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Seawater is water from a sea or ocean with about 3.5% salinity and various dissolved ions. Learn about its density, pH, chemical composition, sources and uses from this comprehensive article.
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- Overview
- Chemical and physical properties of seawater
- Chemical composition
seawater, water that makes up the oceans and seas, covering more than 70 percent of Earth’s surface. Seawater is a complex mixture of 96.5 percent water, 2.5 percent salts, and smaller amounts of other substances, including dissolved inorganic and organic materials, particulates, and a few atmospheric gases.
Seawater constitutes a rich source of various commercially important chemical elements. Much of the world’s magnesium is recovered from seawater, as are large quantities of bromine. In certain parts of the world, sodium chloride (table salt) is still obtained by evaporating seawater. In addition, water from the sea, when desalted, can furnish a limitless supply of drinking water. Many large desalination plants have been built in dry areas along seacoasts in the Middle East and elsewhere to relieve shortages of fresh water.
The six most abundant ions of seawater are chloride (Cl−), sodium (Na+), sulfate (SO24−), magnesium (Mg2+), calcium (Ca2+), and potassium (K+). By weight these ions make up about 99 percent of all sea salts. The amount of these salts in a volume of seawater varies because of the addition or removal of water locally (e.g., through precipitation and evaporation). The salt content in seawater is indicated by salinity (S), which is defined as the amount of salt in grams dissolved in one kilogram of seawater and expressed in parts per thousand. Salinities in the open ocean have been observed to range from about 34 to 37 parts per thousand (0/00 or ppt), which may also be expressed as 34 to 37 practical salinity units (psu). See also salinity.
Inorganic carbon, bromide, boron, strontium, and fluoride constitute the other major dissolved substances of seawater. Of the many minor dissolved chemical constituents, inorganic phosphorus and inorganic nitrogen are among the most notable, since they are important for the growth of organisms that inhabit the oceans and seas. Seawater also contains various dissolved atmospheric gases, chiefly nitrogen, oxygen, argon, and carbon dioxide. Some other components of seawater are dissolved organic substances, such as carbohydrates and amino acids, and organic-rich particulates. These materials originate primarily in the upper 100 metres (330 feet) of the ocean, where dissolved inorganic carbon is transformed by photosynthesis into organic matter.
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Water and its Varying Forms
The chemical composition of seawater is influenced by a wide variety of chemical transport mechanisms. Rivers add dissolved and particulate chemicals to the oceanic margins. Wind-borne particulates are carried to mid-ocean regions thousands of kilometres from their continental source areas. Hydrothermal solutions that have circulated through crustal materials beneath the seafloor add both dissolved and particulate materials to the deep ocean. Organisms in the upper ocean convert dissolved materials to solids, which eventually settle to greater oceanic depths. Particulates in transit to the seafloor, as well as materials both on and within the seafloor, undergo chemical exchange with surrounding solutions. Through these local and regional chemical input and removal mechanisms, each element in the oceans tends to exhibit spatial and temporal concentration variations. Physical mixing in the oceans (thermohaline and wind-driven circulation) tends to homogenize the chemical composition of seawater. The opposing influences of physical mixing and of biogeochemical input and removal mechanisms result in a substantial variety of chemical distributions in the oceans.
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Sep 10, 2016 · Scitable is a blog that explores various topics in science, with a focus on ocean issues. Read about the challenges and solutions of plastic pollution, derelict fishing gear, and marine life in the ocean.
May 29, 2018 · Saltwater is a geological term that refers to naturally occurring solutions containing large concentrations of dissolved, inorganic ions. In addition, this term is often used as an adjective in biology, usually to refer to marine organisms, as in saltwater fish.
Nov 9, 2023 · Learn about the diverse and vital saltwater ecosystems that cover 70% of Earth's surface, from oceans to estuaries, wetlands, reefs, and deep sea. Explore the abiotic and biotic factors, the biological components, and the ecological processes that shape marine biodiversity and services.
Welcome to Rivers to Reefs Aquariums! We are a hobbyist-owned store; everyone here is a dedicated aquarist with years of experience. We strive to bring you the best freshwater & saltwater livestock and supplies available, and to assist you with any questions you may have.
