Standard Article

Major Ions in Seawater


  1. Marie De Angelis

Published Online: 15 JUL 2005

DOI: 10.1002/047147844X.oc1707

Water Encyclopedia

Water Encyclopedia

How to Cite

Angelis, M. D. 2005. Major Ions in Seawater. Water Encyclopedia. 4:159–160.

Author Information

  1. Humboldt State University, Arcata, California

Publication History

  1. Published Online: 15 JUL 2005


Seawater contains all of the natural elements. However, its composition is dominated by relatively few ionic species. These species, which comprise >99.8% of the mass of the total dissolved salts in the ocean, are known as the major ions and are defined as dissolved species having a concentration in seawater of >1 mg kg−1 (1 ppm). Na+ and Cl alone account for 86% of all dissolved chemical species in seawater.

The source of Cl, and most anions in seawater, is outgassing of the Earth's interior, or volcanic emissions. The majority of the major cations are derived from the effects of continental weathering and are delivered to the ocean via rivers. The gross composition of seawater is the result of the partitioning of elements between continental rock and seawater over geologic time. The major ions represent the more soluble elements, which have preferentially partitioned into seawater.


  • seawater;
  • outgassing;
  • volcanic emissions;
  • constant proportions;
  • residence time;
  • seawater changes;
  • sea spray;
  • reverse weathering;
  • hydrothermal circulation