Revital Bookman

Late Holocene lake levels of the Dead Sea

This work presents a high-resolution lake-level record of the late Holocene Dead Sea, a hypersaline terminal lake whose drainage basin encompasses both Mediterranean and hyperarid climatic zones. The lake-level curve reflects the regional hydrologic variations in the drainage basin, which in turn represent the Levant paleoclimates. The curve is based on 46 radiocarbon ages of organic remains from well- exposed sedimentary sequences along the Dead Sea shores. These sequences record fluvial and lacustrine depositional environments. The paleolakeshores are marked by shore ridges, coarse-sand units, and aragonite crusts; in the modern Dead Sea, such features indicate the exact elevation of the shore. The late Holocene Dead Sea level fluctuated within the range of 390 to 415 m below sea level (mbsl). For most of the time the lake was below the topographic sill (402 mbsl) separating the northern and southern basins of the Dead Sea and was confined to the deep northern basin. Nevertheless, short-term rises in the late Holocene Dead Sea level caused the flooding of the shallow and flat southern basin. Highstands occurred in the second and first centuries B.C. and the fourth century A.D. during the Roman and early Byzan tine periods, respectively, in the eleventh and twelfth centuries A.D. during the Crusader period, and at the end of the nineteenth century A.D. The rises mark a significant change in the annual rainfall in the region, which likely exceeded the instrumentally measured modern average. The curve also indicates drastic drops that exposed the sedimentary sequences to erosion. The oldest and probably deepest drop in the lake level culminated during the fifteenth and fourteenth centuries B.C. after a retreat from a higher lake stand. The longest lowstand occurred after the Byzantine period and continued at least until the ninth century A.D. This arid period coincided with the invasion of Moslem-Arab tribes into the area during the seventh century A.D. The dramatic fall of the Dead Sea level during the twentieth century is primarily artificial and has been caused by the diversion of runoff water for the drainage basin, but the magnitude is not considered exceptional for the late Holocene. Although the past drops in the lake never exceeded the modern artificial drop rates, they do represent extreme arid conditions that occurred frequently over the past several thousand years.

Temporal Changes in Radiocarbon Reservoir Age in the Dead Sea-Lake Lisan System

The Holocene Dead Sea and the late Pleistocene Lake Lisan were characterized by varying radiocarbon reservoir ages ranging between 6 and 2 ka in the Dead Sea and between 2 ka and zero in Lake Lisan. These changes reflect the hydrological conditions in the drainage system as well as residence time of (super 14) C in the mixed surface layer of the lake and its lower brine. Long-term isolation of the lower brine led to (super 14) C decay and an increase in the reservoir age. Yet, enhanced runoff input with atmospheric (super 14) C brings the reservoir age down. The highest reservoir age of 6 ka was recorded after the sharp fall of the Dead Sea at approximately 8.1 ka cal BP. The lower reservoir age of zero was recorded between 36 and 32 ka cal BP, when the Lake Lisan mixed layer was frequently replenished by runoff.

Radiocarbon dating of primary aragonite by sequential extraction of CO2

This paper describes the potential of correcting the 14C age shift resulting from the contamination of primary aragonites by detrital carbonates using online sequential extraction of CO2. The experiments were carried out on laminated lacustrine aragonites collected from Holocene Dead Sea sediment sections. X-ray diffraction analysis revealed the presence of detrital calcite interpreted to originate from the watershed and transported to the lake with runoff. The contamination could not be separated physically from the sample, potentially contributing decayed 14C (‘dead carbon’) and increasing the age of the aragonite. Sequential extraction of successive fractions of CO2 unveiled the effect of detrital material on the 14C ages, and showed that the first CO2 extract represents the least contaminated 14C fraction that provides the best approximation for the true 14C age (which includes the lake’s reservoir age). We calculated the age offset contributed by the contamination range encountered in this study (1-21%) to be about 900 years per 10% contamination. The sequential extraction procedure is recommended for 14C dating of Holocene age lacustrine carbonates suspected to be contaminated with extraneous carbon-bearing materials.

Urbanization effects on sediment and trace metals distribution in an urban winter pond (Netanya, Israel)

PurposeThis paper aims to elucidate urban development-induced processes affecting the sediment and the distribution of contaminating metals in a seasonal pond located in the highly populated Israeli Coastal Plain. The paper demonstrates how an integrated approach, including geochemical, sedimentological, geochronological, mathematical, historical, and geographical analyses, may decipher a complicated and dynamic metal pollution history in a sedimentary environment controlled by anthropogenic activity.Materials and methodsThree short sediment cores were collected from the margins and center of a small urban pond (Dora, Netanya), located within the Israeli Coastal Plain. Profiles of grain size, organic matter (OM), trace metals (Pb, Zn, V, Ni, Cu, Cr and Co), Pb isotopic ratios, and 210Pb activities (center and southern cores) were determined and a geochemical mixing model was employed (southern core). The watershed contour was calculated, and aerial photos and satellite images were examined.Results and discussionConstruction activities in the watershed were chronologically associated with coarse sediment transport and deposition in the margins of the pond. The upper sandy layers were superimposed on layers rich in fine particles and OM, high concentrations of trace metals, and with Pb isotopic composition of more recent petrol. In the 210Pb-dated southern core, deep metal-rich layers with petrol-related Pb isotopic ratios were inconsistent with metal emissions history. These findings point to mobility and migration of recent contamination metals through the coarse upper sediment layers and into deeper denser layers, confirmed also by a geochemical mixing model. Conversely, in the center of the pond, homogeneous fine particles were deposited with metal profiles consistent with regional emissions.ConclusionsA small urban pond was found to provide an important case study for understanding heavy metal pollution records in highly populated regions. The margins of the pond depicted the surrounding urban development and the induced coarse sediment erosion, accompanied with post-depositional metal mobility. Due to the proximate developing residential areas, high metal concentrations accumulated in the margins, overshadowing regional atmospheric pollution levels recorded by sediment at the center of the pond.

The interplay between relative sea-level rise and sediment supply at the distal part of the Nile littoral cell

During Holocene sea-level rise, coastal areas became transitional environments as marine incursion covered the land. Changing conditions resulted in dynamic depositional environments that recorded the migration and stabilization of modern shorelines. These processes are viewed in the Zevulun Plain (Haifa Bay, Israel) record located in the northern edge of the Nile littoral cell. Sedimentological and palaeontological analyses combined with dating enabled the reconstruction of the Holocene chrono-stratigraphical frame. The results reveal an unconformity representing a long period of exposure and erosion during the last glacial. The interplay between relative sea-level rise and sediment supply was first set out by the deposition of alluvial sediments, evidence of the hydrological system reactivation and base level landward migration. Sea flooding of the Zevulun Plain started about 7.8 cal ka BP and the coastline was pushed eastward. Nile-driven sands transported by longshore currents formed dunes that blocked the rivers estuaries and led to wetlands formation. Peat accumulation is evident first in the north of the plain at 7.6–6.2 cal ka BP and later in the south at 6.5–5.5 cal ka BP. Both wetlands showed a change from fresh to brackish water environments at the end of their existence. Following the maximum sea-level rise and inland sea invasion at about 4 ka BP, alluvial sediments covered the plain and the coastline moved westward to its current position. This record serves as a model for the development of Mediterranean clastic coasts controlled by sea rise and infill processes.

The role of transport processes of particulate mercury in modifying marine anthropogenic secondary sources, the case of Haifa bay, Israel.

We have assessed the redistribution of a secondary source of sedimentary anthropogenic mercury in the Haifa bay (HB) area (SE Levantine basin), which is the northern sink for Nile-driven sand. A long-term (30years) ~80% decrease of the total sedimentary mercury concentrations (THg) was recorded in the inner bay, while an up to 3-fold increase was recorded in the top sediments of the outer bay. Sedimentary THg depth profiles and their temporal variability were used to model the main re-distribution processes, mainly resuspension associated with winter storm-derived transport. This mechanism transforms a secondary, sandy and well-aerated sink into a tertiary, more silty and hypoxic source at adjacent peripheral areas, affecting mercury bioavailability. We revisited the concept of environmental relaxation, i.e. the rate of return of a polluted environment to an acceptable state, showing that sedimentary transport processes may affect the associated ecological risks, mainly at shallow-water coastal sites.

An Early Islamic Inter-Settlement Agroecosystem in the Coastal Sand of the Yavneh Dunefield, Israel

ABSTRACT This study examines the remains of an agricultural complex found in the Yavneh coastal dunefield, central Israel. Known as a plot-and-berm agroecosystem, the complex consisted of earthworks in a crisscross pattern of sand berms and sunken agricultural plots that were used for groundwater harvesting. The plots, which provided easy access to the high groundwater table and the berms around them, are overlaid by a gray sand unit covered by pottery sherds and artifacts. This gray sand is more fertile than the underlying sand, suggesting refuse enrichment. Artifactual similarity of the finds to those of inland (Tel) Yavneh suggests that Yavneh was the main source for the refuse additive. Based on artifacts and OSL ages it seems that this agroecosystem was active during the 10th to early 12th centuries a.d. The agroecosystem demonstrates an early example of an Early Islamic agrotechnological attempt in marginal and sandy regions of the Mediterranean basin.