Research Article

The Hydromorphology of the Caspian Sea  

Homayoun Khoshravan1 , Ramiz Mammadov2
1 Water Research Center, Coastal Management Group, Caspian Sea Research Center, Iran
2 Geography Institute of Azerbaijan Academy of Science, Azerbaijan
Author    Correspondence author
International Journal of Marine Science, 2017, Vol. 7, No. 3   doi: 10.5376/ijms.2017.07.0003
Received: 23 Jan., 2017    Accepted: 04 Feb., 2017    Published: 15 Feb., 2017
© 2017 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:

Khoshravan H., and Mammadov R., 2017, The hydromorphology of the Caspian Sea, International Journal of Marine Science, 7(3): 19-30 (doi: 10.5376/ijms.2017.07.0003)

Abstract

The analysis of hydrology and morphologic characteristics of the Caspian Sea is main target in this paper. So by long term marine data analysis, the hydromorphology properties of Caspian Sea (morphology, fluctuation, temperature, salinity and transparency) have been studied. The main results show that the Caspian Sea as largest inland sea has unique morphologic condition and rapid sea level changing is the one of the most important natural process. The intensity of physical vulnerability and erosion risk in Caspian Sea is related to fluctuation rhythm and the spatial and temporal of marginal beach morphologic changing.

Keywords
Caspian Sea; Morphology; Hydrology; Fluctuation

Introduction

The Atlas of Caspian Sea Hydromorphology can be applied as a functional manual in designing and exploitation of oil and gas resources in continental shelf and abyssal zones, likewise it can be used in seafaring, fishing, fishery, dealing with problems related to the protection of marine environment, and forecasting the climate of the region (Mammadov and Khoshravan, 2012). The history of scientific researches done on the Caspian Sea water resources reveals that climatological observations were done in Caspian Sea during the eighteenth century. During the last 100 years, important activities have also been done on measurement of marine parameters by Azerbaijan Meteorological Organization (Azhydromet), Azerbaijan Institute of Geography, Transcaucasia Science and Research Institute of Climatology (Zaknigmi), State Oceanographic Institute of Russia (Goin), National Research Center of Caspian Sea (CSNRC), and other research institutes. The fixed and portable stations were chosen as the centennial stations. In this regard, the Baku, Fort-Shevchenko, Krasnovodsk, Makhachkala and Anzali study stations were selected as the water level gauging posts of centennial Caspian Sea water level. In addition, the centennial profiles were defined and eight centennial hydrological stations were specified in the Caspian Sea (Figure 1). As the result of marine explorations done by the above mentioned research and study organizations, a great database was produced and this paper is the outcome of analysis and processing of the data. It is crystal clear that without using these documents, it would be impossible to create a whole picture of the temporal and spatial variability of Caspian Sea hydromorphologic parameters. Caspian Sea hydrological behavior is different comparison to ocean during the Anthropocene period (Khoshravan, 2014). At the past two decade the ocean level has increased slowly but Caspian Sea level has been decreased (Khoshravan, 2014). The fluctuation rate of the Caspian Sea is 100 times more than ocean level changing (Leroy et al., 2013).

 

 

Figure 1 The position of Russians centennial measurement transects on the Caspian Sea

 

Statistic data improve the Caspian Sea level increased about 34 cm in year 1991. This amount is equal to ocean level changing during one century (Khoshravan, 2014). Therefore, the Caspian Sea fluctuation is the vital event and it is so hazardous for riparian countries The rapid sea level changing of the Caspian Sea has major impact on infrastructure and economic properties (Khoshravan, 2014). Therefore, crisis management and risk mitigation of fast fluctuation of Caspian Sea is so important and true predicting needs the historical record and finally precisely forecasting can help us to prevent the next hazard. The most important questions associated to the Caspian Sea integrated coastal zone management (ICZM) are what is reliable prediction of sea level changing during global warming? What natural crisis will happen if the Caspian Sea level decreases? How can we manage the unforeseen disaster? Historical records indicated that global sea level changing has been happening at the past and the ocean level had been increased about 110-135 meters after last glacial phase 18000 years ago (Feng et al., 2014). Geological clues approved that ocean level had been increased about 20-25 meters during early Holocene (7000-9500 years ago) (Warner et al., 2008). At that time the most volcanic activity had occurred and then the huge drought had destructed the Acadian empire in low latitude in mid- Holocene (4200-3800 years ago) (Warner et al., 2008). And the vast drought had been spread globally and Maya civilization in south American extinct in late Holocene (1000-1500 years ago) (Mamedov, 1997). So the fluctuation of sea level around the world was popular event during Holocene epoch. Now a day the human impact has caused the rate of sea level changing varied all around the world. Caspian Sea morphological figures are different around marginal coasts and sea floor (Mammadov and Khoshravan, 2012). And it can effect on erosion hazard impact and coastal vulnerability (Khoshravan, 2014). Low steepness beach in the north, north east to east have high inundation vulnerability when Caspian Sea arise (Khoshravan, 2014). On the other hand, the western and southern coasts of Caspian Sea with high steepness beach have low inundation risk (Khoshravan, 2014). The most important aims of this paper are, Caspian Sea level changing analysis in the past, recent and future and the introducing main characteristics of Caspian Sea hydromorphology.

 

1 Materials and Methods

In preparation of the present paper, the observatory data mentioned in marine calendars of Caspian Sea level changing related to years between 1830 and 2015 were used. For drawing bathymetry maps, first the Caspian Sea map in the scale of 1:1500000 was divided to 74 half degree squares in the environment of vector processing software (Figure 2). Then, the mean values of sea depth were defined in these squares (Figure 2). For each of the squares, the pitch is calculated using the X= tang a/b formula (a is the difference between two depths in one square and b is the distance between two depths. In this map, in addition to isobaths curves, the depth of various parts of Caspian seabed are presented (Figure 2). The depths are defined in proportion to the surface level of -28 from the Baltic Sea water level. The Caspian Sea Geomorphology map contains bathymetry figures, seabed slope angle and big seabed roughness. For drawing the schematic figures different methods were applied for various marine parameters which have been separately explained in the related sections. It should be previously mentioned that various statistical methods were applied for data processing including: averaging, interpolation, extrapolation, regression, etc. Also, the Surfer 8 software program was applied for presentation of data analysis results. This software was also used for drawing the schematic figures of Caspian Sea Hydromorphology. In truth, the study of data presented in the maps of this paper will help us know more about the abiotic features of the Caspian Sea, and the processing results can be exploited in the Caspian Sea applied sciences.

 

 

Figure 2 Caspian Sea division for processing the Hydromorphology data

 

2 Results

2.1 Caspian Sea general hydromorphology

The Caspian Sea which is the largest enclosed body of water in world is situated in an important geopolitical area named Eurasia. This body of water is surrounded by five littoral states of Azerbaijan, Iran, Kazakhstan, Russia, Turkmenistan; each one has respectively the shoreline of 850 km, 865 km, 1800 km, 695 km, and 560 km in the margin of Caspian Sea (Figure 3). The Caspian Sea shape is like a Latin Letter S and is stretched along the meridian ward. It is also situated between the latitudes 47.57 N and 36.33 N and longitudes 45.43 E and 54.30 E. The length of the Caspian Sea is 1200 km and its average width is 310 km. Its most and least breadth are 435km and 196 km. The Caspian Sea water level is 27 meters lower than Baltic Sea water level and in this situation its surface area and water volume are 392600 km2 and 78648 km3 (Kosarev and Yablonskaya, 1994). Caspian Sea is a deep lake with an extensive shelf and its depth is only lower than Baikal (1620 m) and Tanzania (1435 m) lakes which are the world’s largest lakes. The Caspian Sea average depth is 208 meters and the depth curve of its water volume distribution shows that major part of its water volume (62%) is distributed within the depth limit of 100 to 600 meters, 25.7% is distributed within the depth limit of 1-100 meters, and the other 16 percent is distributed within the depth limit of more than 800 meters. The Caspian Sea watershed area, with the surface area of 3.5 million km2. More than 130 rivers flow into this sea, among them Volga River is the first and the most important because of its discharging regime, and Kura River is in the second place (Kostianoy et al., 2005). In terms of the structural geomorphological, physiographical and meteorological features, the Caspian Sea can be divided into three parts of north, south and middle Caspian (Figure 3) (Kostianoy et al., 2005). The line connecting Chechnya islands and Cape Tiob-Karagan is chosen as the contractual border between north and middle Caspian, and the connecting line of Zhiloy and Cape Kuuli is chosen as the contractual border between middle and south Caspian. It is noteworthy that Mangyshlak bulge, as an underwater elevated strip with the depth of less than 10 meters, constitutes the natural border between north and middle Caspian from Tiob-Karagan peninsula to Cape Kulali and to Chechnya peninsula (Mammadov and Khoshravan, 2012). The Absheron bulge also naturally divides the middle and south Caspian. This asymmetric underwater bulge continues from Absheron peninsula to Cheleken peninsula. The seasonal waterways and rivers which flow into the Caspian Sea resulted in development of various deltaic shapes, the best example of which is the Volga river delta (Mammadov and Khoshravan, 2012). In the backshore and near shore zone of the north Caspian, the coast has a gentle slope. One of the important features of the northern coast of Caspian Sea is the low coastal regions which are sensitive to water logging cause by storm tide and seawater quick fluctuations. The Dagestan coast which is situated in the northwest of Caspian Sea is a narrow erosional plain and in its edges the novo Caspian terraces are observable (Mammadov and Khoshravan, 2012). In the south of Camur river delta, the coast is step-shaped and the gravel and sand alleviate sediments are observable on the terraces. The coastal structure of Kizlar region is very interesting. In this place, the great Caucasus Mountains end in Caspian Sea, and as a result the coast is rugged. In this place, the coastal plain narrows and its width reaches to 1 or 2 km. The shoreline in the western area of Caspian Sea is straight and flat, except from the Absheron peninsula region in where a compound series of synclines and arching cut the coastline. Kura Delta has severely progressed toward the sea and is considered as an important morphological component of the Caspian Sea southwest coast. The coast in the south of Lankaran is in shape of a marine plain and is connected to the present sand coast. This coast is restricted by strips of sand ridges in westward. Within the limit of Iran’s coastal strip, the Alborz Mountains range approaches the coast, so that the coast width narrows down and the breadth of the coastal strip reaches to 2 to 40 km. In the Iranian coasts of Caspian Sea, there are two big bays: Gorgan Bay (former Astarabad) and Anzali bay and there are Ashooradeh great island; and some small islands. The southern part of Caspian Sea, with the catchment area of about 174200 km2, includes the northern skirts of Alborz mountains range and the mountains in north of Azerbaijan and Khorasan where rivers are flowing towards the Caspian Sea. These areas generally have a steep slope and the latitude difference between the highest part (Damavand summit) and the surface of Caspian Sea is about 5700 meters (Mammadov and Khoshravan, 2012).

 

 

Figure 3 The physiography features of Caspian Sea

 

2.2 Caspian Sea floor configuration

Obtained bathymetrical map result (1:1500000 scale) shows that hydrography lines are closely spaced in the west and south while in the north and south they are strongly separated (Figure 4). The next map that we present is the map of mean gradients of sea bed surface (Figure 4). It is necessary to note the angles of slopes of the sea bed surface in the Caspian Sea are low and do not exceed 6-7° (shelf slope). The angle does not exceed 30’ in the shelf and in the sea floor. In the west and south of the sea the slope angle increases rapidly, while in the east and north the slope angle increases slowly. Due to low angles of the surface its area is only by 1000 km2 greater than the area of the sea surface. It is necessary to note that slop lines outline the structural features of the sea bed. The main morphological structure map of the Caspian seabed is drawn based on the map of bed slope angles in which some structures such as continental shelf, continental slope, and abysses are distinguishable (Figure 5). The maximal bed slope angle is 30 degrees but its width is not the same all over the sea bed. Meanwhile, in various parts of the sea, the final edge of continental shelf is in various depths of sea bed; in south and west of Caspian Sea, it is situated in depth of 50-100 meters, and in other parts it is in depth of 100-130 meters. As it is clear in the map (Figure 5), the continental slope edge exceeds the line connecting the 30 degrees’ slope dots, begins from continental slope, continues up to 650 meters’ depth and finally there is the Caspian Sea abyss plain. In Caspian Sea, the continental shelf is stretched with a low slope up to the depth of 100 meters of the sea bed (Figure 5). The continental slope, which begins from the terminal edge of continental shelf, continues to the 500-600 meters’ depth of the middle part and with a high slope it continues to the 700-800 meters’ depth of southern part. In the western coast, the continental shelf narrows and its width reaches to 40 km which again decreases in southern coast and the 400 meters’ depth is situated in the 5-6 km distance to the sea. The continental shelf in the Eastern coast is very broad and extensive and its average width is about 130 km (Figure 5). The coast and seabed roughness in north Caspian are covered with plain or precaspian land posts. In this plain, which is called novo Caspian, there are traces of sedimentary terraces of marine deposits related to various surface levels of Caspian Sea. In the south Caspian there are two marine troughs of Lankaran trough (with depth of 1025 meters) and Iran trough (with the depth of 800 meters). In the middle Caspian, there is Derbent trough with the depth of 788 meters). It should be mentioned that Caspian Sea bed slope angles in the continental shelf are not high (about 6-7 degrees). Meanwhile, the pitch in the shelf slope area and seabed doesn’t exceed 30 degrees. In the west and south of Caspian Sea, the seabed slope increases very fast, while in the east and north of Caspian Sea this process happens slowly. The geomorphology map of Caspian Sea bed and coasts of (Figure 6) is one of the main figures of this paper. In preparation of this map, the data of the three before mentioned maps and documents related to the resulted analysis of geological and geophysical research on Caspian Sea troughs were applied. The geomorphology map represents bed roughness of coastal zone and the present Caspian Sea shorelines. The following shapes are defined in the map of the sea bed (it is not provided here): shelf, shelf slop and sea floor and deep water depressions. The slope of the shelf is not greater than 30’ and its width is not the same everywhere while the edge of the shelf has different depths. In the west and south of the sea it is 50-100 m deep. In the other parts of the sea the shelf edge is 100-130 m deep. The edge of the shelf lies on the line that links points with slop 30’. After that the shelf slope starts that extends to the depth of 650 m. Then the sea floor begins where slopes again decrease and do not exceed 30’. Sea floor is followed by deep water depressions. There are two depressions in the Southern Caspian Sea: Azerbaijan depression–1025 m (the deepest one in the Caspian Sea) and Iran depression that is around 800 m deep. In the Middle Caspian Sea, the depth of depression (Derbent) is 788 m.

 

 

Figure 4 Map of slopes of sea bed

 

 

Figure 5 The map of seabed main morphostructure

 

 

Figure 6 Geomorphological map of the seabed of the coast of the Caspian Sea

 

2.3 Historical geology of the Caspian Sea fluctuation

The Caspian Sea is remnant basin of large parathetis ocean. Paleontology records show that the Caspian Sea was born as evaporate basin in late Miocene, Messinian stage (7 million years ago) (Mamedov, 1997). The Mediterranean Sea was separated from Atlantic Ocean by tectonic movements at the same time. And submerged beach had been dominated during this period. This process happened in the east of parathetis basin and Caspian, Aral, Black and Azov Sea had no connection together. In fact, this natural events had caused uplifting, folding and basin separation and huge evaporate sediment such as: gypsum and salts had been deposited on the floor (Khoshravan, 2014). At the same time the vast parts of internal lakes of Iranian platform had been submerged and red iron oxide sediments deposited. But in the early Pleistocene (5 million years ago) frequent raining had caused harsh flooding and rock erosion promoting, then the fresh water lake appeared and productive conglomerate had been deposited (Chelken formation). Then the depth of Caspian basin increased and marine environment had reformed and several mollusks with carbonated sediment made Agchagilian formation in middle to late Pliocene. In the early Pleistocene, Apsheron sandstone with brackish water mollusks fossil had been deposited in the Caspian Sea basin (Khoshravan, 2014). Therefore, there was a full sedimentary cycle along the Pliocene and Pleistocene with apparently thickness 15 Km. Caspian Sea southern basin had been subsided with velocity rate about 44 mm/year along 5.5 million years’ period (Kakroodi et al., 2012). In the late Pleistocene the Caspian Sea level was increased more than 50 meters and it have been continuing for 1000 years and the Caspian Sea has connected to Black sea through Manych-Kretch waterway (Leroy et al., 2014). At that time mollusks of Caspian entered to eastern part of Black sea. Then sea level of Caspian Sea with unprecedented speed decreased and iron oxide and Gypsum had been deposited in Mangheshlagh regression (Leroy et al., 2014). In the early Holocene (10000 years ago), Caspian Sea level had increased and it reached to -22 meter below ocean level (Kroonenberg et al., 2000; Leroy et al., 2014). At that time the salinity of southern coast of the Caspian Sea is less than middle part and it associated to eastern rivers input (Mayewski et al., 2004). Palynological records show that the sea level of Caspian Sea had been standing at the high level and Uzboy river run off had contributed to Caspian transgression (Leroy et al., 2014). In the beginning of early Holocene there were several huge ice sheet on Himalaya mountains and the ice melting created the high volume run off toward the Caspian Sea (Leroy et al., 2013). This process had been happened while the weather was warmer in northern part of Caspian Sea and the amount of northern run off was little. And salinity inversion had occurred toward south basin of the Caspian Sea. Uzboy River received its water from Sarykamish lake and Amoudarya lake and they were depended in Tin shine mountains ice melting (Leroy et al., 2013). Antropogenic impact on Uzboy River during 13 centuries and the first of 20 century caused Caspian Sea hydrological cycle balance disrupted. The derbent regression phase in 1500 years ago is so important. At that time the Caspian Sea level reached to -32 meters (Leroy et al., 2013). Then the transgression phase of the Caspian Sea had occurred in 700 years ago during little ice age and the level of Caspian Sea reached to -22 meters (Leroy et al., 2014). Paleogeography and morphology records approved that the Caspian Sea has alternatively fluctuation since early Holocene (Rychagov, 1997). On the basis of gaining results in the study of marine terraces in Daghestan, five transgression phase has been distinguished which belong to 8000, 7000, 6000, 3000, and 200 years ago (Hoogendoorn et al., 2005). Three sedimentary terraces have been determined in Iranian beach zone with age 2500, 900 and 500 years ago which those are located in -22, -24 and -25 meters below mean global sea level (Kakroodi et al., 2012). So the highest level of Caspian Sea during the Holocene is -22 meters and lowest level is -32 meters (Kroonenberg et al., 2000). There is precisely corresponding between Caspian Sea level changing and Urmia Lake during Holocene epoch (Khoshravan, 2015). There were three regression phase in Urmia lake like Caspian Sea in 12000, 4000 and 1200 years ago (Khoshravan, 2015). Geological clues show the periodic phase of Caspian Sea fluctuation have been happening with duration 400 years (Mamedov, 1997) (Figure 7). On the basis of this theory, we are expected the recent regression phase of Caspian Sea that began from 1900 years will be continuing by 2100 years. But the last transgression phase of the Caspian Sea during 1977-1995 years, ratified all this forecasting.

 

 

Figure 7 Fluctuation curve of the Caspian Sea during Holocene epoch (Rychagov, 1997)

 

The historical geology of the Caspian Sea indicates that tectonic movements has separated parathetis basins from each other during late Miocene and climatologic impact during last glacial phases have caused periodic fluctuation of the Caspian Sea. The limitation of Caspian Sea watershed area has caused this basin hydrologically depend on precipitation amount, run off rate, temperature and evaporation process for water level balance. So in the global warming phases, the evaporation fivefold increased more ratio precipitation and Caspian Sea level intensively dropped. This process has caused the difference behavior of Caspian Sea hydrology to ocean fluctuation function. For example, the separation of Uzboy River from Caspian Sea decreased the water level during late Holocene. Other vital river like Volga has important action in water level balance of Caspian Sea and human activities during 1930 to 1995 had caused a full fluctuation cycle with 6 meters’ amplitude (Rychagov, 1997).

 

2.4 Caspian Sea level fluctuation (1830-2015)

The water level fluctuation is one of the most important non-biological properties of Caspian Sea which makes it distinctive from other great lakes on the earth. The analysis of level change situation in Caspian Sea water in historical periods and in the present time shows that there is a close relationship between the water level fluctuations and the global climate changes. This means that the climatic processes, which cause in change of humidity and heat exchange, influence this area; although, the role of human intervention in the processes of Caspian Sea water level change is noticeable. The ancient historical and geographical information shows that the level change process in Caspian Sea water is periodic and these changes ranged between 15 to 25 meters during the last 5 to 12 thousand years. The most complete historical reconstruction done based on archaeological evidences and the evidences of ancient weather condition have determined the water fluctuations from 2 to 3 thousand years ago with the accuracy of ten years. In the historical period, the long-term mean of Caspian sea water was -27 meters and it’s variance was 0.04 centimeter from 7th century B.C to 7th century A.D and fluctuated +0.03 centimeter from 8th century B.C up to now. In the historical period, the maximal water level stagnation is 40% in the altitudinal range of -25 to -27 meters, and the reiterative period of 70 percent of changes is in -24 to -30 meters level height. The data of historical period shows that the long-term mean of seawater level fluctuation in the present time is oriented toward level rise up to 0.3 centimeter per year. But, after the 7th century this amount was about 0.5 centimeter per year. Since 1837 and in the era of instrumental record observations, the range of Caspian Sea water level fluctuations has been about 4 meters and it has ranged from -25.2 meters in eighties to -29 meters in 1977. To do investigations on the long-term changes of Caspian Sea water level in the instrumental record era, the data of hydrology posts with the long-term observation series were used. The only fluctuation recording station in Caspian Sea which has the complete observatory series is the Baku gauging station (1830-now). Considering the Caspian Sea water level changes, several index periods can be mentioned. For instance, from 1830 to 1883 or in 50 years the condition of water level was almost constant in the height of -25.2 to -26.2 meters. The long-term decline period has started since 1883and lasted for more than 100 years, since then the Caspian sea water level declined with the speed of 2 centimeters per year until 1940 (between 1883-1993), and from 1934 to 1940 it declined with the speed of 20 centimeters per year. After 1940, the sea water level falling process slowed down and reached one centimeter per year. The process of seawater level decline, which has dropped 3.8 meters from 1883, ended in 1977, and from 1978 the Caspian Sea started progressing with a high speed of about 14 centimeters per year. This process continued till 1996 and in this year the water level reached -26.52 meters. In some years, the speed of Caspian Sea water level rise reached 45 centimeters per year. This period of water level rise has been the longest period in the era of fluctuations recording. From 1996, the Caspian Sea water level again started its downward process until the water level reached -27 in the present time. In the era of instrumental record, the fluctuations with the positive growth exceeded 30 centimeters three times (38 centimeters in 1867, 32 centimeters in 1979, and 39 centimeters in 1991). This index was also negative two times (32 centimeters in 1851 and 31 centimeters in 1937). The analysis of long-term changes of Caspian Sea water level reveals that water level in the era of instrumental record was fluctuating between the -25.2 and -29 meters; in other words, the fluctuation range was 4 meters in this period. The frequency probability of 50 percent of Caspian Sea water level has been defined in the -26 height during the instrumental record era. The maximal periodicity of Caspian Sea water level fluctuations with the frequency of 55 percent exists in the level range of -25.5 to -26.3. This range can be considered as the hydraulic index of Caspian Sea water level, and lots of scientists use the water level mean as a criteria for calculations. Like other closed body of waters in the world, the curve of Caspian Sea water level fluctuation is analyzed monthly and seasonally. The annual budget is determined by studying the relation between input and output components. The maximal Caspian Sea water level has been observed in summer and the least level has been observed in winter. The maximal fluctuation range reaches to 50 centimeters in wet years, the least range reaches to 15 centimeters in dry years, and the measured range is -29 centimeters.

 

Average annual levels of the Caspian Sea in the instrument-aided observation period of 1930-2010 are shown on Figure 8. As it shown by the figure in 1830-1930 the average annual sea level varied approximately within one-meter range. Sea level high stands at 25.4 m in the Baltic System and above this level were observed in 1838 and 1939, in 1868 and 1869 and in 1877-1883. In 1882 the average annual level reached 25.2 m (maximum in the observation period). Relatively low sea level of -26.2 m in the Baltic System was observed in the 50s of the last century and in 1911-1914. The highest drop of the sea level to -26.6 m was observed in the last year of 1920-1925 period. Sea level datum in 1830 - 1930 was -25.83 m in the Baltic System or 340 cm above zero level of Baku depth gauge in 1920 elevation. Relative equilibrium state of sea level was followed by the period of abrupt drop in 1930-1941 by 1.9 m. The sea level drop although not such strong was resumed in the end of the 40s; in 1956 sea level was by 2.5 m below the 1929 level. In the 60s the sea datum stabilized at the level of around -28.4 m and in 1970 the sea level abruptly dropped and reached -29.0 m in 1977. Total drop in the entire period of systematic observations was 3.8 m. Total drop of the sea level in the 20th century was 3.2 m. Sea level dropped with an average intensity of around 4 cm/year. In 1930-1941 and 1970-1977 sea level drop intensity increased to 16 cm/year and 14 cm/year, respectively. After 1978 the sea level started to rise and in 1995 the average annual sea level rose to -26.52 m. The intensity of the sea level rise in this period in average was around 14 cm/year and in some years it reached 30 cm. This is most intensive and prolonged sea level rise over the entire period of instrument-aided observations. The change of the sea level affects the water volume and the area of different parts of the sea (Table 1). While the total area of the Northern Caspian Sea is 91942 km2, the area of its water surface is 90129 km2. The Northern Caspian Sea accounts for more than 24.3% of the total sea area. The Middle and the Southern Caspian Sea have almost the same area. Total area of the Middle Caspian Sea is 137812 km2 the Southern Caspian Sea is 148640 km2 or 25.788 m and 1029 m, respectively, average depth 4.4, 192 and 345.

 

 

Figure 8 The Caspian Sea datum in the period of instrument-aided observations according to the data of Baku sea gauge

 

 

Table 1 Variation of the area of the Caspian Sea

 

2.5 Caspian Sea fluctuation future

The forecasting of Caspian Sea level fluctuation is problematic function and more predictions which have done by scientists were no precisely correct. But geological clues approved the cyclic fluctuation rhythm as above mentioned there was 25 meters’ difference in sea level height during Holocene Epoch and 10 meters during past 1500 years ago. Nowadays the global warming impact on Caspian Sea level changing has been accepted and it has been predicted if the atmosphere temperature arise the Caspian Sea level will be dropped about three meters by 2100 years. So more marginal basin like estuaries, Lagoon, swamp and Bay will be submerged and environment vulnerability and crisis threaten human societies along the riparian countries. Now there is enough time for hazard mitigation and crisis management.

 

2.6 Water temperature

The spatial and temporal variability of Caspian Sea water temperature depends on geographical situation, heat exchange between atmosphere and water mass, and the thermal energy transfer between sea and rivers. The distribution of annual mean values of water temperature in long term is considered as the most important thermal index of Caspian Sea. In fact, this criterion confirms the effect size of seawater heat on climate of its surrounding lands (Figure 9). The water temperature in offshore and abyssal zone in precaspian adjacent area (North of Caspian Sea) is 18 degrees centigrade different from the southeast of Caspian Sea. The flow of Volga, Terek, and Kura rivers and the blow of dominant winds in the region cause in reduction of sea water temperature in the northern part (Figure 9). In the eastern half, the outflow of cold waters from Caspian Sea bed impacts the annual temperature distribution and causes in thermal disturbance in the Caspian Sea water temperature. In the western part of south Caspian, the variance of annual mean temperature is not so high (about one degree centigrade). The maximum annual temperature variance of Caspian Sea water surface is 20 degrees centigrade, and this amount is observed in the northern areas and south Caspian coasts (Figure 9). This process is the result of temperature difference of extreme heat in summer and bitter cold in winter. The least temperature change has been observed in the south Caspian Sea waters. In the eastern and western coasts of middle Caspian where the upwelling phenomenon happens, the annual mean temperature variance decreases to 14 to 15 degrees centigrade. In the map of annual mean temperature distribution on the Caspian Sea surface water, in some seasons the water temperature is abnormal and this situation is influenced by factors which in short period impact the sea basin as dominant processes.

 

 

Figure 9 The annual average of Caspian Sea water surface layer temperature

 

2.7 Salinity

The wide range of long-term mean changes of Caspian Sea water salinity is between 1 and 13.5 per thousand. This variance is especially noticeable in north Caspian because of influence of Volga River current. However, the salinity variance is lower in other parts of Caspian Sea. As showed in the salinity map (Figure 10), the salinity fall in Volga river estuary in comparison to Caspian Sea south east water area is about 12.5 per thousand. This salinity rate is the very isohaline line in the western margin of south and middle Caspian. In other parts of Caspian Sea, salinity rate is between 13 and 13.5 per thousand. In the Absheron region, the isohaline curve by a little rotation makes a bulge which represents the saline water mass stretch with the salinity of 12.5 per thousand in this area. The flow of rivers’ sweat water causes in this phenomenon. These rivers first flow into the middle Caspian from the western coast; then, by entrance of other currents they fork to two tributaries which flow in cyclone and anticyclone directions in the Caspian Sea. The lack of river network in Caspian Sea southeast causes in salinity rise of seawater in this region (13.5 per thousand). This particular situation can be clearly observed within the Cheleken peninsula region. In winter months, the total salinity rise generalizes in all the Caspian Sea water area, even the northern part of Caspian Sea is not an exception in this regard. In fact, in the cold season, the major part of Caspian Sea water area has the isohaline salinity range of about 12.5-13 per thousand (Figure 10). In this season, because of glacial the effect of rivers’ sweat water on the coastal waters’ salinity declines and in the western areas of Caspian Sea the salinity stabilizes at the rate of 12.5 per thousand. In summer, the horizontal variability of this salinity index severely rises in north Caspian and lies at the range of 1-12 per thousand. In the continental slope of the northern part, in a short period the changes reach to 8 to 12 per thousand. It should also be mentioned that sea water salinity index in some parts is observed at its extreme level. Although, the salinity of Garaboghazkol bay water with the rate of 300 per thousand is an exception.

 

 

Figure 10 Average annual salinity of Caspian

 

2.8 Transparency

The transparency variability figures of Caspian Sea water were drawn using the Standard centennial observatory data of hydrology profiles (Figure 11). The Caspian Sea water transparency increases with depth incensement. Almost, in all the seasons the water transparency in the central part of Caspian Sea is about 10-15 meters. The maximal transparency has been observed in the region of Lankaran trough. In this area, the maximal water transparency has been measured in the depth of 20 meters in summer, in July. The least water transparency has been recorded with in depth of one meter in Volga river mouth, north Caspian. In north Caspian, the maximal water transparency has been observed in April and July or when the sea waves are less effective and the amount of fluvial drifts are lower. According to the data mentioned in the map of Caspian Sea water transparency, in all the seasons the transparency in the western part is less than the eastern part of Caspian Sea (Figure 11).

 

 

Figure 11 the annual mean of Caspian Sea water transparency

 

3 Conclusions

On the basis of main results can conclude that temporal index of Caspian Sea fluctuation is related to global climate change and glacial period had great effect on the Caspian Sea level changing during late Pleistocene and Holocene. Recent global warming impact and human activities have caused many periodic fluctuations in the Caspian Sea with high velocity which is 100 time more than ocean fluctuation. Low precipitation and high evaporation is vital issue during drought period for Caspian Sea fluctuation. The fluctuation amplitude of Caspian Sea was 150 meters during late Pleistocene and Caspian Sea level has fluctuated about 25 meters at the Holocene epoch. So rapid sea level changing is the most characteristics of Caspian Sea and integrated coastal zone management is so vital plan for crisis management and hazard mitigation. Morphological configuration of Caspian Sea has causes different beach response during rapid sea level changing and the coasts of Caspian Sea have been classified to three morphodynamic condition (Accretion, intermediate and erosion). So low steepness beach in the north to north west and East to south east have high degree physical vulnerability to Caspian Sea fluctuation and the high steepness beach in the south and western part of Caspian Sea have low inundation risk during sea level rise. Now a day Caspian Sea level has been decreasing since 1995 years and many of marginal basins like Miankaleh lagoon and Gorgan bay in the south-eastern of Caspian Sea submerged and drought.

 

Authors’ Contributions

I am interested to have special thanks from Prof. Dr Ramiz Mammedov who has been professional collaboration with me to prepare this paper and I must confess that he had huge effort to monitoring Caspian Sea hydromorphology characteristics. It was appreciated him for all attempting and kindness.

 

Acknowledgments

It is vital pleasure to thank, all experts and academic member who accompanied with us in this research paper, we acknowledged the institute of geography of academy science of Azerbaijan republic and Caspian Sea national research and study center of Iran, which support us to have some data and information associated to Caspian sea hydromorphology and fluctuation.

 

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