction used to irrigate agricultural lands and sustain a growing population. Between 2012 and 2015, California experienced the worst drought in its recorded history, depleting surface water supplies and further exacerbating groundwater depletion in the region. Due to a lack of groundwater regulation, exact quantities of extracted groundwater in California are unknown and hard to quantify. Recent adoption of the Sustainable Groundwater Management Act has intensified efforts to identify sustainable groundwater use. However, understanding sustainable use in a highly productive agricultural system with an extremely complex surface water allocation system, variable groundwater use, and spatially extensive and diverse irrigation practices is no easy task. Using an integrated hydrologic model coupled with a land surface model, we evaluated how water management activities, specifically a suite of irrigation and groundwater pumping scenarios, impact surface water–groundwater fluxes and storage components and how those activities and the relationships between them change during drought. Results showed that groundwater pumping volume had the most significant impact on long-term water storage changes. A comparison with total water storage anomaly (TWSA) estimates from NASA's Gravity Recover and Climate Experiment (GRACE) provided some insight regarding which combinations of pumping and irrigation matched the GRACE TWSA estimates, lending credibility to these scenarios. In addition, the majority of long-term water storage changes during the recent drought occurred in groundwater storage in the deeper subsurface.     

Coastal typology: An integrative “neutral” technique for coastal zone characterization and analysis

Typology, the ‘study or systematic classification of types that have characteristics or traits in common’, has become a commonly used term and technique in coastal zone studies over the past two decades. At least part of this is due to adoption by the first Land–Ocean Interactions in the Coastal Zone (LOICZ) project of a typological approach as a way to understand and organize the daunting diversity of natural and human systems comprising the world coastal zone, and to the concurrent development of tools and databases to support systematic applications. This paper reviews some of the history of the term ‘typology’ and the concepts and techniques that it subsumes, and discusses its adoption and adaptation in coastal studies. It also addresses the continued and increasing relevance of typology to the continuation of the LOICZ project and its objectives, and outlines the opportunities and challenges involved in realizing the potentials of the approach – both within LOICZ and for the scientific and coastal zone communities in general.