Section 7: The Deep Circulation of the Ocean

Vocabulary flashcards covering the physical characteristics, water masses, density controls, circulation mechanisms, and seafloor topography described in EarthComm Chapter 5, Section 7: The Deep Circulation of the Ocean.

Salinity

The concentration of dissolved salts in seawater, expressed as parts per thousand, which averages approximately $35\,\text{parts per thousand}$ ($35\,\text{g}$ of salt per $1000\,\text{g}$ of ocean water).

Water Mass

A large region of water within the ocean characterized by having approximately the same temperature and salinity throughout.

Oceanographers

Scientists who study Earth's oceans and classify water masses primarily by their temperature and salinity.

Convection

The circulation in a fluid from place to place that is caused by differences in fluid density.

Antarctic Bottom Water (AABW)

The densest deep ocean water mass, formed near Antarctica with a temperature of $-0.5^\circ\text{C}$ and a salinity of $34.7\,\text{parts per thousand}$, which flows northward along the deepest ocean floor.

North Atlantic Deep Water (NADW)

A major deep water mass formed around Iceland with an average salinity of $34.9\,\text{parts per thousand}$ and a temperature of about $3^\circ\text{C}$, taking up to $1000\,\text{years}$ to sink and flow southward into other ocean basins.

Continental Shelf

The shallowest part of a continental margin between the shoreline and the continental slope, featuring an extremely gentle gradient (approximately $0.1^\circ$) and rarely exceeding $100\,\text{m}$ in depth.

Continental Slope

The relatively steep zone ($3^\circ\text{ to }6^\circ$) of the continental margin located between the continental shelf and the continental rise.

Continental Rise

The flat, gently sloping (often less than $1:40$) part of the continental margin between the abyssal plain and the continental slope, built of thick piles of transported sediment.

Continental Margin

The region of the ocean floor situated between the shoreline and the abyssal plain, composed of the continental shelf, continental slope, and continental rise.

Abyssal Plain

A flat, broad region of the ocean floor occurring between $4\,\text{km}$ and $5\,\text{km}$ in depth with almost no slope, covered by a sediment blanket that can reach $5\,\text{km}$ thick.

Abyssal Hills

A series of small, rolling sediment-covered rock hills on the ocean floor rising up to $900\,\text{m}$ above the abyssal plains, located next to continental margins and oceanic ridges.

Oceanic Trench

A long, narrow, steep-sided trough that forms the deepest part of the ocean, created where denser oceanic crust bends downward beneath another crustal plate.

Mid-Ocean Ridge

A worldwide underwater mountain system extending over $50,000\,\text{km}$ in length and rising $2\,\text{km}\text{ to }4\,\text{km}$ above the seafloor, formed where magma rises to build new oceanic crust.

Rift Valley

A huge, cracked depression $1\,\text{km}\text{ to }2\,\text{km}$ deep and several kilometers wide running along the central axis of the mid-ocean ridge.

Fracture Zone

Linear breaks running across mid-ocean ridges along which sections of the ridge separate by kilometers to hundreds of kilometers, creating steep cliffs on the ocean floor.

Seamounts

Cone-shaped volcanic mountains rising from the ocean floor that typically form where magma pushes through oceanic crust, often having bases $20\,\text{km}$ wide or more.

Thermocline

The ocean layer between approximately $200\,\text{m}$ and $1000\,\text{m}$ depth where water temperature decreases sharply with increasing depth.

Pycnocline

A layer of ocean water characterized by a rapid change in density with depth, directly coinciding with the thermocline because seawater density is primarily controlled by temperature.

Wind Stress

The friction force exerted directly onto the ocean surface by the blowing wind, driving surface currents and generating waves.

Coriolis Force

The apparent force that makes moving air and water currents appear to curve due to the rotation of Earth beneath them.