Habitat change on Horn Island,Mississippi, 1940-2010, determined from textural features in panchromatic vertical aerial imagery

Habitat-type land cover on Horn Island, Mississippi, northern Gulf of Mexico, was estimated for the years 1940 and 2010 using a combination of panchromatic imagery and 2010 ground survey data. A grey-level co-occurrence matrix was applied to compute reflectance coefficient of variation (CV) and texture indices. The relationships of 2010 CV ranges with known habitat types defined training regions of interest in the 1940 imagery as a substitute for 1940 ground data. Texture indices contrast, correlation, energy and entropy then served as input bands for maximum likelihood classifications which produced 1940 and 2010 habitat maps. Analysis determined that wetter habitats on Horn expanded linearly over the seven-decade period. This is attributed to constraints on sediment supply and the impacts of severe storms which led to decreases in soil depth to the water table. If this trend continues, marsh habitat will cover 31% of Horn Island’s land area by 2050.     

What we know about elemental bulk chondrule and matrix compositions: Presenting the ChondriteDB Database

Chondrules and matrix are the major components of chondritic meteorites and represent a significant evolutionary step in planet formation. The formation and evolution of chondrules and matrix and, in particular, the mechanics of chondrule formation remain the biggest unsolved challenge in meteoritics. A large number of studies of these major components not only helped to understand these in ever greater detail, but also produced a remarkably large body of data. Studying all available data has become known as ?big data? analyses and promises deep insights – in this case – to chondrule and matrix formation and relationships. Looking at all data may also allow one to better understand the mechanism of chondrule formation or, equally important, what information we might be missing to identify this process. A database of all available chondrule and matrix data further provides an overview and quick visualisation, which will not only help to solve actual problems, but also enable students and future researchers to quickly access and understand all we know about these components. We collected all available data on elemental bulk chondrule and matrix compositions in a database that we call ChondriteDB. The database also contains petrographic and petrologic information on chondrules. Currently, ChondriteDB contains about 2388 chondrule and 1064 matrix data from 70 different publications and 161 different chondrites. Future iterations of ChondriteDB will include isotope data and information on other chondrite components. Data quality is of critical importance. However, as we discuss, quality is not an objective category, but a subjective judgement. Quantifiable data acquisition categories are required that allow selecting the appropriate data from a database in the context of a given research problem. We provide a comprehensive overview on the contents of ChondriteDB. The database is available as an Excel file upon request from the senior author of this paper, or can be accessed through MetBase.     

Iron release in aqueous environment by fresh volcanic ash from Mount Etna (Italy) and Popocatépetl (Mexico) volcanoes

In this study, we performed leaching experiments for timescales of hours-to-months in deionized water on fresh volcanic ash from Mt. Etna (Italy) and Popocatépetl (Mexico) volcanos to monitor Fe release as a function of ash mineral chemistry and size, with the aim of clarifying Fe release mechanisms and eventually evaluating the impact of volcanic ash on marine and lacustrine environments. To define sample mineralogy and Fe speciation, inclusive characterization was obtained by means of XRF, SEM, XRPD, EELS and Mössbauer spectroscopies. For Etna and Popocatépetl samples, glass proportions were quantified at 73 and 40%, Fe₂O₃ total contents at 11.6–13.2 and 5.8 wt%, and Fe³⁺/Fe_Tot ratios at 0.33 and 0.23, respectively. Leaching experiments showed that significant amounts of iron, ~?30 to 150 and ~?750 nmol g^?1 l^?1 for pristine Etna and Popocatépetl samples, respectively, are released within the first 30 min as a function of decreasing particle size (from 1 to 0.125 mm). The Popocatépetl sample showed a very sustained Fe release (up to 10 times Etna samples) all along the first week, with lowest values never below 400 nmol g^?1 l^?1 and a maximum of 1672 nmol g^?1 l^?1 recorded after 5 days. This sample, being composed of very small particles (average particle size 0.125 mm) with large surface area, likely accumulated large quantities of Fe-bearing sublimates that quickly dissolved during leaching tests, determining high Fe release and local pH decrease (that contributed to release more Fe from the glass) at short timescale (hours-to-days). The fractional Fe solubility (Fe_S) was 0.004–0.011 and 0.23% for Etna and Popocatépetl samples, respectively, but no correlation was found between Fe released in solution and either ash Fe content, glass/mineral ratio or mineral assemblage. Results obtained suggest that volcanic ash chemistry, mineralogy and particle size assume a relevant role on Fe release mostly in the medium-to-long timescale, while Fe release in the short timescale is dominated by dissolution of surface sublimates (formed by physicochemical processes occurring within the eruption plume and volcanic cloud) and the effects of such a dissolution on the local pH conditions. For all samples, a moderate to sustained Fe release occurred for leaching times comparable with their residence time within the euphotic zone of marine and lacustrine environments (variable from few minutes to few hours), revealing their possible contribution to increase Fe bioavailability.     

Palaeogeographic,climatic and tectonic change in southeastern Australia: the Late Neogene evolution of the Murray Basin

The Murray Basin is a low-lying but extensive intracratonic depocentre in southeastern Australia, preserving an extraordinary record of Late Neogene sedimentation. New stratigraphic and sedimentologic data allow the long-term evolution of the basin to be re-evaluated and suggest a significant role for: (1) tectonism in controlling basin evolution, and (2) progressive and step-wise climatic change beginning in the early Pleistocene. Tectonic change is associated with regional uplift, occurring at approximately the same rate from the early Pliocene until the present day, and possibly associated with changing mantle circulation patterns or plate boundary processes. This uplift led to the defeat and re-routing of the Murray River, Australia’s major continental drainage system. Key to our interpretation is recognition of timing relationships between four prominent palaeogeographic features – the Loxton-Parilla Sands strandplain, the Gambier coastal plain, palaeo megalake Bungunnia and the Kanawinka Escarpment. Geomorphic and stratigraphic evidence suggest that during the Early Pliocene the ancestral Murray River was located in western Victoria, flowing south along the Douglas Depression. Relatively small amounts of regional uplift (<200 m) defeated this drainage system, dramatically changing the palaeogeography of southeastern Australia and forming Plio-Pleistocene megalake Bungunnia. At its maximum extent Lake Bungunnia covered more than 50,000 km², making it one of the largest known palaeo- or modern-lakes in an intracontinental setting. Magnetostratigraphic constraints suggest lake formation c. 2.4 Ma. The formation of Lake Bungunnia influenced the Pliocene coastal dynamics, depriving the coastline of a sediment source and changing the coastal system from a prograding strandline system to an erosional one. Erosion during this period formed the Kanawinka Escarpment, a palaeo sea-cliff and one of the most prominent and laterally extensive geomorphic features in southeastern Australia. Marine sediments c. 800 ka to c. 1.16 Ma represent the time of re-establishment of depositional coastal dynamics and of a permanent outlet for the Murray River. This age range is consistent with our best estimate of the age of the youngest Lake Bungunnia sediments and points towards an early Pleistocene age for the demise of the lake system. The youngest Lake Bungunnia sediment, present on a number of distinct terraces, suggests that progressive, step-wise climatic change played a role in the demise of the lake. However, in order for the ancestral Murray River system to have been able to breach the pre-existing tectonic dam, it is likely that tectonic change and/or temporarily enhanced discharge was also significant. This scenario indicates that the modern Murray River has only been in existence for at most 700 ka.     

Near real time satellite imagery to support and verify timely flood modelling

The study investigates the capability of coarse resolution synthetic aperture radar (SAR) imagery to support flood inundation models. A hydraulic model of a 98‐km reach of the River Po (Northern Italy) was calibrated on the October 2000 high‐magnitude flood event with extensive and high‐quality field data. During the June 2008, low‐magnitude flood event a SAR image was acquired and processed in near real time (NRT) in order to provide adequate data for quick verification and recalibration of the hydraulic model. Copyright © 2009 John Wiley & Sons, Ltd.     

Downscaling the hydrological cycle in the Mackenzie basin with the Canadian regional climate model

Abstract

The Canadian Regional Climate Model (CRCM) has been nested within the Canadian Centre for Climate Modelling and Analysis ‘ second generation General Circulation Model (GCM), for a single month simulation over the Mackenzie River Basin and environs. The purpose of the study is to assess the ability of the higher resolution CRCM to downscale the hydrological cycle of the nesting GCM. A second 1‐month experiment, in which the CRCM was nested within analyzed fields of a global data assimilation system, was also performed to examine the sensitivity of the basin moisture budget to atmospheric lateral boundary forcing.

We have found that the CRCM can produce realistic lee cyclogenesis, preferentially in the Liard sub‐basin, along with associated circulation and precipitation patterns, as well as an improved rainshadow in the lee of the Rocky Mountains compared to the GCM. While these features do quantitatively affect the monthly average climate statistics, the basin scale moisture budgets of the models were remarkably similar, though some of this agreement is due to compensating errors in the GCM. Both models produced excessive precipitation compared to a recent climatology for the region, the cause of which is traced to lateral boundary forcing. A second experiment, identical to the first except that the CRCM was forced with analyzed fields at the lateral boundaries, produced a qualitatively different basin moisture budget, including a much more realistic precipitation field. Errors in the moisture budget of the first experiment appear to be associated with the poor representation of the Aleutian Low in the GCM, and do not appear to be strongly connected to (local) surface processes within the models. This suggests that an effective strategy for modelling the hydrological cycle of the Mackenzie Basin on the fast climate timescale ‐ a major requirement of the Mackenzie GEWEX Study ‐ will involve nesting the CRCM within analyzed (or re‐analyzed) atmospheric fields.     

Long-term modeling of alteration-transport coupling: Application to a fractured Roman glass

To improve confidence in glass alteration models, as used in nuclear and natural applications, their long-term predictive capacity has to be validated. For this purpose, we develop a new model that couples geochemical reactions with transport and use a fractured archaeological glass block that has been altered for 1800 years under well-constrained conditions in order to test the capacity of the model.The chemical model considers three steps in the alteration process: (1) formation of a hydrated glass by interdiffusion, whose kinetics are controlled by a pH and temperature dependent diffusion coefficient; (2) the dissolution of the hydrated glass, whose kinetics are based on an affinity law; (3) the precipitation of secondary phases if thermodynamic saturation is reached. All kinetic parameters were determined from experiments. The model was initially tested on alteration experiments in different solutions (pure water, Tris, seawater). It was then coupled with diffusive transport in solution to simulate alteration in cracks within the glass. Results of the simulations run over 1800 years are in good agreement with archaeological glass block observations concerning the nature of alteration products (hydrated glass, smectites, and carbonates) and crack alteration thicknesses. External cracks in direct contact with renewed seawater were altered at the forward dissolution rate and are filled with smectites (400−500 μm). Internal cracks are less altered (by 1 or 2 orders of magnitude) because of the strong coupling between alteration chemistry and transport. The initial crack aperture, the distance to the surface, and sealing by secondary phases account for these low alteration thicknesses. The agreement between simulations and observations thus validates the predictive capacity of this coupled geochemical model and increases more generally the robustness and confidence in glass alteration models to predict long-term behavior of nuclear waste in geological disposal or natural glass in the environment.