Ra in the Dead Sea

The²²⁸Ra concentrations of the Dead Sea waters range from 0.13 to 1.48 dpm kg⁻¹, two to three orders of magnitude higher than those of ocean waters and lake waters. However, the²²⁸Ra/²²⁶Ra activity ratios, (0.12–1.29) × 10⁻², are in the range reported for the hydrosphere.The surface waters of the Dead Sea are enriched in²²⁸Ra by a factor of about three over the near-bottom waters. There is a factor of about two spatial variability in the mid-depth Ra concentrations at the two profile stations. The near-bottom²²⁸Ra gradients yield vertical eddy diffusivity coefficient (K) of 2.0 and 0.4 cm² s⁻¹ at profile locations 1 and 2 respectively. These values are comparable to those measured in oceans and lakes.     

Tritium in the Dead Sea

Tritium data in the Dead Sea for the period 1960–1979 are given. Tritium levels have increased until 1965 in the upper layers of the Dead Sea reaching a level of 170 TU, in response to the atmospheric buildup of tritium from thermonuclear testing. The levels have been decreasing ever since, both because of rapidly declining atmospheric concentrations of tritium and because of mixing of the surface layers with tritium deficient, deeper water masses. The depth of penetration of the tracer delineated the depth of meromictic stratification and successfully monitored the deepening of the pycnocline, until the overturn in 1979 homogenised the entire tritium profile. Modelling the changing tritium inventory over this period showed the predominance of the direct exchange across the air/sea interface, both in the buildup of tritium in the lake and also in its subsequent removal from it. The good fit between calculated and measured tritium inventories confirmed the evaporation estimate of 1.46 m/yr (the mean value for the period) with a precision unattained by other methods.     

Iron in the Dead Sea

The distributions of dissolved and of particulate iron in the Dead Sea during the period which preceeded its overturn and thereafter (1977–1980) are reported. During 1977–1978, the vertical profiles of the iron phases revealed facets of the mixing pattern: the progressive deepening of the pycnocline, restricted mixing within the upper water mass and penetration of surface waters into the deepest layer. The inventories of particulate iron suggest resuspension of bottom sediments in November 1978 and after the overturn the gradual disappearance from the water column of iron sulfides and iron oxy-hydroxides. Fluxes of iron from and to the lake in the undisturbed meromictic Dead Sea have been estimated: it appears that diffusion of divalent iron from bottom sediments was the major source for the standing crop of iron in the lower water mass. Low settling velocities of solid particles in the dense and viscous Dead Sea is one of the causes for the relatively large concentrations of particulate iron. The rate constant for oxidation of divalent iron in Dead Sea sediment interstitial waters is larger by two orders of magnitude than in other natural waters.     

Barium and radium in the Dead Sea

We have measured Ba in Dead Sea samples collected before and after the 1979 overturn, and²²⁶Ra in nine samples collected after the overturn. Before this overturn, Ba and the²²⁶Ra data measured by Chung and Craig [4] show that a distinct two-layer structure existed, with higher concentrations in the upper layer. After the overturn, both elements were uniformly distributed in the water column. The inventories of Ba and Ra calculated from these data are the same for the periods before and after the overturn. If the inventories were constant during the last meromictic phase then the input rate must be balanced by the removal rate, and a mass balance model can be constructed to estimate physical parameters based on known or deduced sources and sinks. The sources include inputs from the Jordan River, springs around the Dead Sea, and submerged springs or seepages, etc. The sinks include coprecipitation with aragonite, gypsum, precipitation of barite, coprecipitation of Ra with barite, particulate scavenging, and radioactive decay for Ra. Our data include measurements of Ba and²²⁶Ra in gypsum, aragonite and halite from the Dead Sea, as well as in some of the inflowing rivers and springs.The inclusion of particulate scavenging as a sink is a major element of the model. We find that, without inclusion of a Ba scavenging term in the deep water, the lake volume at the previous overturn as calculated from the Ba data would be unrealistically high in comparison with historical records. The inclusion of particulate scavenging for Ra in the model reduces the calculated duration of the last meromictic phase significantly.Our model excludes internal mixing between the upper and lower water masses. With this restriction, various sets of model parameters were calculated as a function of theRa/Ba scavenging rate ratio. If the ratio is one, the calculated age of the last meromictic phase is about a hundred years. A substantial increase in the Ra input rate is required to balance the removal rate by particulate scavenging as well as decay. If the ratio is zero, i.e. no particulate scavenging for Ra, the age is about 260 years, as obtained by Stiller and Chung [2].     

Sea surface temperature anomalies driven by oceanic local forcing in the Brazil-Malvinas Confluence

Sea surface temperature (SST) anomaly events in the Brazil-Malvinas Confluence (BMC) were investigated through wavelet analysis and numerical modeling. Wavelet analysis was applied to recognize the main spectral signals of SST anomaly events in the BMC and in the Drake Passage as a first attempt to link middle and high latitudes. The numerical modeling approach was used to clarify the local oceanic dynamics that drive these anomalies. Wavelet analysis pointed to the 8–12-year band as the most energetic band representing remote forcing between high to middle latitudes. Other frequencies observed in the BMC wavelet analysis indicate that part of its variability could also be forced by low-latitude events, such as El Niño. Numerical experiments carried out for the years of 1964 and 1992 (cold and warm El Niño-Southern Oscillation (ENSO) phases) revealed two distinct behaviors that produced negative and positive sea surface temperature anomalies on the BMC region. The first behavior is caused by northward cold flow, Río de la Plata runoff, and upwelling processes. The second behavior is driven by a southward excursion of the Brazil Current (BC) front, alterations in Río de la Plata discharge rates, and most likely by air-sea interactions. Both episodes are characterized by uncoupled behavior between the surface and deeper layers.     

Dynamic simulation of the Dead Sea

The Dead Sea is a hypersaline terminal lake located in the Rift Valley between Jordan and Israel. In this work a generalised mathematical model describing the behaviour of the Dead Sea has been developed. The model established the condition of the Sea by evaluating a series of ordinary differential equations describing mass balances on the water and major chemical species in the Sea. The Sea was modelled as a two-layer system. The model was validated by comparing its predictions to measured level records. The results obtained highlighted the importance of detailed evaporation modelling, showed the necessity to model the Sea as a two-layer system, validated the usage of average distribution data to estimate the flowrates of rivers, and justified ignoring diffusion effects in further modelling. The model predicted that in the case of continuing current conditions, the level will continue to decline, at a decelerating rate, because the area and evaporation rate are both decreasing. Under these conditions, the model shows that the salinity of both layers will continue to increase, and that seasonal stratification and seasonal crystallisation of gypsum and aragonite will continue.     

The geochemistry of manganese in the Dead Sea

The most important source of dissolved manganese, Mn(II), to the Dead Sea is by upward diffusion from bottom sediments. This source contributes about 80 tons of Mn(II) each year. The concentration of dissolved manganese in the Dead Sea is extraordinarily high (7.03 mg 1^?1). It appears that the content (some 1.026 × 10⁶ tons) of dissolved manganese in the sea has remained constant during 1977–1979, although oxygen was introduced into deeper layers during the deepening of the pycnocline (1977–1978) and during the overturn of its water masses in the winter of 1978/79. The rate of oxidation of Mn(II) in Dead Sea water is extremely slow hence Mn(II) may practically be considered as the stable form of Mn in Dead Sea waters. Dilution by fresh water causes a pH rise and may facilitate faster oxidation of the dissolved divalent manganese. It is shown here that the shape of the Mn(II) profile, observed in the lake during 1963, may have developed by oxidation of Mn(II) in the more diluted upper layers and subsequent reduction of the oxidation products in the anoxic and more saline deeper layers during 260 years of continuous meromixis.     

Estimation of evaporation from the Dead Sea

A project to link the Dead Sea to the Red Sea via a canal is undergoing extensive study. As part of this study, a method to estimate evaporation from the Dead Sea is required as it is a hypersaline lake in which standard methods cannot be applied. Two methods based on Penman and Dalton formulae were examined. The method derived here is a modified Penman model that estimates the evaporation as a function of salinity, humidity, air temperature and wind speed. Other parameters such as water temperature are included implicitly in the model. The results obtained were verified as satisfactory agreement was achieved by comparison with previous measurements. A short‐cut relationship to estimate evaporation as a function of salinity only was also derived. Copyright © 1999 John Wiley & Sons, Ltd.     

Effect of the Dead Sea–Red Sea canal modelling on the prediction of the Dead Sea conditions

A project to link the Dead Sea to the Red Sea via a canal is undergoing extensive study. In previous works, a generalized mathematical model describing the state of the Dead Sea and a simulation model to implement it have been developed. The model is extended to include the proposed canal project and investigates two alternative modelling canal scenarios: (1) introducing the canal water inflow into the bottom layer or (2) the top layer of the sea. The predicted general effects of the canal are the restoration of the water level of the sea to pre‐1970s level; an increase in the total evaporation rate and a decrease in the top layer salinity. Implementing scenario 1, the model predicts that: the water level of the Dead Sea will exceed the desired level design value and therefore shorter filling time can be used; seasonal stratification will persist; total evaporation rate will increase Modestly; there will a small decrease in the salinity of the top layer but a substantial decrease in the salinity of the bottom layer, which will hurt industries severely; there will be a continuation of seasonal crystallization of aragonite and gypsum. Implementing scenario 2 the model predicts that: the water level of the Dead Sea will be maintained at the desired level design value; stratification will be re‐established, with the formation of a permanent two‐layer system; there will be a substantial increase in the total evaporation rate; the salinity of the top layer will decrease significantly but there will be continuous slower salinity increase in the bottom layer; the crystallization of aragonite will cease, but seasonal gypsum crystallization can be expected to continue as soon as the filling period ends and the canal shifts into normal operation. Copyright © 2003 John Wiley & Sons, Ltd.     

Stress tensor and focal mechanisms in the Dead Sea basin

We use the recorded seismicity, confined to the Dead Sea basin and its boundaries, by the Dead Sea Integrated Research (DESIRE) portable seismic network and the Israel and Jordan permanent seismic networks for studying the mechanisms of earthquakes in the Dead Sea basin. The observed seismicity in the Dead Sea basin is divided into nine regions according to the spatial distribution of the earthquakes and the known tectonic features. The large number of recording stations and the adequate station distribution allowed the reliable determinations of 494 earthquake focal mechanisms. For each region, based on the inversion of the observed polarities of the earthquakes, we determine the focal mechanisms and the associated stress tensor. For 159 earthquakes, out of the 494 focal mechanisms, we could determine compatible fault planes. On the eastern side, the focal mechanisms are mainly strike-slip mechanism with nodal planes in the N-S and E-W directions. The azimuths of the stress axes are well constrained presenting minimal variability in the inversion of the data, which is in agreement with the Eastern Boundary fault on the east side of the Dead Sea basin and what we had expected from the regional geodynamics. However, larger variabilities of the azimuthal and dip angles are observed on the western side of the basin. Due to the wider range of azimuths of the fault planes, we observe the switching of σ₁ and σ₂ or the switching of σ₂ and σ₃ as major horizontal stress directions. This observed switching of stress axes allows having dip-slip and normal mechanisms in a region that is dominated by strike-slip motion.     

Radiocaesium distribution in the bottom sediments of the Kara Sea

The article presents the results of radiogeochemical studies carried out by the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, RAS (IGEM RAS), in the Kara Sea and the estuaries of the Ob and Yenisei rivers in 1995–2003. The studies were carried out onboard the Akademik Boris Petrov research vessel, belonging to the Institute of Geochemistry, RAS. Based on studies of circa 1500 samples of bottom sediments, taken from 172 marine and river stations, a map of ¹³⁷Cs distribution in the surface sediments has been compiled. Four zones of radiocesium overactivity (>15 Bk/kg) have been identified: Novaya Zemlya Zone, Vaigach Zone, Ob Zone, and Yenisei Zone. The zones have different radiocesium concentration levels, as well as different input sources, but all of them have formed under the influence of complex geochemical barriers. Data from 47 sectioned cores of bottom sediments, sampled in Ob and Yenisei overactivity zones, demonstrate distinct differences in the vertical radiocesium distribution. These differences have been shown to be due to many-year oscillations of suspended silt discharge, which are main transfer agents of solvable and poorly solvable radiocesium forms and to be independent of sedimentation conditions and the geochemical characteristics of the deposition environment.     

Geochemical studies on the Feshcha Springs,Dead Sea basin

The Feshcha springs issue in a 4 km long strip on the Dead Sea shores. They constitute two separate groups: a) T-N waters, similar in their salt composition, temperature and radon content to the many other members of the Rift Valley “Tiberias-Noit water association”. The hydrologic, radon, tritium and carbon-14 indicate they are mixtures of recent meteoric waters with ancient (trapped) T-N waters of an age of at least 18000 years. b) Z-Y waters which, like other members of the Dead Sea basin “Zohar-Yesha water group”, originate by a mixing of T-N waters with Dead Sea waters. This is seen in the chemical compositions and is confirmed by the oxygen-18 and deuterium data.     

The stable isotope composition of Dead Sea waters

Dead Sea waters are moderately enriched in¹⁸O; the degree of enrichment constitutes a balance between the dilution by freshwater influx and the isotope fractionation which accompanies evaporative water loss and vapour exchange with the atmospheric moisture. Modelling of the seasonal cycle and long-term trends of δ¹⁸O, in response to the changes in the environmental parameters, shows that the major control is exercised by the salinity of the surface waters, through its effect on the vapour pressure gradient between the lake's surface and the atmosphere; the (steady state) isotopic composition of the more saline brines tends towards less enriched¹⁸O values. This fact can explain the relatively high δ¹⁸O levels encountered in the Lisan formation, which was deposited from Lake Lisan, —the less saline Pleistocene precursor of the Dead Sea.     

The water balance of the Dead Sea: an integrated approach

The Dead Sea is the lowest spot on Earth. It is a closed saline lake located in the middle of the Jordan Rift Valley between Lake Tiberias and the Red Sea. Its major tributaries are the Jordan River itself and the Dead Sea side wadis. The Dead Sea has a unique ecosystem and its water has curative, industrial and recreational significance. The level of the Dead Sea has been continuously falling since the early 1930s at an average rate of 0·7 m per year. The water level, as of February 1998, is about 410·9 m below mean sea level. In this paper, a water balance model is developed for the Dead Sea by considering different hydrological components of this water balance, including precipitation, runoff, evaporation and groundwater flow. This model is calibrated based on historical levels of the Dead Sea. Different scenarios are investigated, including the proposed Dead Sea–Red Sea Canal. This project is supposed to halt the shrinking of the Dead Sea and restore it to pre‐1950 levels in the next century. Copyright © 2000 John Wiley & Sons, Ltd.     

Deep water bottom current deposition in the northern South China Sea

There are some active bottom currents on the northern continental slope of the South China Sea (SCS). Reflection seismic profiles show that the bottom current channels occur in the water depth range of 1000 to 2700 m,extending from the NE to the SW,leading to accumulation of discontinuous drifts with higher sedimentation rates on the eastern side of the channel. The stacking pattern of the layers sug-gests that these drifts propagated southwestward,following the direction of the bottom currents. One sedimentary drift to the southeast of the Dongsha Islands has the highest sedimentation rate of 97cm/ka in the last 12 ka. The sedimentary characteristics of the sediment layers indicate that these bottom currents are most likley caused by the water movement of a branch of the West Pacific Ocean Current,which enters the northern SCS via the Bashi Strait. Once formed,the bottom currents trans-port sediments along the northern slope of SCS southwestward and finally disappear into the central basin of the SCS. Due to the bottom current activity,the deep-sea sedimentary process in the northern SCS is complex.     

Model simulations of dense bottom currents in the Western Baltic Sea

Only recently, medium intensity inflow events into the Baltic Sea have gained more awareness because of their potential to ventilate intermediate layers in the Southern Baltic Sea basins. With the present high-resolution model study of the Western Baltic Sea a first attempt is made to obtain model based realistic estimates of turbulent mixing in this area where dense bottom currents resulting from medium intensity inflow events are weakened by turbulent entrainment. The numerical model simulation which is carried out using the General Estuarine Transport Model (GETM) during nine months in 2003 and 2004 is first validated by means of three automatic stations at the Drogden and Darss Sills and in the Arkona Sea. In order to obtain good agreement between observations and model results, the 0.5×0.5$0.5\times 0.5$ nautical mile bathymetry had to be adjusted in order to account for the fact that even at that scale many relevant topographic features are not resolved. Current velocity, salinity and turbulence observations during a medium intensity inflow event through the Øresund are then compared to the model results. Given the general problems of point to point comparisons between observations and model simulations, the agreement is fairly good with the characteristic features of the inflow event well represented by the model simulations. Two different bulk measures for mixing activity are then introduced, the vertically integrated decay of salinity variance, which is equal to the production of micro-scale salinity variance, and the vertically integrated turbulent salt flux, which is related to an increase of potential energy due to vertical mixing of stably stratified flow. Both measures give qualitatively similar results and identify the Drogden and Darss Sills as well as the Bornholm Channel as mixing hot spots. Further regions of strong mixing are the dense bottom current pathways from these sills into the Arkona Sea, areas around Kriegers Flak (a shoal in the western Arkona Sea) and north–west of the island of Rügen.     

Geographical variation and controlling mechanism of eddy-induced vertical temperature anomalies and eddy available potential energy in the South China Sea

Ocean Dynamics - Using observational temperature profiles, this study reveals that eddy-induced oceanic vertical temperature anomalies are geographically varying in the South China Sea (SCS). The...     

Hydrocarbons of bottom sediments at the Shtokman Field in the Barents Sea

Hydrocarbon samples taken from bottom sediments of the Barents Sea in summer 2010 in two grounds near the Shtokman Gas Condensate Field were studied. The concentration of hydrocarbons was found to increase with sampling depth along with a decrease in C_org concentration. The composition of alkanes had mixed genesis: autochthonous homologues (n-C₁₆-C₁₇) dominated in the low-molecular domain, while oil ones dominated in the high-molecular domain; light polyarenes dominated in the composition of polycyclic aromatic hydrocarbons. The seepage of hydrocarbons from the sedimentary stratum and their transformation in the surface layer of bottom sediments are considered as their major source. The relatively low hydrocarbon concentrations converted to dry mass and in the composition of C_org are supposed to be due to a decrease in the intensity of fluid flows, since the hydrocarbon reservoirs of the Shtokman Field are firmly capped by an impermeable stratum of mostly clay rocks.