Ocean Glossary | U.S. Geological Survey

A

Abyssal plain

An underwater plain on the deep ocean floor, usually lying between the foot of a continental rise and a mid-ocean ridge.

Anadromous

A fish that lives in the sea and migrates up fresh water rivers to spawn.

B

three dimensional conceptual drawing of a tectonic plate being pushed down under another plate.

Back arcs

Back arcs are geological regions that form at a subduction zone when the overriding plate thins and begins to spread out

Benthic

Anything associated with or occurring on the bottom of a body of water.

C

A coral worn smooth with a badly eroded base

Carbonate budget

the balance between processes that control reef growth including carbonate production (how much coral skeleton is produced) and erosion (how much coral skeleton is lost)

Image: Deep Sea Crab on Mussels a Mile Below Atlantic Ocean

Chemosynthetic

Chemosynthesis is the process by which organisms produce food using energy released by inorganic chemical reactions. Chemosynthetic organisms thrive around deep-ocean environments such as hydrothermal vents or cold seeps.

Aerial image showing beach and offshore reef

Coastal zone

The interface between the land and sea. USGS studies processes that shape this region and how this affect people, wildlife, and ecosystems.

Continental rise

An area that lies at the deepest part of a continental or island margin between the continental slope and the abyssal plain.

Cerianthid anemones, also known as “tube anemones”, are not true anemones. They live in a tube they build using mucus, surroundi

Continental shelf

The submarine extension of an area’s landmass to the outer edge of the continental margin. Many ecologically and economically important habitats can be found in these areas, including coral reefs and kelp forests. USGS is involved in determining the extent of the U.S. Extended Continental Shelf to better protect, manage, and use the seabed resources contained therein.

Continental slope

The steep slope which descends from the edge of the continental shelf to the deep ocean. These areas are of great interest for determining the presence and threats of marine geohazards and unique chemistry such as underwater landslides and gas hydrates that can trigger tsunamis and support unique ecosystems.

Coral cover

the percentage of the reef that is inhabited by living coral

several branching corals among a relatively flat reef area

Coral restoration

efforts by humans to help coral reefs recover from stressors and coral loss. This can involve planting nursery-grown corals back onto reefs, making sure habitat is suitable for natural coral growth, and building coral resilience to threats like climate change.

D

Deep-sea trench

A long, narrow depression on the deep sea floor, related to tectonic plate movement, specifically subduction zones.

Deep-sea trenches

Long, narrow depressions on the deep sea floor, related to tectonic plate movement, specifically subduction zones.

E

Map of Pacific Ocean with outlines of continents, United States, Alaska, and U.S. Pacific islands labeled, and EEZ outlined.

Exclusive Economic Zone

The EEZ is the area of the ocean where a country has jurisdiction. The EEZ extends 200 nautical miles off the nation's coast.

Extended Continental Shelf

The ESC is an area of the continental shelf that may extend beyond the Exclusive Economic Zone (EEZ) depending on the depth, shape, and geophysical characteristics of the seabed and sub-sea floor

F

Foram

A single-celled planktonic animal with a perforated chalky shell through which slender protrusions of protoplasm extend. Most kinds are marine, and when they die, their shells form thick, ocean-floor sediments.

Foraminifer

A single-celled planktonic animal with a perforated chalky shell through which slender protrusions of protoplasm extend. Most kinds are marine, and when they die, their shells form thick, ocean-floor sediments.

Foraminifera

A single-celled planktonic animal with a perforated chalky shell through which slender protrusions of protoplasm extend. Most kinds are marine, and when they die, their shells form thick, ocean-floor sediments.

Foraminifers

Single-celled planktonic animals with a perforated chalky shell through which slender protrusions of protoplasm extend. Most kinds are marine, and when they die, their shells form thick, ocean-floor sediments.

Forams

Single-celled planktonic animals with a perforated chalky shell through which slender protrusions of protoplasm extend. Most kinds are marine, and when they die, their shells form thick, ocean-floor sediments.

G

Gas hydrate

Gas hydrate is an ice-like crystalline form of water and low molecular weight gas (e.g., methane, ethane, carbon dioxide).

Gas hydrates

Gas hydrates are ice-like crystalline form of water and low molecular weight gas (e.g., methane, ethane, carbon dioxide).

H

Holocene

the current geological epoch, encompassing the last 11,700 years of Earth's history.

A crusty chimney-like feature on the seafloor sends plumes of black smoke into the seawater.

Hydrothermal vent

Structures on the seafloor through which materials related to volcanic activity are extruded. These often form tall, chimney-like structures and can support diverse chemosynthetic biota and associated communities.

Hydrothermal vents

Structures on the seafloor through which materials related to volcanic activity are extruded. These often form tall, chimney-like structures and can support diverse chemosynthetic biota and associated communities.

M

Magma

Magma is extremely hot liquid and semi-liquid rock located under the earth's surface.

cartoon showing the Pacific Plate subducting under the North American Plate

Mid-ocean ridge

The massive, continuous chain of deep-ocean volcanoes, occurring at spreading centers where tectonic plates are moving apart, allows new oceanic crust to reach the surface of the seafloor. The result is an extensive chain of underwater mountains. Average water depth to the top of a ridge is 2,500 meters (8,200 feet).

Mid-ocean ridges

The massive, continuous chain of deep-ocean volcanoes, occurring at spreading centers where tectonic plates are moving apart, allows new oceanic crust to reach the surface of the seafloor. The result is an extensive chain of underwater mountains. Average water depth to the top of a ridge is 2,500 meters (8,200 feet).

Mid-piacenzian

The Piacenzian Age (Pliocene) represents a past climate interval within which frequency and magnitude of environmental changes during a period of past global warmth can be analyzed, climate models can be tested, and results can be placed in a context to better prepare for future change.

O

Ocean acidification

as carbon dioxide in the atmosphere is absorbed by the ocean, it causes the pH to lower. This can lead to dissolution of the shells and skeletons of many marine organisms.

Oceanic trench

A long, narrow depression on the deep sea floor, related to tectonic plate movement, specifically subduction zones.

Oceanic trenches

Long, narrow depressions on the deep sea floor, related to tectonic plate movement, specifically subduction zones.

P

Paleoceanography

The study of oceanographic conditions and processes in the past (usually prior to development of instrumentation).

Paleoclimate

The study of Earth's climate conditions and processes in the past (usually prior to development of instrumentation).

Patch reefs

small areas of coral reef that exist closer to shore than the main reef tract

Map of project research in United States and Canada

Plateau

A mound-like or ridge-like elevated area on the seafloor; it may have a modest-to-substantial extent. Although submerged, this feature can reach close to sea level.

Map of sun-illuminated backscatter, Stellwagen Bank and Massachusetts Bay

Plateaus

Mound-like or ridge-like elevated areas on the seafloor; they may have a modest-to-substantial extent. Although submerged, these features can reach close to sea level.

S

Seamount

An underwater mountain formed by volcanic activity.

Seamounts

Underwater mountains formed by volcanic activity.

Spreading centers

Spreading centers occur at the boundary between two plates that are moving apart, called divergent plate boundaries.

block diagram illustrating tectonic convergent boundary and subduction of two oceanic plates

Subduction zone

In tectonics, a convergent plate boundary where the oceanic plate dives beneath another oceanic plate or a continental plate; typically expressed at the surface as a deep-sea, or oceanic, trench.

Subduction zones

In tectonics, these are a convergent plate boundaries where the oceanic plate dives beneath another oceanic plate or a continental plate; typically expressed at the surface as a deep-sea, or oceanic, trench.

Submarine

submarine simply means 'underwater' or 'under-sea'

Bathymetry of Monterey Canyon and the Soquel Canyon tributary

Submarine canyon

an underwater canyon crossing the continental shelf and slope

Colorfully shaded map of the seafloor showing the many unique canyons created by nearby rivers.

Submarine canyons

underwater canyons crossing the continental shelf and slope

Substrate

The underlying surface or material.

T

Tectonic plates

A tectonic plate (also called lithospheric plate) is a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.

Tsunami

Tsunami is a Japanese word that means “harbor wave.” It is a large wave caused by movements in Earth's outer layer, or crust, which move ocean water; or by landslides near large bodies of water like a fjord or lake.

Tsunamis

Tsunami is a Japanese word that means “harbor wave.” It is a large wave caused by movements in Earth's outer layer, or crust, which move ocean water; or by landslides near large bodies of water like a fjord or lake.

Turbidite

A flow of water down slope carrying a dense suspension of fluid mud or unconsolidated material.

V

View of the active west vent from the south rim of the Halemaʻumaʻu crater on January 29, 2021

Volcanic arcs

Volcanic arcs are a chain of volcanoes, hundreds to thousands of miles long, that forms above a subduction zone.