The inter-relationship between coastal sub-aquifers and the Mediterranean Sea, deduced from radioactive isotopes analysis

Radioactive isotopes were used to estimate the rate of seawater intrusion into the coastal aquifer of Israel, the connection between the different sub-aquifers, and the connection between the sub-aquifers and the sea. This was done by dating both fresh and saline groundwaters from the vicinity of the shoreline, which were analyzed for their ¹⁴C and tritium content together with their chemical and stable isotope composition. The results indicate that the distinct sub-aquifers differ in their water chemistry and age. The saline groundwater in the lower sub-aquifers is older than ca. 10,000 years, as evidenced by the absence of tritium and low ¹⁴C activity (<12 PMC). On the other hand, saline groundwaters in the upper sub-aquifers contain tritium and are thus younger than 50 years, indicating recent intrusion of seawater. The ages of the saline groundwaters become younger upward from the lower sub-aquifers to the upper ones, reflecting the sea-level rise since the last glacial period. The older ages also imply slow groundwater flow in the lower sub-aquifers. The fresh groundwaters in most cases in the lower sub-aquifers were found to be older than ca. 10,000 years and this implies that the flow to the sea is blocked or restricted.     

Parametric study of near-wake structure of spherical and cylindrical bodies in the laboratory

Some aspects of the interaction between metal bodies and streaming rarefied plasmas were studied in a newly constructed Plasma Wind Tunnel as part of an attempt to investigate (via simulation) phenomena relevant to the spacecraft/space plasma interaction. Detailed near-wake ion current profiles for both spherical and cylindrical bodies at different body potentials (φ_S) and at different plasma flow parameters are presented. Various features of the profiles can be correlated, at least qualitatively, with both plasma and body characteristics. For example, the width of the wake zone appears proportional to the Debye length (λ_D) and depends on the potential of the target body although it appears to be relatively insensitive to the ratio $\text{S = V}{}_{\mathrm{<mtext>flow</mtext>}}\text{/(}\text{2kT}{}_{\mathrm{e}}\text{M}{}_{\mathrm{+}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. The amplitude of the ion current peak(s) also appears proportional to λ_D while, for fixed φ_S, the location of the peak is directly related to S and possibly dependent upon body geometry. The general importance of body geometry is qualitatively demonstrated. In addition, a discussion of the relevance of the above studies to previous in situ data obtained from the Ariel I and Gemini/Agena missions is given.     

Stable isotope and Sr2+/Ca2+ evidence of diagenetic dedolomitization in a schizohaline environment: Cenomanian of northern Israel

The Cenomanian—Turonian Upper Judea Group of Israel comprises shallow-marine hypersaline dolomites passing laterally into ‘basinal’ limestones and chalks. Chertbearing diagenetic dedolomites characterize the transitional zone. The restriction of dedolomites to a narrow zone, their light δ¹³C (up to ?11%), and their low Sr²⁺ concentration (<16 ppm) all suggest that the dedolomites were formed diagenetically through exposure of this zone to fresh meteoric waters. This type of partly changing environments was referred to as schizohaline by Folk and Siedlecka (1974).     

Formation of sequential basins along a strike–slip fault–Geophysical observations from the Dead Sea basin

The Dead Sea basin is often cited as one of the classic examples for the evolution of pull-apart basins along strike–slip faults. Despite its significance, the internal structure of the northern Dead Sea basin has never been addressed conclusively. In order to produce the first comprehensive, high-resolution analysis of this area, all available seismic data from the northern Dead Sea (lake)–lower Jordan valley (land) were combined. Results show that the northern Dead Sea basin is comprised of a system of tectonically controlled sub-basins delimited by the converging Western and Eastern boundary faults of the Dead Sea fault valley. These sub-basins grow shallower and smaller to the north and are separated by structural saddles marking the location of active transverse faults. The sedimentary fill within the sub-basins was found to be relatively thicker than previously interpreted. As a result of the findings of this study, the “classic” model for the development of pull-aparts, based on the Dead Sea, is revised. The new comprehensive compilation of data produced here for the first time was used to improve upon existing conceptual models and may advance the understanding of similar basinal systems elsewhere.     

Epipalaeolithic occupations in Nahal Neqarot Rockshelter,Negev, Israel: Radiocarbon dating and identification of charred wood remains

Recent excavations at Nahal Neqarot Rockshelter in the Central Negev, Israel, revealed 60 cm of in situ sediments. The associated lithic industry is mostly attributable to the Middle Epipalaeolithic Ramonian industry, though there is also evidence for sporadic earlier and later Epipalaeolithic use of the site. This is confirmed by three accelerator ¹⁴C dates, which contribute to a better understanding of the chronological framework for the Epipalaeolithic in the region. Microscopic examination of charred wood remains uncovered with the lithics, revealed the dominance of juniper, which is presently extinct in the nearby contemporaneous vegetation, otherwise composed of still extant taxa. © 1998 John Wiley & Sons, Inc.     

Novel mass-aggregation-based calibration of an acoustic method of monitoring bedload flux by infrequent desert flash floods

The monitoring of bedload flux under flash flood conditions has been successfully achieved since 1992 using slot samplers in the semiarid Nahal Eshtemoa. In the present study, a surrogate bedload monitoring technique - the Japanese plate microphone - has been deployed and calibrated against data from the slot samplers. Since a slot sampler has a sensitivity threshold that becomes especially important when transport rates are low, different averaging periods should be considered for high and low fluxes. In order to overcome the deficiencies of time-based aggregation used hitherto, we have developed a new method involving mass aggregation and commensurably variable intervals, thereby enabling a more accurate analysis and optimizing the bedload sampler's capabilities. The data derived with this new method has then been utilized to calibrate the Japanese plate microphone. The Eshtemoa is an ephemeral gravel bed channel with a high proportion of fine gravel (< 0.02 m); for these conditions, acoustic sensors have not been calibrated as yet. Two multiple linear regression models incorporating the effect of median bedload grain size on pulse rate have been established to predict bedload flux and cumulative transported bedload mass. The coefficients in these models are statistically significant. Good predictions are obtained for bedload flux (adj. r² = 0.83) and for cumulative bedload mass (adj. r² = 0.98) during flood recession. Overall, the multiple linear regression models, used in conjunction with the mass aggregation method of estimating bedload flux, suggest that field calibration of acoustic devices is feasible under these conditions for ca. 90% of the duration of bedload transport. © 2020 John Wiley & Sons, Ltd.     

Between plate and salt tectonics—New stratigraphic constraints on the architecture and timing of the Dead Sea basin during the Late Quaternary

The Dead Sea is an extensional basin developing along a transform fault plate boundary. It is also a terminal salt basin. Without knowledge of precise stratigraphy, it is difficult to differentiate between the role of plate and salt tectonics on sedimentary accumulation and deformation patterns. While the environmental conditions responsible for sediment supply are reasonably constrained by previous studies on the lake margins, the current study focuses on deciphering the detailed stratigraphy across the entire northern Dead Sea basin as well as syn and post-depositional processes. The sedimentary architecture of the late Quaternary lacustrine succession was examined by integrating 851 km of seismic reflection data from three surveys with gamma ray and velocity logs and the stratigraphic division from an ICDP borehole cored in 2010. This allowed seismic interpretation to be anchored in time across the entire basin. Key surfaces were mapped based on borehole lithology and a newly constructed synthetic seismogram. Average interval velocities were used to calculate isopach maps and spatial and temporal sedimentation rates. Results show that the Amora Formation was deposited in a pre-existing graben bounded by two N-S trending longitudinal faults. Both faults remained active during deposition of the late Pleistocene Samra and Lisan Formations—the eastern fault continued to bound the basin while the western fault remained blind. On-going plate motion introduced a third longitudinal fault, increasing accommodation space westwards from the onset of deposition of the Samra Formation. During accumulation of these two formations, sedimentation rates were uniform over the lake and similar. High lake levels caused an increase in hydrostatic pressure. This led to salt withdrawal, which flowed to the south and southwest causing increased uplift of the Lisan and En Gedi diapirs and the formation of localized salt rim synclines. This induced local seismicity and slumping, resulting in an increased thickness of the Lisan succession within the lake relative to its margins. Sedimentation rates of the Holocene Ze'elim Fm were 4–5 times higher than before. The analysis presented here resolves central questions of spatial extent and timing of lithology, deposition rates and their variability across the basin, timing of faulting at and below the lake floor, and timing and extent of salt and plate tectonic phases and their effect on syn and post-depositional processes. Plate tectonics dictated the structure of the basin, while salt tectonics and sediment accumulation were primarily responsible for its fill architecture during the timeframe examined here.     

Global climate change and the effect of conservation practices in US agriculture

 Increase in the use of conservation practices by agriculture in the United States will enhance soil organic carbon and potentially increase carbon sequestration. This, in turn, will decrease the net emission of carbon dioxide. A number of studies exist that calibrate the contribution of various individual, site-specific conservation practices on changes in soil organic carbon. There is a general absence, however, of a comprehensive effort to measure objectively the contribution of these practices including conservation tillage, the Conservation Reserve Program, and conservation buffer strips to an change in soil organic carbon. This paper fills that void. After recounting the evolution of the use of the various conservation practices, it is estimated that organic carbon in the soil in 1998 in the United States attributable to these practices was about 12.2 million metric tons. By 2008, there will be an increase of about 25%. Given that there is a significant potential for conservation practices, which could lead to an increase in carbon sequestration, there are a number of policy options that can be pursued. These include education and technical assistance, financial assistance, research and development, land retirement, and regulation and taxes. Received: 27 December 1999 · Accepted: 14 March 2000     

Subduction, collision and initiation of hominin dispersal

Subduction is the main driving force of plate tectonics controlling the physiography of the Earth. The northward subduction of the Sinai plate was interrupted during the Early Pleistocene when the Eratosthenes Seamount began to collide with the Cyprian arc. A series of synchronous structural deformations was triggered across the entire eastern Mediterranean, and local topography was drastically accentuation along the Levantine corridor – one of the main pathways of hominin dispersal out of Africa. However, the choice of this preferred pathway and timing of dispersal has not been resolved. Though causes for dispersal out of Africa are in debate, we show that the transition from subduction to collision in the eastern Mediterranean set the route.