Sea Water Ingredients

The ocean, home to plant and animal marine life, covers 70 percent of the Earth's surface.Beach on Sea image by Valeriy Kirsanov from Fotolia.com

Seawater covers 70 percent of the Earth's surface, and the ocean is home to plant and animal life. Seawater contains dissolved chemical compounds derived from continental rocks, as well as dissolved atmospheric gases. These substances have physiological benefits for marine organisms.

Ions

Seawater contains numerous ions. Approximately 99 percent of chemical compounds found in seawater consists of six ions: chloride (Cl-), sodium (Na+), sulfate (SO4-2), magnesium (Mg+2), calcium (Ca+2) and potassium (K+). Chlorides are the most abundant of these, comprising about 55 percent of the total, followed by sodium (31 percent).

Sodium combines with chloride to form sodium chloride salt (NaCl), which is the main contributor to the properties of seawater and distinguishes it from fresh water. It is commercially extracted directly from the ocean or from salt beds. Magnesium is also extracted from seawater, but it is present in very small quantities; seawater contains only 5 g of magnesium per gallon of seawater.

Seawater contains dissolved oxygen, both from the atmosphere and from photosynthesis of marine plants. Dissolved oxygen is utilized for respiration by marine animals, which extract the oxygen with their gills. Oxygen concentrations decrease when water in the midocean, between the surface and the ocean bed, becomes less ventilated. Eutrophication also contributes to lower oxygen levels, resulting in oceanic dead zones, which disrupt the marine ecosystem.

Carbon dioxide is the key substance in photosynthesis by marine plants. Dissolved carbon dioxide is usually present in bicarbonate form (HCO3). Due to climate change, it is often present in undesirably large amounts. High concentrations of carbon dioxide in seawater lower pH levels, causing ocean acidification and increased ocean temperature, which in turn places stress on marine animals, causing them to utilize energy that would otherwise be used for their reproduction, predation and movement.

Nitrogen is vital for the survival of phytoplankton and other aquatic organisms. An inert gas, it can be transformed to compounds such as nitrate, the most abundance form of nitrogen found in seawater. Nitrogen is released into seawater via the decomposition of organic material and also from the atmosphere. The concentration of nitrates is inversely proportional to oxygen concentration, meaning that oceanic dead zones usually have high amounts of nitrates.