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acid

A substance that releases a hydrogen ion (H+) in solution.

acid rain

Rain containing acids and acid-forming compounds such as sulfur dioxide and oxides of nitrogen.

alkaline

Basic. See also base.

base

A substance that combines with a hydrogen ion (H+) in solution.

buffer

A group of substances that tends to resist change in the pH of a solution by combining with free ions.

chemical equillibrium

In seawater, the condition in which the proportion and amounts of dissolved salts per unit volume of ocean are nearly constant.

chlorinity

A measure of the content of chloride, bromine, and iodide ions in seawater. We derive salinity from chlorinity by multiplying by 1.80655.

colligative properties

Those characteristics of a solution that differ from those of pure water because of material held in solution.

conservative constituent

An element that occurs in constant proportion in seawater; for example, chlorine, sodium, and magnesium.

diffusion

The movement—driven by heat—of molecules from a region of high concentration to a region of low concentration.

dissolution

The dissolving by water of minerals in rocks.

excess volatiles

A compound found in the ocean and atmosphere in quantities greater than can be accounted for by the weathering of surface rock. Such compounds probably entered the atmosphere and ocean from deep crustal and upper mantle sources through volcanism.

ion

An atom (or small group of atoms) that becomes electrically charged by gaining or losing one or more electrons.

ionic bond

A chemical bond resulting from attraction between oppositely charged ions. These forces are said to be "electrostatic" in nature.

mixing time

The time necessary to mix a substance through the ocean, about 1,600 years.

mixture

A close intermingling of different substances that still retain separate identities. The properties of a mixture are heterogeneous; they may vary within the mixture.

nonconservative constituent

An element whose proportion in seawater varies with time and place, depending on biological demand or chemical reactivity. An element with a short residence time; for example, iron, aluminum, silicon, trace nutrients, dissolved oxygen, and carbon dioxide.

osmoregulation

The ability to adjust internal salt concentration.

pH scale

A measure of the acidity or alkalinity of a solution; numerically, the negative logarithm of the concentration of hydrogen ions in an aqueous solution. A pH of 7 is neutral; lower numbers indicate acidity, and higher numbers indicate alkalinity.

precipitate

(1) A solid substance formed in an aqueous reaction. (2) The process by which a solute forms in and falls from a solution. The falling of water or ice from the atmosphere.

principle of constant proportions

The proportions of major conservative elements in seawater remain nearly constant, though total salinity may change with location; also called Forchhammer's principle.

refractometer

A compact optical device that determines the salinity of a water sample by comparing the refractive index of the sample to the refractive index of water of known salinity.

residence time

The average length of time a dissolved substance spends in the ocean.

salinity

A measure of the dissolved solids in seawater, usually expressed in grams per kilogram or parts per thousand by weight. Standard seawater has a salinity of 35‰ at 0°C (32°F).

salinometer

An electronic device that determines salinity by measuring the electrical conductivity of a seawater sample.

saturation

State of a solution in which no more of the solute will dissolve in the solvent. The rate at which molecules of the solute are being dissolved equals the rate at which they are being precipitated from the solution.

solute

A substance dissolved in a solvent. See also solution.

solution

A homogeneous substance made of two components, the solvent and the solute.

solvent

A substance able to dissolve other substances. See also solution.

trace element

A minor constituent of seawater present in amounts of less than 1 part per million.

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