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1.10.3. Sea Hydrology 1.10.3.1. Hydrological structure Conditions of hydrological structure formation are determined by internal and external factors: thermal and dynamic state of atmosphere, interaction of fluvial run off, coasts configuration, sea bottom relief. Apsheron rapids limits water-exchange between basins of Middle and South Caspian, promoting the formation in each of them by various hydrological structure. According to physical, chemical and biological characteristics of Azerbaijan section of the sea the following water masses were distinguished: Caspian upper water mass, Middle-Caspian deep water mass and South-Caspian water mass. Processes of winter cooling and mixing and summer warming as well as dynamic processes (stir, wind-generated current, subsurface waves) play an important role in the formation of Caspian upper water mass. Low border of this water mass is determined by deep spread of winter vertical circulation and located in Middle Caspian in the layer 150-200 m, in South Caspian-50-150 m. Middle water temperature insignificantly decreases by depth: from 6,8-7,90C on the surface to 6,0-7,40C on horizon 100 m. Saltiness of this water mass 12,7-13%, content of oxygen is high: in upper bed 7,5-8,0 ml/l in winter and 6,0-6,5 ml/l in summer on low border-no less than 4,5-5,5 ml/l. Deep water masses are formed owing to dense run off of cold waters from the north and eastern parts of sea into Middle Caspian basin and overflowing via Apsheron rapids into South Caspian basin. Deep water masses have the following characteristics: Middle Caspian - temperature 3,9-5,20C, saltiness 12,7-13%, content of oxygen 3,0-5,5 ml/l; South Caspian- temperature 5,7-6,30C, salinity 12,8-13,1%, content of oxygen 2,0-3,5 ml/l. Dense run off of cold waters promotes to renovation of deep water masses down. Their upper beds are pushed into bed covered by winter convection and subjected by season changes and transformed into Caspian upper water mass. 1.10.3.2. Thermal balance Thermal balance of sea surface (Fig. 27, 28) varies within wide ranges depending on season. In winter around the whole water area one can observe negative thermal balance. In January the most warm loss occur on Apsheron rapids (to -800 MJ/m2 per month), less loss (to -300 MJ/m2/per month) are observed in the coastal zone of Middle and South Caspian. Transition from negative thermal balance to positive one occur in March and there starts warming of surficial water bed. In April the most warm inflow is observed in distant from coast regions of Middle and South Caspian (400-500 MJ/m2/ per month, while in the coastal zone it makes 200-300 MJ/m2/per month. In summer distribution of thermal balance is more irregular. In July it makes 350-500 MJ/m2/per month in Middle Caspian and reaches to 500-600 MJ/m2 per month on Apsheron rapids and South Caspian. In the coastal zone values of thermal balance are 300-350 MJ/m2/per month in Northern Caspian and decrease to 100-300 MJ/m2 per month southward from Apsheron peninsula. In autumn negative balance is established above the water area. In October in Middle Caspian it makes –150-250 MJ/m2 per month in the coastal zone and 50-100 MJ/m2 in the open sea. In south direction negative values decrease in the open sea (-200-50 MJ/m2/per month). In the annual enumeration Middle and South Caspian are characterized by positive thermal balance-accordingly 1000 and 1500 MJ/m2 and Apsheron region-negative (-1000 MJ/m2 a year). 1.10.3.3 Temperature of surficial water layer Average-many-year spatial-time temperature changes (Fig. 29) are in the direct dependence upon thermal balance and advective transportation. In March one can observe a warming of water masses in the direction of the north to the south. Temperature on the coastal zone changes from 3-40C in the Samur mouth to 6-70C in Apsheron region to 80C in the south part of the sea. From April till August one can observe a continuation of temperature increase. In Middle Caspian water is warmed to 24-250C in Apsheron region to 25-26% and in South Caspian to 270C. In September water temperature near coast decrease to 2,5-3,50C and to the end of October makes 15-170C on the north of the water area 17-180C in Apsheron region and 18 -200C on the south. In open sea water temperature increase from 16-170C in the Middle Caspian to 19-210C in the South Caspian. Since November till February water temperature subsequently decrease: in the Middle Caspian to 3-50C, in Apsheron region-to 7-90C, in South Caspian - to 9-100C. 1.10.34. Saltiness of surficial water layer Formation of fields of saltiness in the upper sea bed occurs mainly under influence of fluvial run off, wind and water circulation (Fig. 30). Middle salinity of surficial waters in open sea is within 12,7-12,9%. Maximal long-standing fluctuations of saltiness in the northern part of Azerbaijan part of Middle Caspian has amount 1,6-3% in bed 0-5 m in the region of Apsheron trough-1,6%, in surficial bed and 2,1% at depth 5 m, in region of Kura river mouth (Kyur Dashy is.)-2% in surficial bed and 1,1% at depths 40-70 m. Average long-standing saltiness of surficial waters of coast in winter makes 10-12,5% on Middle and South Caspian and doesn't decrease less than 12% on Apsheron and Gobustan coast. In spring due to increase of fresh water tributary from Northern Caspian saltiness on coast of Middle Caspian decrease to 9-12%, bur is unchangeable in the rest part of water area. In summer (august) saltiness of surficial waters varies within 11-12,5%, abnormally increasing on coast of Apsheron to 13%. in autumn saltiness of surficial waters practically incompatible with its spring values. 1.10.3.5. Density Water and air temperature as well as wind force and continental flow influence upon field density formation (Fig. 31) in various seasons. In winter density in surficial bed decrease from the north to the south from 10,6-10,9 conventional unit in Middle Caspian to 10,1 conventional unit on Apsheron rapids and 10,0 conventiona unit in South Caspian. In spring transportation of freshened waters from the north by currents along the western coast promotes the formation of significant horizontal gradients. Density makes 10,0-10,1 conventional unit in region of the northern border increase to 10,3-10,4 conventional unit in Apsheron region and reduce to 10,2-9,8 in the south. In summer high air temperature promotes the decrease of density and in the surficial bed it varies within 7,3-7,4 conventional unit in Middle Caspian and Apsheron rapids to 6,8-7,3 conventional unit in South Caspian. In autumn density field reflects penetration of more cold waters from Middle Caspian into South. Here density of surficial waters varies from 9,8-10,1 conventional unit in Middle Caspian and Apsheron rapids to 9,5-9,6 conventional unit in South Caspian. Stable stratification with gradual density increase to 11,2 conventional unit in benthonic layers is typical for density distribution by depth. 1.10.3.6. Turbidity, transparency and water colour In different regions of Middle and South Caspian transparency is not the same and increase in the direction of open sea (Fig. 32). Minimal transparency (several centimeters) is observed near water flowing into Samur and Kura. On the rest parts of coast in winter, spring and summer makes 3-5 m and only in autumn (November) its values reduce in Middle and South Caspian to 1,5-3,0 m. Almost in all season year toward the central part of the sea transparency increase to 10-15 m, and in the South Caspian to 20 m. Wind mixing, mixture of marine and freshened water, different development of phytoplankton, organic matter carrying by rivers exert an influence upon water color (Fig. 33). In general water color on the most part of water area is green-blue or blue-green, on the local parts of coastal zone it under influence of various factors takes green rarely yellow tint. Blue color is retained by small zone in central part of South Caspian. 1.10.3.7. Currents Basic factors causing marine currents in Azerbaijan part of sea,-is a wind influence, especially upon the upper beds of the sea, and density field irregularity in the water thickness. Substantial influence upon character of currents makes also shore configuration and sea bottom relief, and in the pre-mouth regions-rivers run off. In the coastal one can observe mainly south-eastern and south, rarely northern and north-west currents (Fig. 34). Current on the area between Makhachkala and Apsheron peninsula is directed to the south-east, i.e. along the shore. Rod of current follows along isobit 50-70 m with velocities 30-40 cm/s, maximal rates can reach to 80-100 cm/s. Width of the main flow is almost 20-30 km. In the coastal zone between the basic stream and shore one can observe poor currents with rates approx. 10-15 cm/s. Rates decrease when they are distant from the rod of main flow toward the deep sea. There is a quasi-stationary anticyclone whirls-40 km in region between Derbent and Gilyazy Dili cape and quasistationary cyclone and anticyclone whirls 50-80 km with frontal side of Apsheron peninsula. Their formation is linked with peculiarities of bottom relief and coastline configuration. Stability of south currents within Apsheron peninsula between Chilov and Neft Dashlary is. is great enough. South current dominates by all wind directions, except the south one, causing currents toward the north. Currents toward the south are not only stable, but strong-to 80 in surficial and 50-60 cm/s in benthonic layers. Currents near the western shore of South Caspian mainly (70-80%) have a tendency to follow the wind. Within Baku archipelago and Kura mouth there dominate current toward the south. Near to the shore currents are frequently directed toward the north (50-60%). In the direct proximity off islands and banks currents direction is distorted. By poor winds rates 10-20 cm/s, by moderate-approx. 30 cm/s are typical for currents. By winds of northern directions with magnitude 8-9, rates approx. 40-50 cm/s and more were fixed. Typical currents peculiarity of studied region-presence of local anticyclone circulation being between Apsheron peninsula and Kura mouth. Calculation of total currents in Caspian sea showed, that in upper bed 0-10 m they are directed by wind, where by increase of wind direction above deep sea currents directions become more stable and rates increase. With depth vector of currents rotates to the right and in horizons 20-30 m currents directions become opposite the wind, i.e. there occur compensation water movement. Significant decrease of their rates and formation of distinct cyclone circulation in Middle Caspian is typical for vertical structure of currents lower the bed of friction in horizons 50-100. Anticyclone movement dominates on the north-west south part of the sea, in its eastern part in winter there occur water transportation toward the north. Seasonal change of currents field is manifested by their rates increase and more complicated distribution in summer, when baroclinity of water mass is large enough. In February currents are more poor and homogenous by direction. 1.10.3.8. Wind stir Wind stir (Fig. 35) reaching significant force determine conditions of upper water mass formation, thermocline depth of occurrence, represent a basic relief-forming factor in the coastal zone of sea. Strong and storm winds (rate more than 10 m/s) arefrequently established over regions of Middle Caspian, where storm activity has the most continuity. The more stable and hard storms are marked within Baku and Apsheron peninsula. The most water-dangerous directions of storm winds-north-western (north-north-western) and south-eastern. Maximal waves heights (10-11 m) by north-western storms are usually observed within Apsheron archipelago. Character of stir in various regions of Middle and South Caspian is differentiated by following peculiarities. In Samur-Devechi marine region by winds of northern directions the most waves heights 7-8 m in the coastal zone and 9-10 m in open sea. Eastern water mass transportation over Caspian sea by all wind rates (maximal 16-20 m/s) cause waves with height approx. 1,5 m. Large swells are observed by eastern winds. By south-eastern storms in the open part of sea the most wave height makes 6-7 m. Waves height varies within 2,5-3,5 m near shore to 5,5-7,5 m in open sea. Within Apsheron peninsula storm activity reaches the most intensity by northern and northern-western winds. Wind rate of northern directions almost every year can exceed 28-30 m/s. Area with maximal stir is toward the north-west from Neft Dashlary. By force increase of the north-west storm up to the hard stage (rates over 25 m/s) in epicentre of storm stir-to the north and east from Apsheron peninsula-one can observe waves with height 7,5-8,0 m, and during external storms to 9-10 m. here maximal waves height can reach 11-12 m. Storm activity within Baku archipelago of coastal zone and South Caspian considerably yield by force of stir within Apsheron. The strongest storms are observed by winds of northern directions. Waves heights vary within 1 m by moderate wind (5-9 m/s) to 4-5 m by strong storm (21-25 m/s). Eastern winds with rate 5-9 m/s cause the development of waves with a height to 1m with rate 10-15 m/s-waves with height to 2 m by rate of eastern wind 16-20 m/s waves heights reach 3-3,5 m, and periods-6 s. Poor stir (0,5-1,0 m) corresponds to the field of south-eastern wind on the whole water area of South Caspian. 1.10.3.9. Regression and surging phenomena Regression and surging phenomena are determined by strong and continuos winds. Water surging occur slowly and lasts several days, remove is frequently short. Northern winds promote the water transportation from Middle Caspian to the South with corresponding level decrease in the northern and level increase in the south part of water area. South and south-eastern winds are followed by reverse processes. In the northern part of water area of Apsheron archipelago winds of western rhombs determine level decrease and in the eastern ones-increase. In Baku Bay and water area of Baku archipelago regression is observed by northern winds, surge by south ones. Compensation benthonic currents toward the sea follow water surging; by water regression there occur benthonic currents of reverse directions. The most recurrence have surging and regression within interval 30-49 cm. Maximal surge in some cases reached 100 cm and more, maximal regression-80-85 cm. 1.10.3.10. Sea level change Observations over Caspian level near Baku footstock has been conducted since 1830. For the whole period of instrumental observations the highest level was in 1882 (-25,2 m). Condition relatively level balance which existed at the beginning of XX century changed by period of sharp decrease since 1930-1941 to 1,8 m. To 1977 sea level gradually decreased to -29,0 m, which is the lowest for the last 500 years. Since 1978 Caspian level started sharply increase and to 1995 reached -26.54 m. Starting since 1996 sea level subsequently decrease and to the end of 1999 was -27,11 m. Analysis of information shows, that average level position for the period 1830-2000 is -26,6 m. Reference
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