Interhemispheric synchrony of Late-glacial climatic instability as recorded in proglacial Lake Mascardi,Argentina

Several high-resolution continental records have been reported recently in sites in South America, but the extent to which climatic variations were synchronous between the northern and southern hemispheres during the Late-glacial–Holocene transition, and the causes of the climatic changes, remain open questions. Previous investigations indicated that, east of the Andes, the middle and high latitudes of South America warmed uniformly and rapidly from 13 000 ¹⁴C yr BP, with no indication of subsequent climate fluctuations, equivalent, for example, to the Younger Dryas cooling. Here we present a multiproxy continuous record, radiocarbon dated by accelerated mass spectroscopy, from proglacial Lake Mascardi in Argentina. The results show that unstable climatic conditions, comparable to those described from records obtained in the Northern Hemisphere, dominated the Late-glacial–Holocene transition in Argentina at this latitude. Furthermore, a significant advance of the Tronador ice-cap, which feeds Lake Mascardi, occurred during the Younger Dryas Chronozone. This instability suggests a step-wise climatic history reflecting a global, rather than regional, forcing mechanism. The Lake Mascardi record, therefore, provides strong support for the hypothesis that ocean–atmosphere interaction, rather than global ocean circulation alone, governed interhemispheric climate teleconnections during the last deglaciation. © 1997 John Wiley & Sons, Ltd.     

Correction to: Using Causal Inference in Field Development Optimization: Application to Unconventional Plays

Mathematical Geosciences - Unfortunately, in the original version of the article the first and second name of the fourth author were wrong.     

Evaluating social vulnerability indicators: criteria and their application to the Social Vulnerability Index

Natural Hazards - As a concept, social vulnerability describes combinations of social, cultural, economic, political, and institutional processes that shape socioeconomic differentials in the...     

Coronal activity from dynamos in astrophysical rotators

We show that a steady mean-field dynamo in astrophysical rotators leads to an outflow of relative magnetic helicity and thus magnetic energy available for particle and wind acceleration in a corona. The connection between energy and magnetic helicity arises because mean-field generation is linked to an inverse cascade of magnetic helicity. To maintain a steady state in large magnetic Reynolds number rotators, there must then be an escape of relative magnetic helicity associated with the mean field, accompanied by an equal and opposite contribution from the fluctuating field. From the helicity flow, a lower limit on the magnetic energy deposited in the corona can be estimated. Steady coronal activity including the dissipation of magnetic energy, and formation of multi-scale helical structures therefore necessarily accompanies an internal dynamo. This highlights the importance of boundary conditions which allow this to occur for non-linear astrophysical dynamo simulations. Our theoretical estimate of the power delivered by a mean-field dynamo is consistent with that inferred from observations to be delivered to the solar corona, the Galactic corona, and Seyfert 1 AGN coronae.     

Implications of biological and physical diversity for resilience and resistance patterns within Highly Dynamic River Systems

The structure and function of alluvial Highly Dynamic River Systems (HDRS) are driven by highly variable hydrological disturbance regimes, and alternate between resistant, metastable states and resilient, transitional states. These are in turn subject to influences of feedback loops within hydrogeomorphic and biological processes. Here we consider how resistance and resilience largely determine HDRS ecosystem trajectories and how these characteristics can be modified by natural and anthropogenic processes. We review the mechanisms by which biodiversity can affect both resistance and resilience and introduce a conceptual framework that incorporates some unique HDRS characteristics. We suggest that resilient and resistant patterns frequently coexist in the active tract of these river systems, and that this coexistance promotes the return of metastable states after major disturbances. In contrast, highly resistant and poorly resilient patterns dominate at their external boundaries. The loss of these natural dynamics resulting from direct and indirect human impacts causes deviations to resistance and resilience patterns and therefore to HDRS trajectory. We propose that understanding the role of interactions between biological and physical processes that control resistance and resilience is crucial for system restoration and management.     

Simulation of the Vapor Intrusion Process for Nonhomogeneous Soils Using a Three-Dimensional Numerical Model

This paper presents model simulation results of vapor intrusion into structures built atop sites contaminated with volatile or semivolatile chemicals of concern. A three-dimensional finite element model was used to investigate the importance of factors that could influence vapor intrusion when the site is characterized by nonhomogeneous soils. Model simulations were performed to examine how soil layers of differing properties alter soil-gas concentration profiles and vapor intrusion rates into structures. The results illustrate difference in soil-gas concentration profiles and vapor intrusion rates between homogeneous and layered soils. The findings support the need for site conceptual models to adequately represent a site's geology when conducting site characterizations, interpreting field data, and assessing the risk of vapor intrusion at a given site. For instance, in layered geologies, a lower permeability and diffusivity soil layer between the source and building often limits vapor intrusion rates, even if a higher permeability layer near the foundation permits increased soil-gas flow rates into the building. In addition, the presence of water-saturated clay layers can considerably influence soil-gas concentration profiles. Therefore, interpreting field data without accounting for clay layers in the site conceptual model could result in inaccurate risk calculations. Important considerations for developing more accurate conceptual site models are discussed in light of the findings.     

A flux-limiting wetting–drying method for finite-element shallow-water models,with application to the Scheldt Estuary

We present a flux-limiting wetting–drying approach for finite-element discretizations of the shallow-water equations using discontinuous linear elements for the elevation. The key ingredient of the method is the use of limiters for generalized nodal fluxes. This method is implemented into the Second-generation Louvain-la-Neuve Ice-ocean Model (SLIM), and is verified against standard test cases. The method is further applied to the wetting and drying of sand banks in the Scheldt Estuary, which is located in northern Belgium and the southern Netherlands. The results obtained for both the benchmarks and the realistic problem illustrate the accuracy of the method in describing the hydrodynamics in the vicinity of dry areas. In particular, the method strictly conserves mass, and there is no transport through dry areas.     

Application of an intelligent model developed from experimental data to building design for fire safety

Computational fluid dynamics (CFD) techniques are widely adopted to simulate the behavior of fire. However, CFD suffers from the shortcoming of requiring extensive computer storage and a lengthy computational time. In practical applications, although comprehensive field information on velocities, temperatures, pressure, and the fractions of different constitutes can be obtained from CFD simulations, the user may only be interested in few important parameters that index the performance of a compartment design in the event of a fire. The height of the thermal interface (HTI) is one such key index, and refers to the average height above floor level inside a fire compartment at which the temperature gradient is highest. In practice, a fire compartment is considered untenable when the HTI drops below the respiratory level of the occupants, and in optimizing the design of a fire system, another set of design parameters (e.g., the width of the door opening) must be examined if the HTI of a fire compartment design is evaluated by CFD as being too low. This trial and error exercise then continues until a close to optimum set of design parameters is achieved. This approach is theoretically feasible, but requires lengthy computational time. This paper proposes the application of an Artificial Neural Network (ANN) approach as a fast alternative to CFD models to simulate the behavior of a compartment fire. A novel ANN model named GRNNFA has been specially developed for fire studies. It is a hybrid ANN model that combines the General Regression Neural Network (GRNN) and Fuzzy ART (FA). The GRNNFA model features a network structure that grows incrementally, stable learning, and the absence of the noise embedded in experimental fire data. It has been employed to establish a system response surface based on the training samples collected from a full-scale experiment on compartment fire. However, as the available training samples may not be sufficient to describe the behavior of all systems, and especially those involving fire data, this paper proposes that extra knowledge be acquired from human experts. Human expert network training has thus been developed to remedy established system response surface problems. After transforming the remedied system response surface to the problem domain, a Genetic Algorithm (GA) is applied to evaluate the close to optimum set of design parameters.     

Direct evidence of the feedback between climate and weathering

Long-term climate moderation is commonly attributed to chemical weathering; the higher the temperature and precipitation the faster the weathering rate. Weathering releases divalent cations to the ocean via riverine transport where they promote the drawdown of CO₂ from the atmosphere by the precipitation and subsequent burial of carbonate minerals. To test this widely-held hypothesis, we performed a field study determining the weathering rates of 8 nearly pristine north-eastern Iceland river catchments with varying glacial cover over 44 years. The mean annual temperature and annual precipitation of these catchments varied by 3.2 to 4.5 °C and 80 to 530%, respectively during the study period. Statistically significant linear positive correlations were found between mean annual temperature and chemical weathering in all 8 catchments and between mean annual temperature and both mechanical weathering and runoff in 7 of the 8 catchments. For each degree of temperature increase, the runoff, mechanical weathering flux, and chemical weathering fluxes in these catchments are found to increase from 6 to 16%, 8 to 30%, and 4 to 14% respectively, depending on the catchment. In contrast, annual precipitation is less related to the measured fluxes; statistically significant correlations between annual precipitation and runoff, mechanical weathering, and chemical weathering were found for 3 of the least glaciated catchments. Mechanical and chemical weathering increased with time in all catchments over the 44 year period. These correlations were statistically significant for only 2 of the 8 catchments due to scatter in corresponding annual runoff and average annual temperature versus time plots. Taken together, these results 1) demonstrate a significant feedback between climate and Earth surface weathering, and 2) suggest that weathering rates are currently increasing with time due to global warming.     

Extraterrestrial amino acids and L‐enantiomeric excesses in the CM2 carbonaceous chondrites Aguas Zarcas and Murchison

The abundances, distributions, enantiomeric ratios, and carbon isotopic compositions of amino acids in two fragments of the Aguas Zarcas CM2 type carbonaceous chondrite fall and a fragment of the CM2 Murchison meteorite were determined via liquid chromatography time‐of‐flight mass spectrometry and gas chromatography isotope ratio mass spectrometry. A suite of two‐ to six‐carbon aliphatic primary amino acids was identified in the Aguas Zarcas and Murchison meteorites with abundances ranging from ~0.1 to 158 nmol/g. The high relative abundances of α‐amino acids found in these meteorites are consistent with a Strecker‐cyanohydrin synthesis on these meteorite parent bodies. Amino acid enantiomeric and carbon isotopic measurements in both fragments of the Aguas Zarcas meteorites indicate that both samples experienced some terrestrial protein amino acid contamination after their fall to Earth. In contrast, similar measurements of alanine in Murchison revealed that this common protein amino acid was both racemic (D ≈ L) and heavily enriched in ¹³C, indicating no measurable terrestrial alanine contamination of this meteorite. Carbon isotope measurements of two rare non‐proteinogenic amino acids in the Aguas Zarcas and Murchison meteorites, α‐aminoisobutyric acid and D‐ and L‐isovaline, also fall well outside the typical terrestrial range, confirming they are extraterrestrial in origin. The detections of non‐terrestrial L‐isovaline excesses of ~10–15% in both the Aguas Zarcas and Murchison meteorites, and non‐terrestrial L‐glutamic acid excesses in Murchison of ~16–40% are consistent with preferential enrichment of circularly polarized light generated L‐amino acid excesses of conglomerate enantiopure crystals during parent body aqueous alteration and provide evidence of an early solar system formation bias toward L‐amino acids prior to the origin of life.