Amos Frumkin

Desert speleothems reveal climatic window for African exodus of early modern humans

One of the fi rst movements of early modern humans out of Africa occurred 130–100 thousand years ago (ka), when they migrated northward to the Levant region. The climatic conditions that accompanied this migration are still under debate. Using high-precision multicollector– inductively coupled plasma–mass spectrometry (MC-ICP-MS) U-Th methods, we dated carbonate cave deposits (speleothems) from the central and southern Negev Desert of Israel, located at the northeastern margin of the Saharan-Arabian Desert. Speleothems grow only when rainwater enters the unsaturated zone, and this study reveals that a major cluster of wet episodes (the last recorded in the area) occurred between 140 and 110 ka. This episodic wet period coincided with increased monsoonal precipitation in the southern parts of the SaharanArabian Desert. The disappearance at this time of the desert barrier between central Africa and the Levant, and particularly in the Sinai-Negev land bridge between Africa and Asia, would have created a climatic “window” for early modern human dispersion to the Levant.

The Sahara–East Mediterranean dust and climate connection revealed by strontium and uranium isotopes in a Jerusalem speleothem

This paper explores the potential of Sr and U isotope systems in speleothems as tracers of eolian dust transport and hydrological conditions. The study focuses on a speleothem from Jerusalem spanning the past 220 kyr. This speleothem provides a precisely dated record of dust flux from the Sahara to the East Mediterranean. Enhanced dust flux and Terra Rossa soil development are reflected by elevated 87Sr/86Sr ratios in the speleothem (0.7082–0.7086), while lower 87Sr/86Sr ratios (∼0.7078) indicate higher contribution of the local bedrock due to low dust flux and low soil accumulation. The strontium isotope system in the speleothem is a robust monitor of the Sahara monsoon-modulated climate, since dust uptake is related to development or reduction in vegetation cover of Sahara soil. The [234U/238U] activity ratios in the speleothem range between 1.12 and 1.0. The high activity values may indicate selective removal of 234U from the soil while the low values converge to the bedrock. The migration of 234U to the cave reflects mainly the regional hydrological conditions that are modulated by the North Atlantic–Mediterranean climate system. Thus, the speleothem provides a combined record of the monsoon–North Atlantic climatic systems. Long-term stability in glacial 87Sr/86Sr ratios (0.7083±0.0001 over the past 220 kyr) suggests an overall similarity in eolian dust sources, and uniformity in the synoptic conditions that dominate the dust storm tracks during glacial periods.

Paleoclimate and vegetation of the Last Glacial Cycles in Jerusalem from a Speleothem Record

A speleothem isotopic record taken from Jerusalem is used to reconstruct regional climate over the last 170,000 years. Glacial periods in Jerusalem were generally cooler and wetter than the present climate. Stage 5e in the desert margin of Jerusalem was extremely unstable, dry, and warm, and instability persisted throughout the transition to glacial conditions. The climate after stage 5e became gradually cooler and wetter over a 20,000-year interval and did not recover to interglacial conditions in stages 5c and 5a. The δ 13 C varied by up to 12‰, from glacial (stages 6, 4, 3, 2) values of -10 to -12‰ that reflect dense C 3 vegetation above the studied cave, and up to 0‰ in early stage 5 when there was probably complete loss of vegetation. The climatic instability during interglacial periods is much larger than during glacial periods, and glacial/interglacial transitions do not behave the same in each climatic cycle in this region.

Possible paleohydrologic and paleoclimatic effects on hominin migration and occupation of the Levantine Middle Paleolithic

This paper explores the impact of major glacial/interglacial paleohydrologic variations in the Middle-Paleolithic Levant on hominin migration and occupation. The climatic reconstruction is based primarily on the most straight-forward paleohydrologic records recently published. These terrestrial proxies convey direct paleoenvironmental signals of effective precipitation and aquifer recharge. The two main proxies are temporal changes of terminal lake levels in the Dead Sea basin and periods of deposition or non-deposition of speleothems. Other records, such as stable isotopes, if interpreted correctly, correspond well with these two direct proxies. All the records consistently indicate that the last two glacial periods in the central Levant were generally wet and cool, while the last two interglacials were dry and warm, so more water was available for the ecosystem and thus hominins during glacial periods than during interglacials. Some proxies indicate that the higher precipitation/evaporation ratio during glacial periods involved higher precipitation rather than only reduced evaporation. Beyond the general mean glacial/interglacial climate suggested here, variations occurred at all temporal scales throughout glacial or interglacial periods. In the Sahara-Negev arid barrier, moister conditions occurred during Marine Isotope Stage (MIS) 6a-5e, when Anatomically Modern Humans apparently migrated out of Africa. We suggest that this migration, as well as the later Neanderthal expansion from Southeast Europe or the Anatolian plateau into the Levant during early MIS 4, could be facilitated by the observed major climatic variations.

Hydrology and denudation rates of halite karst

Salt karst terrains exist mainly in arid climates where rock salt outcrops may escape complete destruction by dissolution. Such is the case with Mount Sedom, on the SW shore of the Dead Sea, one of the most arid parts of Israel. Many small catchments developed over the relatively insoluble cap rock which overlies the highly soluble rock salt. The catchments were surveyed and classified. Some 57% of the surface area is drained by an underground karst system. Water samples from various points in the system were analysed, and water development was inferred. Waters in cave conduits do not reach saturation during flood flow, unless the water is ponded for at least several hours. Based on the available evidence, regional karst denudation is tentatively estimated to be about 0.5-0.75 mm year−1, occurring mainly within the rock salt.

Collapse and subsidence associated with salt karstification along the Dead Sea

Two types of sinkholes are observed along the Dead Sea shore, Israel. The first is associated with vadose dissolution in Mount Sedom salt diapir. The second is associated with dissolution under the watertable along the retreating Dead Sea shore. The Dead Sea level is falling dramatically, mainly because of human activity. Simultaneously, the lake shores suffer tremendous impact since the late 1980s: The ground is collapsing and subsiding in hundreds of points along the lake, with people, roads and property being swallowed in the more catastrophic events. The collapse is believed to result from dissolution of salt by aggressive groundwater, following the retreat of Dead Sea level and the groundwater halocline. Geological evidence suggests that a previous major lake level fall occurrednaturally∼2000 BCE. This may provide a new explanation for a curious historical-geological phrase in the book of Genesis, suggested to record formation of collapse sinkholes which occurred in response to the historic falling lake level, associated with climatic desiccation.

A Holocene millennial-scale climatic cycle from a speleothem in Nahal Qanah Cave, Israel

Nahal Qanah Cave, located in the east Mediterranean region, has been inhabited by humans during several periods of the Holocene. These well-dated cultures are used here to establish the age of a speleothem growing over archaeological remains. d18O and d13C from a stalagmite through the last 6000 years display a 1000–2000-year cycle. Depleted d18O and d13C value correlate well with high Dead Sea levels and increased arboreal pollen, suggesting common climatic control affecting the entire region.

Hydrometeorological daily recharge assessment model (DREAM) for the Western Mountain Aquifer, Israel: Model application and effects of temporal patterns

[1] Recharge is a critical issue for water management. Recharge assessment and the factors affecting recharge are of scientific and practical importance. The purpose of this study was to develop a daily recharge assessment model (DREAM) on the basis of a water balance principle with input from conventional and generally available precipitation and evaporation data and demonstrate the application of this model to recharge estimation in the Western Mountain Aquifer (WMA) in Israel. The WMA (area 13,000 km 2 )i s a karst aquifer that supplies 360–400 Mm 3 yr −1 of freshwater, which constitutes 20% of Israel’s freshwater and is highly vulnerable to climate variability and change. DREAM was linked to a groundwater flow model (FEFLOW) to simulate monthly hydraulic heads and spring flows. The models were calibrated for 1987–2002 and validated for 2003– 2007, yielding high agreement between calculated and measured values (R 2 = 0.95; relative root‐mean‐square error = 4.8%; relative bias = 1.04). DREAM allows insights into the effect of intra‐annual precipitation distribution factors on recharge. Although annual precipitation amount explains ∼70% of the variability in simulated recharge, analyses with DREAM indicate that the rainy season length is an important factor controlling recharge. Years with similar annual precipitation produce different recharge values as a result of temporal distribution throughout the rainy season. An experiment with a synthetic data set exhibits similar results, explaining ∼90% of the recharge variability. DREAM represents significant improvement over previous recharge estimation techniques in this region by providing near‐real‐time recharge estimates that can be used to predict the impact of climate variability on groundwater resources at high temporal and spatial resolution. Citation: Sheffer, N. A., E. Dafny, H. Gvirtzman, S. Navon, A. Frumkin, and E. Morin (2010), Hydrometeorological daily recharge assessment model (DREAM) for the Western Mountain Aquifer, Israel: Model application and effects of temporal patterns, Water Resour. Res., 46, W05510, doi:10.1029/2008WR007607.

Radiometric dating of the Siloam Tunnel, Jerusalem.

The historical credibility of texts from the Bible is often debated when compared with Iron Age archaeological finds (refs . 1, 2 and references therein). Modern scientific methods may, in principle, be used to independently date structures that seem to be mentioned in the biblical text, to evaluate its historical authenticity. In reality, however, this approach is extremely difficult because of poor archaeological preservation, uncertainty in identification, scarcity of datable materials, and restricted scientific access into well-identified worship sites. Because of these problems, no well-identified Biblical structure has been radiometrically dated until now. Here we report radiocarbon and U–Th dating of the Siloam Tunnel, proving its Iron Age II date; we conclude that the Biblical text presents an accurate historic record of the Siloam Tunnels construction. Being one of the longest ancient water tunnels lacking intermediate shafts, dating the Siloam Tunnel is a key to determining where and when this technological breakthrough took place. Siloam Tunnel dating also refutes a claim that the tunnel was constructed in the second century bc.

Salt cave cross-sections and their paleoenvironmental implications

Salt caves respond rapidly to environmental changes. Direct measurement and 14C dating show that complex cross-sections may develop in a few hundred years. Two basic forms are discussed: (1) ingrowing vadose canyons where changing width may correspond to changing discharge; (2) wide low passages with flat ceilings, developed by upward dissolution, which may indicate rising base level. Some cross-sections are deformed by Holocene tectonics.