What happened to the Caspian sand in the death note?

The largest closed inland sea in the world. Located between Europe and Asia, most areas in the east, south and west are surrounded by Karakum Desert, Elbers Mountains and Great Caucasus Mountains respectively, and the Volga River and ural river flow into the north. The length from north to south is about1200km, and the average width from east to west is 320km. The coastline is about 7,000 kilometers long, and now the total area is about 394,000 square kilometers. Average water depth 180m and maximum water depth 1025m.

The Caspian Sea is a part of the ancient Mediterranean Sea, which was once connected with the Black Sea and the Atlantic Ocean. It was not until the late Miocene that it gradually became a closed water area. Up to now, the South Caspian Sea still retains the characteristics of marine bottom water. Therefore, oceanographers believe that although the Caspian Sea is surrounded by land on all sides, it can still be regarded as a sea.

Geology and geomorphology The whole sea area can be divided into three parts: north, middle and south, separated by many islands and shoals. Beili coastal slope is gentle, and the water depth is very shallow, only 4 ~ 8 meters, and the deepest part is only 25 meters. The seabed is a corrugated sedimentary plain, and the water volume only accounts for 1% of the total water volume. In the Middle Caspian Sea, there are many steep slopes on the coastline of the Great Caucasus Mountains, and the east coast is relatively steep near the Mangeshlak Plateau. The bottom is the shelf in the east and the Gerbat basin in the west, with a water depth of 790 meters; Water accounts for about one third of the Caspian Sea. The South Caspian Sea has a low coast, a broad east-west continental shelf and a depression in the west. It is the deepest part of the Caspian Sea, with a large amount of water, accounting for about two-thirds of the entire Caspian Sea. Seabed sediments and sand containing shells in the North Caspian Sea; There is much mud and sand in the middle Caspian depression, and there are many shells, gravel sand and clay on the east and west coasts. The deep water area of the South Caspian Sea is silt and clay containing thin layers of iron sulfide, and the marginal areas on the east and west banks are sand, lime mud, shells and gravel.

The climatic sea area spans several different climatic zones. Although the North Caspian Sea has a continental climate, the change is not drastic. The middle Caspian Sea has a mild climate in the west and a dry desert climate in the east. The South Caspian Sea has a subtropical climate and is dry in summer. In winter, the weather in Caspian Sea is unstable and the temperature changes greatly. The average temperature in the north is -8 ~- 10℃, and the average temperature in the south is 8 ~ 10℃. The wind direction is changeable, mainly from the east and northeast. The wind force is 5.5 ~ 10.7 m/s, and sometimes it can reach 20.8 ~ 28.4 m/s in the middle. In summer, the ocean is controlled by high pressure, and there is often a weak sea breeze blowing to the land, so the weather is very stable. The temperature has not changed much. The average temperature in the hottest month is 28 ~ 29℃, the extreme maximum temperature can reach 44℃, and the annual average precipitation is 200 ~ 1700 mm, which is unevenly distributed, with less in the east coast and more in the southwest coast. The annual evaporation is generally 1000mm, reaching 1400mm in the eastern part of the South Caspian Sea and the Apsheron Peninsula.

The hydrological characteristic flow is mainly cyclone circulation, and some local circulation can be formed in each sea area. After entering the sea, the North Caspian Sea and Volga River are divided into two tributaries: the main river flows south along the west bank; The other branch flows eastward along the north shore, forming a small anticyclone circulation in the northeast. The velocity changes with the wind, generally between10 ~15 cm/s. When there is strong northerly wind, the velocity in the west reaches 30 ~ 40 cm/s, and the maximum can reach100 cm/s. The central Caspian Sea is controlled by large cyclone circulation. There is cyclone circulation in the northwest and southeast of the South Caspian Sea. Therefore, a coastal current from north to south is formed in the west of the Caspian Sea, with an average velocity of 25 ~ 35 cm/s, while a coastal current from south to north appears in the east. The average speed is about10 ~15cm/s.

The distribution of water temperature varies with seasons and regions. In winter, there is a great difference in surface water temperature between the north and the south. In February, the temperature in the North Caspian Sea is only 0. 1 ~ 0.5℃, and the temperature in the South Caspian Sea can reach 8 ~ 10℃. In summer, the temperature difference is small, generally 24 ~ 27℃, and the vertical distribution of water temperature also changes with the seasons. In winter, the water temperature in the North Caspian Sea and the Middle Caspian Sea is almost unchanged, and there is a thermocline in the South Caspian Sea at a depth of 50 ~ 100 meters. In summer, the temperature difference between the upper and lower layers at the depth of 30 ~ 50 meters in the central and southern waters is large.

There are 130 rivers flowing into the Caspian Sea, and the annual runoff into the sea is more than 300 cubic kilometers. Among them, the runoff of Volga River into the sea is 256 cubic kilometers, accounting for 85% of the total runoff of Caspian Sea. The discharge into the sea has great seasonal and interannual changes, which directly affects the changes of salinity and water level. Seawater is low in chloride and high in sulfate and carbonate. The salinity of seawater is about two-thirds lower than the standard salinity of seawater. Generally, the south-central part is 12.0 ~ 13.0, and the salinity outside the Volga River Delta is only 0.2. The seasonal variation of salinity is often between 0. 17 and 0.2 1. From February 65438 to April the following year, the North Caspian Sea often freezes. The ice thickness is generally 0.5 ~ 0.6m, with the maximum thickness of1m.. Under the strong north wind, drifting ice can drift south to the vicinity of the Apsheron Peninsula.

The remarkable change of water level in long period and ultra-long period is the most remarkable phenomenon in Caspian Sea. Studies have confirmed that the water level of the Caspian Sea in the early19th century was 22 meters lower than that before 4000 ~ 6000 years. During 7 ~ 1 1 century, there was a low water level. During 1930 ~ 1957, the water level dropped again due to the construction of reservoirs on the Volga River, excessive industrial and agricultural water use and dry climate. Since the early 1970s, the water level of the Caspian Sea has remained at around -28.5 meters. The water level varies greatly in seasons, high in spring and summer and low in winter, with an annual variation of up to 33 cm. The winds in the Caspian Sea significantly increase or decrease the water. In the Volga River Delta, sometimes the wind reduces the water by 4-5 meters, and the wind increases the water by 2 meters.

There are many kinds of creatures and resources, animals and plants. More than 500 kinds of plants. There are 850 species of animals, of which 15 are typical arctic and Mediterranean animals. In addition, there are warm-water animals in the middle of the Atlantic. Common fish are sturgeon, herring, perch and herring. Due to the decline of water level and the change of salinity, the growth of organisms is affected, resulting in a significant reduction in fishing.

Rich in oil and gas resources. The exploitation of submarine oil is mainly concentrated in the offshore of Azerbaijan in the Soviet Union. The sodium sulfate mined in Kara-Bogaz-Goer is also of great economic significance. However, the exploitation of mineral resources has had a negative impact on the development of fisheries in the Caspian Sea.