Age,origin and climatic controls on vegetated linear dunes in the northwestern Negev Desert (Israel)   总被引：1，自引：0，他引：1  

Joel Roskin  Naomi Porat  Haim Tsoar  Dan G. Blumberg  Anja M. Zander 《Quaternary Science Reviews》2011,30(13-14):1649-1674

The stabilized northwestern (NW) Negev vegetated linear dunes (VLD) of Israel extend over 1300 km² and form the eastern end of the Northern Sinai – NW Negev Erg. This study aimed at identifying primary and subsequent dune incursions and episodes of dune elongation by investigating dune geomorphology, stratigraphy and optically stimulated luminescence (OSL) dating. Thirty-five dune and interdune exposed and drilled section were studied and sampled for sedimentological analyses and OSL dating, enabling spatial and temporal elucidation of the NW Negev dunefield evolution.In a global perspective the NW Negev dunefield is relatively young. Though sporadic sand deposition has occurred during the past 100 ka, dunes began to accumulate over large portions of the dunefield area only at ～23 ka. Three main chronostratigraphic units, corresponding to three (OSL) age clusters, were found throughout most of the dunefield, indicating three main dune mobilizations: late to post last glacial maximum (LGM) at 18–11.5 ka, late Holocene (2–0.8 ka), and modern (150–8 years). The post-LGM phase is the most extensive and it defined the current dunefield boundaries. It involved several episodes of dune incursions and damming of drainage systems. Dune advancement often occurred in rapid pulses and the orientation of VLD long axes indicates similar long-term wind directions. The late Holocene episode included partial incursion of new sand, reworking of Late Pleistocene dunes as well as limited redeposition. The modern sand movement only reactivated older dunes and did not lengthen VLDs.This aeolian record fits well with other regional aeolian sections. We suggest that sand supply and storage in Sinai was initiated by the Late Pleistocene exposure of the Nile Delta sands. Late Pleistocene winds, substantially stronger than those usually prevailing since the onset of the Holocene, are suggested to have transported the dune sands across Sinai and into the northwestern Negev.Our results demonstrate the sensitivity of vegetated linear dunes located along the (northern) fringe of the sub-tropical desert belt to climate change (i.e. wind) and sediment supply.  相似文献   

Estimating ground water recharge using flow models of perched karstic aquifers   总被引：3，自引：0，他引：3  

Weiss M  Gvirtzman H 《Ground water》2007,45(6):761-773

The fraction of rain that is annually recharged to ground water is a function of the transient quantities of precipitation (wet vs. dry years) as well as other meteorological and geologic factors, and thus it is very difficult to estimate. In this study, we have used long records (20 to 30 years) of precipitation and spring discharge to reconstruct the transient character of yearly recharge. These data sets were used to calibrate numerical ground water flow models on the less than 3 km(2) scale for four separate perched karstic aquifers in the Judean and Samarian Mountains of Israel. The stratification and karstic character of the local carbonate rock aquifers cause ground water to flow through discrete dissolution channels and to discharge at isolated springs. An innovative, dual-porosity approach was used where a finite-difference solution simulates flow in the rock matrix, while the karstic channels are simulated using computationally simple drains. Perched conditions are also simulated innovatively using MODFLOW by treating the bottom unsaturated layer as if it is saturated, but by assuming zero pressure head throughout the "unsaturated" layer. Best fitting between measured and computed spring hydrograph data has allowed us to develop a set of empirical functions relating measured precipitation to recharge to the aquifer. The generic methodology presented gives insight into the suspected changes in aquifer recharge rates between particularly wet or dry years.  相似文献   

B and Li isotopes as intrinsic tracers for injection tests in aquifer storage and recovery systems     

Wolfram Kloppmann  Haim Chikurel  Géraldine Picot  Joseph Guttman  Marie Pettenati  Avi Aharoni  Catherine Guerrot  Romain Millot  Irina Gaus  Thomas Wintgens 《Applied Geochemistry》2009

Boron and Li isotopes have been tested as environmental tracers of treated sewage injected into a sandy aquifer (Shafdan reclamation project, Israel). During a 38 days injection test in a newly dug injection well, a conservative artificial tracer (Br⁻) was monitored together with δ¹¹B and δ⁷Li in the injectate, in the unsaturated soil zone (porous cup) and an observation well in the aquifer. In spite of B and Li concentrations in the injectate close to background values, significant shifts of the isotope signatures could be observed over the duration of the injection test. Boron isotope ratios show a breakthrough curve delayed with respect to Br⁻ breakthrough due to some reversible sorption on the aquifer material. No isotope fractionation was observed in the unsaturated or the saturated zone so that B isotopes can be considered as conservative in the investigated part of the aquifer system. Lithium isotopes are strongly fractionated, probably due to sorption processes. Lithium concentrations point to a Li sink in the system, δ⁷Li values vary strongly with a tendency of ⁷Li depletion in the liquid phase over the duration of the experiment. This is opposite to the expected preferential sorption of ⁶Li onto clay minerals. Boron isotopes reveals a valuable tracer of artificial recharge of freshwaters derived from treated sewage, both for short term tracer tests and for long-term monitoring of artificial recharge, even if in aquifers with higher clay contents, sorption-linked isotope fractionation cannot be excluded. More data are needed on Li isotope fractionation in natural groundwater systems to assess the potential of this tracer as monitoring tool.  相似文献   

Considered parameters in a least squares adjustment process     

Haim B. Papo 《Journal of Geodesy》1973,47(1):89-95

Least squares adjustment processes occasionally utilize constants with a known degree of uncertainty. If the covariance matrix of the adjusted parameters is estimated without considering those uncertainties the resulting estimate is invariably too optimistic. A method is proposed by which without altering the values of the adjusted parameters their a posteriori (after the adjustment) covariance matrix can be improved by the inclusion of the effect of uncertainties in the constants.  相似文献   

“A brief response to our critics”     

Oren Yiftachel Haim Yacobi 《Geoforum》2002,33(3):287

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Late Holocene climates of the Near East deduced from Dead Sea level variations and modern regional winter rainfall     

Yehouda Enzel  Revital Bookman  David Sharon  Haim Gvirtzman  Uri Dayan  Baruch Ziv  Mordechai Stein 《Quaternary Research》2003,60(3):263-273

The Dead Sea is a terminal lake of one of the largest hydrological systems in the Levant and may thus be viewed as a large rain gauge for the region. Variations of its level are indicative of the climate variations in the region. Here, we present the decadal- to centennial-resolution Holocene lake-level curve of the Dead Sea. Then we determine the regional hydroclimatology that affected level variations. To achieve this goal we compare modern natural lake-level variations and instrumental rainfall records and quantify the hydrology relative to lake-level rise, fall, or stability. To quantify that relationship under natural conditions, rainfall data pre-dating the artificial Dead Sea level drop since the 1960s are used. In this respect, Jerusalem station offers the longest uninterrupted pre-1960s rainfall record and Jerusalem rains serve as an adequate proxy for the Dead Sea headwaters rainfall. Principal component analysis indicates that temporal variations of annual precipitation in all stations in Israel north of the current 200 mm yr⁻¹ average isohyet during 1940–1990 are largely synchronous and in phase (70% of the total variance explained by PC1). This station also represents well northern Jordan and the area all the way to Beirut, Lebanon, especially during extreme drought and wet spells. We (a) determine the modern, and propose the past regional hydrology and Eastern Mediterranean (EM) climatology that affected the severity and length of droughts/wet spells associated with multiyear episodes of Dead Sea level falls/rises and (b) determine that EM cyclone tracks were different in average number and latitude in wet and dry years in Jerusalem. The mean composite sea level pressure and 500-mb height anomalies indicate that the potential causes for wet and dry episodes span the entire EM and are rooted in the larger-scale northern hemisphere atmospheric circulation. We also identified remarkably close association (within radiocarbon resolution) between climatic changes in the Levant, reflected by level changes, and culture shifts in this region.  相似文献   

Salt accumulation in the loessial sequence in the Be'er Sheva Basin,Israel     

Mordeckai Magaritz  Haim Gvirtzman  Arie Nadler 《Environmental Geology》1988,11(1):27-33

Evidence of climatic changes is recorded in the salt content of the surface sediments in arid zones. In wetter periods airborne salts are removed downward by leaching to the groundwater, whereas in drier periods they accumulate. The period of salt accumulation in the loessial sediments of the northern Negev is about 10,000 yr. This period represents the recent aridification phase. The beginning of this stretch of time followed the last humid period in the region. Top paleo soil (calcic horizon) found in the region and dated 12,000 yr B.P. is an indicator of this humid period. This article is a contribution from the Agricultural Research Organization, The Volcani Center, Bet Datan, Israel, No. 1751E, 1986 series.  相似文献   

Extended free net adjustment constraints     

Haim B. Papo 《Journal of Geodesy》1985,59(4):378-390

The contribution of geodetic measurements to the establishment of a control network can be partitioned into global and local (individual) components. The global component epitomized in a number of geometrically meaningful parameters can be estimated together with the individual point coordinates. The additional rank defect created by the extension of the parameter list is corrected by free net adjustment constraints which are extended beyond those needed for a solution of the network datum problem. Two applications of extended free net adjustment are outlined and illustrated by elementary numerical examples. A non-Cartesian (skew) reference system discussed in the Appendix provides an exotic interpretation of the estimated global and individual parameters. Prepared during a grant period (September 1984 through February 1985) while serving as a Visiting Senior Scientist in Geodesy, National Research Council, National Academy of Sciences, Washington, D.C.  相似文献   

Spatial and Temporal Characteristics of Saline Springs: Sea of Galilee, Israel   总被引：1，自引：0，他引：1  

Alon Rinimer  Shaul Hurwitz  Haim Gvirtzman 《Ground water》1999,37(5):663-673

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Rainfall, spring discharge and past human occupancy in the Eastern Mediterranean     

Nadav Peleg  Efrat Morin  Haim Gvirtzman  Yehouda Enzel 《Climatic change》2012,112(3-4):769-789

In ancient times human activities were tightly related and sensitive to rainfall amounts and seasonal distribution. East Mediterranean settlements were concentrated around numerous small to large springs, such as the Judean Mountains area. The goals of this study were to determine (a) the sensitivity of total discharge, recession curve, and response time of such springs to annual precipitation patterns, and (b) how spring hydrology responds to series of drought or wet years and to transitions from drought to normal and/or wet episodes (and vice versa). These goals were achieved by setting a finite-element hydro-geological flow model for selected perched springs that characterize the numerous springs throughout the carbonate karst terrain in the Judean Mountains. In addition, we estimated the effect of proposed regional past climate changes on the springs; in so doing, we transfer climate change to community size, livelihood and economic strength that were highly dependent on agricultural productivity. The results of the hydro-geological model revealed that these mountainous communities had the potential to prosper during historically wetter episodes and were probably adapted to short-term variability in annual rainfall. However, moderate to extreme droughts lasting only a few years could have led to a partial or even total abandonment of the springs as focal sites of intensive agricultural production. Spring drying eliminated the primary cause for the location of settlement. This occurred simultaneously in numerous settlements around the mountains of the southern Levant and therefore, must have caused dramatic economic and societal changes in the entire region, perhaps even resonating afar.  相似文献