Chemical Structure of Seawater

Amazingly, chemical elements in sea water do not work on their own. It is the action and reaction of the chemical ions that make-up the ocean’s water.

Seawater contains almost everything. It includes materials released from marine organisms. The most essential materials are the components that influence life forms. This is salinity, temperature, dissolved gases of oxygen and carbon dioxide, nutrients in the sea and pH. Understanding the factors that make up the ocean’s chemical composition is a tool. A person can observe the effects of global warming, and the effects of pollution on marine organisms.


Interaction of chemical ions contributing to salinity is chloride, sodium, sulfate, magnesium, calcium, potassium, bicarbonate, bromide, borate, strontium, fluoride and minute quantities of other chemicals.

Salinity in the ocean varies through several factors. One effect on salinity is the amount of evaporation or precipitation. Other factors that can change salinity are large rivers such as the Amazon that run into the ocean. The Amazon wipes out salinity for a mile or two out to sea. Little rivers have no effect.

Why is Salinity Important?

Salinity influences ocean organisms by the process of osmosis. Osmosis is the way water moves in and out of living cells. There are two types of osmosis. One is Osmotic conformers (poiklosmotic – animals unable to control pressure of body fluids when there is a change in salinity). These are bivalve mollusks, annelids and echinoderms. The other is homoiosmotic animals. They are able to control their body pressure by excreting excess fluids.

A Closer Look at Osmotic Animals

Osmotic Conformers

Their liquid environment controls them. If one were to put them in fresh water, osmosis would cause the fresh water to enter the cells. The cells expand, pop, and kill them. If one were to put them in extremely salty water, the cells would dehydrate.

Osmotic regulators have mechanisms that help them regulate the salt content. Most osmotic animals are fish, reptiles, birds and mammals. These animals are migratory. They have a specific chemical, chloride, in their cells that help them excrete excess salt.

Temperature of the Oceans

Temperature of seawater varies with the amount of sun that heats the area. This means that tropical areas get more sun and polar areas go for months without sun. This helps one understand why under the ocean there three layers.

>> Upper mixed layer is all one temperature. It is only two percent of the volume of the ocean.

>> The main layer or thermocline is an area of rapidly decreasing temperatures. This layer shifts up and down with the seasons in temperate zones. The main thermocline makes up 18 percent of the volume of the ocean water. This zone does not exist in polar regions.

>> The deep (bottom) water is always one cold temperature. This layer exists in all areas of the hemisphere.

Sea water temperature, like salinity, affects marine life. It changes the reactions in the animals’ cells. Each marine species has a range of temperatures they need for survival. When temperatures change, the chemical ions react. Most marine animal that go outside its temperature range will die. The rules of poiklosmotic (cold-blooded – controlled by outside influences) and homoiosmotic (warm-blooded – internal control) apply to all sea life.


Temperature, salinity and pressure effect seawater density. The layers of the ocean are dependent on the density. Warm temperatures influence on water makes it less dense. More salinity makes the water denser.

Concentration of Dissolved Oxygen and Carbon Dioxide

Oxygen and carbon dioxide are gases outside of the water. In water, they dissolve. Sea animals’ gills use the dissolved oxygen for respiration. When they release dissolved carbon dioxide, sea plants use this for photosynthesis.

PH Buffer

The pH buffer is a stable element in the ocean. It controls the amount of water interaction with carbon dioxide. This maintains a stable pH for marine life.

The world’s vast and mysterious oceans are the key to human survival. People must take care of the oceans and be aware of factors that humans influence by their actions.