The composition of seawater is very complex, including many different elements and compounds. Among them, water is the main component of seawater, but it is not the only component.

1. Seawater contains a lot of salt.

These salts mainly come from rain erosion on land and salt brought by rivers. These salts exist in the form of ions in seawater, such as sodium ions, calcium ions and magnesium ions. These ions have an important influence on the physical and chemical properties of seawater.

2. Seawater also contains a lot of dissolved gases, such as oxygen, nitrogen and carbon dioxide.

These gases mainly come from gas exchange between the ocean surface and the atmosphere. Among them, oxygen is one of the most important dissolved gases in seawater and plays a vital role in the survival of marine life.

3. Seawater also contains a lot of organic matter, such as amino acids, sugar, fat and so on.

These organic substances mainly come from the metabolism and decomposition of marine organisms. They play an important role in marine ecosystem and provide necessary nutrition for marine life.

In addition to the above components, seawater also contains a lot of minerals, such as iron, zinc and copper. These minerals also play an important role in the survival and growth of marine life. They mainly come from the erosion of land by rain and minerals brought by rivers.

In addition, seawater also contains some trace elements, such as iodine, selenium and fluorine. These trace elements play an important role in the health of human beings and marine life. For example, iodine is one of the essential trace elements for human body and plays an important role in children's intelligence and physical development.

Generally speaking, the composition of seawater is complex, so it also contains many different elements and compounds. These components play an important role in marine ecosystem and the health of human beings and marine life. Therefore, we need to know more about the composition and nature of seawater in order to better protect and manage our marine resources.