1, the main component (a large number of constant elements).
The main components (major elements and major elements) refer to the components whose concentration in seawater is greater than 1× 106mg/kg. There are five cations Na+, K+, Ca2+, Mg2+ and Sr2+, and anions Cl? ，SO42？ ，Br？ ，HCO3？ (CO32？ )，F？ Five kinds and molecular forms of H3BO3 account for 99.9% of seawater salinity. So it is called the main component.
Because the content of these components in seawater is large, the concentration ratio of each component is approximately constant, and biological activities and total salinity changes have little effect on them, so they are called conservative elements. The content of Si in seawater is sometimes greater than 1mg/kg, but its concentration is greatly influenced by biological activities and its nature is unstable, so it is not included in the discussion of main components.
2. Gas composition dissolved in seawater.
Gases dissolved in seawater, such as oxygen, nitrogen and inert gases.
Oxygen, chemical formula o? . Chemical formula: 32.0, colorless and odorless gas, the most common elemental form of oxygen. Melting point -2 18.4℃ and boiling point-183℃. Insoluble in water, about 30mL of oxygen is soluble in 1L water. Oxygen in the air accounts for about 2 1%. Liquid oxygen is sky blue. Oxygen fixation is a blue crystal. The activity is not very strong at room temperature, and it is not easy to react with many substances. However, it is very active at high temperature and can be directly combined with many elements, which is related to the electronegativity of oxygen atoms second only to fluorine.
Nitrogen is a chemical element with chemical symbol N and atomic number 7. It was discovered by Swedish pharmacist Scheler in 1772, and was later confirmed by French scientist lavoisier. There is little nitrogen in the earth's crust. Most of the nitrogen in nature exists in the atmosphere in the form of elemental molecular nitrogen, accounting for 78% of the air volume. The most important mineral is nitrate.
3. Nutritional elements (nutrients, biogenic elements).
It is mainly related to the growth of marine plants, usually referring to N, P and Si. The contents of these elements in seawater are often influenced by plant activities. When the content is very low, it will limit the normal growth of plants, so these elements are of great significance to biology.
But as far as the ecosystem is concerned, it also includes trace metal elements such as iron, manganese, copper and organic matter. When the content of phosphorus and nitrogen in seawater is less than a certain level, plants can't carry out photosynthesis smoothly and their reproduction is limited. Therefore, phosphorus and nitrogen become important factors to control plant growth. Generally speaking, the best ratio of nitrogen to phosphorus is 16.
In the sea area rich in phosphorus and nitrogen salts, the water quality is fertile and organisms can multiply in large quantities. Affected by land runoff and human activities, the content of nutrient elements in nearshore shallow sea is higher than that in open sea. The vertical distribution of nutrients is generally less in surface water and more in deep water. Therefore, the surface layer of upwelling sea area is continuously supplemented by deep water.