Determination of the fluctuation of the Caspian sea water in recent century by surveying calcium amounts in coastal sediments-A case study at Sari region

1520-1525<span style="font-size:9.0pt;font-family: " times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";mso-bidi-font-family:="" mangal;mso-ansi-language:en-gb;mso-fareast-language:en-us;mso-bidi-language:="" hi"="" lang="EN-GB">In this study fluctuation of the Caspian Sea level in recent century was determined by surveying the sediments types, facial changes and calcium amount in sediment samples. Study was done by collecting 3 sedimentary cores of the Southern shores of the Caspian Sea in Sari region. In field operation after complete description of the cores and consideration of the color, organic matter content, sedimentation rate and cohesion characteristics, etc, facies were separated and from each facies a sedimentary sample was taken. Findings suggest that there is a positive correlation between the changes in calcium concentration in samples and the Sea water level but a negative correlation between the Sea water level and size of gravel in various periods. Indeed, it was found out that with an increase in the amounts of calcium from surface (new) to depth (old) and decrease in the percentage of gravel from the surface to depth the Sea water level decreases.</span

Distribution of coccolithophores as a potential proxy in paleoceanography: The case of the Oman Sea monsoonal pattern

High abundances of coccoliths have been observed in surface sediment samples from near the coasts of the Oman Sea in February 2011. At the end of the NE monsoon, the locally observed high Gephyrocapsa oceanica production is hypothesized to respond to local injections of nutrient-rich deep water into the surface water due to sea-surface cooling leading to convection. The most abundant coccolithophore species are G. oceanica followed by Emiliania huxleyi, Helicosphaera carteri, Calcidiscus leptoporus. Some species, such as Gephyrocapsa muellerae, Gephyrocapsa ericsonii, Umbilicosphaera sibogae, Umbellosphaera tenuis and Florisphaera profunda, are rare. The G. oceanica suggested a prevalence of upwelling conditions or high supply of nutrients in the Oman Sea (especially West Jask) at the end of the NE monsoon. E. huxleyi showed low relative abundances at the end of the NE monsoon. Due to the location of the Oman Sea in low latitudes with high temperatures, we have observed low abundances of G. muellerae in the study area. Additionally, we have identified low abundances of G. ericsonii at the end of the NE monsoon. Helicosphaera carteri showed a clear negative response with decreasing amounts (relative abundances) at the end of the NE monsoon. C. leptoporus, U. sibogae and U. tenuis have very low relative abundances in the NE monsoon and declined extremely at the end of the NE monsoon. F. profunda, which is known to inhabit the lower photic zone (<100 m depht) was rarely observed in the samples

Subsidence risk assessment based on a novel hybrid form of a tree-based machine learning algorithm and an index model of vulnerability

Among natural hazards, land subsidence (LS) is considered to be one of the most significant natural disasters which occur in populated and inhabited regions of Iran. The Varamin aquifer, as one of the regions near the capital of Iran, where this geo-hazard has occurred widely and extensively, requires conducting comprehensive researches on LS. In this research, for LS risk assessment, the combination of a GIS-based hybrid model of the fuzzy-support vector machine (FSVM) as a new approach in the LS hazard assessment and an index model of vulnerability for LS vulnerability assessment were employed. From the hazard assessment viewpoint and according to the review of literature, fifteen factors affecting subsidence were arranged, and these parameters were normalized with the fuzzy membership functions based on their type of impact on LS. Moreover, for overlapping the parameters, the support vector machine (SVM) model and its three main kernels functions were used. Then, seventy percent (2919 pixels) of the data were used for the train and thirty percent (1251 pixels) were used for the test. The results of hazard model verification using receiver operating characteristic (ROC) showed the RBF kernel has the best performance result. From the vulnerability assessment viewpoint, an index model was developed using nine factors that can be damaged and affected by the LS, based on the literature review. In this regard, the Saaty’s paired comparison method was used to assign a weight to each of the vulnerability parameters, and then the parameters were aggregated to build the vulnerability map. Considering the vulnerability, 21% of the Varamin aquifer was classified as high and very high. Lastly, the risk map was obtained with the overlay of the hazard and vulnerability maps. The resulting map can be used by risk managers to make decisions that lead to reducing injuries and damages of LS

A study of textural and accumulation heavy metals of sediments in mangrove ecosystem of Persian Gulf, South Iran

78-85Sediment samples this area were collected during December 2013 to April 2015. Seven heavy metal concentrations, grain size, organic carbon and carbonate contents were studied in order to assess the extent of distribution pollution and to discuss the origin of these contaminants in sediments. These sediments contain varieties of sediment types including sandy silt, silty sand and sandy. The mangrove area was characterized as poorly to extremely poorly sorted sediment environments. Sediments were identified as strongly fine skewed with very leptokurtic character. Contamination of sediments was assessed on basis of geoaccumulation index (Igeo), contamination factor (CF), Modified degree of contamination (mCd) and Pollution load index (PLI). Result of Contamination indices indicated that the sediments were uncontaminated with Pb, Zn, Cu and Fe, uncontaminated to moderately contamination with Cr and Ni, moderately to heavily contaminate with Cd in mangrove ecosystem in Hara Biosphere Reserve, Persian Gulf

Mineralogical reconstruction of Late Pleistocene -Holocene climate and environmental changes in southern wetlands of Lake Urmia

International audienceTo determine the effect of climate changes on current critical conditions of Lake Urmia, paleoclimate of southern wetlands of Lake Urmia was investigated based on clay mineralogy. Kani Barazan and Solduz wetlands on the southern margin of Lake Urmia and also the southern part of the lake have been briefly studied in this research. A total of 24 sedimentary cores were taken for sedimentology and mineralogy study from south to north of Lake Urmia. The clay mineralogy analysis were done by XRD method. The main minerals in the sediments include quartz (over 40%), calcite, feldspars, mica, dolomite and clay minerals. Chlorite and kaolinite were the main clay minerals in the southern coastal plains of Lake Urmia. Distribution of surface samples represents reduction of clay minerals in the sediments from the margin to the center of the basin. This indicate that the percentage of detrital sediments decreases and chemical sediments increase from the margin to the center. Increasing the distance from the edge of the wetland causes it to move away from the source of the sediments. The concentration of water salts in the central part of the basin increases. In the central part of the lake, due to greater depth and high salinity of water, chemical sediments have been predominant and in the margins of the lake, according to low salinity and the volume of clastic materials, this kind of sediments have been predominant. This is consistent with the changes in other clastic minerals (quartz) in the lake. The level of clay minerals increased from the surface to the depth of boreholes indicating a high water level and a more warm-wet paleoclimate. According to the changes in the type of clay minerals in the sediment sequence of the southern part of Lake Urmia, it seems that in the Late Pleistocene (20 cal ka BP) the weather was more humid than the current conditions and the volume of clastic material to the lake was higher

Identifying the effects of climate changes on sedimentary environments and determining the sedimentation rate of south wetlands of Lake Urmia during Late Pleistocene and Holocene

International audienceThis study investigated the evolutionary history of the Late glacial in number of wetlands in south part of Lake Urmia. Twenty-six cores with a maximum depth of 12 m, average 8 m and total depth of about 190 m were collected from sediments under the southern and southwestern wetlands using a handi auger. Sedimentary facies were identified and separated based on sediments texture and structure, composition of evaporite minerals and organic materials, also color and other macroscopic elements. The results indicated the presence of eight distinct sedimentary facies belonging to the lacustrine, wetland and fluvial (river) sedimentary environments. In the last 20 cal ka BP, the two dominant dry periods, about 4 cal ka BP and 13 cal ka BP, have been associated with the transgression of dry (alluvial) facies towards the lake and the regression of Lake facies. The dry period 4 cal ka BP affected the southern part of Lake Urmia and marginal wetlands, while the dry period 13000 years ago was more intense and longer and lasted at least 3 cal ka BP

Sedimentary evolution and lake level fluctuations of Urmia Lake (north-west Iran) over the past 50 000 years; insights from Artemia faecal pellet records

A 25 m long sediment core from hypersaline Urmia Lake (north-west Iran) was studied for the Late Quaternary depositional history and palaeoclimate variations using the abundance and compositional characteristics of Artemia faecal pellets. Sediment analysis is supported by scanning electron microscopy - energy dispersive X-ray spectroscopy, organic and inorganic carbon content measurements, and stable isotopes (delta C-13 and delta O-18) from faecal pellet carbonates. The imprecise chronology of the core back to 50 kyr bp is supported by ten radiocarbon ages from faecal pellets and bulk sediments. The palaeoenvironmental record is subdivided into four periods: (i) During much of Marine Isotope Stage 3, a period of lake level lowering is characterized by a decreasing amount of faecal pellets, and an increasing amount of coated grains, sulphate minerals and reworked shell fragments. (ii) During late Marine Isotope Stage 3 and early Marine Isotope Stage 2 a lake level lowstand and a lake floor exposure is interpreted based on the relatively low abundance of pellets, which are multicoloured and appear together with volcanic lithics and rounded sulphate minerals. (iii) During late Marine Isotope Stage 2 the record is devoid of pellets but dominated by large sulphate crystals suggesting a prolonged low lake level. (iv) During Marine Isotope Stage 1 a relative lake level highstand is rapidly established with sediments that are highly abundant in fresh pellets. The modern lake level lowstand is represented by a salt crust. The delta C-13 and delta O-18 records measured from faecal pellet carbonates suggest a link with the precipitation versus evaporation balance in the lake over time. From bottom to top the linear trend towards more negative delta values illustrates the increasing amount of precipitation arriving at the lake from the Late Pleistocene to the Holocene. Two prominent isotope minima during the Late Pleistocene and one prominent minimum in the early Holocene mark relative high lake levels, which can also be linked to Lake Van in Turkey.ISSN:0037-0746ISSN:1365-309

Distribution of benthic foraminifera along the Iranian coast

This study focuses on the distribution of benthic foraminifera along the Iranian coast of the Gulf, extending over 1000km from the northeast close to Shatt Al-Arab/Arvand Rud to the southeast near the Strait of Hormuz where it connects to the Indian Ocean. The Gulf is a naturally stressed environment due to extremes of salinity and temperature and anthropogenically affected by rapid urbanization, maritime transport, desalination plants, and oil platforms. Historical records and distributional studies have commonly underestimated the benthic foraminiferal diversity in the Gulf. Thirty-two samples collected from depths between 20 and 45m were analyzed for total (unstained) foraminiferal assemblages. A total of 221 benthic foraminiferal species and subspecies belonging to 69 genera, 34 families, and 6 orders were recognized. The assemblages are dominated by hyaline taxa (49%) and porcelaneous foraminifera (36%), while agglutinated foraminifera represent only a minor part (15%). The ten most abundant species are Nonion sp. 1 (5.8%), Quinqueloculina sp. 1 (4.7%), Asterorotalia dentata (4.2%), Bolivina cf. B. persiensis (3.9%), Asterorotalia sp. 3 (3.5%), Rotalinoides gaimardi (3.4%), Ammonia sp. 1 (3.3%), Quinqueloculina sp. 8 (3.3%), Bolivina cf. B. striatula (3.0%), and Nonion sp. 2 (2.8%). We speculate that increase of finer sediments (mud), availability of nutrients, and the presence of oxygen are factors controlling the diversity and distribution of benthic foraminifera. The current thermal regime in the Gulf has been cited as a model for the tropical ocean in 2090-2099. In light of it, foraminiferal assemblage structure, composition, and distribution may provide an insight into the nature of biotic response to future climate change in the Gulf region under conditions of global warming and a baseline for future comparison within and beyond the Gulf. This study also updates the knowledge on the types and distributions of benthic foraminiferal groups in this poorly known area