Q: Why is the ocean salty, and is it getting saltier?

A: The ocean is much saltier than the rivers which empty into it and has a very different composition. This is because atoms are selectively removed from seawater at about the same rate they are added. Salt begins in rocks as atoms which are chemically bonded in the form of minerals. When weathering frees the atoms most of the them are carried away to the ocean by running water either as sediment or as dissolved ions. River water is fresh but it is not pure. Even the purest natural waters contain a hodgepodge of dissolved ions in very small amounts. These are collectively referred to as "salt." Salt is added to the ocean by rivers and removed by physical, chemical, and biological processes. A balance of additions and removals keeps the amount relatively constant. One important removal process is biological. Corals extract calcium and use it to build reefs. Other processes may be chemical such as the removal of potassium and aluminum ions by clay particles which settle slowly through the water. For every kind of ion there are specific processes which remove it. In general the most abundant ions in seawater are those which have the fewest removal processes and the slowest rates of addition. Sodium and chlorine are the most abundant constituents of seawater but they are relatively scarce in river water. They are most abundant in the ocean because the processes which remove them are so few that they remain in the sea for a long time. Seawater is much more than just concentrated river water. It is a complex mixture of atoms, molecules, ions, and gases which exist in a state of dynamic equilibrium. Its composition depends on a complexly interacting multitude of processes which remove various substances at the same rate they are added. This equilibrium has been gained through the long history of the earth and reflects the interaction between chemical, physical and biological processes that make our planet both precious and unique.

Richard Brill is assistant professor of science at Honolulu Community College where he teaches earth and physical science. Send questions to him at Honolulu Community College, 874 Dillingham Blvd. , Honolulu, HI 96817 or email to rickb@hcc. hawaii. edu

Salt of The Sea. ©1995 Richard C. Brill