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We describe a new method for the measurement of U/Pb ratios by isotope dilution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for the dating of geologically young clean carbonates, particularly speleothems. The method is intended for materials containing little or no initial 232Th. We illustrate and validate the method with four examples ranging from 0.57 to 20 Ma. The new method is capable of applying the 235U–207Pb and 238U–234U–206Pb chronometers, common Pb and quantifiable residual 234U/238U disequilibrium permitting. These provide an alternative to the more widely used 238U–206Pb chronometer, which can be highly inaccurate for samples that are

Recent accelerating global temperature rise increases the likelihood and susceptibility of the Siberian taiga to more frequent and extreme wildfires [1] [2]. This leads to enhanced permafrost thaw and subsequent greenhouse gases emissions, in a positive feedback loop [3]. Various studies have examined these paleofires in Siberia on limited, modern timescales [4, 5], but long-term reconstructions of wildfire occurrences are scarce [6]. This study reconstructs wildfire occurrence during the Holocene using stalagmites from southern Siberia. We provide a new means for assessing Siberian wildfires during interglacial periods and the first southern Siberian Holocene wildfire record. Three stalagmites from Botovskaya Cave (55˚17’59”N, 105˚19’46”E) have been U/Th-dated at the Oxford geochronology laboratory. These speleothem samples were collected deep inside the poorly ventilated cave, which is overlain by 40-130 m of sandstone covered by a thin soil and boreal taiga forest. Drip sites are active year-round, and cave air temperature is stable at ca. 1.3±0.5°C. Wildfires sporadically occur above the cave.We use novel speleothem biomarkers, levoglucosan and lignin, as tracers for wildfire activity and vegetation composition above the cave, respectively. Levoglucosan is an anhydrous monosaccharide solely produced by the combustion of cellulose, and thus an ideal proxy for wildfires. Lignin is a biopolymer with three monomers. The monomer ratio can inform on relative changes between gymnosperm vs. angiosperm plant communities. Using both proxies we can decipher not only wildfire recurrence, but also changes in vegetation (e.g., from pine forest to peatbogs or grassland).We took subsamples between 300 and 1000 mg and attribute the levels of levoglucosan to variance of the composition of lignin monomers, corresponding with vegetation composition. The required sample size (1 g) and the low observed carbonate growth rates of ca. 4-8 mm/a mean that we can only achieve multi-centennial resolution for the Holocene. To gain complementary insights into environmental conditions we combine the biomarker information with stable isotopes and element concentrations. References [1] V. I. Kharuk, et al., "Wildfires in the Siberian Taiga," Ambio , vol. 50, pp. 1953-1974, 2021. [2] M. B. S. Flannigan, et al., "Impact of climate change on fire acivity and fire management in the circumboreal forest," Global Change Biology, vol. 15, pp. 549-560, 2009. [3] M. R. Turetsky, et al., "Carbon release through abrupt permafrost thaw," Nature Geoscience , vol. 13, pp. 138-143, 2020. [4] M. M. Grieman, et al.,"Aromatic acids in a Eurasian Arctic ice core: a 2600-year proxy record of biomass burning," Climate of the Past , vol. 13, pp. 395-410, 2017. [5] R. Glückler, et al., "Wildfire history of the boreal forest of south-western Yakutia (Siberia) over the last two millennia document by a lake-sediment charcoal record," Biogeosciences , vol. 18, pp. 4185-4209, 2021. [6] E. Dietze, et al., "Relationships between low-temperature fires, climate and vegetation during three late glacials and interglacials of the last 430 kyr in northeastern Siberia reconstructed from monosaccharide anhydrides in Lake El'gygytygyn sediments," Climate of the Past, vol. 16, pp. 799-818, 2020.

We describe a new method for the measurement of U/Pb ratios by isotope dilution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for the dating of geologically young clean carbonates, particularly speleothems. The method is intended for materials containing little or no initial 232Th. We illustrate and validate the method with four examples ranging from 0.57 Ma to 20 Ma old. The new method is capable of applying the 235U-207 and 238U-234U-206Pb chronometers, common Pb and quantifiable residual 234U/238U disequilibrium permitting. These provide an alternative to the more widely used 238U-206Pb chronometer, which can be highly inaccurate for samples a few million years old, owing to uncertainties in the excess initial 234U (hence, excess radiogenic 206Pb) commonly observed in speleothems.

Latest advances in laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) allow for accurate in situ U-Pb dating of carbonate material, with final age uncertainties usually >3% 2σ. Cross-laboratory reference materials (RMs) used for sample-bracketing are currently limited to WC1 calcite with an age of 254.4±6.5 (2σ). The minimum uncertainty on any age determination with the LA-ICPMS method is therefore ≥2.5 %, and validation by secondary RMs is usually performed on in-house standards. This contribution presents a new reference material, ASH-15, a flowstone that is dated here by isotope dilution (ID) thermal ionization mass spectrometry (TIMS) analysis using 37 sub-samples, 1-7 mg each. Age results presented here are slightly younger compared to previous ID isotope ratio mass spectrometry (IRMS) U-Pb dates of ASH-15 but within uncertainties and in agreement with in situ analyses using WC1 as the primary RM. We provide new correction parameters to be used as primary or secondary standardization. The suggested 238U/206Pb apparent age, not corrected for disequilibrium and without common-lead anchoring, is 2.965±0.011 Ma (uncertainties are 95 % confidence intervals). The new results could improve the propagated uncertainties on the final age with a minimal value of 0.4 %, which is approaching the uncertainty of typical ID analysis on higher-U materials such as zircon. We show that although LA-ICPMS spot analyses of ASH-15 exhibit significant scatter in their isotopic ratios, the down-hole fractionation of ASH-15 is similar to that of other reference materials. This high-U (≈1ppm) and low-Pb (, Geochronology, 3 (1)

Recent environmental processes are studied in ʻA’rak Naʻasane Cave at the northern Judean Desert, Israel. The outer zone of the cave is heavily influenced by the outside environment through a large entrance, facilitating entry of air flow, fauna and humans, with minor cave-forming modifications. Conversely, the inner cave sustains humid and warm conditions, favoring modifications by condensation corrosion of convective air flow, associated with deposition of popcorn speleothems at the lower parts of dissolution pockets. The warm humid air of the inner cave may be associated with an underlying thermal water table. Active condensation corrosion is decreasing, possibly because of gradual change in the cave microclimate, associated with falling water table and ventilation. Increasing connection with the surface is indicated by high collapse domes, rare flood invasion, and a large Trident Leaf-nosed bat community which spends the winter within the innermost parts of the cave. Bat guano supports bedrock corrosion and a rich invertebrate fauna, but humans preferred the outer parts of the cave, particularly for refuge during the second Jewish revolt against the Romans. Rare occasions of ancient human entry into the inner cave support this scenario by the small number of artifacts compared with the outer cave. Enigmatic small cairns in the largest inner hall were probably erected during the Intermediate Bronze Age.

Permafrost is widely present throughout the Northern Hemisphere high latitudes, and stores large amounts of carbon in the form of frozen soil organic matter. The response of permafrost regions to anthropogenic climate change remains uncertain, in part because of a lack of information on their response to past changes in global climate. Here we test the use of stalagmites from two caves in Siberia as a novel, precisely dated, and highly localised archive of past permafrost carbon cycle dynamics. Stalagmite growth at these sites is controlled by the presence/absence of permafrost above the cave over glacial-interglacial time scales. We target the transition layer between two subsequent growth phases (interglacials) and the interval directly following growth resumption after the last glacial in three stalagmites, as this is where a geochemical imprint of thaw-related processes in the frozen zone between surface and cave would be recorded. We apply a multi-proxy approach including carbon isotopes (δ13C and 14C) and trace element concentrations, combined with petrographic analyses and high-resolution U-Th chronology. Our dataset indicates complex growth patterns and possible intervals of microbial colonisation of the stalagmite surface in the transition layers. High-resolution U-Th ages confirm that the transition layer is not a single, long growth hiatus, but rather a period of extremely slow or episodic growth phases, possibly during “skipped” interglacials. However, we find no conclusive evidence for a geochemical signature related to permafrost degradation and related local carbon cycle dynamics, which might be related to insufficient sensitivity of the archive for high-frequency processes and/or insufficient measurement resolution.

Terrestrial chemical weathering of silicate minerals is a fundamental component of the global cycle of carbon and other elements. Past changes in temperature, rainfall, ice cover, sea-level and physical erosion are thought to affect weathering but the relative impact of these controls through time remains poorly constrained. This problem could be addressed if the nature of past weathering could be constrained at individual sites. In this study, we investigate the use of speleothems as local recorders of the silicate weathering proxy, Li isotopes. We analysed δ7Li and [Li] in speleothems that formed during the past 200 ka in two well-studied Israeli caves (Soreq and Tzavoa), as well as in the overlying soils and rocks. Leaching and mass balance of these soils and rocks show that Li is dominantly sourced from weathering of the overlying aeolian silicate soils. Speleothem δ7Li values are ubiquitously higher during glacials (~23‰) than during interglacials (~10‰), implying more congruent silicate weathering during interglacials (where “congruent” means a high ratio of primary mineral dissolution to secondary mineral formation). These records provide information on the processes controlling weathering in Israel. Consideration of possible processes causing this change of weathering congruency indicates a primary role for temperature, with higher temperatures causing more congruent weathering (lower δ7Lispeleo). The strong relationship observed between speleothem d7Li and climate at these locations suggests that Li isotopes may be a powerful tool with which to understand the local controls on weathering at other sites, and could be used to assess the distribution of weathering changes accompanying climate change, such as that of Pleistocene glacial cycles.

Africa” exodus of early modern humans: evidence from desert stalactites A.VAKS , M. BAR-MATTHEWS, A. AYALON, A. MATTHEWS, L. HALICZ, AND A. FRUMKIN 1 Institute of Earth Sciences, Hebrew University, Jerusalem 91904; Israel; antonv@pob.huji.ac.il; alan@vms.huji.ac.il 2 Geological Survey of Israel, 30 Malkhe Israel St., Jerusalem 95501; Israel matthews@gsi.gov.il; ayalon@gsi.gov.il 3 Department of Physical Geography, Hebrew University, Jerusalem 91905; Israel; msamos@mscc.huji.ac.il

Speleothems in arid and hyper-arid areas of Negev Desert, Israel, are used in paleoclimate reconstruction of northern margins of Saharan-Arabian Desert, focused on the following objectives: 1) precise U–Th dating of the timing of speleothem growth as an indicator of periods of humid climate, i.e. positive effective precipitation; 2) the origin of rainfall using the speleothem δ18O and changes in spatial pattern of speleothem deposition and speleothem thickness along a north–south transect; 3) changes of vegetation cover based on speleothem δ13C variations. During the last 350 ka major humid periods, referred to herein as Negev Humid Periods (NHP), occurred in the central and southern Negev Desert at 350–310 ka (NHP-4), 310–290 ka (NHP-3), 220–190 ka (NHP-2), and 142–109 ka (NHP-1). NHP-4, NHP-2 and NHP-1 are interglacial events, whereas NHP-3 is associated with a glacial period. During NHP-1, 2 and 3 the thickness and volume of the speleothems decrease from the north to the south, and in the most southern part of the region only a very thin flowstone layer formed during NHP-1, with no speleothem deposition occurring during NHP-2 and 3. These data imply that the Eastern Mediterranean Sea was the major source of the rainfall in northern and central Negev. More negative speleothem δ18O values, relative to central parts of Israel (Soreq Cave) are attributed to Rayleigh distillation because of the increasing distance from the Mediterranean Sea. Speleothem deposition during the NHP-4 in the southern Negev was more intensive than in most of the central Negev, suggesting the prominence of the tropical rain source. Decrease in speleothem δ13C during NHP events indicates growth of the vegetation cover. Nevertheless, the ranges of δ13C values show that the vegetation remained semi-desert C4 type throughout the NHPs, with an additional significant carbon fraction coming from the host rock and the atmosphere. These observations, together with small thickness of the speleothem layers, favor that NHP events consisted of clusters of very short humid episodes interspersed with long droughts. NHP events were contemporaneous with climate periods with monsoon index of ≥51 (cal/cm2 × day) and with the formation of sapropel layers in the Mediterranean Sea. Such simultaneous intensification of the monsoon and Atlantic-Mediterranean cyclones is probably related to the weakening of the high pressure cell above sub-tropical Atlantic Ocean, which enabled more rainfall to penetrate into the Saharan-Arabian Desert from the north and south. The contemporaneous occurrence of the NHP events and the increased monsoon rainfall could have opened migration corridors, creating climatic “windows of opportunity” for dispersals of hominids and animals out of the African continent.

The Qesem karst system may serve as an example for aging chamber caves. It includes two caves which have undergone several stages of natural and human-induced deposition, as well as subsidence and collapse. Natural deposits include calcite speleothems, bedrock collapse debris, and clay fill. Karst dissolution and associated sagging and decomposition have operated since the initial cave formation. Inclined sediments are attributed to several processes, mostly dominated by gravitational sagging into underlying dissolution voids, affecting cave deposits and sometimes the host-rock. U-Th dating shows that speleothem deposition has been common during the mid-late Quaternary, but deposition sites shifted according to local conditions. The aging of caves occurs when they become totally filled by sediments and ultimately consumed by surface denudation, as documented in Qesem Cave. © 2008 Elsevier B.V. All rights reserved.

A varied assemblage of algal stromatolites was encountered in caves along the northern section of the Dead Sea Fault Escarpment. The caves are situated at the lower part of the escarpment at altitudes -310 to -188 m relative to mean sea level (m.s.l.), i.e. ca 110-230 m above the present Dead Sea level. The cave stromatolites are mainly composed of aragonite yielding U-Th ages of ∼75-17 ka. The altitude, mineralogy and ages, as well as comparison with previously documented stromatolite outcrops in the area, ascribe the cave stromatolites to the aragonite-precipitating hypersaline Lake Lisan-the Late Pleistocene predecessor of the Dead Sea. The stromatolites are used as a lake level gauge, based on the algae being reliant upon the light of the upper water layer. Preservation of the original structure and aragonite mineralogy of the stromatolites, suggests a closed system regarding the radioactive elements, enabling reliable U-Th dating. A curve of Lake Lisan levels is constructed based on the stromatolite ages and cave elevations. The following points are noted: (1) Lake levels of -247 m relative to m.s.l., are recorded at ∼75-72.5 ka; (2) relatively high lake levels above -220 m relative to m.s.l., are achieved at ∼41.5 ka, and are still recorded at ∼17 ka; (3) the peak level is -188 m relative to m.s.l., at ∼35.5-29.5 ka. These results indicate lake stands up to 80 m higher than previously accepted, for large parts of the Lake Lisan time span. This difference is explained by tectonic subsidence of up to 2.2 m/ka within the Dead Sea depression since the latest Pleistocene. This subsidence rate is in the same order of magnitude with previously calculated subsidence rates for the Dead Sea depression [Begin, Z.B., Zilberman, E., 1997. Main Stages and Rate of the Relief Development in Israel. Geological Survey of Israel report, Jerusalem]. Unlike previous Lake Lisan level estimations, the new curve is measured at the relatively stable shoulders of the Dead Sea depression. © 2008 Elsevier Ltd. All rights reserved.

Speleothem bearing karstic caves of the northern Negev Desert, southern Israel, provides an ideal site for reconstructing the paleoclimate and paleo-location of the border between Mediterranean climate region and the Saharo-Arabian Desert. Major periods of speleothem deposition (representing humid periods) were determined by high resolution 230Th-U dating and corresponding studies of stable isotope composition were used to identify the source of rainfall during humid periods and the vegetation type. Major humid intervals occurred during glacials at 190-150 ka, 76-25 ka, 23-13 ka and interglacials at 200-190 ka, 137-123 ka and 84-77 ka. The dominant rainfall source was the Eastern Mediterranean Sea, with a possible small contribution from southern tropical sources during the interglacial periods. When the interglacial interval rainfall was of Eastern Mediterranean origin, the minimum annual rainfall was ∼ 300-350 mm; approximately twice than of the present-day. Lower minimum amounts of precipitation could have occurred during glacial periods, due to the cooler temperatures and reduced evaporation. Although during most of the humid periods the vegetation remained steppe with mixed C3 + C4 vegetation, Mediterranean C3 type steppe-forest vegetation invaded southward for short periods, and the climate in the northern Negev became closer to Mediterranean type than at present. The climate was similar to present, or even more arid, during intervals when speleothem deposition did not occur: 150-144 ka, 141-140 ka, 117-96 ka, 92-85 ka, 25-23 ka, and 13 ka-present-day. Precipitation increase occurred in the northern Negev during the interglacial monsoonal intensity maxima at 198 ka, 127 ka, 83 ka and glacial monsoonal maxima at 176 ka, 151 ka, 61 ka and 33 ka. However, during interglacial monsoonal maxima at 105 ka and 11 ka, the northern Negev was arid whereas during glacial monsoonal minima it was usually humid. This implies that there is not always synchroneity between monsoonal activity and humidity in the region. Oxygen isotopic values of the northern Negev speleothems are systematically lower than contemporaneous speleothems of central and northern Israel. This part is attributed to the increased rainout of the heavy isotopes by Rayleigh fractionation processes, possibly due to the farther distance from the Mediterranean coast. © 2006 Elsevier B.V. All rights reserved.

Speleothem fluid inclusions potentially provide vital data on the paleohydrological conditions in glacial and interglacial periods. We show here that δD analyses of fluid inclusions from speleothems in three caves in the Eastern Mediterranean region (Israel) provide a basis for understanding hydrological and temperature variations in the last 140ka. Using measured δD fluid inclusion values and temperature ranges constrained by the present-day Mediterranean Meteoric Water Line (MMWL) and the global MWL, we show a strong compatibility between the land and marine temperature records, with the highest land temperatures occurring at 120-130ka (17-22°C) and the present (18°C) and the lowest temperatures during the LGM, about 10°C lower than present. Interglacial waters are constrained to follow the MMWL and most glacial waters also plot close to the MMWL, with a slight shift towards the MWL. However, during two remarkable brief periods at the termination of the LGM, the waters plot on the MWL, suggesting that both sharp cooling and an increase in relative humidity above the EM Sea reduced d-excess values to those of the global system. © 2004 Elsevier Ltd. All rights reserved.

High-resolution 230Th/234U ages and δ18O and δ13C compositions of speleothems in Ma’ale Efrayim Cave located to the east of the central mountain ridge of Israel enable us to examine the nature of the rain shadow aridity during glacial and interglacial intervals. Speleothem growth occurred during marine glacial isotopic periods, with no growth during the two last marine isotope interglacial intervals and during the peak of the Last Glacial Maximum. This contrasts with speleothem growth in caves located on the western flank of the central mountain ridge, in the Eastern Mediterranean semiarid climatic zone, which continued throughout the last 240,000 yr. Thus, during glacial periods water reached both sides of the central mountain ridge. A comparison of the present-day rain and cave water isotopic compositions and amounts at the Ma’ale Efrayim Cave site with those on the western flank shows that evaporation and higher temperatures on the eastern flank are major influences on isotopic composition and the lack of rainfall. The δ18O and δ13C profiles of the speleothems deposited between 67,000 and 25,000 yr B.P. match the general trends of the isotopic profiles of Soreq Cave speleothems, suggesting a similar source (eastern Mediterranean Sea) and similar climatic conditions. Thus, during glacial periods the desert boundary effectively migrated further south or east from its present-day location on the eastern flank, whereas interglacial periods appear to have been similar to the present, with the desert boundary at the same position. The decrease in overall temperature and a consequent reduction in the evaporation to precipitation ratios on the eastern flank are viewed as the major factors controlling the decay of the rain shadow effect during glacial periods.

One of the first 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 Saharan-Arabian 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. © 2007 The Geological Society of America.