The characteristics of Bohai water system are as follows, which shows the natural causes of severe sea ice and its disasters.

The inland sea of China is basically surrounded by land between Liaoning Province, Hebei Province, Tianjin City and Shandong Province. Only the Bohai Strait is connected with the Yellow Sea in the east, with an area of 77,000 square kilometers and an average water depth of18m. The sediments are mainly silt and silt. There are three main bays around Bohai Sea: Liaodong Bay in the north, Bohai Bay in the west and Laizhou Bay in the south. Because Liaohe and Laizhou Bay are rich in bait, they are large mariculture bases in China. Shrimp and yellow croaker are abundant here. There are many saltworks along the coast, especially Luchang saltworks on the west coast. The main islands are miaodao islands, Changxing Island, Xi Zhong Island and Chrysanthemum Island. In recent years, abundant oil has been discovered at the bottom of Bohai Sea and has been exploited on a large scale.

The Bohai Sea is a nearly closed inland sea, located at the northernmost part of eastern Chinese mainland, that is, between 37 07 ′ ~ 41east longitude17 35 ′ ~12215 ′, facing the sea on the one hand and the sea on the other. The line between Laotieshan in Liaodong Peninsula and Penglai Cape on the northern shore of Shandong Peninsula is the dividing line between Bohai Sea and Yellow Sea. Liaodong Peninsula and Shandong Peninsula, like open arms, constitute the sea gateway of the capital Beijing. Looking around, the Bohai Sea looks like a gourd slightly inclined from northeast to southwest, lying on its side in North China, with Laizhou Bay and Bohai Bay at the bottom and Liaodong Bay at the top.

The Bohai Sea covers an area of 77,284 square kilometers, with a coastline of 2,668 kilometers. The average water depth is18m, and the maximum water depth is 85m. The shallow sea area accounts for more than half of 20m. Bohai Sea is located in the north temperate zone, with no heat in summer and no severe cold in winter. The annual average temperature is 65438 00.7℃, the precipitation is 500-600 mm, and the salinity of seawater is 30.

The bottom of Bohai Sea is flat, mostly silt and soft mud, and the terrain is inclined from Sanwan to Bohai Strait. Coasts can be divided into three types: muddy coast, sandy coast and bedrock coast. The coasts of Bohai Bay, Yellow River Delta and Liaodong Bay are muddy coasts, the west coast of Bohai Sea north of Luanhekou is sandy coast, and the north shore of Shandong Peninsula and the west coast of Liaodong Peninsula are mainly bedrock coasts.

Sea ice refers to salt water ice directly frozen by seawater, including continental glaciers (icebergs and Iceland), river ice and lake ice entering the ocean. Salt water ice is a mixture of solid ice and salt water (including some salt crystals), its salinity is 2 ~ 10 ‰ lower than that of seawater, and its physical properties (such as density, specific heat, heat of solution, latent heat of evaporation, thermal conductivity, etc.). ) as follows.

The specific heat capacity of sea ice is greater than that of pure water ice, and it increases with the increase of salinity. The specific heat capacity of pure water ice is not affected by temperature, while sea ice decreases with the decrease of sea ice temperature. At low temperature, it does not change much with temperature and salinity, and is close to the specific heat capacity of pure water ice. However, at high temperature, especially near freezing point (-2℃), the salt water in sea ice will change phase with the rise and fall of temperature, that is, when it is cooled. When the temperature rises, ice melts into salt water, so its specific heat capacity decreases and increases respectively. Because of the different salinity, the decrease value and increase value are very different. At low salinity, its specific heat capacity is small, while at high salinity, its specific heat capacity will be several times or even ten times larger than that of pure water ice. The latent heat of melting of sea ice is also greater than that of pure water ice. The thermal conductivity of sea ice is smaller than that of pure water ice because it contains bubbles. However, the thermal conductivity of air is very small. The thermal conductivity of sea ice is slightly higher than that of seawater, which limits the heat transfer from the ocean to the atmosphere and greatly reduces the evaporation loss of the ocean, thus forming a protective layer of the ocean. Because there are more gaps in the upper part of sea ice than in the lower part, its thermal conductivity increases with the depth, that is, the thickness from the ice surface down. The thermal conductivity of sea ice above 1m is similar to that of pure water ice, which is about 1/3 of that of near-surface pure water ice. The coefficient of thermal expansion of sea ice varies with the temperature and salinity of sea ice. For low-salt sea ice, with the decrease of temperature, it expands first and then contracts. The critical temperature from expansion to contraction decreases with the increase of sea ice salinity. For high-salt sea ice, with the decrease of temperature, it always expands, but the expansion coefficient is getting smaller and smaller. The compressive strength of sea ice is about 3/4 of pure water ice, which is obviously caused by many cracks. The reflectivity of sea ice to solar radiation is much greater than that of sea water, and the average reflectivity of sea water is only 0.07, while sea ice can reach 0.5 ~ 0.7. Because the coverage area of sea ice is larger than that of land ice, its reflected energy has no influence on the ocean itself or climate conditions.

Sea ice will not only have a great impact on marine hydrology, atmospheric circulation and climate change, but also directly affect human social practice. For example, it can directly block ports and waterways, block maritime transportation, and destroy offshore engineering facilities and ships; The annual navigation period of some segments of the Russian northern route is only 2-4 months. Icebergs are the enemy of navigation. The 45,000-ton luxury cruise ship Titanic was sunk by an iceberg in the early morning of April 19 12 in the North Atlantic, and 1500 people were killed. The sea ice in China is also dead. 1969 From February to March, the Bohai Sea was severely frozen. Except near the Strait, the Bohai Sea is almost completely covered with ice, the port is frozen, the navigation channel is blocked, the offshore oil drilling platform is pushed down by ice, the offshore ships are damaged by ice, and the 10,000-ton cargo ship is held hostage by ice, drifting with the tide for four days. Almost all sea activities have stopped. Serious ice conditions occurred in 1936 and 1947. Since the 1940s, high-latitude coastal countries have successively carried out sea ice observation and research, and issued iceberg disasters and sea ice forecasts.

At present, sea ice and icebergs are observed by shore stations, ships, planes, ice floes, radars and satellites, and long-term, medium-term and short-term forecasts of sea ice are issued by using mathematical statistics, meteorology and dynamic numerical methods. China has also stepped up its efforts in this regard.

Huge ice cubes and icebergs floating on the ocean move under the action of wind and ocean currents, and their thrust is related to the size and speed of ice cubes in Liaodong Bay of Bohai Sea. According to the observation results of 197 1 on the new "Haier Well" platform in Bohai Bay, China, a large square ice block with a diameter of 6 kilometers and a height of 1.5 meters was calculated. Under the condition that the speed is not too high,

The destructive power of sea ice to offshore ports and ships includes not only the above thrust, but also the damage caused by sea ice expansion pressure. According to the calculation, when the sea ice temperature drops by 1.5 degrees, the sea ice with the length of 1000 meters can expand by 0.45 meters, which will deform and damage the ships in the ice. In addition, there is the vertical force of ice. When the sea ice frozen in offshore buildings is subjected to vertical force caused by tidal fluctuation, the foundation of buildings is often destroyed. The passenger ship Titanic hit the iceberg +09 1965438 in April 2002, which was one of the biggest disasters caused by sea ice in the 20th century. The floating ice destroyed Hai-II well, an all-steel oil platform, which was made of 15 manganese steel plate, with a thickness of 2.2 cm, a diameter of 0.85 m, a length of 4 1 m and a depth of 28 m. The supports of another 500-ton Hai-I well platform were all cut off by sea ice, which shows how serious the destructive power of sea ice has brought to ships and marine engineering buildings. This is called sea ice closure. The sea ice is closed and connected with the coast, with a huge area. Even if the Arctic area shrinks in summer, it has more than 8 million square kilometers, equivalent to the area of Oceania. The Antarctic continent is frozen by sea ice all the year round.

After the sea ice was broken, many scientific stations attached to the ice layer of the North and South poles studied and explored the mysteries of the polar regions as ocean currents drifted around. In the history of navigation, there was a tragic record that some seagoing ships were taken hostage by sea ice and could not return to the mainland. In 2002, the seagoing vessel "Santa Anna" from Petersburg, Russia, was blocked by sea ice and drifted with the ice for nearly two years until it was completely destroyed by ice. 18860 . 6886868886 17