The Atlantic Ocean is the second largest of the world’s five oceanic divisions and covers about 85.1 million km²; it is a major oceanic division called the .

Context: Core concept identification: Atlantic Ocean as a major oceanic division

are seas connected to the main ocean basin that may be included or excluded depending on the definition used.

Context: Key term meaning: Marginal seas

Including marginal seas changes reported totals because changes the Atlantic’s area and volume values.

Context: Cause→effect: definitions of marginal seas affect area/volume

The Atlantic’s limits and even the number/extent of marginal seas depend on definitions, so depend on definitions.

Context: Core concept: Extent and boundaries depend on definitions

The Equator divides the Atlantic into northern and southern parts for oceanographic/geographic classification, so the division is based on geography, not tectonics.

Context: Core concept: North vs South Atlantic division

is a submarine mountain range that runs through the Atlantic and divides it longitudinally into two halves.

Context: Key term meaning: Mid-Atlantic Ridge (MAR)

Mid-ocean ridges can be crossed by deep-water exchange only where the ridge is interrupted; acts as a barrier to bottom water except at transform faults.

Context: Cause→effect: MAR barrier role

When the ridge is interrupted by transform faults, deep-water currents can pass between sides at Romanche Trench and Gibbs fracture zone; the key enabling term is a .

Context: Key term meaning: Transform fault

The Atlantic Ocean’s maximum depth is found in the , with a maximum depth of 8,376 m.

Context: Key term meaning + bathymetry fact: Puerto Rico Trench

is a deep trench in the South Atlantic region associated with very large depths, with a maximum depth of 8,264 m.

Context: Key term meaning + bathymetry fact: South Sandwich Trench

is the process that deflects moving fluids, producing opposite rotational directions in the North vs South Atlantic.

Context: Key term meaning: Coriolis effect

Coriolis effect acts on moving water masses, which causes North Atlantic circulation to be and South Atlantic circulation to be counter-clockwise.

Context: Cause→effect: Coriolis effect determines circulation direction

The occurs as an east–west oscillation pattern in higher latitudes of the North Atlantic.

Context: Key term meaning: North Atlantic oscillation

Atlantic surface temperatures vary with latitude, currents, and season, and the South Atlantic is generally warm year-round while the North Atlantic is temperate; this idea is captured by .

Context: Core concept: Atlantic Ocean temperature and climate patterns

Evaporation, precipitation, river inflow, and sea-ice melting vary by region; this causes surface salinity to range from 33 to 37 parts per thousand, with low values near the equator and high values near ~25°N/S, which is explained by .

Context: Core concept: Salinity controls and spatial patterns