Sinkhole characterization in the Dead Sea area using airborne laser scanning

Since the early 1980s, the Dead Sea coast has undergone a near catastrophic land deterioration as a result of a rapid lake-level drop. One conspicuous expression of this deterioration is the formation of sinkholes fields that puncture the coastal plains. The evolution of sinkholes along nearly 70-km strip has brought to a halt the regional development in this well-known and toured area and destroyed existing infrastructures. Great efforts are being invested in understanding the phenomena and in development of monitoring techniques. We report in this paper the application of airborne laser scanning for characterization of sinkholes. We demonstrate first the appropriateness of laser scanning for this task and its ability to provide detailed 3D information on this phenomenon. We describe then an autonomous means for their extraction over large regions and with high level of accuracy. Extraction is followed by their detailed geometric characterization. Using this high-resolution data, we show how sinkholes of 0.5 m radius and 25 cm depth can be detected from airborne platforms as well as the geomorphic features surrounding them. These sinkhole measures account for their embryonic stage, allowing tracking them at an early phase of their creation.     

The Cosmolian program for simulating aeolian dynamics and its application to central Australia

The wide spatial coverage of sand dunes in continental interiors makes the understanding of their activity and accumulation history valuable for palaeoenvironmental reconstructions and the interpretation of landscape evolution. Nevertheless, the study of aeolian landscape development at the million-year timescale is hampered by the complex interaction of factors determining dune migration and the inherently self-destructive nature of their chronostratigraphy, thus limiting the applicability of traditional dating methods. This study presents a standalone program that simulates aeolian transport based on luminescence-derived chronologies coupled with numerical modelling of the accumulation of cosmogenic nuclides. This integrative approach to modelling the history of aeolian landforms reveals phases of emergence of aeolian sand into the landscape, and provides a data-based scheme that facilitates the morphodynamical study of aeolian processes over multiple timescales and up to several millions of years. The application of the program for reanalysing previously reported data from the Australian Simpson Desert reveals multiple pulses of sand dispersion into central Australia at 3.8–3.4, 2.9–2.5 and 1.5–1 Ma, corresponding to pronounced changes in climatic conditions and landscape deformation events. The synchronicity of the results with the established environmental framework that would promote the production and aeolian distribution of sand exemplifies the applicability of process-based modelling in constructing a timeframe of key landscape evolution events in arid environments by studying aeolian deposits. The dependence of the parameters used to determine environmental settings on sand transportation patterns additionally makes the program a powerful tool to further investigate the triggers and mechanisms of aeolian processes.     

The impact of planning on pedestrian movement: contrasting pedestrian movement models in pre-modern and modern neighborhoods in Israel

Most pedestrian movement volume models were constructed for urban areas that developed on the basis of pre-modern planning. In this paper, we confront neighborhoods that were built upon modern planning doctrines, combining the functional hierarchy of streets with the neighborhood unit concept, with neighborhoods that developed from pre-modem non-hierarchical street-based planning. We use space syntax analysis to investigate how their street network’s structural attributes interact with pedestrian movement distribution. The investigation was conducted in 14 neighborhoods from 4 cities in Israel by examining the correlation of observed pedestrian volume with models using different axial- and segment-based topological, angular, and metric syntactic attributes across different radii (scales). The results indicate that the street network and the distribution of pedestrian movement interact differently in the two neighborhood types. In pre-modern neighborhoods: (i) there is significantly more walking; (ii) the street network’s syntactic attributes tend to be much more consistent in their correlation with pedestrian volume across all scales; (iii) the correlation of pedestrian volume with these attributes and with commerce is relatively high; and (iv) pedestrian movement distribution is more predictable. We relate these differences to the absence of a self-organized circular causality between street network structure, commerce, and movement in modern planned neighborhoods.     

Land–sea carbon and nutrient fluxes and coastal ocean CO2 exchange and acidification: Past,present, and future

Epochs of changing atmospheric CO₂ and seawater CO₂–carbonic acid system chemistry and acidification have occurred during the Phanerozoic at various time scales. On the longer geologic time scale, as sea level rose and fell and continental free board decreased and increased, respectively, the riverine fluxes of Ca, Mg, DIC, and total alkalinity to the coastal ocean varied and helped regulate the C chemistry of seawater, but nevertheless there were major epochs of ocean acidification (OA). On the shorter glacial–interglacial time scale from the Last Glacial Maximum (LGM) to late preindustrial time, riverine fluxes of DIC, total alkalinity, and N and P nutrients increased and along with rising sea level, atmospheric PCO₂ and temperature led, among other changes, to a slightly deceasing pH of coastal and open ocean waters, and to increasing net ecosystem calcification and decreasing net heterotrophy in coastal ocean waters. From late preindustrial time to the present and projected into the 21st century, human activities, such as fossil fuel and land-use emissions of CO₂ to the atmosphere, increasing application of N and P nutrient subsidies and combustion N to the landscape, and sewage discharges of C, N, P have led, and will continue to lead, to significant modifications of coastal ocean waters. The changes include a rapid decline in pH and carbonate saturation state (modern problem of ocean acidification), a shift toward dissolution of carbonate substrates exceeding production, potentially leading to the “demise” of the coral reefs, reversal of the direction of the sea-to-air flux of CO₂ and enhanced biological production and burial of organic C, a small sink of anthropogenic CO₂, accompanied by a continuous trend toward increasing autotrophy in coastal waters.     

Global Nitrogen Cycle: Pre-Anthropocene Mass and Isotope Fluxes and the Effects of Human Perturbations

We present a nitrogen cycle model for pre-industrial times based on an extensive literature database. The model consists of 18 reservoirs in the domains of the atmosphere, land, and ocean. The biotic reservoirs on land and in the ocean (N-fixing plants, non-N-fixing plants, and marine biota) interact with atmospheric N₂ and dissolved inorganic nitrogen (DIN, consisting of N₂, NO₃ ^?, and NH₄ ⁺) in the ocean and soil waters. Marine DIN is taken up by marine biota and transformed from ocean particulate organic matter to dissolved organic nitrogen and the ocean sediment. The atmosphere, the largest nitrogen reservoir, supplies N₂ to the system by N fixation, deposition, and dissolution, and these input fluxes are balanced by denitrification and volatilization back to the atmosphere. The land and ocean domains are linked by river transport, which carries both dissolved and particulate nitrogen to the oceanic coastal zone. The isotope–mass balances of the N reservoirs are calculated from the isotopic composition of the reservoirs and the fractionation factors accompanying the fluxes between the reservoirs based on reported values from different natural conditions. The model sensitivity was tested for different biouptake rates and was run with various human perturbations, including fertilization, nitrous oxide emissions, population-related sewage disposal, land-use changes, and temperature-dependent rate kinetics. The new N mass–isotope cycle model provides the basis for assessment of the impact of artificial fertilization between 1700 and 2050. The perturbation experiments in this study suggest that land-use change is the key factor altering the N mass cycle since industrialization.     

Rates of dissolution of aluminosilicates in seawater

Dissolution of eight clay minerals, four zeolites, and quartz in seawater has been monitored for81/2 years. For most of the minerals, dissolution can be described as a first-order reaction in which dissolved silica approaches from undersaturation steady concentration values with time. Characteristic reaction rate constants (k₁) are of the order of 10^?7 sec^?1. One of the zeolites, clinoptilolite, shows a different dissolution behavior: SiO₂ concentration in solution reaches a high value within one year, followed by a decline to a lower value, suggestive of precipitation of another silicate phase (possibly sepiolite).A mathematical solution is given for a kinetic equation combining the parabolic-rate and first-order rate processes. It is shown that in a wide range of silicate dissolution reactions taking place over long periods of time, the presence of the parabolic-rate dissolution processes cannot be detected, thereby making its inclusion in the kinetic equations unnecessary. The experimental rates of dissolution are comparable to the SiO₂^? dissolution rates in oceanic sediments near the sediment/water interface. But deeper in the sediment, the calculated dissolution rates are significantly lower than the near-interface and experimental values.