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Valley width is a fundamental morphologic property of rivers that plays a key role in drainage networks' hydrology, ecology, and geomorphology. In many cases, defining and measuring valley width is far from trivial. Therefore, similar to channel width, the valley width (W) is commonly approximated as a power law function of the drainage area (A) and expressed as W = kcAd. Global observations have shown that the exponent (d) can vary widely but is typically ~0.5. However, in fluvial systems that have undergone drainage reorganization, gradual or abrupt changes in drainage areas along the valley could produce widths that are disproportionate to their drainage areas. As a result, the valley width - drainage area relationship in reorganized systems is expected to differ from undisturbed drainages that have not undergone reorganization.To test this prediction, we studied 12 valleys in the Negev desert, Israel, and classified them into three categories, based on field evidence and remote sensing data: (i) undisturbed valleys, which are minimally affected by reorganization; (ii) beheaded valleys, whose headwaters were beheaded; and (iii) reversed valleys, which have reversed their flow direction by 180 degrees while exploiting their antecedent valleys. Using a new semi-automatic tool to measure valley width on high-resolution DEMs, we calibrated the best-fit power law for each valley to explore the relationships between drainage area and valley width for each valley category.Our results show that the valley width-drainage area scaling in reorganized valleys deviated significantly from those in undisturbed valleys in our field area and global observations. The drainage area exponents (d) were lower in beheaded valleys compared to undisturbed valleys but remained positive. In contrast, reversed valleys were characterized by negative d exponents, indicating valley width decrease with increasing drainage area. For the reversed category, we also explored the independent effect of channel slope (S), where the valley width is W = kb AbSc, which resulted in negative and overall similar values of b and c.In one reversed valley section, we compared the scaling of valley versus channel width as a function of drainage area. We found that in contrast to the downstream narrowing valley, the channel width shows an opposite trend and widens downstream, suggesting that the channel has mostly adjusted to the post-reorganization drainage area distribution. The narrow reversed channel shapes the width of the formative flows, which contrasts significantly with the wide flows of the beheaded valley across the divide. This difference results in a step-change in the unit stream power between the reversed and beheaded channels, potentially leading to a "width feedback" that promotes further divide migration.Our findings can be used to identify landscapes that have been affected by recent drainage reorganization and should be taken into consideration in studies that use the relationship between valley width and drainage area for valley width predictions, stream power calculations, and landscape evolution models.

Current dust storms, originating from afar, are common in Israel and the eastern Mediterranean, and thus most dust sources are considered to be distal. However, recent studies suggest that the latest Quaternary loess accreted in the Northern Negev can also serve as a proximal source of dust. These sources were mostly neglected in past discussions as contributors of dust. Here, we demonstrate that such proximal dust sources, mostly the Negev loess, currently contribute relatively large amounts of recycled dust to the regional dust cycle. We conducted a sampling campaign of deposited dust during individual dust storms and identified high content of coarse silt grains and quartzo-feldspathic minerals within and adjacent to the Negev loess that gradually decreases toward the north. These grains, characteristics of the Negev loess, indicate a short transport distance. In addition, our data reveal that local wind speed is the limiting factor for emitting proximal dust, regardless of the synoptic system. We determined that proximal sources in Israel emit dust during either local events or as a part of regional dust storms originating from afar. We evaluate the minimal contribution of this proximal dust to the total mass of deposited dust as 58–74%, 54–70%, 52–64%, and 26–34% for the northern Negev, central Negev, central mountainous region, and northern Israel, respectively. These estimates indicate that at the desert fringe, both proximal and distal sources of dust should be considered when inferring dust sources from dust geochemistry that can sometimes be similar due to the long dust history.

Two oil spills occurred in the Evrona Nature Reserve (southern Israel), in 1975 and 2014. This oil contamination induced highly persistent soil hydrophobicity. The objective of this study was to investigate the decrease in oil-induced soil hydrophobicity under different environmental conditions and to assess the relationship between the hydrophobicity and hydrocarbon content. A laboratory incubation experiment was conducted over 1.5 years to monitor the soil hydrophobicity and total hydrocarbon concentration under different environmental conditions. We hypothesized that the addition of water (20% or 50% saturation), nutrients, and biosurfactants can accelerate the reduction in hydrophobicity and decomposition of hydrocarbons. Water drop penetration time and molarity of ethanol droplet tests were used to assess soil hydrophobicity. In parallel, alkane composition and total petroleum hydrocarbons were evaluated to indicate oil attenuation. The addition of water, nutrients, and biosurfactants resulted in a concomitant reduction in hydrophobicity and hydrocarbon concentration of varying degrees, exhibiting enhanced degradation and hydrophobicity reduction observed in treatments to which nutrients and biosurfactants were added. At the end of the incubation, however, soil hydrophobicity in all treatments remained severe, even though total petroleum hydrocarbon removal was fairly high and reached 40%–80% in the treatments to which water with or without nutrients and/or surfactants was added.

The width of valleys and channels affects the hydrology, ecology, and geomorphic functionality of drainage networks. In many studies, the width of valleys and/or channels (W) is estimated as a power-law function of the drainage area (A), W=kcAd. However, in fluvial systems that experience drainage reorganization, abrupt changes in drainage area distribution can result in valley or channel widths that are disproportional to their drainage areas. Such disproportionality may be more distinguished in valleys than in channels due to a longer adjustment timescale for valleys. Therefore, the valley width–area scaling in reorganized drainages is expected to deviate from that of drainages that did not experience reorganization. To explore the effect of reorganization on valley width–drainage area scaling, we studied 12 valley sections in the Negev desert, Israel, categorized into undisturbed, beheaded, and reversed valleys. We found that the values of the drainage area exponents, d, are lower in the beheaded valleys relative to undisturbed valleys but remain positive. Reversed valleys, in contrast, are characterized by negative d exponents, indicating valley narrowing with increasing drainage area. In the reversed category, we also explored the independent effect of channel slope (S) through the equation W=kbAbSc, which yielded negative and overall similar values for b and c. A detailed study in one reversed valley section shows that the valley narrows downstream, whereas the channel widens, suggesting that, as hypothesized, the channel width adjusts faster to post-reorganization drainage area distribution. The adjusted narrow channel dictates the width of formative flows in the reversed valley, which contrasts with the meaningfully wider formative flows of the beheaded valley across the divide. This difference results in a step change in the unit stream power between the reversed and beheaded channels, potentially leading to a “width feedback” that promotes ongoing divide migration and reorganization. Our findings demonstrate that valley width–area scaling is a potential tool for identifying landscapes influenced by drainage reorganization. Accounting for reorganization-specific scaling can improve estimations of erosion rate distributions in reorganized landscapes.

Drainage reversals occur when a channel reverses its flow direction by 180o while exploiting its antecedent valley. This reorganization mode can critically impact landscapes' hydrologic and geomorphic functionality, but the processes inducing reversals and the related landscape dynamics have not been studied in detail. Reversals are commonly attributed to tectonic tilting. However, in many cases, independent evidence for tilting is missing. Furthermore, when reversals occur toward great escarpments, as was documented in many terrains around the globe, isostatic tilting is expected to occur away and not toward the escarpments.The current study explores a natural laboratory for drainage reversals in the southeastern Negev Desert, Israel. We identified in this field area tens of highland channels that reversed their flow direction eastward and toward the Arava Valley Escarpment.Reversals are established by observations of (1) barbed tributaries that join the main trunk with junction angles > 90o and preserve the antecedent pre-reversal drainage topology; (2) a valley confined drainage divide (windgap) that separates the reversed channel from the antecedent, beheaded channel; and (3) series of terraces that grade west, toward the windgap and opposite to the active flow direction.Based on field observations and morphometric analysis, we propose a new, tilting-independent, mechanism for inducing flow reversals. According to this mechanism, reversal is linked to localized windgap migration within the antecedent channel and away from the escarpment. Migration is driven by slope imbalance across the windgap with steeper slopes at the escarpment side, and by erodibility differences between the hard rocky interfluves and the more erodible valley fill.Using a new algorithm for quantifying valley width, we find that the scaling between drainage area (A) and width (W) differs between reversed, beheaded, and non-reorganized valleys. In addition to providing markers for reorganization, the unique A-W scaling leads to feedback that promotes further windgap migration and generates longer reversals.The oppositely grading terraces that accompany some reversed channels present an outstanding opportunity for quantifying the dynamic and rate of windgap migration. We hypothesize that the abandonment age of each terrace reflects the timing at which the paleo-windgap migrated past the location of the terrace, promoting the incision of the reversed channel that generated the terrace. Accordingly, the abandonment ages of the terraces can inform us about the timing and dynamics of windgap migration.Absolute ages of terrace abandonment were constrained by luminescence dating, with complementary relative ages inferred from chronosequence of reg soils, which develop on abandoned terraces in hyper-arid environments. In agreement with the reversal model, we found that the degree of soil development and the abandonment ages of terraces increase with distance from the windgap eastwards. The average windgap migration rate has been ~1 mm/yr since 200 Kyr, an order of magnitude greater than the vertical incision rate of the reversed channel. The age-distance relations of the terraces indicate episodic windgap migration with a recent stalling. A similar age for other dated windages in the region hints at a regional, possibly climatic control on windgap migration.

Carbonate hillslopes are often soil mantled and display a classic convex morphology. In this study we examine controls on carbonate hillslope denudation and morphology using a modified regolith mass balance equation to account for chemical weathering and dust input—two fluxes that are commonly neglected in settings with silicate-dominated bedrock. We utilize seven study sites in the Eastern Mediterranean across a significant gradient in the mean annual rainfall and dust deposition flux. Combining cosmogenic 36Cl-derived hilltop denudation rates with an estimate of the regolith chemical depletion and the quantified fraction of dust in the regolith we predict hilltop curvature and compare our predictions with observations based on high-resolution airborne LiDAR (light detection and ranging). Denudation rates vary from 5 to 210 mm/k.y. and increase with mean annual rainfall. Less resistant carbonates (chalk) experience faster denudation rates relative to more resistant dolo-limestone and are less prone to chemical weathering. Soil production exhibits a humped dependency on soil thickness. The observed hilltop curvature varies as a function of rainfall and dust flux with a minimum at sub-humid sites. While trends in hilltop convexity are often solely attributed to variations in erosion rate, our results illustrate the additional effects of dust production and chemical depletion. Our mass balance model implies that drier sites in the south probably experienced a more intricate history of regolith production due to dust flux fluctuations. Thus, by incorporating dust flux and chemical weathering to the classic hillslope evolution model we are able to identify a complex relation between hilltop curvature, soil production, and climate.

The carbonate mountainous landscape around most of the Mediterranean is karstic, is almost barren, and has thin soils. Erosion of preexisting thicker soils is a common hypothesis used to explain this bare terrain. An alternative hypothesis is that in the Mediterranean region, thin soils are attributed to long-distance transport of very fine, silty clay dust, resulting in low mass accumulation rates. Even if accreted over millennia, such dust cannot produce thick, highly productive soils. A pronounced anomaly in the Mediterranean is the thick, more productive soil of the semiarid southern Levant (SL). These soils contain order-of-magnitude coarser grains than the characteristic thin soils in the Mediterranean and a high proportion (>70%) of coarse silt quartz sourced from the nearby Sinai-Negev erg, the primary contributor of the Negev loess. This proximal intense dust supply produced greatly thicker soils. However, influx of coarse silt quartz loess is a geologically recent phenomenon in the SL. Pre-loess (i.e., older than 200 ka, pre-coarse-silt influx) SL soils are much finer and were generated by long-distance dust from the Sahara and Arabia like most other Mediterranean soils. Thus, we hypothesize that the geologically recent Negev Desert loess interval caused a drastic change in mountainous soil properties within the SL, enriching the Levant’s ecology and affecting early human development. The high amounts of coarse silt deposited on the landscape have contributed to the unique sustainable agriculture in the SL, which assisted in transforming the Levant into “the land of milk and honey” and a cradle of civilizations.

The width of valleys and channels affects the hydrology, ecology, and geomorphic functionality of drainage networks. Valley and channel widths are often estimated through a power-law scaling between width (W) and drainage area (A), and where lithologic variability or differential uplift rates dominate, width was suggested to scale with both slope (S) and drainage area, through the relation W = kb Ab Sc. However, in fluvial systems that experience drainage reorganization, abrupt changes in drainage area distribution can result in widths that are disproportional to their drainage areas. Consequently, in such cases, the width-area-slope scaling is expected to deviate relative to drainages that did not experience reorganization. To explore the effect of reorganization on width-area-slope scaling, we studied 12 valley sections in the Negev desert, Israel, categorized into undisturbed, beheaded, and reversed valleys. We found that the drainage area exponent, b, differs between valley categories, and that reversed valleys are characterized by a negative b exponent, indicating valley narrowing with increasing drainage area. A detailed study of a reversed valley reveals that unlike the negative b exponent that links drainage area to valley width, the relation between drainage area and channel width is best fitted with a positive b exponent. This difference indicates that the timescale of channel width adjustment to post-reorganization drainage area distribution is faster than that of the valley width adjustment. We find that the difference in channel width across the divide causes a step change in unit stream power between the adjusted reserved channel and the unadjusted, beheaded channel. Gradients in width and unit stream power across the divide, lead to a width-feedback that promotes ongoing divide migration and reorganization. The identified distinct width-area-slope scaling of reorganized valleys could assist in recognizing and constraining the dynamics of landscapes influenced by drainage reorganization and likely has critical implications for the distribution of erosion rates in reorganized landscapes.

Agricultural terraces are the most widespread archaeological landforms worldwide. Despite their far-reaching prevalence in many inhabited parts of the world, archaeological soils in terraces (hereafter ‘terrace soils’) are scarcely studied and their nature is poorly defined. This study aims to depict a space–time framework for the development of calcareous soils in archaeological stone-wall bench terraces and suggest modifications to their soil classification and mapping. To do so, we examined soils at the forefront of five terraces in Catalonia (Spain), that had been previously dated with optically stimulated luminescence to periods from Medieval-Late Middle Ages (1200 ± 60 CE) to Modern (1810 ± 15 CE). Local soils surrounding the terraces are Entisols and Inceptisols in the relatively drier areas and Mollisols in the moister areas. Methods applied are field survey, standard physico-chemical analyses, and soil micromorphology. CaCO3 content, P, OM and CEC show irregularly trending values throughout the profiles. Micromorphology shows abundant content of charred components throughout the profiles and slight discontinuous carbonate recrystallization, mostly biogenic. Based on these observations, the main parent material was determined to be local soil that was redeposited by workforce as fill material for terracing. We further interpret that pedogenesis mainly involved structure development under the influence of anthroturbation and bioturbation, inheritance of ex situ aggregates from parent soil, reaggregation with little occurrence of organic matter, and low levels of lessivage and CaCO3 redistribution. We found that pedogenesis in these terraces started in a chaotic manner, considerably faster than pedogenesis in natural soils, primarily influenced by the act of terracing, the maturity of its inherited parent soil material, and relatively large depth. Therefore, early stages of terrace soil development can differ greatly from known soil models, questioning paradigms of pedogenic ‘time zero’ and ‘maturity’ in terrace soil. We suggest four terrace fill settings for terrace material and propose a model for the state of entropy and development of terrace soils. We classify the studied soils as Archaeo-Anthroportic Xerorthents, (Anthrosols (Calcaric, Escalic)), and Archaeo-Anthroportic Typic Haploxerolls (Anthrosols (Calcaric, Escalic, Relocatic, Anthromollic)), both overlying buried Inceptisols (Cambisols). Our primary conclusion is that terrace soils should be separately classified and mapped by treating terracescapes as distinct morpho-stratigraphic units in which age is the same as the age of their geomorphic surface. This study advances the pedological understanding of archaeological stone-wall bench terraces and identifies gaps in the understanding of terrace soils. We acknowledge the review of Brian Needelman, who highly advanced the pre-submission version of this paper. We thank Georges Stoops for his essential comments and advice. We appreciate the suggestions made by Jaume Boixadera, Jérôme Juilleret, Hanna Koyumdjisky, Sara Vero and Eric Verrecchia. Jonathan Gottlieb (University of Haifa) prepared the thin sections. Basic soil analyses were done by Yelena Schukin (Zemach E. Agriculture technologies). Gypsum analysis was done by Montserrat Antúnez (UdL). PSD was analyzed by Ruth Binstock and Yael Jacoby-Glass (Geological Survey of Israel). This research was partly supported by the United States-Israel Binational Science Foundation grant 2014-341. Yafa Naftalovitch and Rachel Yonayov (BGU) provided the kindest and most efficient administrative assistance. We acknowledge the review of three anonymous reviewers, who substantially contributed to this paper. Danny Itkin wishes to thank his family.

Convex, soil-covered hillslopes are ubiquitous in various tectonic and climatic settings and their morphologic characteristics can be significantly altered by dust flux and chemical weathering. Carbonate hillslopes across the Eastern Mediterranean display a classic convex morphology despite high rates of dust deposition, which are apparently similar in magnitude to denudation rates and despite a highly soluble bedrock lithology. These high rates of dust flux and bedrock dissolution result in soil composition which is strikingly different from the underlying bedrock. In this study we apply a modified regolith mass balance equation which includes dust input and chemical depletion and utilize a combination of field work and geochemical methods (immobile and major elements, XRD) to estimate the fraction of dust-derived materials in the soil and the fraction of the soil that was lost via dissolution. Soil and bedrock were sampled at 7 Eastern Mediterranean study sites, across a prominent north-to-south gradient in both precipitation (250 to 900 mm yr−1) and dust flux (150 to 40 g m−2 yr−1) and compared with dust composition. Our results indicate that the dust fraction in the soil correlates with modern measurements of dust deposition rates and decrease from nearly 100% of the 2 mm) indicating that mechanical weathering of the underlying bedrock contributes to regolith formation and plays a role in shaping carbonate hillslopes. Using a commonly used soil transport model, we show that the observed dust fraction and chemical weathering can potentially account for a 50% change in hillslope curvature. Furthermore, the predicted steady state hilltop curvature, based on our results, fits well the observed curvature based on high-resolution LiDAR-derived topographic data. Our results highlight the potential importance of dust and chemical weathering in soil production formulations and hillslope evolution models and we propose that these contributors to soil mass balance could also be relevant for silicate terrain. In addition, we also demonstrate that the source material of Mediterranean soils varies with environmental factors such as rainfall, dust deposition rates and bedrock mechanical properties.

In order to study the dynamics of sediment fluxes at the northern end of the Nile littoral cell, sediment traps were deployed for one year over the shallow shelf of the Mediterranean Sea offshore Israel. The sediment traps (replaced monthly) were suspended on a mooring line two kilometers offshore of the Hadera power station, 10 m above a 25 m deep seafloor. Sea-state conditions near the traps were measured by an acoustic Doppler profiler that provided the bottom water temperature, wave heights and current's velocities and direction. The measured sediment fluxes greatly varied between sampling periods, with a minimum value of 1.8 g m−2 d−1 in autumn and a maximum value of 83 g m−2 d−1 in winter. This variation was mostly effected by wave-induced resuspension of sediment. A strong correlation (R2 = 0.97) was found between integrated wave heights that exceeded 1.5 m and the measured sediment fluxes. Based on the sea state conditions and sediment trap data we conclude that the direction of sand transport at the study area was strictly northwards and that almost all of the annual sand transport occurred during several high-energy events in the winter. Fine particles that consisted the majority of the mass flux were absent in the underlying, 25 m deep, seafloor suggesting that they are very effectively winnowed off beyond the sand strip.

Long-term relationships between climate and dust emission remain unclear, with two prevailing but opposite hypotheses for effects of climate shifts: (1) increased dust emission due to increasing aridity imposing a vegetation change, or (2) decreased dust emission due to increasing aridity which imposes less stormy climate and reduced sediment supply. Here we test these hypotheses by analyzing an ~11-m-long core archiving Holocene dust trapped in Montezuma Well, a natural sinkhole in Arizona (southwestern United States), alongside current dust sources and transport pathways. Major elements indicate that Montezuma Well sediments originate from two end members: local carbonate bedrock and external siliceous dust. Core sediments are similar to the adjacent siliceous soils accumulated atop the bedrock, pointing to their eolian origin. Particle-size distributions reveal fine dust transported during winter from the northwestern Sonoran Desert and the Mojave Desert and coarse dust transported during summer from the southwestern Sonoran Desert, similar to current climate systems and dust pathways. A survey of potential dust sources indicates that current summer and winter dust sources in the Sonoran Desert are under a supply-limited state. Dust fluxes were higher during wetter phases of the Holocene when winter sources dominated. During the middle Holocene drought, dust fluxes were minimal and dominated by summer sources until dust input ceased as drought conditions did not produce enough floods to refill sources with sediments. We propose that in the Sonoran Desert, dust emission is strongly connected with climate, increasing during humid intervals and enhanced by fluvial sediment replenishment at dust sources.

Hyperarid (< 80 mm yr-1) soils in hot deserts are characterized by accumulations of soluble salts (gypsum and halite) in diagnostic horizons as a result of limited moisture availability. In most desert terrains, the source for pedogenic gypsum and halite is atmospheric dust and rainwater. The interplay between climatic properties such as frequency and intensity of rain events, rainfall composition, dust flux, and evaporation rates, govern the depth and concentration of these salts. Better understanding of these relationships can improve our estimation of regional paleoenvironmental and paleoclimate conditions. Up to date, only empirical correlations between annual rainfall and pedogenic salt horizons are available.The goals of this study are to: 1) quantify rates of pedogenic gypsum accumulation with time and the role of controlling climatic conditions that govern its accumulation, 2) estimate the most likely climatic scenarios that led to the formation of the diagnostic gypsic horizon developed in late Pleistocene (~ 60 ka) abandoned alluvial fan surfaces in the hyperarid Negev desert, southern Israel. To achieve these goals, we constructed a compartment model that simulates gypsum accumulation in soil and tests its sensitivity to various changes in the long-term climate properties. The model predicts gypsum content and depth of accumulation in the soil profile over thousands of years and more. The input parameters are stochastically simulated rainstorms, evaporation, dust flux, and sulfate concentration in rainwater, at daily time steps. The model was tested and calibrated using data of Holocene (< 11 ka) soil profiles developed on stable alluvial fans in the hyperarid Negev. With the assumption that the climate during the Holocene was not much different than today (i.e., mean annual rainfall < 50 mm). Sensitivity analyses indicate that gypsum accumulation is highly sensitive to mean annual rainfall and sulfate concentration in rainwater. Synthetic gypsum profiles were calculated using different climate scenarios and compared to late Pleistocene soils. Our results suggest that: (a) gypsum accumulation in late Pleistocene soils cannot occur simply by extending current climate conditions for a much longer duration. (b) The plausible climate scenarios for the late Pleistocene must include additional rain input (1.5 – 2.0 times than mean annual rainfall today) and increased sulfate concentration in rainwater (2.0 – 2.5 times than today) to successfully reconstruct the observed accumulated gypsum in mature (60 – 12 Ka) soil profiles.

Quaternary loess covers desert margins and vast areas of the Negev, southern Israel. The Negev loess is among the best-studied desert loess, with research going back to the early 20th century. The contrast between carbonate rocks of the Negev and its silicate-rich coarse-silt loess allows determining the loess sources, learning the synoptic-scale paleoclimatology, and exploring processes of coarse silt formation. Here, we present an overview of new perspectives on the origins and climatic significance of the Negev loess, expand on how (a) coarse silts affected soils farther downwind, and (b) how the loess has now turned into an active dust source.The sources of the Negev loess are the (a) distal Sahara and Arabia delivering fine silts and clays, transported over thousands of kilometers, and (b) proximal sand dunes in Sinai and Negev, advancing and concurrently supplying the coarse silts to the loess accretion through eolian abrasion of sand grains. It was found that the coarse silts which compose the majority of the loess, commenced during the late middle Pleistocene – early late Pleistocene, coeval with the appearance of the advancing Sinai/Negev sand dunes and the first coarse silt accretion in regional soils; The main loess formation episode is ~95-10 ka, when the dunes appeared in the Negev. Within the loess, the dust mass accumulations rates (MAR), and consequently, soil formation rates, spatiotemporally vary according to specific site location and distance relative to the proximal sources. With increasing distance beyond the loess zone, both dust MARs and grain size gradually decrease; thus, whereas Mediterranean mountains located in central Israel, tens of kilometers downwind the loess, exhibit thick soils on top of the carbonate bedrock, the even wetter regions in northern Israel, located hundreds kilometers away from the loess, exhibit only thin soils. Thus, in Mediterranean regions located at the desert fringe, coarse silt influx is one of the main factors in determining the environmental sustainability, rather than only the precipitation amount.During the Holocene, dust MARs in the Negev were much lower than late Pleistocene ones, and loess was not formed. Recently, the Negev loess became a prime source of dust mainly due to anthropogenic interferences, contributing to the regional dust cycle, and thus, at present the loess zone is a dust source rather than a dust sink. Today, the Negev loess is a non-replenishable natural resource that is slowly eroding and disappearing from the landscape.

In this study we (1) mapped the areal extent of current dust sources over Northern Africa between 8°W–31°E and 22°N - Mediterranean coast; and (2) identified and characterized the geomorphic units and soil types that emit dust from these areas. We used the full resolution (3 km) data from the MSG-SEVIRI to map dust sources over a 2-year period between 2005–2006, and examined these regions with remotely sensed images and geomorphic and soil maps. A total of >2600 individual dust emission events were mapped; with frequency up to 34 events in the 2-year study period. The areal extent of dust emission sources exhibited a lognormal distribution with most sources ranging from 20 to 130 km2. Most dust events were singular and related to a variety of specific geomorphic units. Dust events that created hotspots were mostly located over playas and fluvial landforms, and to a lesser extent over sand dunes and anthropogenic affected regions. About 20% of dust hotspots were offset a few kilometers from clear geomorphic units. Quantitative analysis of emissions revealed that dust sourced from various geomorphic units, among them playas (12%) and fluvial systems (10%). The importance of sand dunes as dust-emission sources greatly differs between examined datasets (7% vs. 30%). Our study emphasizes the importance of scattered dust emission events that are not considered as hotspots, as these sources are usually neglected in dust emission modeling.

Soil hydrophobicity was extensively investigated in the context of fire-induced, naturally-occurring and wastewater related hydrophobicity. Oil-induced soil hydrophobicity, however, received much less attention and was not yet investigated under regions characterized by hyper-arid climate. In this study, we investigate the hydrological effects and the persistence of oil-induced soil hydrophobicity in Evrona nature reserve located in the hyper-arid region of southern Israel. The Evrona nature reserve has experienced two oil spills that occurred in 1975 and 2014, providing a unique opportunity to study the hydrophobicity of oil-polluted soils over time. In this study, we 1) apply field monitoring to investigate how the severe hydrophobicity affects water flow in the polluted soils, and 2) conduct laboratory incubation experiments to assess the natural attenuation of hydrophobicity and its relation with the content and composition of hydrocarbons.We set up two monitoring stations in two adjacent streams, of which one is polluted and the other is clean. In each section, an array of water content sensors was installed. Analyses of data measured during two years reveal that during rain and runoff events infiltration in the oil-contaminated soil was much lower relative to the clean soil. Furthermore, infiltration in the oil-contaminated stream showed highly preferential patterns, typical of hydrophobic soils. The reduced infiltration and the establishment of preferential flow paths may lead to negative consequences including increased runoff and erosion, reduction in the water available to native plants, and the generation of fast conduits for contaminant transport.In the second part of the research, incubation experiments were conducted with contaminated soils from the 2014 and 1975 sites. Soils were treated with the addition of either water alone or different combinations of water, nutrients and surfactant. Treated soils were sampled periodically to assess soil hydrophobicity and hydrocarbon content. The results show a concomitant decrease in the hydrophobicity and hydrocarbon content in soils to which water or water and nutrient and/ or surfactants were added. The fastest hydrophobicity reduction was observed in soil to which both nutrients and surfactants were added, while when only water was added to 50% saturation, degradation and hydrophobicity reduction were very slow. Overall, during the one year and a half incubation, the total petroleum hydrocarbon of the treated soils decreased by 40% in the 2014 soil and by up to 80% in the 1975 soil. However, although hydrophobicity was reduced during incubation, the soils still remained severely hydrophobic. This suggests that considering the concentration of hydrocarbons as the sole criterion for the endpoint of soil remediation is not sufficient and the degree of soil hydrophobicity should be evaluated as well.

Convex soil-covered hillslopes are ubiquitous in various tectonic and climatic settings and are often modeled based on a mass balance relating hillslope convexity to regolith transport and soil production. In order to account for chemical weathering of carbonate rocks and dust input to the regolith, two fluxes that are commonly neglected in settings with silicate-dominated bedrock, we modify this mass balance.We studied 7 study sites in carbonate rocks across an Eastern Mediterranean gradient in the mean annual rainfall (250 to 900 mm yr-1) and dust flux (150 to 40 g m-2 yr-1). Combining cosmogenic 36Cl-derived hilltops denudation rates with an estimate of the regolith chemical depletion and dust fraction based on immobile elements, we predict the hillslope curvature and compare our predictions with observations based on high-resolution airborne LiDAR.Our results demonstrate that soft carbonates (chalk) experience faster denudation rates relative to resistant dolo-limestone. However, the harder carbonates are more prone to chemical weathering, which systematically constitutes around half of their total denudation. Soil production rates exhibit a humped dependency on soil thickness, with an apparent maximum at a depth of 8-16 cm.The observed hillslope curvature vary as function of rainfall and dust flux with a minimum at sub-humid sites with intermediate rainfall of 500-600 mm/yr. The predicted curvature based on our new mass balance is not far from the observed curvature, illustrating the prominent effects of dust flux and chemical weathering on hillslope morphology. Our model also implies that drier sites in the south probably experienced a more complex history of regolith production due dust flux fluctuations.By incorporating dust flux and chemical weathering to the classic hillslope evolution model we identify a complex relation between hillslope curvature, soil production, and climate. These two fluxes are not unique to carbonate bedrock and should be incorporated in hillslope evolution models.

Tells (archaeological mounds) predominantly consist of poorly consolidated to unconsolidated sediments, and soils that are highly anthropogenic. This study examines pedogenic processes related to carbonate mobilization in tells in comparison with their peripheral soils (reference soil profiles). The key objective of this study is to test the hypothesis that tell deposits evolve through concurrent processes of sedimentation and pedogenesis (synlithogenic pedogenesis), and further explain it. Case studies are presented from three tells in semi-arid and Mediterranean climatic zones of the Levant. The methods applied included field survey, analyses of particle size distribution, pH, %CaCO3 and organic carbon content, and soil micromorphology. Soils of the tells contain miscellaneous cultural materials that derive mainly from degraded mud bricks, pottery and burnt wood. Chemical data show basic pH values, high CaCO3 content, and minor amounts of organic carbon. Field observations and lab analyses both indicate high similarity amongst the tells and their reference soil profiles. Buried tell soils show same characteristics as near-surface soils. However, the reference soil profiles show incipient horizonation, slightly darker colours, and more developed structure. Micromorphology of both the tells and the reference profiles show cohesively welded peds in a vughy microstructure, groundmass with an open porphyric c/f-related distribution, and discontinuous carbonate recrystallization. Relative rates of soil formation in the tells can be estimated when archaeological records are established. Contrary to the tells, the reference soil profiles show lower porosity and only minor remnants related to earth construction materials. We classify the soils of the studied tells as archaeological Calcareous Anthraltic Xerorthents. The correlative WRB classification would be Calcic Urbic Technosols (Archaic). The anthropogenic materials are as calcareous as the natural soils, but due to human action, carbonates in the tells are distributed differently. Based on these observations, ancient human actions and the dry climate have led to very little mobilization and accumulation of carbonates. The information provided in this study adds to the pedological understanding of archaeological environments. Specifically, it can be useful for the study of site formation processes of tells.

A common spatial feature within loess deposits worldwide is a downwind decrease in thickness and grain size, trends that are powerful tools for reconstructing paleowinds and past atmospheric circulation. Although such trends have been identified, there is limited knowledge of similar trends farther downwind from the loess region, where eolian influx can influence soil formation and hydrological processes. To examine these impacts we studied Quaternary sequences in prehistoric sites in Jerusalem, located only ∼50 km downwind from the edge of the Negev loess. All sequences are composed of two units separated by an unconformity. The lower unit is of middle Pleistocene age, it is composed of unimodal clay to silty clay dust deposits with chert clasts and Lower-Middle Paleolithic artifacts. A non-deposition interval characterized the middle to late Pleistocene transition, when dust accumulation rates were low. The upper unit age is late Pleistocene to Holocene; it is composed of bimodal silty clay to silty clay loam. Quartz, K-feldspars, and plagioclase contents together with the location and amplitude of grain-size coarse mode increase up-sequence. The addition of coarse silts to the upper unit of the sequences was coeval with episodes of loess accretion in the Negev. These silts were generated most likely by eolian abrasion of sand grains in the upwind dunes. Similar to the Negev, the addition of silts resulted in burial of the drainage network and reduced runoff and soil erosion rates. We stress the importance of desert loess in determining soil composition and surficial hydrology in wetter areas located in adjacent downwind regions.

The present study sought to quantitatively characterize the live and dead benthic foraminifera communities of the deep southeastern Levantine basin of the Mediterranean Sea (33.4o–31.7 oN, 31.3o–34.9 oE; 100–1900 m water depth) and their relationships to environmental conditions. Box corer samples were collected at 50 sites between June and July 2013. The foraminiferal macrofauna (> 250 µm) were enumerated and identified (76% to the species level). Six live foraminiferal assemblages were identified, inhabiting six biotopes, the shelf margin (SM), two upper continental slopes (UCS1 and UCS2), the lower continental slope (LCS), the eastern bathyal plain (EBP) and the western bathyal plain (WBP). The dead communities were divided into four biotopes, generally compatible with the live ones, excluding the UCS2 and the EBP. The foraminiferal density in the various live biotopes was relatively stable across the studied area, excluding the UCS2 and EBP, unlike the density of the dead shells, which increased with depth. The number of taxa per biotope was estimated by rarefaction curves and compared to the observed numbers, with a decreasing number of live taxa with water depth. The alpha-diversity, which was evaluated in relation to the number of sampled individuals, reached an asymptote in all biotopes, with very low values in the WBP. The within-biotope heterogeneity was evaluated by the average Chao-Sorensen similarity index and by a beta-diversity index (exp(gamma diversity) - exp(alpha diversity)), revealing variable heterogeneities in both assemblages. Water depth, sediment grain size mode, CaCO3 (wt%), and clay fraction (wt%) were jointly but feebly correlated with live faunal composition.

Although hillslope evolution has been subject to much investigation for more than a century, the effect of climate on the morphology of soil-mantled hillslopes remains poorly constrained. In this study, we perform numerical simulations of volcanic cinder cones in the Golan Heights (eastern Mediterranean) to estimate soil transport efficiency across a significant north–south gradient in mean annual precipitation (1100 to 500 mm). We use the initial cinder cone morphology (constrained by stratigraphy), the modern hillslope form (surveyed with sub-meter accuracy) and the eruption age (based on 40Ar–39Ar chronology) to predict the best-fit value of the soil transport coefficient (‘diffusivity’) based on a nonlinear transport model. Our results indicate that the best-fit diffusivity (K) varies from 1 to 6 m2 ka−1 among the five cinder cones in our field area. Diffusivity (K) values vary systematically with precipitation and hillslope aspect; specifically, K is higher on south-facing (drier) hillslopes and decreases with mean annual precipitation. We interpret this climate dependency to reflect vegetation-driven variations in apparent soil cohesion, which increases with root network density, and attenuation of rain splash and overland flow erosion, which increases with vegetative ground cover. To assess how vegetative root mass and ground cover vary with precipitation and aspect, we quantified the spatial distribution of NDVI (normalized difference vegetation index) from ASTER satellite images and observed spatial variations that correlate with our calibrated values of K. Analysis of previously studied cinder cones in the USA can be used to extend our framework to arid domains. This endeavor suggests a humped relationship between K and precipitation with maximum diffusivity at mean annual precipitation of 400–600 mm. Copyright © 2017 John Wiley & Sons, Ltd.

Meso-scale weather systems, such as convective haboobs, are considered to be an important dust generation mechanism. In Israel, however, rather than of meso-scale weather systems, most dust storms are generated by synoptic-scale systems, originating from Sahara and Arabia. Consequently, only distal sources of suspended and deposited dust in Israel are currently reported. Here we report the first detailed study on the merging of synoptic- and meso-scale weather systems leading to a prominent dust outbreak over the Negev, Israel. During the afternoon of May 2 nd , 2007, a massive dust storm covered the northern Negev, forming a one kilometer high wall of dust. The haboob was associated with PM 10 concentrations of 1000–1500 μg m −3 that advanced at a speed of 10–15 m s −1 and caused temporary closure of local airports. In contrast to most reported haboobs, this one was generated by a sea breeze front acting as a weak cold front enhanced by a cold core cyclone positioned over Libya and Egypt. The sea breeze that brought cold and moist marine air acted as a gravity current with strong surface winds. The sources for the haboob were the loessial soils of the northwestern Negev, especially agricultural fields that were highly disturbed in late spring to early summer. Such surface disturbance is caused by agricultural and/or intensive grazing practices. Our study emphasizes the importance of local dust sources in the Negev and stresses loess recycling as an important process in contemporary dust storms over Israel.

We quantify the volumetric erosion of Israel's actively retreating Mediterranean coastal cliffs between 2006 and 2015 with airborne LiDAR. Our results reveal annual sand contribution of ~ 45,000 m3 from the coastal cliffs into the Nile's littoral cell (NLC), which amounts to ~ 50% of the annual long-shore sand transport previously measured at the northern termination of the NLC. Accordingly, we find that implementation of cliff-retreat mitigation engineering efforts planned for Israel's coastline can lead to a sand deficit in the NLC that may result in increased beach erosion.

The River Nile catchment is considered the major source of nutrient-rich freshwater and sediment draining into the eastern Mediterranean Sea. Thus, exceptional high-resolution record from the Nile Littoral Cell likely traces changes in the Nile outflows related to climatic changes driven by the monsoonal system. This study used multi-proxy analyses combining sedimentological, geochemical and organic stable isotope data along with foraminiferal data in a southeastern Levantine inner shelf sedimentary sequence to understand Mid - to Late Holocene northeast African climate variability. The palynological record is used to reconstruct local scale changes in the regional vegetation related to the Mediterranean climate system. The analyzed records reveal multi-decadal to centennial pacing of paleoceanographic and paleoclimatic changes, with most prominent events recorded at 4.28, ∼3.6 and at 2.9 kyr BP. These transitional periods characterized by simultaneous high δ15N values and low total organic carbon (TOC) suggest drier climatic conditions, decrease in Nile discharge, leading to lower nutrient supply. A stable and arid climate during Mid-Late Holocene (∼4.5–3.6 cal kyr BP) associated with a weaker monsoon system as well as with a weaker Mediterranean climate system is indicated based on high and constant sedimentation rates (∼400 cm kyr−1), along with relatively stable values and only occasional weak fluctuations documented in all of the proxies. This climatic pattern is punctuated by a peak in maximum aridity at 4.28 kyr BP evidenced by low TOC value and low arboreal pollen (AP) and Artemisia/Chenopodiaceae (A/C) pollen ratios and the sharp decline in the abundance of benthic foraminifera Cribroelphidium poeyanum and Valvulineria bradyana. This change corresponds with the well-studied 4.2 kyr BP drought event in the Middle East, Mesopotamia and south Asia. During the late Holocene (∼3.6–2.8 cal. Kyr BP) the climate became unstable characterized by shifts between relatively wetter and drier conditions as evident in considerable fluctuations in all proxies. Maximum positive excursions of TOC values, C/N ratio along with high dominance of opportunistic foraminiferal species (e.g., Ammonia tepida) indicate northeast African wetter conditions and increased Nile discharge at 3.5, 3.3, 3.2 and 3.0 kyr BP. The distinct and abrupt transition from a stable to an unstable climate regime around 3.6 kyr BP may have been influenced by the Thera volcanic eruption. Thus, the sedimentary record investigated in this study may provide evidence for the impacts of this well-known volcanic eruption not just on the climate regime in the Levant but also on the ancient Near East and Egypt.

Far’ah II is an open-air site in the north western Negev desert (Israel). Previous excavations in the 1970’s revealed a rich, in situ Middle Paleolithic (MP) assemblage composed of flint and limestone artifacts, animal bones and charcoal. Renewed excavation at the site were undertaken in 2017, to re-date it and provide a more accurate constrain to the sites’ age, as well as collect samples for paleoclimatic proxies. Our new Optically Stimulated Luminescence and 14C ages together with the stable oxygen isotope signature of the loess sediments, constrain the age of the upper archaeological horizon to

Kalahari Group sediments accumulated in the Kalahari basin, which started forming during the breakup of Gondwana in the early Cretaceous. These sediments cover an extensive part of southern Africa and form a low-relief landscape. Current models assume that the Kalahari Group accumulated throughout the entire Cenozoic. However, chronology has been restricted to early–middle Cenozoic biostratigraphic correlations and to OSL dating of only the past ~ 300 ka. We present a new chronological framework that reveals a dynamic nature of sedimentation in the southern Kalahari. Cosmogenic burial ages obtained from a 55 m section of Kalahari Group sediments from the Mamatwan Mine, southern Kalahari, indicate that the majority of deposition at this location occurred rapidly at 1–1.2 Ma. This Pleistocene sequence overlies the Archaean basement, forming a significant hiatus that permits the possibility of many Phanerozoic cycles of deposition and erosion no longer preserved in the sedimentary record. Our data also establish the existence of a shallow early–middle Pleistocene water body that persisted for > 450 ka prior to this rapid period of deposition. Evidence from neighboring archeological excavations in southern Africa suggests an association of high-density hominin occupation with this water body.

This study estimates the relative magnitude of decadal-scale soil redistribution (i.e., soil loss or gain) by slope wash using 137Cs inventories measured in 46 soil profiles at four study sites in the Ft. Irwin area of the Mojave Desert of California, USA. The variability in 137Cs inventories on a

The present study sought to quantify the infauna and environmental characteristics of the deep SE Levantine Basin, Mediterranean Sea (33.4–31.7 N, 31.3–34.9E; 100–1900 m water depth). Box corer samples were collected at 50 sites in June–July 2013. The infauna (>250 μm) were enumerated and identified to the lowest possible taxonomic level (~37 % to the species level). Three faunal assemblages were identified, inhabiting three biotopes, the shelf margin (SM), the continental slope (CS) and the bathyal plain (BP). The within-biotope heterogeneity was evaluated by the average Chao-Sorensen similarity index and the beta diversity (exp(gamma diversity)—exp(alpha diversity)), revealing values of 0.64–0.7 and 1.73–2.77, respectively, upon applying the pooled bathyal plain samples. The corresponding non-pooled samples revealed higher heterogeneity, with values of 0.26 and 6.27, respectively, likely due to insufficient sampling. The infaunal density in the various biotopes (geometric mean 59–2220 ind m− 2) exhibited a logarithmic decline with water depth. The estimated number of taxa per biotope was calculated by rarefaction analysis in relation to the sampled area and the number of sampled individuals, resulting in 203 (sampled area)−206 (number of individuals) (SM), 170–163 (CS) and 144–130 (BP) taxa. The rarified alpha diversity in relation to the sampled area revealed decreasing values toward the deeper biotopes. However, similar rarified alpha diversities were found in all the biotopes in relation to the number of sampled individuals. Water depth, sediment grain size mode, CaCO3%, and clay% were jointly correlated with faunal composition; water depth provided the single strongest correlate.

The Chinese Loess Plateau (CLP) is a large, spatially well defined and persistent zone of loess accumulation developed near the fluctuating northwest margin of the East Asian monsoon. Many studies have analyzed its loess sediments to provide insights into paleoclimatic conditions. Although spatial and temporal variations in the grain sizes of CLP sediments are fundamental to this effort, controversy over the origin of the dominant coarse quartz silt has limited interpretations. Reexamination of the spatial pattern of grain-size distribution across the CLP and a field-scale experiment conducted in the Gobi Desert revealed a genetic association between the coarse silt fraction of the loess and primary production of coarse silt through eolian abrasion of sand in the proximal Mu-Us, Tengger, and Badain Jaran sandy deserts. Our results demonstrate the effectiveness of eolian abrasion of quartz sand in primary coarse silt production in Central Asia and identify this process as the most consistent with the wellrecognized systematic northwest-southeast depositional pattern of the CLP. We suggest that only abraded coarse quartz grains transported short distances by long-term persistent eolian activity can build up thick loess sequences to form a massive and spatially well defined loess plateau. These results decouple the production and transport of coarse silt and finer silt and clay particles, which have a more distant and wider provenance, changing the constraints on previous paleoclimatic reconstructions. © 2013 Geological Society of America.

Soil thickness and soil texture, and their spatial variability at hillslope scales, are important inputs for hydrologic models. Recent studies have demonstrated that mechanistic models can accurately predict the spatial distribution of soil thickness in areas where soil thickness varies gradually along hillslope profiles. To date, however, these models have not been tested in arid regions, where soils are often thin and highly variable at small scales (i.e., 1–10 m) and where the influence of aeolian accretion on soil thickness and soil texture may be significant. In addition, most of the data available for the fraction of the soil derived from aeolian deposition (which can serve as a proxy for soil texture) originate from soils developed on stable depositional landforms; data for aeolian fractions from upland soils are scarce. In this study, we developed and tested a numerical model for the prediction of thickness and aeolian fraction of soils in arid upland areas. The model assumes a long-term balance between the rates of soil production from bedrock, aeolian accretion, and soil erosion. Rates of soil production are quantified in the model using the exponential and humped soil production functions, and soil erosion rates are quantified using the nonlinear depth- and slope-dependent transport functions, assuming that only the upper soil horizons (A + B) are capable of transport. The rate of aeolian deposition is assumed to be spatially uniform. We calibrated the three free parameters of the model at a site in the Mojave Desert with a granite lithology using a combination of 1) field-measured data for soil thickness and 2) estimation of the aeolian fraction in the soil using laboratory analysis of immobile element concentrations. We validated the model results in three nearby sites using a combination of measured soil thickness in soil pits and the presence/absence of soil, and laboratory analysis of the aeolian fraction of soil. The study area is characterized by generally thin soils (

The Batsheva de Rothschild Seminar on Atmospheric Dust, Dust Deposits (Loess) and Soils in Deserts and Desert Fringe: The Sahara-Sinai-Negev as an Analogue for the Global Arid Regions; Jerusalem and the Negev Desert, 14–19 October 2015

During the past three decades, the U.S. armed forces have been called on repeatedly to operate in the deserts of the Middle East and southwest Asia. Avoiding locations susceptible to extreme dust emissions and other terrain-related hazards requires the ability to predict soil and terrain conditions, often from limited information and under dynamic environmental conditions. This paper reports the approach used to develop an integrated, predictive tool for forecasting terrain conditions to support military operations in desert environments at strategic, operational, and tactical scales. The technical approach relies on the systematic integration of desert landform parameters in geomorphic models for predicting terrain conditions. This integrated effort is performed in a geographic information system (GIS) framework using expert-based analysis of airborne and spaceborne imagery to identify terrain elements. Advances in earth science research have established that unique, predictable relations exist among landscape position, soils, vegetation, and geology. Furthermore, new instrumentation allows the collection of a wide range of environmental information to characterize surface and subsurface conditions. By integrating models and methods from geomorphology, soil science, climatology, and atmospheric science with remote sensing and other technologies, a predictive model can be developed to support military operations.

The time at which deserts established their current arid or hyper-arid conditions remains a fundamental question regarding the history of Earth. Cosmogenic isotope exposure ages of desert pavement and welded, calcic–gypsic–salic Reg soils that developed on relatively flat alluvial surfaces ∼2 Ma ago in the Negev Desert indicate long geomorphic stability under extremely dry conditions. Over a short interval during their initial stage of development between 1–2 Ma, these cumulative soils are characterized by calcic soils reaching maximum stage III of carbonate morphology. This interval is the only period when calcic soil horizons formed on stable abandoned alluvial surfaces in the southern Negev Desert. Since ∼1 Ma pedogenesis changed toward more arid soil environment and the formation of gypsic–salic soil horizons that were later followed by dust accumulation. The dichotomy of only moderately-developed calcic soil (stages II–III) during a relatively long time interval (105–106 years) indicates an arid environment that does not support continuous development but only occasional calcic soil formation. The very low δ18O and relatively high δ13C values of these early pedogenic carbonates support soil formation under arid climatic conditions. Such an environment was probably characterized by rare and relatively longer duration rainstorms which occasionally allowed deeper infiltration of rainwater and longer retention of soil moisture. This, in turn enabled the growth of sparse vegetation that enhanced deposition of pedogenic carbonate. At ∼1 Ma these rare events of slightly wetter conditions ceased and less atmospheric moisture reached the southern Negev Desert leading to deposition of soluble salts and dust deposited in the soils. The combination of long-term hyperaridity, scarcity of vegetation and lack of bioturbation, salts cementation, dust accumulation and tight desert pavement cover, has protected the surfaces from erosion forming one of the most remarkably stable landscapes on Earth, a landscape that essentially has not eroded, but accumulated salt and dust for more than 106 yr.

The late middle Pleistocene initiation of loess accretion in the Negev Desert, Israel, resulted from a chain of events starting with the exposure of shallow offshore Nile delta sands beginning ∼180 ka, during a period of glacially lowered eustatic sea level. This exposure allowed the formation of the dunes of the Sinai-Negev erg and the eastward movement of the dunes under the gusty glacial-time winds in northern Sinai. This eastward dune advance occurred by eolian saltation that generated the coarse silts that accumulated downwind as loess. We postulate that the absence of earlier Negev loess is not a result of interglacial erosion as previously proposed but is due to the relatively recent convergence of the above conditions necessary for loess formation. We based our interpretation on analyses of two long-term natural dust traps and the association of coarse quartz silt production with the advancing quartz-rich dunes over this carbonate terrain. Although the Nile delta is considered an early to middle Pleistocene feature, and therefore could have been the source of sand throughout the Quaternary, it attained the shallow depth range of glacial-interglacial sea-level changes only during late marine oxygen isotope stage 7 to early stage 6, allowing its wide exposure. In Quaternary times prior to erg formation, Negev dust was finer, composed of silt and clays derived from distal sources in the Sahara and Arabian deserts.

Soils in similar geomorphic settings in hyperarid deserts (< 50 mm yr−1) should have similar characteristics because a negative moisture balance controls their development. However, Reg soils in the hyperarid southern Negev and Namib deserts are distinctly different. Soils developed on stable alluvial surfaces with only direct input of rainfall and dust depend heavily on rainfall characteristics. Annual rainfall amount can be similar (15–30 mm), but storm duration can drastically alter Reg soil properties in deserts. The cooler fall/winter and dry hot summers of the southern Negev Desert with a predominance brief (≤ 1 day) rainstorms result in gypsic-saline soils without any calcic soil horizon. Although the Namib Desert receives only 50–60% of the southern Negev annual rainfall, its rainstorm duration is commonly 2–4 days. This improves leaching of the top soil under even lower annual rainfall amount and results in weeks-long grass cover. The long-term cumulative effect of these rare rain-grass relationships produces a calcic-gypsic-saline soil. The development of these different kinds of desert soils highlights the importance of daily to seasonal rainfall characteristics in influencing soil-moisture regime in deserts, and has important implications for the use of key desert soil properties as proxies in paleoclimatology.

Quaternary desert loess and sandstone–loessite relationships in the geological record raise questions regarding causes and mechanisms of silt formation and accretion. In the northern Sinai–Negev desert carbonate terrain, only sand abrasion in active erg could have produced the large quantities of quartzo-feldspathic silts constituting the late Quaternary northwestern Negev loess. In the continuum of source (medium to fine sand of dunes) to sink (silts in loess) the very fine sand is unaccounted for in the record. This weakens the sand abrasion model of silt formation as a global process. Here, we demonstrate that, as predicted by experiments, abrasion by advancing dunes generated large quantities of very fine sand (60–110 μm) deposited within the dune field and in close proximity downwind. This very fine sand was generated 13–11 ka, possibly synchronous with the Younger Dryas under gusty sand/dust storms in the southeastern Mediterranean and specifically in the northern Sinai–Negev erg. These very fine sands were washed down slope and filled small basins blocked by the advancing dunes; outside these sampling basins it is difficult to identify these sands as a distinct product. We conclude that ergs are mega-grinders of sand into very fine sand and silt under windy Quaternary and ancient aeolian desert environments.