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abductive reasoning coming to a conclusion based on experience, especially where data are limited.

abiogenesis the origin of life from non-living materials.

absorption (in geology) the incorporation of a trace element by a particle.

absorption (in physics) the transfer of energy from a light ray to an object.

abyssal benthic zone a zone occupying depths between 3,000 and 6,000 meters on the seafloor.

abyssal fan a fanlike deposit that forms on the seafloor at the mouths of submarine canyons.

abyssal hill a region of an ocean basin with relief between 300 and 1,000 meters.

abyssal mountain a region of an ocean basin with relief greater than 1,000 meters.

abyssal plain a region of an ocean basin with relief less than 300 meters.

abyssal province the region of the seafloor that extends from the foot of the continental slope to the start of the hadal regions.

abyssal waters dense waters found on or near the bottom of the ocean.

abyssobenthic See abyssal benthic zone.

abyssopelagic zone a poorly characterized ocean depth zone beneath the bathypelagic zone.

active microwave sensor sensor that transmits and receives electromagnetic radiation to make measurements of Earth’s surface.

activity model of the scientific method the interactive, back-and-forth, collaborative approach of teams of scientists for discovering knowledge about the natural world.

adaptive radiation the diversification of a lineage of organisms into different environments and ecological roles.

adaptive tracking system artificial intelligence–enhanced computer software that enables AUVs to navigate according to environmental conditions.

adsorption the attachment of a trace element to a sinking particle.

aeolian dust particles of sediment transported by winds.

aerial investigation a scientific investigation that employs sensors aboard crewed or uncrewed airborne platforms to make observations or obtain measurements of natural processes.

aerobic respiration the metabolic breakdown of organic matter in the presence of oxygen.

aerosol a group of solid or liquid particles less than 1 micrometer in diameter, important in the formation of clouds and other atmospheric processes.

Africa  second-largest continent, where modern humans originated.

aggregation the sticking together of particles.

agronomic revolution the transformation of the seafloor from crusty to soft during the Ediacaran.

Agulhas Current the western boundary current in the South Indian Ocean.

air column an undefined cylinder of air from Earth’s surface to a given altitude.

air density the number of molecules in a given volume of air.

air–sea interface the boundary between the ocean and the atmosphere.

Alaskan Gyre a subpolar gyre off the coast of Alaska.

albedo the reflectivity of Earth’s surface.

anaerobic respiration the metabolic breakdown of organic matter using substances other than oxygen as an electron acceptor.

ancient sunlight energy from the Sun that fell on Earth millions of years ago.

Andes the largest continental mountain range in the world.

animal-tagging investigation a scientific investigation that uses sensors attached to animals to obtain observations or measurements of natural processes, generally in places inaccessible to humans.

anion a negatively charged ion.

Annelida a phylum that includes segmented worms.

anoxygenic photosynthesis photosynthesis that does not yield oxygen as a by-product.

Antarctic Circle 66.5°S; the latitude below which no or little sunlight reaches between the fall and spring equinoxes in the Southern Hemisphere.

Antarctic Circumpolar Current the eastward-flowing current that encircles Antarctica.

Antarctica the southernmost continent, host to 60 percent of Earth’s freshwater.

anthroposphere the human system.

aphelion the point in Earth’s slightly elliptical orbit where its distance from the Sun is greatest.

aphotic zone the dark waters of the ocean.

aquifer a water-bearing stratum of permeable rock, sand, or gravel.

Archaea unique single-celled organisms found throughout the world ocean and in extreme environments.

archaeal organelle complex subcellular structure in Archaea analogous to that of a eukaryote.

Archean Oxidation Event one of several whiffs of atmospheric oxygen present in the Archaean prior to the Great Oxidation Event.

Archean the second geologic eon, occurring from 4 to 2.5 billion years ago.

Arctic Circle 66.5°N; the latitude above which no or little sunlight reaches between the fall and spring equinoxes in the Northern Hemisphere.

Arctic Ocean the polar ocean at the North Pole.

Arthropoda a phylum of organisms with jointed legs that includes crustaceans, insects, and spiders.

artificial intelligence a broad category of computer science that aims to mimic how humans think, act, and adapt.

Asia Earth’s largest continent and home to some 60 percent of the human population.

asphaltum a tar-like substance found on beaches that forms from seeps of oil beneath the ocean

astronomical unit the average distance between the Earth and the Sun.

Atlantic Ocean the second-largest ocean in the world.

atmosphere the gases surrounding Earth.

atmospheric cell the large-scale convection of one part of the atmosphere.

atmospheric diving suit a self-contained, pressurized, one-person diving suit used to explore waters deeper than scuba permits.

atmospheric river extremely wet upper-air currents that appear like rivers on satellite images.

atmospheric window the selectivity of the atmosphere to different wavelengths of electromagnetic radiation.

atom a building block of matter.

aurora australis the southern lights, caused by interactions of the Earth’s magnetic field and atmosphere with the solar wind.

aurora borealis the northern lights, caused by interactions of the Earth’s magnetic field and atmosphere with the solar wind.

Australia the least populous continent (not including Antarctica, which has a small temporary population).

autonomous profiling float sensor-enabled robotic device that rises and sinks in the water column to carry out various ocean measurements and transmit the data to shore stations using satellites.

autonomous underwater vehicle a self-propelled, self-navigating, sensor-equipped underwater vehicle for collecting oceanographic data or conducting search-and-rescue operations in the ocean.

autotroph an organism capable of manufacturing its own food.

axial tilt the angle of Earth’s axis relative to its plane of orbit around the Sun.

Azores Current an eastward-flowing, southerly branch of the North Atlantic Current.


backshore the flat portion of a beach adjacent to terrestrial vegetation, only occasionally inundated by waves and tides.

bacteria unique single-celled organisms found virtually everywhere on Earth.

bacterial organelle complex subcellular structures in bacteria analogous to those of a eukaryote.

barystatic sea level rise sea level rise due to melting glaciers, changes in land storage of water, and changes in the atmosphere.

basalt an extrusive, dense, dark-colored igneous rock.

bathyal benthic zone a zone extending from the shelf break to the bottom of the continental rise.

bathybenthic See bathyal benthic zone.

bathypelagic zone the depth zone beneath the mesopelagic zone, characterized by a complete absence of surface light.

bathyscaphe a hollow steel sphere attached to a giant, gasoline-filled balloon for exploring the ocean depths.

bathysphere a hollow steel sphere with transparent baseball-sized portholes for making observations in the deep ocean.

beach cusp crescent- or scallop-shaped deposits of sand parallel to the beach.

beach diamond mining the removal of diamonds from beaches or the seafloor by commercial enterprises.

beach face the sloped portion of a beach alternately submerged and exposed during a tidal cycle.

beach loose bits and fragments of material along the shore of a body of water, including lakes, rivers, and the world ocean.

beach nourishment the artificial supply of sand to a beach to increase its size.

beach profile a cross-sectional view of the slope of a beach.

beach sand budget a quantitative accounting of the sources and sinks of sand for a beach.

beach scarp a clifflike berm at the boundary of the foreshore and backshore.

beach starvation the loss of sand from a beach due to a decrease in its supply.

Beaufort Gyre a polar gyre in the Beaufort Sea.

Beaufort wind force scale a visual guide for determining wind speed from sea state.

Benguela Current the equatorward-flowing eastern boundary current in the South Atlantic Ocean.

benthic depth zone ocean depth zone along the seafloor from the shoreline to the deepest trench.

benthic lander autonomous, sensor-enabled platform that sinks to the seafloor, carries out observations and experiments, and returns to the surface when signaled or at a predetermined time.

benthic organism organism that lives on or within the seafloor.

benthic-pelagic coupling the ecological interaction between the seafloor and the overlying water column.

benthopelagic zone the portion of the water column within 100 meters of the seafloor.

berm a shelf of sand left by high-energy waves in a receding tide.

bias a less than objective, partial view of evidence.

big data a subdiscipline of computer science for analyzing data sets whose size or complexity exceeds the capabilities of traditional software and computers.

big wave surfer a surfer who rides waves greater than 20 feet in height.

bilateral symmetry a shape that can be divided into two halves.

Bilateria a group with bilateral symmetry that includes all animals except sponges, comb jellies, and cnidarians.

binomial nomenclature a two-part naming system that includes the genus as the first part of the name and the species as the second part.

bio-optical oceanographer a human, robot, or animal that carries out optical measurements of the ocean’s living systems.

bio-optical oceanography the scientific study of the optical properties of living systems in the ocean.

biogeochemical cycle the assembling and disassembling of molecules in a continuous recycling of Earth’s matter.

biogeography the study of the relationship between the distribution of organisms and their environment.

biological oceanography the scientific study of the biological properties and processes in the world ocean.

biological weathering the breakdown of rocks by biological processes.

biologically important nutrient a dissolved substance required for the growth of phytoplankton.

bioluminescence biologically produced light.

biomineralization the process by which organisms incorporate minerals into their body structures.

bionic AUV autonomous underwater vehicle that mimics the appearance and swimming behavior of a marine organism (also known as a robofish).

biosphere the Earth’s living systems.

biotite a gray or black silicate mineral containing mica found as grains in beach sand.

bioturbation the disturbance and mixing of sediments by organisms.

black carbon a type of aerosol formed from the incomplete combustion of fossil fuels; an air pollutant.

blue water oceanography the study of the oceanic waters.

bond a sharing or exchange of electrons by two or more atoms that results in their attraction to each other.

boundary current a current that flows along the outer edge of an ocean basin where it meets a continent.

Brazil Current the western boundary current in the South Atlantic Ocean.

breaker See surf.

brine rejection the precipitation of salts from seawater during the formation of sea ice.

brine the salty syrup that remains when freshwater has been removed from seawater.

bubble injection the penetration and dissolution of bubbles of air caused by breaking waves.

buoyancy compensator a device worn by scuba divers to control buoyancy.

buoyancy the tendency of an immersed object to rise, sink, or remain in place.

buoyancy-driven mixing the homogenization of the water column as a result of an increase in the density of surface waters.

buoyant force the upward force exerted on a fluid or object immersed within a fluid.

byssal thread a tough, fibrous, threadlike material used by mussels to attach to rocks.


calibration the process of verifying the accuracy of an instrument.

California Countercurrent a northerly flow of the California Current along the coastlines of San Diego, Orange County, and Los Angeles.

California Current System the system of eastern boundary currents that flow along the western US in the North Pacific Ocean.

California grunion run the twice-monthly periods when the California grunion swim onto the beach face to reproduce.

California Undercurrent a subsurface, northward-flowing current beneath the Davidson Current.

calving the fracture and fragmentation of a glacier and its discharge into the ocean.

Cambrian a geologic period from 541 to 485.4 million years ago.

Cambrian radiation the rapid increase in animal diversity in the Cambrian.

Canary Current the equatorward-flowing eastern boundary current in the North Atlantic Ocean.

capillary wave a wave whose wavelength is smaller than 1.73 centimeters.

carbon dioxide a molecule composed of carbon and oxygen that provides a carbon source for plants and acts as a greenhouse gas in Earth’s atmosphere.

carbonate platform limestone platform attached to a continental shelf, built by a combination of biological, sedimentary, and geological processes.

cardinal directions north, south, east, and west.

carnivory the eating of one animal by another.

cation a positively charged ion.

Celsius scale a temperature scale that sets zero as the freezing point and 100 as the boiling point of water.

Central South Equatorial Current the central branch of the South Equatorial Current in the Atlantic Ocean.

chain of reasoning a logical extension of previous scientific work on a problem.

Challenger Deep a part of the Mariana Trench, the deepest location in the world ocean.

charismatic megafauna species of large animals best known and loved by the general public.

chemical oceanography the scientific study of the chemical properties and processes in the world ocean.

chemical symbol the letter or letter combination that represents an element.

chemical weathering the breakdown of rocks by chemical processes.

chemisorption the chemical attraction of elements to particles.

chemoautotroph an organism that uses chemical energy to manufacture its own food.

chemosynthesis the manufacture of organic carbon from carbon dioxide and inorganic substances using energy obtained from inorganic chemicals.

chloride ion the ionic form of chlorine.

chlorofluorocarbon a class of gas molecules containing chlorine and fluorine.

chlorophyll the primary light-absorbing pigment of all oxygen-producing photosynthetic organisms.

Chlorophyta a phylum that includes single-celled and multicellular green algae.

circalittoral zone the region below the infralittoral zone extending to the bottom of the euphotic zone.

citizen science the reporting and collection of scientific data by the public.

clade a group of organisms that share a common ancestor.

cladistics a method of classification that uses measurable characteristics to determine degrees of similarity between organisms.

clam gun a cylindrical device used to capture clams buried in the sand.

classification the organization of life into groups that share certain characteristics.

cleaning station place on a seamount or reef where cleaner organisms remove parasites from other organisms.

climate the long-term average of weather conditions at a given location or globally.

climate zone a region of Earth defined by a particular average weather.

cloud a visible form of suspended liquid or solid water.

cloud condensation nucleus aerosol that acts as a site of condensation for water vapor in the formation of clouds.

Cnidaria a phylum that includes sea anemones, corals, and jellies that use stinging cells.

coastal armoring the hardening of a beach to prevent its erosion by waves.

coastal array ocean observatory deployed on a continental shelf (i.e., near a coastline).

coastal benthic zone See sublittoral zone.

coastal bluff a rounded seaside cliff formed by wave erosion and uplift.

coastal cell See littoral cell.

coastal ocean the ocean waters overlying the continental shelves.

coastal oceanography the study of coastal waters.

coastal waters waters overlying the continental shelves.

cohesion the sticking together of water molecules.

cold seep places in the seafloor where methane and other energy-rich fluids leak through the sediments.

cold-core ring a mesoscale eddy with a cold interior relative to its perimeter.

collapsing breaker a wave where the entire wave face disintegrates into foam.

colonial organism an organism with hundreds to thousands of identical cells, each of which may produce a whole new organism.

comet an icy object that travels across the solar system in a highly eccentric orbit.

compass rose an illustration that depicts the cardinal and ordinal directions.

compound molecules composed of different atoms.

compressional heating the heating that occurs due to increases in air pressure as wind flows from higher to lower elevations.

computer modeling investigation a scientific investigation that uses computers to visualize or quantify natural processes.

conceptual model a mental picture, often in visual form, of how we think something works.

conduction the transfer of heat through molecule-to-molecule contact.

conductivity-temperature-depth instrument an electronic depth-profiling instrument with sensors for measuring conductivity (i.e., salinity), temperature, and depth.

conservative element an element whose ratio with other elements remains constant.

constructive interference the interaction of two or more waves that produces a wave larger than the original waves.

continent the elevations in Earth’s crust.

continental crust the part of Earth’s crust that forms the continents.

continental margin the submerged edges of the continents.

continental rise a gently sloping region of sediments at the base of the continental slope.

continental shelf province the submerged flat portion of the continental margins.

continental slope province the steeply sloped part of the continental crust that extends from the shelf break to the abyss.

contour current a current that flows along depth contours of continental slopes.

contourite a sedimentary deposit formed by contour currents.

convection current the heat-driven, circular motion of fluids (air and water) from one place to another.

convection the transfer of heat by moving fluids.

convective heating motions of the atmosphere or ocean that transfer heat from one location to another.

coral bleaching the expulsion of photosynthetic symbionts by a coral polyp in response to prolonged elevated water temperatures.

Coriolis force the apparent deflection of moving objects across Earth’s surface.

coronal mass ejection an intense outburst of particles from the Sun.

covalent bond the chemical bond formed when atoms share electrons

crescent Moon the illuminated slivers of Moon visible just after and just b.efore the new Moon

Cromwell Current See Equatorial Undercurrent.

cross-shore transport the wave-generated movement of sediments toward and away from the beach face.

cryosphere the frozen parts of Earth.

crystal lattice the three-dimensional, symmetrical, and repetitive arrangement of atoms in a crystal.

CTD See conductivity-temperature-depth instrument.

Ctenophora a phylum that includes comb jellies.

cycloid the curve traced by a point on the perimeter of a wheel as it moves forward.


Day Zero the day that a city’s water supply will run out.

daylength the number of hours in the lighted portion of the day.

deductive reasoning the approach of eliminating all possible hypotheses until only one cannot be disproven.

deep circulation the three-dimensional flows of water in the abyssal ocean.

deep sea everywhere beneath the euphotic zone.

deep water wave a wave that travels in water deeper than one half its wavelength.

deforestation the removal of trees from a landscape.

delta a large deposit of sediments formed at the mouth of a river.

density the mass of molecules occupying a given volume.

depocenter a site of enhanced organic matter sedimentation in oceanic trenches.

desalination the process of creating freshwater from saltwater.

destratification the disappearance of the seasonal thermocline due to mixing.

destructive interference the interaction of two or more waves that produces a wave smaller than the original waves.

detritus a general term for particles of dead matter in the ocean.

diatomic molecule two atoms bound to each other.

diffusion the movement of molecules across a boundary due to a concentration gradient.

digital thermometer a temperature-measuring device that displays digital data.

dipole a substance that exhibits a separation of electrical charges.

dissolution the dissolving of substances in water.

dissolved gas gas-phase elements in seawater.

dissolved organic matter organic matter dissolved in seawater.

dissolving the mixing of a solute into a solvent.

disturbing force a force that creates an ocean wave.

diurnal tide a once-daily tide.

diving bell dome-shaped, air-filled chamber that permits divers to work at depth.

domain the highest level of organization in the classification of life.

downslope wind a wind that blows from high to low elevations.

drift bottle method the use of buoyant containers for tracking ocean currents.

drifter a platform that floats on the ocean’s surface to track currents.

duck dive a technique of plowing the nose of a surfboard under a wave.


Earth system  the various interdependent, interconnected systems that collectively regulate Earth.

Earth’s axis the imaginary line around which the Earth rotates.

Earth’s energy imbalance the excess (or deficit) between solar radiation levels to and from Earth’s surface.

Earth’s geophysical fluids the air, water, and molten rock found on our planet.

Earth’s orbit the movement of Earth around the Sun.

Earth’s rotation the turning of Earth on its axis.

Earth’s surface reservoirs water found just beneath and above Earth’s surface.

East Australian Current the western boundary current in the South Pacific Ocean.

eastern boundary current a boundary current that flows along the eastern edge of an ocean basin.

Echinodermata a phylum of organisms with a spiny exoskeleton that includes sea urchins, sea stars, brittle stars, sea cucumbers, and sand dollars.

ecology the study of interactions between a co-occurring community of organisms and their environment.

ecosystem engineering the restructuring of a habitat through the activities of organisms.

ecosystem service an economic, ecological, restorative, or cultural benefit provided by an ecosystem to humans.

Ediacara biota the fossil assemblage that appeared from 571 to 541 million years ago, representing the oldest macroscopic marine communities preserved in rocks.

Ediacaran  a period of geologic time 635 to 541 million years ago that set the stage for the widespread diversification of life that occurred in the Cambrian.

Ekman depth the depth where the current flow is 37 percent of the surface current flow and in a direction 180° opposite to the direction of the wind.

Ekman spiral the wind-generated, Coriolis-influenced, multidirectional flow that resembles a spiral stack of books from the sea surface to the limit of wind energy penetration.

Ekman transport the average flow from an Ekman spiral in a direction 90° to the right (or left) of the wind (depending on the hemisphere).

electrical conductivity the flow of electrons through a wire.

electrode a piece of metal through which electricity flows.

electromagnetic radiation all of the types of radiant energy emanating from stars.

electromagnetic spectrum a chart of the range of all types of electromagnetic radiation in order of increasing or decreasing wavelength.

electron a negatively charged subatomic particle that orbits the nucleus.

electronegative the negatively charged region of a polar molecule.

electropositive the positively charged region of a polar molecule.

electrostriction the slight reduction in volume that occurs when salts dissolve in water.

element an atom with a specific and unique number of protons.

elittoral zone a term proposed to account for depths deeper than the circalittoral but shallower than the bathyal.

emergent property a property of a system not apparent when studying its parts alone.

emersion when an organism or object is exposed to air.

Emery method a technique employing two 2-meter sticks and a tape measure for determining the beach profile.

endoskeleton a skeleton on the inside of an animal.

endosymbiosis the merging of two single-celled organisms into one.

energy the ability to do work.

environment the geological, chemical, physical, and biological conditions present at a given time and place.

eon the largest division of geologic time.

epifauna organisms living upon a substrate.

epipelagic zone the region of the upper ocean from just beneath the sea surface microlayer to the lower boundary of the euphotic zone.

equatorial current a current that flows east to west along the equator.

equatorial doldrums a region of calm air over the equator.

equatorial plane the imaginary horizontal plane that passes through Earth’s equator.

Equatorial Undercurrent a subsurface current flowing west to east along the equator.

equilibrium model of tides a simplified model of ocean tides on an Earth with no continents.

equinox the two times of the year when the Sun is directly overhead at the equator.

Eukarya unique single-celled and multicellular organisms descended from Archaea and bacteria.

eukaryogenesis the sequence of events that gave rise to the Eukarya.

eukaryote a cell type with visible organelles characteristic of Eukarya.

euphotic zone the lighted region of the upper ocean from the sea surface to the depth where sunlight diminishes to 1 percent of its surface value.

Europe part of the Eurasian landmass, home to the third-largest human population on Earth.

evaporation fog the condensation of water vapor over a warm lake.

evaporation the transformation of liquid water into water vapor.

evaporite deposit of salt formed by evaporation of seawater trapped during uplift of isolated basins.

evolutionary arms race the diversification of structures, physiologies, and behaviors to compete with predators or prey.

exoskeleton a skeleton on the outside of an animal.

exosphere the layer above the thermosphere that may extend beyond the Moon.

external particle a particle delivered to the ocean from an external source.

extreme sea level rise a rapid change in sea level due to waves, tides, and storm surge.


Fahrenheit scale  a temperature scale that sets 32 as the freezing point and 212 as the boiling point of water.

fall equinox the time of year when daylength is decreasing and the Sun is passing directly over the equator into the opposite hemisphere.

falsification the process of disproving a hypothesis.

fantail the back end (i.e., stern) of a ship.

feedback loop a process that exerts a change on a system.

feldspar a yellow-to-red aluminosilicate mineral containing calcium, sodium, or potassium found as grains in beach sand.

Ferrel cell the atmospheric cell that occurs between the Hadley and polar cells.

fetch a distance over which the wind blows in the same direction.

fetch width the width of the wind field that generates a wave.

field investigationSee oceangoing investigation.

first quarter the point halfway between the new and full Moon, when the right half of the Moon is illuminated.

float a platform that drifts beneath the ocean’s surface to track currents.

flux a pathway and rate of flow of a substance into and out of a reservoir.

fog a cloud formed near the ground.

forebulge a region of uplift adjacent to a glacier.

forebulge collapse the subsidence of land following retreat of a glacier.

foreshore the portion of a beach nearest the water extending from the beach scarp (if present) to the lower boundary of the beach face.

fourth paradigm the use of computers to explore and mine big data for information.

frost wedging the freezing and expansion of water in rock cracks that bursts rocks apart.

full Moon when the side of the Moon facing Earth is fully illuminated.

fully developed sea a sea exhibiting the maximum wave size under existing wind conditions.


Gaia hypothesis the idea that Earth resembles a living organism.

galaxy collection of star systems bound together by gravity.

gamma ray electromagnetic radiation with the highest energy and shortest wavelength.

gas a fluid of indefinite shape and volume that will expand to fill any container in which it is held.

gas planet a planet whose composition is predominantly gaseous materials.

gene a segment of genetic material that codes for proteins and other cellular functions.

genus the second-lowest level of organization in the classification of life; above species and below family.

geobiology the study of life’s interactions with the Earth and their evolution over geologic time.

geoid the theoretical equal-gravity surface of Earth.

geologic time the history of Earth from its beginning.

geological oceanography the scientific study of the geological properties and processes in the world ocean.

geomagnetic storm disruptions of Earth’s magnetic field caused by coronal mass ejections.

geophysical fluid dynamics the study of fluid flows in nature.

geosphere the solid Earth.

geostrophic current a current that results from a balance between the pressure gradient force and the Coriolis force.

gibbous Moon when three quarters of the Moon is illuminated.

glacial isostatic adjustment the changes in land surface elevation as a result of the disappearance of glaciers.

glider winged, sensor-enabled, buoyancy-driven platform for carrying out various measurements over large expanses of the ocean.

global array ocean observatory deployed in a deep water location.

global atmospheric circulation the three-dimensional motions of air within the troposphere.

global climate change the change in Earth’s climate over geologic time.

global mean sea level rise the global increase in the volume of the ocean.

global scale distances greater than a thousand kilometers.

global warming the increase in Earth’s average temperature since 1850.

global water crisis the lack of water for billions of people around the globe.

global water cycle a conceptual (or mathematical) model of the movement of water between various reservoirs on Earth’s surface.

grain an individual particle of sand.

grain size distribution the frequency of different grain sizes in a sediment deposit.

granite  an intrusive, light-colored igneous rock.

gravitational force the force of attraction between objects with mass.

gravitySee gravitational force.

Gravity Recovery and Climate Experiment a satellite-based measurement of the variations in gravity that result from changes in the distribution of mass across Earth’s surface.

Great Barrier Reef the largest coral reef in the world, located off the east coast of Australia.

Great Ordovician Biodiversity Event one of several periods of rapid diversification of organisms during the Early to Middle Ordovician.

Great Oxidation Event  the rise in atmospheric oxygen about 2.5 billion years ago.

greenhouse effect  warming as a result of gases in Earth’s atmosphere.

greenhouse gas an atmospheric gas that absorbs longwave radiation.

Greenland the world’s largest island.

groin a structure built perpendicular to the shore to trap sediments on a beach.

ground truthing the process of independently verifying the accuracy and precision of measurements made from satellites.

groundwater water stored in natural underground reservoirs.

group speed the speed of a wave train equal to half the speed of individual waves.

Gulf Stream the western boundary current in the North Atlantic Ocean.

guyot a flat-topped seamount.


habitat the range of environments that support the survival and reproduction of a species.

hadal benthic zone an ocean zone occupying depths below 6,000 meters on the seafloor.

hadal lander benthic lander capable of reaching the deepest parts of the world ocean.

hadal province the seafloor at depths below 6,000 meters.

Hadean the first division of geologic time, from 4.56 to 4 billion years ago.

Hadley cell the atmospheric cell that occurs over the tropics.

hadobenthic zoneSee hadal benthic zone.

hadopelagic zone a depth zone bounded by the walls of oceanic trenches.

halite the crystalline form of sodium chloride.

headland a point of land that juts out into the ocean.

headless canyon a class of submarine canyon confined to the continental shelf.

headwaters the source of a stream or river.

heliosphere the Sun and solar system.

heritage the properties of sediments inherited from their parent rock.

heteronuclear molecule two atoms of different elements bound to each other.

hierarchical system a system characterized by different levels, one above or below the other.

high high tide the highest of the high tides in a mixed tide.

high low tide the highest of the low tides in a mixed tide.

high tide when sea level reaches its highest extent during the day.

high-pressure region a region whose air pressure is higher than surrounding regions.

high-tide floodingSee nuisance flooding.

Himalayas Earth’s tallest mountains.

holey sock drogue a large, subsurface cloth cylinder attached to a surface float that improves the accuracy of current measurements.

homonuclear molecule two atoms of the same element bound to each other.

horse latitudes a region of calm air at about 30°N/S.

Humboldt CurrentSee Peru–Chile Current.

hybrid remotely operated vehicle a cross between an ROV and an AUV that permits operation with or without a tether.

hybrid-type trace element trace elements with multiple pathways for their removal from seawater.

hydrogen bond a type of bond formed between hydrogen atoms and other molecules.

hydrogen fusion a reaction of hydrogen atoms that sustains the release of energy from the Sun.

hydrographic station a shipboard sampling location in the ocean, usually arranged as points on a grid.

hydrosphere Earth’s waters.

hydrostatic equilibrium the balance between the downward pull of gravity and the upward force of pressure, where no net movement of the air occurs.

hydrostatic skeleton a skeleton whose shape is maintained by water pressure.

hyperspectral imager sensor capable of detecting hundreds of narrow bands of electromagnetic radiation.

hypothesis a carefully worded, conditional, and testable explanation of how nature works.

hypothetico-deductive approach the general process of generating and disproving hypotheses based on observations or experiments.

hypsographic curve a graph of the percentages of Earth’s crust at a particular elevation or depth.


ice the solid form of water.

iceberg a chunk of glacier floating in the ocean.

igneous rock a rock formed from volcanic activity within or upon Earth’s surface.

Indian Ocean the third-largest ocean in the world.

Indonesian Throughflow the system of currents flowing through Indonesia that acts as a control valve on the world ocean circulation.

inductive reasoning the process of extracting general principles and possible hypotheses from a limited set of observations or data.

infauna organisms living within a substrate.

infiltration the flow of water through soil and porous rock.

infragravity wave waves with periods from 30 seconds to 5 minutes.

infralittoral zone the region immediately below the littoral zone, exposed only on the lowest tides.

infrared light the portion of the electromagnetic spectrum with wavelengths greater than visible light and shorter than radio waves.

inherited character the trait of an organism coded in its genes and passed down by its ancestors.

interdisciplinary science a science that integrates the tools, approaches, knowledge, and understanding of multiple disciplines to solve scientific problems.

intermediate wave a wave that travels in water shallower than one half and greater than one twentieth its wavelength.

internal particle a particle formed within the ocean.

internal wave a wave along a density boundary beneath the surface of the ocean.

International System of Units the system of units used by scientists.

intertidal zonation the grouping of organisms into horizontal bands along vertical gradients in elevation along a shoreline.

intertidal zone a subdivision of the littoral zone, the region of alternating submersion and emersion as a result of tides or waves.

Intertropical Convergence Zone the region where the trade winds meet, characterized by bands of clouds and high rainfall.

invertebrate an organism lacking a backbone.

ion an atom or molecule whose number of positively charged protons differs from its number of negatively charged electrons.

ionic bond a bond formed when atoms exchange electrons.

isobar a line of equal pressure.

isobath a line of constant depth.

isostasy the equilibrium height of Earth’s crust as it floats on the mantle.

isothermal a layer of water whose temperature is identical over a range of depths.


jet stream swift currents of air that blow west to east at high altitudes.


Kármán line the boundary between Earth’s atmosphere and outer space.

kelp highway the idea that early humans traveled by watercraft from Asia to North America consuming seafood along the way.

kinetic energy energy in motion.

king tide an extremely high tide.

kite aerial photography a type of above-surface photography that uses kites to elevate the camera.

Kuiper Belt a donut-shaped system of icy objects found just beyond the orbit of Neptune.

Kuroshio Current the western boundary current in the North Pacific Ocean.


laboratory investigation a scientific investigation carried out in a laboratory.

Lagrangian platform a platform that moves with the currents.

land breeze an offshore wind generated by temperature differences between the land and ocean.

land of the midnight sun polar regions that experience 24 hours of daylight during the summer.

Late Heavy Bombardment a period during the Hadean characterized by a high number of asteroid and comet impacts.

latent heat of fusion the heat required to transform a solid to a liquid or vice versa.

latent heat of vaporization the heat required to transform a liquid to a gas or vice versa.

latent heat the heat required to change the state of a substance.

lava molten rock that spills onto Earth’s surface.

law of conservation of energy the observation that energy can neither be created nor destroyed, but it can change forms.

Leeuwin Current the poleward-flowing eastern boundary current in the South Indian Ocean.

lichen a symbiotic organism formed by a fungus and an alga.

liquid a fluid with an indefinite shape but a near-constant volume (as opposed to a gas).

liquid water the liquid form of water.

littoral cell a conceptual model of the watershed–beach–submarine canyon system that governs the size of beaches.

littoral zone the region between the tides (where present) along the very edge of the ocean.

living sea the interconnected, self-replicating, and self-sustaining network of diverse life forms that inhabit the world ocean.

living shoreline a structure that employs artificial and natural landscapes to protect coastlines and preserve the ecological services provided by coastal habitats.

long period wave waves with periods from 5 minutes to 12 hours.

longshore current a wave-generated flow of water parallel to the beach.

longshore transport the transport of sediments and debris by the longshore current.

longwave radiation collectively, the portion of the electromagnetic spectrum that includes mid- to far-infrared wavelengths.

Low Elevation Coastal Zone lands with an elevation of less than 10 meters

low high tide the lowest of the high tides in a mixed tide.

low low tide the lowest of the low tides in a mixed tide.

low tide when sea level reaches its lowest extent during the day.

low-pressure region a region whose air pressure is lower than surrounding regions.

low-tide terrace a flat portion of the lower foreshore exposed at low tide.

lower intertidal  in the North American West Coast littoral classification system, the fourth zone (Zone 4), occupying tide heights from zero to the height of the lowest tide.

lower middle intertidal in the North American West Coast littoral classification system, the third zone (Zone 3), occupying the lower part of the middle intertidal at tide heights of zero to 0.5 meter.


macronutrient a biologically important nutrient required in high concentrations.

Madden–Julian Oscillation an intraseasonal, eastward-traveling, globe-trotting atmospheric wave that influences weather.

magma molten rock beneath Earth’s surface.

major constituent an element whose concentration exceeds 1 part per million in seawater.

Malvinas Current a cold, northward-flowing current off the coasts of Uruguay and Argentina.

manganese noduleSee polymetallic nodule.

manipulator arm human-controlled, mechanical extension on an ROV for collecting samples, drilling holes, or deploying instruments in the ocean.

marine big data the enormous volumes of oceanographic data now available and growing daily.

marine geomorphometry the quantitative study of the seafloor.

marine layer a low-altitude cover of stratus clouds that forms over a cool ocean.

marine phosphorite  a phosphate-rich sedimentary rock formed in oceanic upwelling regions with high biological productivity.

marine virus a noncellular entity inhabiting the ocean with a protein shell that encapsulates genetic information.

mass extinction a rapid and global decrease in the abundance and diversity of organisms.

matground surface crust formed as a result of interactions between microbes and sediments.

mathematical models simple or complex mathematical expressions or sets of expressions to describe or simulate how something works.

mean sea level the average sea level.

mega-evaporite enormous deposit of salt formed by evaporation of seawater trapped during uplift of extensive ocean basins.

megacity a city whose population exceeds 10 million people.

meltwater water that originates from frozen sources.

membrane-based desalination  a process that uses membranes to produce freshwater.

meridional current a current flowing along a line of longitude.

meridional overturning circulation the combined three-dimensional surface and deep circulation of the ocean; see also world ocean circulation.

mesopelagic zone a zone characterized by dim and diffuse light, extending from the bottom of the euphotic zone to approximately 1,000 meters.

mesophotic coral ecosystems coral reefs that grow in dimly lit waters.

mesoscale distances on the order of a few to a hundred kilometers.

mesoscale structure the regional scale of physical, chemical, or biological features of the ocean, from a few to a few hundred miles.

mesosphere the layer above the stratosphere in the middle of Earth’s atmospheric layers, where meteors become visible as they are heated through friction.

metamorphic rock a rock transformed by heat, pressure, and fluids.

metazoan true animals; multicellular animals with differentiated cells.

meteorology the scientific study of the atmosphere.

methane a molecule composed of one carbon and four hydrogen atoms that acts as a greenhouse gas in Earth’s atmosphere.

methane hydrate a frozen form of methane found on the seafloor.

methanogen a type of microbe that converts organic matter into methane.

metric systemSee International System of Units.

microbial mat a carpet of photosynthetic and sediment-dwelling bacteria.

microfossil the hardened remains of a microscopic organism.

microlayer the lower part of the sea surface microlayer, inhabited by a unique assemblage of microbes and various abiogenic and biogenic particles, found from 1 to 1,000 micrometers in depth.

micronutrient a biologically important nutrient required in low concentrations.

microwave electromagnetic radiation with wavelengths between 1 millimeter and a meter.

middle intertidal in the North American West Coast littoral classification system, the second zone (Zone 2), occupying the region at tide heights of zero to 1.5 meters.

midnight zoneSee bathypelagic zone.

Milky Way the galaxy in which Earth resides.

Mindanao Current the southward flow of the North Equatorial Current at its western terminus.

mineral a solid of inorganic material with a unique chemical composition and crystalline structure.

mini-autonomous underwater explorer small, autonomous, sensor- and GPS-enabled platform that works in a swarm beneath the surface of the ocean to track currents or carry out other kinds of observations and measurements.

minor constituent an element whose concentration in seawater is less than 1 part per million.

minus tide a tide whose tide height is less than zero.

mitochondria the cell structure that supplies energy to eukaryotic cells.

mixed layer depth the depth to which the surface mixed layer extends, usually the top of the thermocline.

mixed semidiurnal tide a twice-daily tide with unequal heights.

mixed tideSee mixed semidiurnal tide.

mixed-type distribution the existence of different distributions of a trace element in seawater depending on its form.

mixground a slurry of soft seafloor sediments formed by the activities of organisms.

mixing the homogenization of seawater.

mixture a collection of molecules with an indefinite or varying composition, such as air or seawater.

molecule two or more atoms bound together.

Mollusca a phylum that includes bivalves, gastropods, chitons, and cephalopods.

molting the shedding of an exoskeleton by an organism.

momentum the product of a molecule’s mass and its velocity.

momentum transfer the transfer of momentum from a moving molecule to a nonmoving molecule.

monophyletic  descending from a common ancestor.

monsoon the wind that arises from seasonal heating of the interior of continental regions.

Mount Erebus the world’s southernmost active volcano.

Mount Everest the highest mountain on Earth.

mouth (of river or watershed) the lowermost elevation of a river; where it ends.

moving water flow of water.

multicellular organism an organism with many different specialized cells which carry out specific functions and cannot independently create a whole organism.

multiple thermocline the presence of two or more thermoclines in a water column.

multispectral imager sensor capable of detecting multiple wide bands of electromagnetic radiation.

mystery zoneSee abyssopelagic zone.


nanolayer the thin organic coating at the very surface of the ocean, from zero to 1 micrometer in depth.

National Tidal Datum Epoch a 19-year average of low or low low tide heights used to establish that tidal datum at different locations around the US.

natural gas hydrate a potential source of energy found in great quantities on the seafloor.

neap tide a tide of minimum range occurring at the first and the third quarters of the Moon.

near-bottom zoneSee benthopelagic zone.

negative buoyancy the tendency of a fluid or object to sink in a fluid.

negative feedback loop a process that acts to maintain, reduce, or reverse changes in a system.

negative tideSee minus tide.

nekton organisms that propel themselves through the water column.

Neoproterozoic Oxygenation Event a period of increase in atmospheric oxygen sufficient to oxygenate at least some deep ocean basins around 570 million years ago.

neritic watersSee coastal waters.

neutrally buoyant the tendency of a fluid or object to remain at rest in a fluid.

neutron a neutrally charged subatomic particle found in the nucleus of an atom.

new Moon when the side of the Moon facing Earth is not visible.

night vision technology devices that detect infrared radiation and permit viewing of objects in the dark.

Niskin bottle a type of seawater sampling bottle that can be triggered electronically.

nitrogen-fixing bacteria microbes capable of turning nitrogen gas into biologically available forms of nitrogen.

nitrous oxide a molecule composed of nitrogen and oxygen produced naturally by microbial activity; acts as a greenhouse gas in Earth’s atmosphere.

nondispersive waves that do not separate according to their wavelength or wave period.

noon sun angle the angle of the Sun above the equatorward horizon at noon.

North America the third-largest continent.

North Atlantic Current the eastward-flowing west wind drift current in the North Atlantic Ocean.

North Atlantic Gyre the subtropical gyre circulation in the North Atlantic Ocean.

North Equatorial Countercurrent a west-to-east current just north of the equator.

North Equatorial Current the equatorial current that flows just north of the equator.

North Pacific Current the eastward-flowing west wind drift current in the North Pacific Ocean.

North Pacific Gyre the subtropical gyre circulation in the North Pacific Ocean.

North South Equatorial Current the northerly branch of the South Equatorial Current in the Atlantic Ocean.

Northeast Monsoon Current the westward-flowing current that occurs during the winter monsoon.

northeast trade wind the trade wind that blows from northeast to southwest north of the equator.

Norwegian Current a northerly current along the coast of Norway.

nowcast forecast of ocean or atmospheric conditions in near real time.

nucleus (in biology) the cell structure in which most of a cell’s genetic material is housed.

nucleus (in chemistry) the central portion of an atom, composed of protons and neutrons.

nuisance flooding local flooding caused by sea level rise that now occurs at high tides.

numerical models computer models that solve sets of mathematical equations to make forecasts or projections of natural processes at some time in the future.

nutrientSee biologically important nutrient.


obligate anaerobe an organism that cannot tolerate oxygen in its environment.

ocean basin a depression in Earth’s crust covered by seawater extending from the shelf break to the deepest trench.

ocean climate the average of ocean conditions over a specified period of time.

ocean color the colors of visible light emanating from the surface of the ocean.

ocean depth zone a system for classifying the general conditions for organisms present at various depth ranges in the water column and on the seafloor.

ocean eddy a self-sustaining, rotating loop of water tens to hundreds of miles wide.

ocean heat content the heat stored in the ocean.

ocean life zoneSee ocean depth zone.

ocean mining the extraction of mineral resources from the seafloor.

ocean mooring seafloor-anchored cable on which various ocean sensors can be attached and held vertically by a float.

ocean observatory an integrated array of ocean-observing sensors and platforms on and above the seafloor designed to address questions of scientific and societal importance.

ocean tide the daily rising and falling of sea level.

ocean tracer a substance used to track the movement and evolution of water masses.

ocean wave the physical expression of energy moving forward at the interface between two fluids of different density, including surface and internal waves.

ocean weather the instantaneous state of the ocean.

ocean-observing systems a broad category of sensor-outfitted platforms that fly above, glide on top of, or dive below the surface of the ocean.

oceangoing investigation a scientific investigation carried out at sea.

oceanic crust the part of Earth’s crust that forms the ocean basins.

oceanic gyre the rotation of currents around a common center in an ocean basin.

oceanic plateau flat or nearly flat region of the seafloor that drops off abruptly on one or more sides.

oceanic ridge a narrow region of varying complexity whose height exceeds 1,000 meters and whose length-to-width ratio is greater than 2.

oceanic trench a V-shaped depression in the seafloor with steep walls.

oceanic waters waters overlying the ocean basins.

oceanographer  any person, robot, or animal engaged in the scientific study of the ocean.

oceanography the scientific study of the world ocean.

offshore the region beyond the surf zone.

offshore wind a wind that blows from the land to the ocean.

onshore wind a wind the blows from the ocean to the land.

ooid light-colored oval of calcium carbonate.

Oort Cloud a spherical-shaped system of dust, icy objects, and comets at the far reaches of our solar system.

open ocean oceanographySee blue water oceanography.

open ocean the oceanic waters beyond the continental shelves.

operational oceanography the acquisition and dissemination of oceanographic and meteorological information useful to navigating or carrying out activities in the ocean.

orbital plane the imaginary horizontal plane on which Earth orbits the Sun.

ordinal direction northeast, southeast, northwest, southwest.

ordinary gravity wave waves with periods from 1 to 30 seconds.

Ordovician a geologic period from 485.4 to 443.8 million years ago.

organelle a subcellular, specialized structure present in eukaryotes and possibly Archaea and bacteria.

oxygen minimum zone a region of reduced or absent dissolved oxygen in the water column.

oxygenic photosynthesis photosynthesis that yields oxygen as a by-product.

Oyashio Current a southward-flowing current off the island of Hokkaido, Japan.

ozone hole a region where stratospheric ozone concentrations are greatly reduced.

ozone layer the part of the stratosphere containing ozone.


Pacific Ocean the largest ocean in the world.

pale blue dot the name given to the blue speck of Earth as seen from millions of miles away in outer space.

paleoshoreline an ancient shoreline formed during lowstands of sea level.

Pangea a supercontinent that formed and broke apart over an interval from 320 to 195 million years ago.

paraphyletic not including all descendants of a common ancestor.

parent rock the source material for sediments.

particulate organic carbon anything living or once living that occurs as a particle in seawater.

particulate organic matter living and dead particles of organic matter.

passive microwave sensor sensor that measures the intensity of microwave radiation emanating from Earth’s land, ice, and sea surface.

passive sensor sensor that measures the electromagnetic properties of the ocean.

peer review the process whereby scientists receive feedback on their work by other scientists and experts.

pelagic depth zones ocean depth zones within the water column from the surface to the deepest trenches.

pelagic organism organism that inhabits the water column.

perihelion the point in Earth’s slightly elliptical orbit where its distance from the Sun is smallest.

periodic table of elements a chart depicting all of the known elements.

Periodic Table of the Elements in the Ocean an online chart of the elements found in seawater and their concentrations with depth in the ocean.

permanent thermocline the boundary between polar water masses and seasonally mixed water masses.

Peru CurrentSee Peru–Chile Current.

Peru–Chile Current the equatorward-flowing eastern boundary current in the South Pacific Ocean.

Pettersson–Nansen bottle a type of sampling bottle for obtaining seawater at depth.

Phaeophyta a phylum that includes multicellular brown algae.

Phanerozoic the eon of visible life from 541 million years ago to the present.

photic zone the lighted waters of the upper ocean.

photoautotroph an organism that uses light to manufacture its own food.

photophore the light organ of bioluminescent animals.

photosynthesis the manufacture of organic carbon from carbon dioxide and inorganic substances using energy obtained from sunlight.

photosynthetically available radiation the wavelengths of visible light that stimulate photosynthesis in plants, generally from 400 to 700 nanometers.

phylogenetic tree a branching diagram that illustrates the hypothetical evolutionary relationships between organisms.

physical model a scaled-down, three-dimensional, semirealistic representation of a physical object or part of nature.

physical oceanography the scientific study of the physical properties and processes in the world ocean.

physical state the state of matter: solid, liquid, or gas.

physical weathering the breakdown of rocks by physical processes.

physisorption the physical attraction of elements to particles.

phytoplankton photosynthetic microbes that drift with the currents in the sunlit waters of the ocean.

phytoplankton thin layer narrow layer with high concentrations of phytoplankton.

pillow basalt a basaltic rock formation that resembles pillows.

Pineapple Express the popular name given to the subtropical jet stream when it carries humid subtropical air from Hawaii to California.

plasma a fourth state of matter consisting of free-moving electrons and ions.

plunging breaker wave that creates a tube with a lip that shoots over the face of the wave in a kind of waterfall.

plus tide a tide whose height is greater than zero.

point break a type of breaking wave that wraps around a headland.

polar cell the atmospheric cell that occurs over polar regions.

polar day the six-month period of continual or near-continual sunlight in polar regions.

polar easterlies the easterly directed prevailing winds that blow at polar latitudes.

polar gyre a gyre circulation at polar latitudes.

polar jet stream a high-altitude flow of cold air that meanders like a river around the North and South Poles.

polar molecule a molecule that exhibits a separation of charges.

polar night the six-month period of continual or near-continual darkness in polar regions.

polar submarine canyon submarine canyon found on Arctic and Antarctic continental shelves.

polar zone region north of the Arctic Circle or south of the Antarctic Circle characterized by freezing weather.

polychaete a segmented marine worm with bristles.

polymetallic crust similar to nodules in composition, forming as a coating on rocks along the flanks and summits of seamounts.

polymetallic nodule tennis ball–sized globe of different metals that precipitates slowly around a nucleus (a shell or bone fragment, for example) on the seafloor.

poorly sorted having grain sizes that vary widely.

Porifera a phylum that includes sponges.

positive buoyancy the tendency of a fluid or object to rise in a fluid.

positive feedback loop a process that acts to amplify or accelerate changes in a system.

positive tideSee plus tide.

potential energy stored energy or energy inherent in an object in a gravitational field.

practical salinity scale a unitless scale used to define salinity.

precipitation the gravity-driven falling of liquid or solid water from the atmosphere.

pressure gradient force the force that arises when two locations have different air pressure.

pressure the force exerted by a fluid (a gas or a liquid) on an object immersed within it.

principle of constant proportions the observation of constant proportions among the major constituents of seawater.

principle of unity the idea that there is but one ocean on Earth, the world ocean.

progressive wave a wave moving forward along a density boundary.

prokaryote a cell lacking a visible nucleus and other organelles.

Proterozoic the eon of early life, from 2.5 billion to 541 million years ago.

protist a single-celled or multicellular species with a eukaryotic cell type.

proton a positively charged subatomic particle found in the nucleus of an atom.

protostar the earliest stage in the evolution of a star.


qualitative data described by its properties or relationships with other variables.

quantitative  numerical data that can be analyzed mathematically.

quartz a white or clear mineral composed of silica found as grains in beach sand.


radial component the vertical component of the tidal force.

radial symmetry a shape arranged around a central axis, like a cake or pie.

radiation the transfer of heat via electromagnetic energy.

radio wave the longest wavelength of radiation in the electromagnetic spectrum, by which analog radio is transmitted.

radiometer sensor that detects electromagnetic radiation.

ray the path of a beam of light.

recirculation gyre a regional gyre-type flow that recirculates water along a western boundary current.

reference ellipsoid the best-fit ellipsoid to Earth’s geoid.

reflection the rebound of a light ray at the same angle at which it strikes an object.

regional cabled array seafloor-based ocean observatory spanning a region of geologic interest.

relative sea level rise the increase in local mean sea level measured at a particular location.

relief the change in height of a seafloor feature from its highest to lowest point.

remotely operated vehicle human-controlled, camera-equipped, propelled vehicle attached to a shipboard tether for gathering images, making measurements, or collecting samples from the water column or seafloor.

reservoir a place where something is stored.

reservoir model a conceptual (or mathematical) model identifying (and quantifying) the sources and sinks of substances to a reservoir.

residence time the time an element spends in a reservoir like the ocean.

respiration the metabolic breakdown of organic matter.

restoring force a force that restores sea level.

reverse osmosis system the movement of water across a concentration gradient.

reversing thermometer a type of oceangoing thermometer that turns upside down when triggered at depth to obtain an accurate measure of temperature.

Rhodophyta a phylum that includes single-celled and multicellular red algae.

rill a treelike pattern of sand formed when water seeps from a beach exposed during a low tide.

ring a type of mesoscale eddy that forms in association with western boundary currents.

ripple wind waves larger than capillary waves and smaller than wind chop.

robotic investigation a scientific investigation that employs robotic devices to make observations and measurements of the natural world or under artificially created conditions.

rocks aggregates of minerals

rock cycle the transformations of one rock type to another.

rock tumbler a device used to polish small rocks.

rockslide the tumbling of rocks downhill.

rocky intertidal zone the region bounded by the highest and lowest tides.

rocky planet a planet whose composition is predominantly solid materials.

Rodinia the second supercontinent, appearing about a billion years ago.

rolling the tumbling of a sediment grain in the direction of fluid flow.

rooted tree a phylogenetic tree with a main trunk and branches depicting ancestry among species.

rosette a circular arrangement of sampling bottles attached to a CTD.

Ross Gyre a polar gyre in the Ross Sea.

Rossby wave a large-scale, wavelike motion of the upper troposphere, often associated with the polar jet stream.

runnel a strip of shallow water parallel to the beach on the seaward side of the beach face.


Sahara Desert the world’s largest hot desert.

saildrone a wind-propelled, solar-powered surfboard to which instruments may be attached for gathering oceanographic and meteorological information.

salinity the concentration of dissolved salts in seawater.

salinometer an electronic device used to measure salinity.

salt a general term applied to all dissolved substances found in seawater.

saltation the hopping of a sediment grain in a fluid flow.

sand mining the removal of sand from beaches or the seafloor by commercial enterprises.

sandbar a shallow, usually submerged, accumulation of sand on the seaward side of the beach face.

Santa Ana wind an episodic, often intense, offshore wind that occurs in Southern California and Northern Baja California.

satellite altimeter an active microwave sensor used to determine the bumps and depressions of the sea surface.

satellite oceanography the use of Earth-orbiting satellites to make observations and collect data on ocean features and processes.

satellite product any of a number of computed variables derived from measurements using satellites.

saturation concentration the maximum concentration of a solute that can be dissolved by a solution under a given set of conditions.

scattering the change in direction of a light ray as it interacts with an object.

scavenging the removal of trace elements by sinking particles.

science communication the widespread and transparent dissemination of scientific knowledge and understanding, especially in a manner accessible to the public.

science literacy the knowledge and understanding of science required to participate meaningfully in personal and societal discussions and decisions that use science.

scientific discussion the presentation in oral or written form of the conclusions of a particular scientific study.

scientific diving the use of scuba diving to carry out scientific investigations underwater.

scientific inquiry a general term to describe the diverse approaches scientists use to investigate the natural world.

scientific method the systematic and self-correcting set of practices that scientists use to discover knowledge about the natural world.

scientific name the standardized name given to all scientifically described species.

scientific question a well-formed question that lends itself to investigation using the scientific method.

scuba an acronym for self-contained underwater breathing apparatus.

sea bean any of a number of tropical seeds transported by ocean currents to faraway beaches.

sea breeze an onshore wind generated by temperature differences between the land and ocean.

sea level the theoretical height of the ocean at rest.

sea surface height the elevation of the sea surface relative to Earth’s geoid—the bumps and depressions of the sea surface.

sea surface microlayer the top 1 millimeter of seawater at the surface of the ocean.

sea surface salinity the concentration of dissolved salts at the surface of the ocean.

sea surface temperature the temperature of the surface skin of the ocean.

sea surface the ever-changing upper boundary of the ocean.

sea surface topography the shape of the sea surface.

seafloor feature part of the seafloor with measurable relief or delimited by such a feature.

seafloor massive sulfide deposit the sulfur-rich chimneys and deposits of hydrothermal vents.

seafloor province region of the seafloor bounded by recognizable features produced as a result of geologic processes.

seafloor the part of Earth’s crust submerged beneath the ocean.

seamount an isolated underwater mountain with a relief greater than 1,000 meters.

season the changes in sunlight that occur as a result of Earth’s orbit around the Sun.

seasonal thermocline the thermocline that appears during surface warming and disappears during surface cooling over the course of a year.

seawater parcel an oceanographer’s term for an unspecified volume of seawater.

sediment solid particles of various sizes fragmented from rocks.

sediment transport the movement of sediments over space and time.

sediment trap device that collects and stores sinking particles

sedimentary rock a rock formed from fragmentation and consolidation of other rock types.

sedimentologist a scientist who studies sediments.

semidiurnal tide a twice-daily tide with near-equal heights.

semipermeable membrane a filter the separates salts from water.

sensible heat heat that can be detected by human senses or instruments.

shallow-water wave a wave that travels in water shallower than one twentieth its wavelength.

shark cage a metal cage that permits safe viewing of sharks and other pelagic ocean species.

shelf break the place on the continental shelf where the slope of the seafloor increases sharply.

ship of opportunity private, commercial, or nongovernmental ship enlisted to take oceanographic and meteorological measurements on its voyage.

shortwave radiation collectively, the portion of the electromagnetic spectrum that includes ultraviolet, visible, and near-infrared wavelengths.

SI unitsSee International System of Units.

sidereal month the time it takes the Moon to complete one orbit around the Earth.

sine wave a geometric pattern that resembles the shape of a wave.

sink a process that decreases the mass or volume of a reservoir.

skeleton any framework that provides support, shape, or protection to an organism.

Skeleton Coast the name given to the coast of Namibia where shipwrecks and the skeletons of marine animals are abundant.

snailfish the deepest known vertebrate

Snowball Earth a period of time when Earth was entirely or mostly covered in glaciers and ice.

sodium chloride the most common salt in seawater.

sodium ion the ionic form of sodium.

solar path the path of the Sun across the sky.

solar system the name for the system of celestial bodies orbiting the Sun

solar wind the steady stream of charged particles from the Sun.

solid a substance that maintains its own form.

solstice the time of year when the Sun is at its highest or lowest point in the sky.

solute the substance being dissolved in a solution.

solvent a substance that dissolves another substance.

sorting the separation of sediment grains by size in a fluid flow.

source a process that increases the mass or volume of a reservoir.

South America the fourth-largest continent.

South Atlantic Current the eastward-flowing west wind drift current in the South Atlantic Ocean.

South Atlantic Gyre the subtropical gyre circulation in the South Atlantic Ocean.

South Equatorial Current the equatorial current that flows just south of the equator.

South Indian Current the eastward-flowing west wind drift current in the South Indian Ocean.

South Indian Gyre the subtropical gyre circulation in the South Indian Ocean.

South Pacific Current the eastward-flowing west wind drift current in the South Pacific Ocean.

South Pacific Gyre the subtropical gyre circulation in the South Pacific Ocean.

southeast trade wind the trade wind that blows from southeast to northwest south of the equator.

Southern California Continental Borderland an offshore expanse of submarine canyons, sea valleys, and ocean basins adjacent to Southern California from Point Conception to the US–Mexico border.

Southern Ocean the wheel-shaped ocean surrounding Antarctica.

Southwest Monsoon Current the eastward-flowing current that occurs during the summer monsoon.

space weather solar activity that may disrupt human activities and technology.

spaceborne investigation a scientific investigation that employs sensors aboard Earth-orbiting platforms to make observations and obtain measurements of Earth’s surface.

spatial resolution relating to units of space (distance, area, volume).

speciation the presence of multiple forms of a trace element in seawater.

species a group of individuals that share near-identical genetic code and can produce fertile offspring with each other.

specific gravity the density of a substance divided by the density of water.

specific heat the heat required to change the temperature of 1 gram of a substance by one degree.

spicule needle of calcium carbonate or silica in the skeleton of a sponge.

spilling breaker a wave whose lip trickles down the front of the wave.

splash zone a subdivision of the littoral zone; the upper limit of marine life, characterized by occasional wetting from strong waves and extremely high tides.

spongin a fibrous network of protein in sponges.

spreading loss the decrease in energy along a wave front as it expands.

spring equinox the time of year when daylength is increasing and the Sun is passing directly over the equator into the opposite hemisphere.

spring tide the periods in a month when tidal range is greatest.

St. Elmo’s fire an electrical discharge from the masts of ships.

stable water column a water column whose layers increase in density from the surface to the bottom.

standard seawater seawater used to calibrate instruments that measure salinity.

standing wave a wave that appears to sand still.

star classification an alphanumeric system for describing the characteristics of a star.

steerable stratospheric balloon a high-altitude balloon capable of staying aloft for long periods of time.

still water level the surface of the ocean in the absence of disturbing forces.

stratification the layering of the water column due to surface heating.

stratosphere the atmospheric layer above the troposphere.

stromatolite layered rock structure created in shallow waters out of fine sediments trapped by filamentous cyanobacteria.

subatomic particle one of the constituent parts of an atom.

sublittoral zone the region from the zero tide height to the shelf break.

submarine a human-occupied vessel capable of propelling itself underwater and remaining submerged for long periods of time.

submarine canyon a steep-sided underwater valley whose shallow end comes close to shore.

submersible a small submarine capable of reaching the deepest depths of the ocean.

submersion when an organism or object is covered by seawater.

subpolar gyre a gyre circulation in the vicinity of the Arctic and Antarctic Circles.

subseafloor environment a region extending a mile or more beneath the seafloor; host to microbial life.

subsidence a decrease in the elevation of the land or seafloor.

substance a general term for atoms, molecules, and compounds.

subtidal zone  a subdivision of the littoral zone, the region below the zero tide height.

subtropical gyre oceanic gyre found at middle latitudes in the major ocean basins.

subtropical jet stream a fast-moving flow of air that flows between 20° and 30° latitude and at altitudes of 6 to 10 miles.

summer solstice the time of year when the Sun is at its highest point in the sky and daylength is greatest.

sunny-day floodingSee nuisance flooding.

sunrise point the point on the eastern horizon where the Sun rises.

sunset point the point on the western horizon where the Sun sets.

supersaturated when the concentration of a solute is greater than the saturation concentration.

surf a breaking wave.

surf prediction a forecast of the timing, location, and intensity of breaking waves.

surf report a regularly updated source of information on weather and surf conditions for surfers.

surf zone the part of the nearshore where waves are breaking.

surface circulation the largely horizontal flows of water at the surface of the ocean.

surface mixed layer the topmost layer of waters in the upper ocean with homogeneous properties.

surface runoff water that flows over the land surface.

surface tension the enhancement of cohesion at the surface of a liquid.

surface wave the physical expression of energy moving forward at the surface of the ocean, the air–sea interface.

surface wind stress the transfer of energy from the wind to the ocean surface along the horizontal plane of the ocean.

surface zoneSee epipelagic zone.

surfing using a specialized board (or your body) to ride waves.

surging breaker a wave that slides up onto the beach in a swoosh.

suspension the lifting and transport of a sediment grain within a fluid flow.

Swallow float a subsurface platform with acoustic transmitters for tracking ocean currents.

swell direction the compass direction from which ocean swell arrives at a beach.

swell shadow the reduction or absence of ocean swell at a beach location due to the presence of islands.

swell the sinusoidal waves that travel out beyond the winds that generate them.

synodic month the time it takes for the Moon to transit around the Earth and return to its starting point relative to the Earth and Sun.

synoptic scale distances on the order of hundreds to a thousand kilometers.

synthetic aperture radar an active microwave sensor used to generate two- and three-dimensional images of Earth’s surface, especially sea ice.

system  an assemblage of parts and processes working together.

systematics the study of the diversity of life forms and their relationships with each other.


taxa the different levels in the hierarchical system used to classify life.

taxonomy the naming of organisms.

telepresence a livestream from a ship-based ROV transmitted via satellite that permits remote users to watch live video and interact with scientists and technicians on board.

temperate zone  region between the tropical and polar zones in both hemispheres, characterized by mild weather.

temperature loosely defined, the average kinetic energy of molecules in a system, substance, or object.

temporal resolution relating to units of time, from fractions of seconds to millennia.

tether a metal-strengthened fiber-optic cable that transmits two-way signals between an operator and an ROV.

Tethys Ocean the ocean surrounding the supercontinent of Pangea.

texture a characteristic of sediment rocks that takes into account the size, shape, and arrangement of their particles, individually or collectively.

theory of common descent the idea that all life on Earth shares a common ancestor.

thermal a heat-driven, rising column of air.

thermal contraction the contraction of rocks caused by cooling.

thermal expansion the expansion of rocks caused by heating.

thermal-based desalination a process that uses heat and evaporation of seawater to produce freshwater.

thermocline a layer of the water column in which temperature declines rapidly.

thermometer a device used to measure temperature.

thermosphere the layer above the mesosphere named for its high temperature.

thermosteric sea level rise sea level rise due to ocean heating.

third quarter the point halfway between the full and new Moon, when the left half of the Moon is illuminated.

three-cell model an idealized conceptual model depicting three cells of atmospheric motion in each hemisphere.

threshold velocity the fluid speed at which a sediment particle begins to move.

tidal current a horizontal motion of water caused by tidal forces.

tidal datum benchmark a metal, land-based marker with a known elevation from which the tidal datum can be determined.

tidal datum the baseline from which tide height is determined.

tidal day the time of one complete revolution of Earth beneath the Moon, a period of 24 hours and 50 minutes.

tidal force the variations in the Moon’s (and Sun’s) gravity across Earth’s surface.

tidal height the vertical distance of sea level above or below a standard baseline.

tidal period the time between successive high (or low) tides.

tidal range the difference between the highest and lowest tides in a day.

tide gauge an instrument that tracks and continuously records sea level.

tide graph a chart of the change in sea level over time.

time-series investigation a scientific investigation that observes and measures natural processes over time.

tipping point a change in the state of a system that is unstoppable or irreversible.

tomol wood plank canoes constructed by the Chumash people

tow-yo pattern a W-shaped pattern of sampling using a towfish alternately raised and lowered on its path.

towfish a winged, sensor-enabled platform towed behind a vessel on a cable.

trace elementSee minor constituent.

trace fossil the fossilized mark of an animal’s activity.

tractive component the horizontal component of the tidal force.

trade wind a near-constant easterly wind that blows north and south of the equator.

transect a line of stations on a grid.

transitional waveSee intermediate wave.

transmission the movement of light energy through a medium.

transpiration the uptake of water by roots and its subsequent evaporation through the stems, leaves, and flowers of plants.

Transpolar Drift Stream an extension of the Beaufort Gyre, this current flows off the Siberian Shelf and transports water and sea ice into the Norwegian, Greenland, and Iceland Seas.

Transpolar Sea Route a hypothesized shipping lane from the Atlantic to the Pacific during future ice-free periods in the Arctic Ocean.

tree of lifeSee phylogenetic tree.

trench zoneSee hadopelagic zone.

triatomic molecule three atoms of the same or different elements bound to each other.

tributary source of water to a watershed.

trochoid the curve traced by a point on a wheel as it moves forward.

Tropic of Cancer 23.5°N; the location where the Sun is directly overhead on the June solstice.

Tropic of Capricorn 23.5°S; the location where the Sun is directly overhead on the December solstice.

tropical zone the region between the Tropics of Cancer and Capricorn, characterized by warm weather.

troposphere the lowest layer in Earth’s atmosphere, where humans live.

tsunami long-period waves generated by vertical motions of the seafloor during shallow earthquakes.

turbidite a sedimentary deposit formed by turbidity currents.

turbidity current an underwater, gravity-driven slide of sediments that carves submarine canyons.

turbulence the chaotic and irregular changes in the speed and direction of flowing water or air.

twilight zoneSee mesopelagic zone.


Udden–Wentworth scale a geological classification system for sediment sizes from clay to boulders.

ultragravity wave waves with periods from 0.1 to 1 second.

ultraviolet light electromagnetic radiation with wavelengths shorter than visible light and longer than x-rays.

uncrewed aerial platform uncrewed, human-controlled, or autonomous platform that carries out missions in Earth’s atmosphere.

uncrewed surface vessel a self-propelled, self-navigating, sensor-equipped vehicle carrying out various missions on the surface of the ocean.

uncrewed underwater vehicle a self-propelled, self-navigating, sensor-equipped vehicle carrying out various missions beneath the ocean.

undersampling problem the lack of sufficient data to fully understand the ocean over all scales of space and time.

undersaturated when the concentration of a solute is less than the saturation concentration.

underwater research station semipermanent undersea structure designed for human habitation and scientific research on the seafloor.

underwater swarm robotics an emerging field of robotics in which multiple autonomous platforms interact with each other to solve problems or carry out missions.

universal solvent a term used to describe water’s ability to dissolve many substances.

unrooted tree a phylogenetic tree lacking a trunk and with branches that resemble a starburst pattern depicting relatedness among species.

unstable water column a water column whose layers are not arranged according to density from the surface to the bottom.

uplift an increase in the elevation of the land or seafloor.

upper intertidal in the North American West Coast littoral classification system, the uppermost zone (Zone 1), centered on the high high tide and inclusive of the splash zone.

upper middle intertidal in the North American West Coast littoral classification system, the third zone (Zone 3), occupying the upper part of the middle intertidal at tide heights of 0.5 to 1.5 meters.

upwelling the upward movement of subsurface waters toward the surface.

Ur the first supercontinent, appearing about three billion years ago.


variable gas a substance whose concentration varies in the atmosphere.

vertical land movement the increase or decrease in the elevation of a land surface or the seafloor.

visible light electromagnetic radiation detected by the human eye.


waning crescent the crescent Moon following the third quarter.

waning gibbous the gibbous Moon between the full Moon and third quarter.

waning when the Moon’s lighted portion is diminishing in size.

warm-core ring a mesoscale eddy with a warm interior relative to its perimeter.

wastewater water into which human waste and chemicals from homes and businesses have been discharged.

water column an unspecified volume of water from the surface to a particular depth.

water conflict dispute over water.

water molecule the substance formed by the bonding of two hydrogen atoms with one oxygen atom.

water particle a term representing a dot of water molecules within a wave.

water scarcity a lack of sufficient water in a region.

water security the ability of a community to protect access to sustainable quantities of water for practical and peaceful purposes.

water vapor the gaseous form of water.

watershed  an interconnected region of waterways that drains water, dissolved materials, sediments, and debris to a common outlet.

wave base the depth at which the orbital motion of water particles in a surface wave becomes negligible.

wave crest the peak of a wave.

wave diffraction the lateral shifting of wave energy along a wave front in response to seafloor bathymetry or the presence of an island or structure.

wave dispersion the separation of swell with different speeds.

wave focusing the concentration of energy at a point along the wave front in response to seafloor bathymetry.

wave front a moving line perpendicular to the direction of motion of a wave that stretches across its full width.

wave glider a sensor-enabled platform that uses solar and wave power to glide through the ocean.

wave height the vertical distance between the crest and the trough in a wave.

wave interference the interaction of two or more waves to produce waves of smaller or greater height.

wave orbital the circular motion of water particles in a wave.

wave period the time between successive crests of a progressive wave.

wave reflection a change in the direction of a progressive wave when it encounters a boundary, such as a beach or seawall.

wave refraction the bending of a wave front in response to changes in seafloor bathymetry.

wave set a series of similarly sized waves that arrive on a shore in close progression.

wave speed the forward motion of a wave crest over time.

wave steepness the ratio between a wave’s height and its wavelength.

wave train waves of similar speed traveling together.

wave trough the valley of a wave.

wavelength the horizontal distance between successive crests in a wave.

waxing crescent the crescent Moon following the new Moon.

waxing gibbous the gibbous Moon between the first quarter and full Moon.

waxing when the Moon’s lighted portion is growing in size.

weather the instantaneous state of the atmosphere.

weathering  the disintegration and alteration of rock at Earth’s surface.

Weddell Gyre a polar gyre in the Weddell Sea.

well sorted having similar grain sizes.

West Australian Current the broad northward flow of water in the eastern half of the Indian Ocean (no longer classified as a boundary current).

west wind drift current an eastward-flowing current along the poleward edge of a subtropical gyre.

westerlies the westerly directed prevailing winds that blow at middle latitudes.

western boundary current a boundary current that flows along the western edge of an ocean basin.

western intensification the increase and narrowing of flows along the western boundaries of ocean basins as a result of latitudinal differences in the Coriolis force.

Western Subarctic Gyre a subpolar gyre off the Kamchatka Peninsula.

whitecap the broken top of a wave crest, usually caused by wind.

Wien’s law a principle that defines the relationship between temperature and the wavelength of maximum emission: the hotter an object, the shorter its wavelength of maximum emission.

wind a movement of air.

wind chop short and steep irregular waves smaller than swell.

wind duration the length of time that the wind blows in a given area.

wind speed the distance moved by a parcel of air over a specified time.

wind wave wave generated by the wind.

winter solstice the time of year when the Sun is at its lowest point in the sky and daylength is shortest.

world ocean all of the waters contained within the ocean basins.

world ocean circulation the interconnected, interdependent flows of water throughout the world ocean; see also meridional overturning circulation.

wrack line a line of seaweed and debris parallel to the beach.


x-ray electromagnetic radiation with wavelengths between 0.03 and 3 nanometers.

XZ graph a graph oriented with one or more horizontal X-axes across the top and a vertical, downward-pointing Z-axis to indicate depth in the water column.


zero tide heightSee tidal datum.

zonal current a current flowing along a line of latitude.t