Glossary

abyssal plain

The flat part of the ocean floor that lies between about 4 and 6 km below the sea surface.

albedo

The reflection coefficient of a surface - the fraction of the amount of incoming radiation that is reflected from a surface.

Antarctic Bottom Water (AABW)

Cold, dense bottom water mass that forms around the Antarctic continent (especially in the Ross and Weddell Seas) and spreads northwards in all three ocean basins.

bathymetry

The study of underwater depth of lake or ocean floors.

constancy of composition

The principle for seawater that, although the concentration of dissolved salts can vary from place to place, the relative proportions of the ions remains virtually constant.

continental shelf

The part of the ocean floor bordering the continents at a depth of 200 m or less below the sea surface.

continental slope

The part of the ocean floor extending from the edge of the continental shelf to the start of the continental rise. The continental slope has an average gradient of around 4deg.

Coriolis force

An apparent force invented to explain the deflection of bodies moving over the surface of the Earth without being frictionally bound to it. It acts 90° to the right of the direction of motion in the Northern Hemisphere, and 90° to the left in the Southern Hemisphere.

eddy viscosity

Internal friction between the molecules of a liquid that transfers momentum.

Ekman drift

The mean current across the Ekman layer.

Ekman layer

The depth of influence of the Ekman spiral.

Ekman spiral

The vertical spiral pattern of water velocities that develops in the upper ocean as a result of the Coriolis force acting on moving water. The pattern develops to the right in the Northern Hemisphere, and to the left in the Southern Hemisphere.

Ekman transport

The volume of water transported by the Ekman drift.

frazil ice

The initial form of sea ice: a slurry-like suspension of ice crystals.

gyre

A large-scale circulatory feature of the ocean circulation, usually extending across many thousands of kilometres.

hydrographic section

The standard way for presenting a series of CTD (seawater conductivity and temperature, and depth) measurements taken across an ocean or a feature in the ocean.

hydrothermal vents

Fissures on the seafloor out of which flows water that has been heated by underlying magma.

isohalines

Contour line joining points of equal salinity either on maps or in vertical sections.

isotherms

Contours of constant temperature.

Mid-Atlantic Ridge (MAR)

A north-south suboceanic ridge in the Atlantic Ocean from Iceland to Antarctica on whose crest are several groups of islands.

North Atlantic Deep Water (NADW)

Deep water mass formed mainly in the Norwegian and Greenland Seas.

pack ice

A mass of ice floating in the sea, formed by smaller pieces freezing together.

pancake ice

Sea ice rind broken up into pieces a few centimetres in diameter, with upturned edges resulting from multiple collisions.

permanent thermocline

The region beneath the mixed layer where temperature decreases with depth.

salt rejection

A process that occurs during sea ice formation where salt is pushed from forming ice into the surrounding seawater, increasing the salt concentration there.

stratified

(In the context of water) Where water masses with different properties of salinity, oxygenation, density and temperature form layers that act as barriers to water mixing.

thermohaline circulation

Global oceanic circulation through a series of strong currents, driven by deep water formation in the polar seas and heating of water in the tropical seas; an effect of temperature and salinity differences. Also called the ocean 'conveyor belt'.

water mass

A very large volume of water with uniform temperature, salinity and, therefore, density.

wind stress

The frictional force that transfers energy from the wind to the surface of the water.

wind-mixed layer

Surface water that has been mixed by the wind to create a layer with uniform physical properties.