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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.

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.

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.

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.

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

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.

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.

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.

Grain size analyses of three hilltop, primary eolian loess sequences in the Negev desert, southern Israel, show a bimodal grain-size distribution at 50–60 μm and 3–8 μm. Using analyses of mineralogy and OSL ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time, suggesting an enhancement of a time-transgressive proximal dust source compared to a distal, Saharan fine-grain dust. The only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into Sinai and the Negev concurrently with the loess accretion during the late Pleistocene as a result of the exposure of the Mediterranean shelf. We therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea. This relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as Northern Africa, China and Australia.

[1] Most wind erosion studies that characterize dust emission potential measure particulate matter smaller than 10 mm (PM10) for air quality purposes or atmospheric modeling. Because the PM10 size fraction is only a portion of the total range of fine‐grained particles potentially emitted from desert landforms, we modified the miniature Portable In Situ Wind Erosion Lab (PI‐SWERL) by adding a new instrument to measure total suspended particulate matter (TSP). The modified PI‐SWERL is capable of measuring TSP with diameters

[1] Although high-latitude loess sequences have been studied extensively for reconstructing past climates, loess in desert margins has been mostly overlooked. Moreover, many low-latitude loess studies have focused on secondary, reworked sequences for which paleoclimatic inferences are complicated owing to postdepositional processes acting under local control. In this respect, the spatial distribution of the loess and its different types are crucial. In this study, we differentiate primary and secondary loess using remote sensing and field criteria. We present remote sensing and geographic information system procedures for mapping loess distribution, in general, and for identifying pristine hilltop loess sequences in particular. Then, we present the mineralogical and textural analyses combined with optically stimulated luminescence ages of one such primary, hilltop loess sequence in the Negev desert that show that the late Pleistocene Negev loess started accumulating at ∼95 ka, much earlier than previously proposed (∼70 ka). It was preceded by a previously unknown middle Pleistocene period of loess formation at ∼180–130 ka. The ages also suggest that the threshold of dust accretion rate needed for loess formation is ∼0.02 mm a−1 (∼30 g m−2 a−1), a factor of 2 or more lower than previously thought (0.04 to 1.0 mm a−1). Our results also provide insights into causes of late Pleistocene loess accretion and its close association with regional dune field activity. The methodology for mapping the loess distribution may potentially be generalized to help understanding loess formation in other, more remote desert areas.