Glossary

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Glossary Entries
Word(s)	Definition	Image	Caption	Link	Source
acidification	An increase of hydrogen ion concentration to make a solution more acidic or less alkaline. In ocean acidification refers to the addition of anthropogenic carbon dioxide to the oceans that reduces the pH and renders calcium carbonate more soluble.
anoxia, anoxic	Total absence of dissolved or free molecular oxygen.
anthropogenic	Produced by humans and their activities.
archaea, archean, archeal	Microorganisms of the domain Archaea (previously called Archaeobacteria) that belong to an ancient group of organisms that are separate from bacteria and from which eukaryotes (multicelled organisms) may have evolved. Many archaeal species are chemosynthetic and live in extreme environments.
bathymetry, bathymetric	Seafloor mapping; the study of landform features beneath the water surface. A bathymetric map gives the depth contours of the seafloor.
chart	A specialized map used for navigation, especially at sea or in the air, showing features such as coastlines, water depths, hazards, and navigation aids.
chemosynthesis, chemosynthetic	Production of organic compounds from inorganic substances by use of energy obtained from the oxidation of substances such as hydrogen sulfide, ammonia, hydrogen, and methane.
chronometer	Clock that has sufficient long-term accuracy and tolerance of motion that it can be used as a portable time standard.
contour, contoured	Line on a chart or graph that connects points of equal value of the parameter charted (e.g., ocean depth, temperature, salinity).
coral reef	Mainly calcareous reef composed substantially of coral, coralline algae, and sand. Coral reefs are present only in waters where the minimum average monthly temperature is 18°C or higher.
crust	Outer shell of the solid Earth. The lower limit of the crust is usually considered to be the Mohorovi˘ci´c discontinuity (top of the asthenosphere). The thickness of the crust ranges from about 6 km beneath the oceans to 30 to 40 km beneath the continents.
deoxygenation	Reducing the concentration of dissolved oxygen. Applied to oceans refers to the lowering of dissolved oxygen in deep waters due to anthropogenic influences, including excessive nutrient inputs, and climate change induced increased surface layer temperature that leads to higher primary production and a strengthened pycnocline that slows deep ocean water circulation. May lead to hypoxia and anoxia.
detritus	Any loose material, but generally decomposed, broken, and dead organisms.
environment	Physical and chemical characteristics of a location or area.
fossil fuel	Fuel that is derived directly from fossilized organic matter. Fossil fuels include oil, natural gas, coal, and peat.
greenhouse effect	Tendency of the atmosphere or greenhouse glass to be transparent to incoming solar radiation while absorbing (or reflecting) longer-wavelength heat radiation from the Earth.
invertebrate	Animal that has no backbone.
isobar, isobaric	Line that connects values of equal pressure on a map or graph.
isopycnal	Line that connects values of equal density on a map or graph.
isotherm	Line that connects points of equal temperature on a graph or map.
latitude, latitudinal	Partial designation of location on the Earth’s surface. Latitude is expressed as the angular distance north or south of the equator. The equator has a latitude of 0°, the North Pole 90°N, and the South Pole 90°S
longitude, longitudinal	Partial designation of location on the Earth’s surface. Longitude is expressed as the angular distance east or west of the Greenwich meridian (0° longitude). 180° longitude is the international date line.
molal, molality	Concentration of a dissolved substance in moles per kiogram of solvent.
molar, molarity	Concentration of a dissolved substance in moles per liter of solvent.
monsoon, monsoonal	Seasonally reversing winds, especially those in the Indian Ocean and southern Asia that blow from the southwest during summer and from the northeast during winter. The term is derived from the Arabic word for season, mausim.
pH, acidity, alkalinity	Measure of acidity or alkalinity. pH is measured on a logarithmic scale of 1 to 14 in which lower values indicate higher hydrogen ion concentration and therefore higher acidity.
photosynthesis, photosynthesize, photosynthetic	Production of carbohydrate from carbon dioxide and in the presence of chlorophyll or related pigments by the use of light energy.
phototroph, phototrophic	Organism that uses light energy (photon capture) to produce food (generally from inorganic substances). Includes but is not limited to organisms that use photosynthesis.
phototrophy	Any process by which an organisms produces food (usually from from inorganic substances) using light as the source of energy.
pycnocline	Depth range in the water column in which density changes rapidly in the vertical dimension.
respiration, respire	Process by which organisms use organic materials (food) as a source of energy. Respiration normally uses oxygen and produces carbon dioxide.
sediment	Particles of organic or inorganic origin that accumulate in loose form.
steady state	Condition of equilibrium in a system in which the inputs of a substance or energy are equal to the outputs and the distribution of the substance or energy within the system does not change with time.
topography, topographic	Shapes, patterns, and physical configuration of the surface of the land or seafloor, including its relief (local differences in elevation or depth) and the positions of natural and human-made features.
absorption spectrum, absorption spectra	Wavelengths of electromagnetic energy that substances can absorb and convert to heat. Absorption spectra are plotted as the relative efficiency of absorption versus wavelength. Compare emission spectrum.
abyssal fan	Fan-shaped sediment accumulation spreading out and decreasing in thickness from a point of large sediment input. Abyssal fans are located usually off the mouth of a river or at the foot of a submarine canyon.
abyssal hill	Sediment-covered volcanic peak that rises less than 1 km above the deep-ocean floor.
abyssal plain	Flat seafloor extending seaward from the base of the continental slope and continental rise or from the seaward edge of an oceanic trench.
abyssal zone	Benthic environment between 4000 and 6000 m depth.
acid rain	Rain with acidity higher than normal because of dissolved gaseous emissions of industry and automobiles, notably sulfur compounds.
acoustic	Pertaining to sound.
adiabatic expansion	Expansion of a gas without the addition of external heat. Adiabatic expansion causes the temperature of the gas to decrease. Adiabatic compression causes the temperature of the gas to increase.
adsorption, adsorbed	Attraction and adhesion of ions to a solid surface.
aerobic	In the presence of oxygen.
algae, alga	Simple single-celled or many-celled photosynthetic organisms that have no root, stem, or leaf systems.
algal ridge	Irregular ridge located on the wave-exposed seaward edge of many coral reefs. The ridge is composed largely of encrusting algae.
alkalinity, alkaline	The opposite of acidity. Measure of the degree to which the concentration of hydroxyl ions (OH^–) is greater than the concentration of hydrogen ions (H⁺) in a solution. Seawater is slightly alkaline.
amino acids	Members of a group of compounds that combine in varied proportions to form proteins.
amoebas	Microscopic single-celled animals that move by making continuous protrusions of the body and that feed by engulfing bits of food.
amphidromic system	Tide wave that rotates around an ocean basin during one tidal period. An amphidromic system rotates around an amphidromic point (a node) at which the tidal range is zero.
amphipods	Members of an order of the subphylum Crustacea, phylum Arthropoda, that includes laterally compressed species such as the “sand hoppers.”
amplitude	Vertical distance from the mean level of a wave (the still sea surface for an ocean wave) to the crest or to the trough. A wave’s amplitude equals one-half of the wave height.
anadromous	Pertaining to species of fishes that are spawned in freshwater, migrate to the ocean to live until they reach maturity, then return to freshwater to spawn. Compare catadromous.
anemones	Multicelled animals of the class Anthozoa, phylum Cnidaria. There are both single and colonial polypoid forms.
angle of incidence	Angle between a wave front (usually an electromagnetic wave) or a wave ray and the plane of an interface that it meets.
angle of approach	The angle of incidence is important in refraction.
anion	Negatively charged ion. Compare to cation.
annelids	Members of the phylum Annelida. Elongated segmented worms.
antinode	The part of a standing wave where the vertical motion is at a maximum. Compare to node.
aphotic zone	The part of the ocean in which light is insufficient for phototrophy (which includes photosynthesis). The aphotic zone comprises all the oceans below about 1000 m in areas where ocean water is clear and extends to shallower depths in more turbid waters. Compare to photic zone.
aragonite	A mineral form of calcium carbonate. Aragonite is less common than calcite, but it comprises shells of many pteropod species.
aspect ratio	Index of the propulsive efficiency of a fish species that is obtained by dividing the square of the height of the caudal fin by the area of the caudal fin.
assimilative capacity	Maximum rate at which a particular segment of the environment or ocean can accommodate the input of a substance. The term usually applies to anthropogenic waste materials.
asteroid	Rocky object orbiting the sun. An asteroid is smaller than a planet. Most asteroids are found in a belt between the orbits of Mars and Jupiter, but some have orbits that take them close to the sun and across the orbits of the planets.
asthenosphere	Plastic or partially molten layer of the Earth’s upper mantle upon which the continents “float.” The asthenosphere varies in thickness, with its upper boundary at depths of 10 km or more and its lower boundary at depths as great as 800 km.
atoll	Ring-shaped coral reef that grows upward from a submerged volcanic peak and encloses a lagoon. Atolls may support low-lying islands composed of coral debris. Compare barrier reef and fringing reef.
autotrophs, autotrophic	Algae, bacteria, archaea, or plants that can synthesize organic compounds from inorganic nutrients by phototrophy or chemosynthesis. Compare to heterotrophs.
back-arc basin	Generally shallow sea created on the non-subducting plate at an oceanic convergent plate boundary where the subduction is fast enough to stretch the edge of the nonsubducting plate. The back-arc basin lies behind the volcanic island arc. Also called “back-island basin.”
backscatter, backscattered	The portion of the light or sound randomly reflected off particles suspended in a fluid that is scattered back in the general direction of the light or sound source. Compare to scatter.
backshore	Inner portion of the shore that is landward of the mean spring-tide high-water line. Waves act on the backshore only during exceptionally high tides and severe storms. Compare to foreshore.
backwash	Water flowing down a beach after the swash of one wave has stopped and before the swash of the next wave arrives.
bacteria, bacterium, bacterial	Microscopic single-celled organisms that comprise one of the three recognized biological domains. Other than cyanobacteria, most bacteria species are autotrophs and decomposers, and most are parasitic. They reproduce by cell division.
baleen	Horny material consisting of numerous plates with fringed edges that grows down from the upper jaw of plankton-feeding whales. Baleen is used to filter (strain) the plankton food from the water.
bar-built estuary	Shallow estuary (lagoon) separated from the open ocean by a bar such as a barrier island. Water in bar-built estuaries is usually well mixed vertically.
barnacles	Members of an order of the subphylum Crustacea, phylum Arthropoda, that attach to the substrate, secrete a protective covering of calcareous plates, and strain food particles from the water with a weblike structure.
barrier island	Long, narrow island built of wave-transported sand, separated from the mainland by a usually shallow lagoon.
barrier reef	Coral reef that parallels the shore but is separated from the landmass by open water. Compare to fringing reef and atoll.
basalt, basaltic	Dark-colored volcanic rock, rich in iron, magnesium, and calcium, characteristic of the oceanic crust.
bathyal zone	Benthic environment from 200 to 2000 m depth.
baymouth bar	Shallow bar, usually of sand, that extends partially or completely across the mouth of a bay.
beach	Sand- or sediment-covered zone between the seaward limit of permanent vegetation and the mean low-water line. Beaches sometimes include the seafloor from the mean low-water line to the surf zone.
benthic	Pertaining to the seafloor, or to organisms that live on or in the seafloor.
benthos	Organisms that live on or in the ocean bottom.
berm	Nearly horizontal portion of a beach backshore at the seaward edge of which the beach slopes abruptly seaward. Compare to scarp.
bioaccumulation, bioaccumulate	Process by which dissolved chemicals are taken up by organisms until the concentrations in the tissues are at equilibrium with those in the solution. See CC18.
bioassay	Test in which organisms are exposed to different concentrations of a substance to determine the concentration at which the substance is toxic to that species. See CC18.
bioavailable	Existing in a chemical form that is suitable for uptake by organisms.
biochemical	Pertaining to the synthesis, conversion, use, and decomposition of organic chemicals in the life processes of organisms.
biodegradable	Capable of being decomposed by organisms in the environment. The term generally refers to decomposition to harmless substances.
biodiversity	Poorly defined term that refers to a combination of genetic diversity, species diversity, ecosystem diversity, and physiological diversity within a community or ecosystem. See CC17.
biogenous	Pertaining to material of a biological origin. Usually applied to sediments in which the hard-part remains of organisms (e.g., diatom tests, radiolarian shells) constitute a high proportion of the grains. Compare to cosmogenous, hydrogenous, and lithogenous.
biogeochemical cycle	Transfers of compounds among the living and nonliving components of an ecosystem.
bioluminescent	Light-producing. Referring to organisms that use chemical reactions to produce light.
biomagnification, biomagnify	rocess by which dissolved chemicals are taken up by organisms and continuously accumulated to higher concentrations throughout the life cycle. Tissue concentrations are not in equilibrium with concentrations in the surrounding environment. See CC18.
biomass	The total amount of living matter, expressed in units of weight in the entire water column per unit area of water surface, or weight per unit of water volume.
biota	All living organisms in a given ecosystem, including archaea, bacteria, protists, fungi, algae, plants, and animals.
biome	Any defined area or volume of the environment that is characterized chiefly by the dominant species present and the prevailing physical and chemical environmental conditions (e.g. topical rain forest, or kelp forest, or tundra).
bioturbation	Reworking (churning and mixing) of sediments by organisms that burrow in them.
bloom	Very dense aggregation of phytoplankton, resulting from a rapid rate of reproduction.
blubber	Outer fat layer of whales.
cyanobacteria, cyanobacterium, cyano-bacterial, blue-green algae	Phylum of organisms within the domain Bacteria. Cyanobacteria were originally called “bluegreen algae” because they have the ability to photosynthesize.
bottom trawling	A widely used fishing technique where a net is dragged across the sea floor to catch bottom dwelling species.
brackish	Pertaining to water that is a mixture of freshwater and seawater and has a low salinity.
breakwater	Artificial structure constructed in the ocean to protect a shore from the action of ocean waves.
brine	Water that has a higher salinity (generally much higher) than normal seawater.
brittle stars	Organisms of the class Ophiuroidea, phylum Echinodermata, that have long, slender arms covered in bristles attached to a small central disk.
bulkhead	Structure constructed to separate land and water areas at the shoreline and designed to reduce earth slides and slumps or to lessen wave erosion at the base of a cliff.
buoyancy, buoyant	Ability of an object to float (or rise through a fluid) that results from a density difference between the object and the fluid in which it is immersed.
bycatch	Fishes and other marine animals caught in fishers’ nets that are not the target of the fishing. Bycatch is generally thrown overboard as waste.
calcareous, calcium carbonate	Composed of or containing calcium carbonate.
calcite	The most common mineral form of calcium carbonate. Compare to aragonite.
caldera	Crater in a volcano, usually at the center, created by an explosion or collapse of the volcanic cone.
calorie	Obsolete unit of heat energy defined as the amount of heat needed to raise the temperature of 1 g of water by 1°C.
capillary wave	Small ocean wave that has a wavelength less than 1.5 cm. The primary restoring force for capillary waves is surface tension.
carbonate compensation depth, CCD	Depth below which all calcium carbonate particles falling from above are dissolved before they can be incorporated in the sediments.
carcinogens, carcinogenic	Compounds that cause cancer in animals. Compare to mutagens and teratogens.
carnivores, carnivorous	Animals that depend solely on other animals for their food supply. Compare herbivores and omnivores.
cartilaginous	Pertaining to vertebrate animals that have skeletons made of cartilage, a tough elastic tissue.
catadromous	Pertaining to species of fishes that are spawned at sea, migrate to a freshwater stream or lake where they live until they reach maturity, then return to sea to spawn. Compare to anadromous.
cation	Positively charged ion. Compare to anion.
central rift valley	Steep-sided linear valley that runs along the crest of many parts of oceanic ridges. Central rift valleys are created by pulling apart of the diverging plates.
centripetal force	Force that acts toward the center of rotation of an orbiting body and that is needed to maintain the object in its circular path and prevent it from moving off in a straight line. See CC12.
cephalopods	Animals belonging to the class Cephalopoda, phylum Mollusca, that have a well-developed pair of eyes and a ring of tentacles surrounding the mouth. Most have no, or an internal, shell. Cephalopods include squid, octopi, and Nautilus.
cetaceans	Marine mammals belonging to an order that includes whales, porpoises, and dolphins.
chlorofluorocarbons, CFC, CFCs	Class of compounds used as refrigerants and for many other purposes. When released to the atmosphere, CFCs migrate upward to the ozone layer, where they react with ozone, reducing its concentration.
chaos, chaotic	Apparently random behavior of systems that involve nonlinear relationships. See CC11.
chlorophylls	Group of green pigments that are essential to algae and plants and are active in the capture of light energy for photosynthesis. See CC14.
chordates	Members of the animal phylum Chordata, to which mammals, reptiles, birds, fishes, and tunicates belong.
chronic toxicity	Sublethal or lethal effects due to long-term exposure of an organism to a toxic substance at concentrations below that at which the organism suffers immediate (within days or weeks) sublethal or lethal effects.
climate, climatic	Long-term averages of weather conditions such as temperature, rainfall, and percentage cloud cover, and the distribution of these averages among the seasons at a given location.
clones	Members of a species that are genetically identical because they are asexually reproduced.
cnidarians, coelenterates	Members of the phylum Cnidaria, consisting of predominantly marine animals with a saclike body and stinging cells on tentacles that surround a single opening to the gut cavity. The two basic body forms are the medusa and the polyp. Medusal forms are pelagic and include jellies. Polypoid forms are predominantly benthic and include sea anemones and corals. Also called “coelenterates.”
coast	Strip of land that extends from the shore inland to the seaward limit of terrain that is unaffected by marine processes.
coastal plain	Low-lying land next to the ocean extending inland until the first major change in the features of the terrain.
coastal-plain estuary	Estuary formed by flooding of a coastal river valley as sea level rises.
coastal upwelling	Vertical transport and mixing of deep, nutrient-rich water into the surface water mass as a result of offshore Ekman (windblown) transport of surface water.
coastal zone	Zone between the coastline and the point offshore to which the influence of freshwater runoff extends (often the shelf break). The term can also mean this area of coastal ocean plus the adjacent coast.
coastline	Landward limit reached by the highest storm waves on the shore. Compare to shoreline.
coccolithophores	Microscopic planktonic algae surrounded by a cell wall embedded with calcareous disks called “coccoliths.”
cohesive	Pertaining to the molecular force between particles within a substance that acts to hold the particles together. Cohesive particles behave as though they were sticky.
colloidal	Pertaining to substances that have a particle size smaller than clay.
community	All of the organisms that live within a definable area or volume of ocean or land.
compensation depth	Depth at which algae consume oxygen for respiration at the same rate that they produce oxygen by photosynthesis.
complexed	Generally pertaining to a dissolved ion that has an association (a weak electrostatic bond) with the molecules of a polar organic substance. The association can alter the ion’s solubility, bioavailability, and toxicity.
conduction, conducted	Transfer of heat (or electricity) through a material or between two materials in contact with each other by passing directly from one molecule to another adjacent molecule.
contaminant, contaminate	Substance added to an ecosystem (or to a sample, an organism, or other object) in an amount that causes the concentration of the substance to exceed its natural range of levels Contaminants may or may not have harmful effects. Compare to pollution.
continental collision plate boundary	Region where two lithospheric plates converge, each of which has continental crust at its margin.
continental divergent plate boundary	Region where a continent is splitting apart to form the edges of two new lithospheric plates.
continental drift	Movement of the continents over the Earth’s surface. Continental drift is the theory that preceded plate tectonics.
continental margin	Zone of transition from a continent to the adjacent ocean basin. The continental margin generally includes a continental shelf, continental slope, and continental rise and often the land adjacent to the coast.
continental rise	Gently sloping seafloor between the base of a continental slope and the abyssal plain. A part of the deep-ocean floor.
continental shelf	Zone bordering a continent that extends from the low-water line to the depth at which there is a marked increase in the downward slope of the seafloor that continues to the deep-ocean floor.
continental slope	Relatively steeply sloping seafloor seaward of the continental shelf that ends where the downward slope markedly decreases at the edge of the deep-ocean floor.
convection, convect, convective	In a fluid being warmed at its bottom and/or cooled at its upper surface, process by which warmer fluid rises and cooler fluid sinks in a density-driven circulation. See CC1, CC3.
convection cell	Circulatory system established by convection in which water (or other fluid) is warmed, rises, is displaced by newly upwelled warm water, cools, and sinks to be warmed again. See CC3.
convergence, converge, convergent	Location at which fluids of different origins come together, usually horizontally (often in a convection cell). Convergence results in sinking (downwelling) or rising (upwelling) when it is at the top or bottom surface of a fluid layer, respectively. See CC3. Compare to divergence.
convergent plate boundary	Lithospheric plate boundary where the relative motion of adjacent plates is toward each other, producing ocean trench/island arc systems or ocean trench/continental mountain and volcano complexes. Compare to divergent plate boundary.
copepods	Small shrimplike animals of the subphylum Crustacea that are zooplankton.
corals	Group of benthic cnidarians that exist as individuals or in colonies and may secrete external skeletons of calcium carbonate.
Coriolis effect	Apparent deflection of a freely moving object caused by the Earth’s rotation. The deflection is cum sole.
cosmogenous	Pertaining to material that originated in outer space (e.g., meteorite fragments). The term is generally applied to particles of such origin within sediments. Compare to biogenous, hydrogenous, and lithogenous.
countershading	Coloration of pelagic fishes, in which the upper half is dark and nonreflective and the lower half is light-colored and more reflective. Countershading reduces visibility to predators from above and below.
covalent bond	Chemical bond in which atoms are combined to form compounds by sharing one or more pairs of electrons.
crest	For a wave, the portion that is displaced above the still-water line. The term is often used to refer to the highest point of the wave (or other topographic feature) only. Compare to trough.
crinoids	Animals of the class Crinoidea, phylum Echinodermata. Also called “feather stars.”
crustaceans	Animals of a subphylum (Crustacea) of the phylum Arthropoda that have paired, jointed appendages and hard outer skeletons. Crustaceans include barnacles, copepods, lobsters, crabs, and shrimp.
CTD	Abbreviation for conductivity, temperature, and depth. A CTD is an instrument package that measures these parameters continuously while being lowered and raised through the water column.
ctenophores	Animals of the phylum Ctenophora of transparent planktonic animals that are spherical or cylindrical in shape and have rows of cilia. Ctenophores include comb jellies.
cum sole	Literally translated from Latin as “with the sun.” To the right in the Northern Hemisphere and to the left in the Southern Hemisphere. If you are facing toward the sun’s arc in the sky (toward the equator), the sun appears to move from left to right in the Northern Hemisphere and from right to left in the Southern Hemisphere.
current	Horizontal movement of water.
cyclonic	Pertaining to counterclockwise circulation in the Northern Hemisphere and clockwise circulation in the Southern Hemisphere.
cyst	Saclike structure. Sometimes, a protective covering of a microorganism during a metabolic resting phase.
Dichloro-diphenyl-trichloroethane, DDT	Insecticide widely used in the United States in the 1950s and 1960s. DDT caused major damage to birds and marine mammal populations. It is now banned in many countries, but it is still widely used in the tropics.
declination	Measure of the sun’s (or moon’s) apparent north–south seasonal movement. The angle between a line from the Earth’s center to the sun (or moon) and the plane of the equator.
decomposers	Heterotrophic microorganisms (mostly bacteria and fungi) that break down nonliving organic matter to obtain energy. During decomposition, nutrients are released to solution and become available for reuse by autotrophs.
deep-water wave	Ocean wave that is traveling in water depth greater than one-half its wavelength. Compare intermediate wave and shallow-water wave.
delta	Low-lying deposit of river-borne sediment at the mouth of a river. Deltas are usually triangular in shape.
absolute density	The mass per unit volume of a substance (usually expressed as grams per cubic centimeter). Compare to relative density.
relative density	The ratio of the mass per unit volume of the substance divided by the mass of the same volume of a standard substance. The standard substance is usually pure water at 4°C. Relative density is a dimensionless number, but since the mass of 1 cm³ of pure water at 4°C is almost precisely 1 g, relative density and absolute density are numerically almost identical. Compare to absolute density.
deposit feeders, deposit-feeding	Organisms that feed by ingesting particles of sediment and metabolizing organic matter in or on the particles.
deposition, depositional	Accumulation of sediment on the seafloor (or of solid particles from the atmosphere onto the land or ocean surface).
detritivores, detritivorous	Organisms that eat organic detritus.
diagenesis, diagenetic	Chemical or mineralogical changes that take place in a sediment or sedimentary rock after its formation.
diatoms	Microscopic unicellular algae of the phylum Chrysophyta that have an external skeleton of silica.
diffusion, diffuse	Movement of a substance (or property such as heat) by random molecular motions from a region of higher concentration to a region of lower concentration (along a concentration gradient).
dinoflagellates	Single-celled microscopic organisms in the kingdom Protista. Dinoflagellates may have chlorophyll, be autotrophic, and belong to the phylum Pyrrophyta; or they may be heterotrophic and belong to the phylum Zoomastigophora.
dip angle	Angle to the horizontal of the direction of the magnetic field in rock. The dip angle is approximately equal to the latitude at which the rock formed.
dissolved constituents	Chemicals dissolved in seawater, which are usually measured in parts per million (mg·kg^–1) or parts per billion (µg·kg^–1).
diurnal	Having a cycle that occurs during a 24-h day and that generally recurs daily.
diurnal tide	Tide with one high water and one low water during a tidal day (approximately 24 h 49 min). Compare to semidiurnal tide and mixed tide.
divergence, diverge, divergent	Horizontal flow of a fluid away from a common center. The fluid is replaced by upwelling if the divergence is at the surface of the fluid and by downwelling if it is at the bottom. Compare to convergence.
divergent plate boundary	Lithospheric plate boundary where adjacent plates are pulling apart from each other. Compare to convergent plate boundary.
diversity, diverse	Presence of variety or variation within an ecosystem. The term may be applied to variety of species, variety of genes within a species, variety of habitat, etc. See CC17.
DNA, Deoxyribonucleic acid	Complex organic molecule that contains the genetic code.
downwelling, downwelled	Vertical movement of a fluid downward due to density differences or where two fluid masses converge, displacing fluid downward. In the ocean, the term often refers to coastal downwelling, where Ekman transport causes surface waters to converge or impinge on the coast, displacing surface water downward and thickening the surface layer. Compare to upwelling.
drift net	Net hung vertically like a drape that may extend for many kilometers. Drift nets indiscriminately catch anything that swims into them.
dynamic height	Height of the water column above a depth below which no currents are assumed to be present.
eastern boundary current	Surface layer current that flows toward the equator on the eastern side of a subtropical gyre. Eastern boundary currents are slow, wide, and shallow. Compare to western boundary current.
ebb	Period of a tidal cycle when the tidal current is flowing seaward or when the tide level is falling. Compare to flood.
echinoderms	Animals of the phylum Echinodermata, which have bilateral symmetry in larval forms and usually a five-sided radial symmetry as adults. Echinoderms are benthic organisms with rigid or articulating external skeletons of calcium carbonate that have spines. Echinoderms include sea stars, brittle stars, sea urchins, sand dollars, sea cucumbers, and sea lilies.
echolocation	Use of sound by some marine animals to locate and identify underwater objects from their echoes.
ecology, ecological	Study of relationships between species and between the species and their environment.
ecosystem	Organisms in a community and the nonliving environment with which they interact.
eddy	Circular movement of water.
effluent	Outflow of water from a system. The term is often applied to wastewater discharges that flow out of a treatment plant, sewer, industrial outfall, or storm drain.
Ekman transport	Net wind-driven transport of surface water at an angle cum sole to the wind direction as a result of the Coriolis effect.
El Niño	Episodic movement of warm surface water south along the coast of Peru that is associated with the cessation of upwelling in this region. The term is often used to refer to a complex episodic sequence of events in the oceans and atmosphere called “El Niño/Southern Oscillation” (ENSO).
electrical conductivity	Measure of a substance’s ability to conduct an electrical current. In seawater, electrical conductivity is related to (and used to measure) salinity.
electromagnetic radiation	Energy that travels at the speed of light as waves. Electromagnetic waves range in wavelength from very long (up to 10 km) radio waves to very short (10–12 m) cosmic rays.
electrostatic	Pertaining to the attractive or repulsive force between two electrically charged bodies that does not involve electrical current flow between the bodies.
embryo	Early or undeveloped life stage of an animal.
emission spectrum, emission spectra	Wavelengths at which warm bodies emit electromagnetic energy. Emission spectra are plotted as the relative intensity of emission versus wavelength. Emission spectra vary with an object’s temperature. Compare to absorption spectrum.
encrust	To grow on the surface of and form a crust on a solid substrate.
ENSO	El Niño/Southern Oscillation. See El Niño
enzymes	Organic substances that are synthesized by organisms and behave as catalysts for biochemical reactions.
epifauna	Animals that live on the surface of the seafloor or other substrate, either moving freely or attached. Compare to infauna.
epipelagic zone	Upper region of the oceanic province. The water column from the surface to a depth of 200 m.
equinox	Time of year when the sun is directly overhead at the equator. Equinoxes occur on March 20 or 21 and September 22 or 23 each year. Compare to solstice.
erosion, erode, erosional	Process of being gradually worn away. Erosion is usually caused by the action of winds and currents on rocks and sediments.
estuary, estuarine	Any region where freshwater and seawater mix.
eukaryotes	Organisms (single-celled or multi-celled) whose cells are surrounded by a membrane and that have a structurally discrete nucleus and other well-developed subcellular compartments. Eukaryotes include all organisms except archaea, and bacteria. Compare to prokaryotes.
euphausiids	Members of an order of shrimplike planktonic animals of the subphylum Crustacea, phylum Arthropoda. Euphausiids include several species commonly called “krill.”
eustasy, eustatic	The equilibrium level of the ocean surface. Eustatic changes of sea level take place in response to changes in ocean volume and take place worldwide, as distinct from locally. See CC2.
eutrophication	Physical and biological changes that occur when excessive nutrients are released into an aquatic environment. Eutrophication may lead to blooms and anoxia.
evaporite	Mineral deposit formed by the evaporation of seawater.
exclusive economic zone, EEZ	Zone in which the coastal state (nation) has ownership of resources including fishes and seafloor minerals. EEZs are generally 200 nautical miles (370 km) wide.
excretion, excrete	Substances (generally waste products) released to the external environment from the tissues of a living organism, or the process of releasing such substances.
excurrent	In animals that feed by pumping or passing water through the body (e.g., tunicates), pertaining to the opening through which the ingested water is expelled from the organism. Compare to incurrent.
exotic terrane	Fragments of continental crust or sometimes oceanic crust and sediment that have been accreted (attached) to other continents.
extratropical cyclone	Cyclonic storm formed in high latitudes at the polar fronts. Extratropical cyclones resemble and can be as strong as hurricanes.
family	Level of taxonomic classification of species that is between the levels of order and genus.
fault	Fracture in the Earth’s crust in which one side has been displaced in relation to the other.
fauna	Animal population of an ecosystem or region. Compare to flora.
fecal pellet	Solid waste product excreted by animals.
feedback	Reaction to a process of change that either reinforces or moderates that change. See CC9.
fetch	Uninterrupted distance over which the wind blows (measured in the direction of the wind) without a significant change of direction.
filter feeders, filter-feeding	Animals that feed by sifting or straining small particles suspended in the water. Compare suspension feeders.
fjord	Long, narrow, deep inlet. Usually the seaward end of a valley flooded by rising sea level after it was cut by a glacier that has since retreated.
flagellates	Protozoa that have flagella.
flagellum, flagella	Whiplike appendage used by some microscopic organisms to provide propulsion for locomotion.
flood	Period of a tidal cycle when the tidal current is flowing landward or when the tide level is rising. Compare to ebb.
flora	Plant population of an ecosystem or region. Compare to fauna.
focus	Location within the Earth’s crust where an earthquake occurs.
food chain	Sequence of organisms in which each is the food source for the next in sequence. Compare to food web.
food chain efficiency	Percentage of food ingested by organisms at a particular trophic level that is converted into biomass at that trophic level. Also called “trophic efficiency.” See CC14.
food web	Series of food chains that are interconnected in a complex way to create a mosaic of feeding relationships.
foraminifera, foraminiferan, foraminiferal	Planktonic and benthic protozoa of the phylum Sarcodina, protected by shells, and usually calcareous.
foreshore	Zone between the low- and high-tide lines. Compare to backshore.
fossil	Remains of an organism or its imprint that has been preserved in rocks.
foul, fouling	To attach to or lie on the surface of an underwater object. The term applies especially to barnacles and other marine organisms that grow on vessel hulls and other human-made structures.
fracture zone	Linear zone of steep-sided irregular seafloor topography. Most fracture zones are inactive remnants of transform faults.
frequency	Number of periodic events that occur within a specified interval. For waves, the number of crests (or troughs) that pass a given point per unit time; the inverse of wave period.
friction	Retarding force that resists the motion of two objects (or an object and a fluid, or two fluids; see shear stress) that are moving in relation to each other and whose surfaces are in contact.
fringing reef	Reef that is attached to the shore of an island or continent with no open water lagoon between the reef and shore. Compare to barrier reef and atoll.
front	Well-defined boundary between two air masses or two water masses of different density.
frustule	Siliceous covering of a diatom.
fundamental niche	Range of environmental variables within which a species can both survive and successfully reproduce. Compare to survival niche.
fungi	Members of the kingdom Fungi, organisms that reproduce by means of spores. Most marine fungi are microscopic benthic decomposers.
galaxy, galactic	Assemblage of stars (millions to hundreds of billions) held together by the gravitational attraction of the member stars on one another. Most galaxies are either a flattened, spiral form like the Milky Way, the galaxy in which our sun is located, or elliptical without a spiral pattern.
genetic	Pertaining to the genes of an organism. The term refers to the information (genetic code) encoded in DNA and other substances that describes the characteristics of an organism and that can be passed on to the offspring during reproduction.
genus, genera	Level of taxonomic classification of species that is between the levels of family and species.
geostrophic	Pertaining to cyclonic fluid motions that are maintained as a result of a near balance between a gravity-induced horizontal pressure gradient and the Coriolis effect. See CC13.
gill	Thin-walled organ of marine animals used for respiration.
glaciation	Extent to which glaciers are developed in a given area or at a given time.
glacier, glacial	Large mass of ice that forms on land by the recrystallization of old compacted snow. Glaciers flow from the area where they are formed downhill to an area where ice is removed by melting or calving (breaking off) into a water body.
gobies	Members of a family of small bony fishes (class Ostreichthyes, subphylum Vertebrata, phylum Chordata). Many goby species have pelvic fins modified to form a suction disk.
graded bed	Vertical sequence of sediments or sedimentary rock in which each layer comprises particles of smaller grain size from bottom to top.
grain size	Diameter of grains that compose a sediment.
gravity	Attractive force between any two bodies in the universe.
grazers, graze	Strictly, animals that eat plants or algae. More generally, the term includes animals that eat detritus (or other animals) that covers the surface of a substrate.
groin	Artificial structure that projects into the ocean from the shore. Groins block longshore transportation of sediment and usually are intended to trap sand and prevent its loss from a beach.
groundwater	Water beneath the ground surface that has seeped through the soil and rock from above.
guyot	Conical, volcano-shaped feature on the ocean floor whose top has been eroded to form a flat top.
gyre	Circular motion. The term generally refers to a circular current system centered in the subtropical high-pressure region of a major ocean basin.
habitat	Place where a particular organisms lives.
hadal zone	Deepest environment of the oceans. Restricted to ocean trenches deeper than 6 km.
half-life	Amount of time required for half the atoms of a radioactive isotope sample to decay to atoms of another element. See CC7.
halocline	Depth range in the water column in which there is a gradient of salinity in the vertical dimension. Compare to pycnocline and thermocline.
hard parts	Rigid structural material of plants and algae and the shells and skeletons of animals. Hard parts are usually siliceous or calcareous.
harmonics	Component simple waves that are added together to make up the complex waveform observed as a result of the interference of waves of different frequencies and/or from different directions.
heat capacity	Amount of heat required to raise the temperature of 1 g of a substance by 1°C.
herbicides	Chemicals that are used to kill or inhibit the growth of plants.
herbivores, herbivorous	Animals that rely primarily or solely on plants, algae or photosynthetic bacteria for their food. Compare to carnivores and omnivores.
hermatypic corals	Reef-building corals that have symbiotic algae in their tissues and that cannot grow successfully below the photic zone.
hermit crabs	Any of a number of species of crabs of the suborder Reptantia, order Decapoda, subphylum Crustacea, phylum Arthropoda that have no shell of their own. Hermit crabs live in shells of dead gastropod mollusks and move to a larger shell as they grow.
herrings	Members of a family of small plankton-eating bony fishes (class Ostreichthyes, subphylum Vertebrata, phylum Chordata) that have oily tissues and are extremely abundant in some areas. Herrings include sardines and anchovies.
heterotrophs, heterotrophic	Animals or bacteria that do not use perform phototrophy or chemosynthesize and therefore depend for food and energy on organic compounds produced by other species. Compare to autotrophs.
high seas	Area of the world oceans that is outside the territorial control of any nation.
high-tide line	Highest point on the shore that is covered by water at high tide. Compare to low-tide line.
high-tide zone	Zone of the shore that is mostly exposed and lies between the lowest (neap) high-tide line and highest (spring) high-tide line. Compare to low-tide zone and middle-tide zone.
holoplankton	Organisms that spend their entire life as members of the plankton. Compare to meroplankton.
hot spot	Surface expression of a persistent convection plume of molten mantle material rising to the Earth’s surface.
humidity	Amount of water vapor in the air. It is measured as relative humidity, the ratio of the water vapor concentration to the saturation concentration at the same temperature and pressure, expressed as a percentage.
hurricane	Tropical cyclonic storm with winds that have velocity greater than 120 km·h–1. The term applies to such storms in the North Atlantic Ocean, eastern North Pacific Ocean, Caribbean Sea, and Gulf of Mexico. Such storms in the western Pacific Ocean are known as “typhoons,” “cyclones,” or “willy willys.”
hydrated, hydration	Chemically combined with water or, for ions, surrounded by water molecules in a weak electrostatic association.
hydrocarbons	Large group of chemicals containing carbon and hydrogen atoms. The carbon atoms may be arranged in chains of varying length or in one or more six-atom rings. These compounds are the predominant components of petroleum, and some are also produced by plankton.
hydrogen bond	Bond between molecules that forms because of the dipolar nature of the molecules. Hydrogen bonds are present in water and a few other compounds.
hydrogenous	Pertaining to solid material formed by chemical precipitation from solution. The term usually applies to the component particles or coatings of sediments that are precipitated from seawater. Compare to biogenous, cosmogenous, and lithogenous.
hydrographic	Pertaining to mapping of the oceans and their depth.
hydroids	Group of animal species of the class Hydrozoa, phylum Cnidaria. Polypoid forms attach to the substrate. Most are colonial, many with a branching form resembling a feather or fern on which individual polyps are arranged. Hydroids reproduce by budding and have a pelagic medusal stage.
hydrophone	Device that senses underwater sound.
hydrosphere	Gaseous, liquid, and solid water of the Earth’s upper crust, ocean, and atmosphere. The hydrosphere includes lakes, groundwater, snow, ice, and water vapor.
hydrostatic pressure	Pressure that results from the weight of the water column that overlies the depth at which the pressure is measured.
hydrothermal minerals	Predominantly fine-grained particles precipitated from the water that is discharged at hydrothermal vents. Hydrothermal minerals are rich in iron and manganese.
hydrothermal vent	Location where heated water is vented through the seafloor. This water is seawater that has percolated down through fractures in recently formed ocean floor and has been heated by underlying magma. Most known vents are near the central axis of oceanic ridges and rises.
hypoxia, hypoxic	Presence of dissolved oxygen in the aquatic environment at concentrations low enough to be detrimental to organisms. Hypoxia is usually considered to exist when dissolved oxygen concentrations are at or below 2 mg·l^–1. Compare to anoxia.
ice age	Period during which the Earth’s average climatic temperature was colder, glaciers were more extensive, and sea level was lower. Several such periods have occurred in the past million years, each lasting for several thousand years.
ice exclusion	Process whereby salts are excluded from the ice that forms as seawater freezes, resulting in a higher salinity in the remaining liquid water.
in situ	Literally translated from Latin as “in place”—that is, not removed from its natural environment.
incubation	Maintenance of eggs or embryos in a favorable environment for hatching and development.
incurrent	In animals that feed by pumping or passing water through the body (e.g., tunicates), pertaining to the opening through which the ingested water is taken into the organism. Compare to excurrent.
infauna	Animals that live buried in soft sediments (sand or mud). Compare to epifauna.
intermediate wave	Surface water wave that, at a given water depth, has a wavelength between those of deepwater waves and shallow-water waves. Wave in water depth between one-half and one-twentieth of the wavelength. Compare to deep-water wave and shallow-water wave.
internal wave	Wave that develops below the surface of a fluid at a pycnocline and travels along this boundary.
intertidal zone	Zone covered by the highest normal tides and exposed by the lowest normal tides, and any tide pools within this zone. Also called “littoral zone.”
intertropical convergence	Zone where northeast trade winds and southeast trade winds converge.
ion, ionic	Atom (or combined group of atoms) that becomes electrically charged by gaining or losing one or more electrons to produce a negatively charged anion or a positively charged cation, respectively.
ionic bond	Chemical bond that is formed by the electrical attraction between cations and anions.
isopods	Animals with flattened bodies belonging to an order of the phylum Crustacea. Most isopods are scavengers or parasites on other crustaceans or fishes.
isostasy, isostatic	Equilibrium, comparable to buoyancy, in which the rigid lithospheric plates float on the underlying mantle. See CC2.
isostatic leveling	Tendency of lithospheric plates to rise or fall to an equilibrium level with respect to the level at which they float on the asthenosphere after their density or mass has changed—for example, after cooling of the crust or changes in the extent of glaciation. See CC2.
isothermal	Of the same or uniform temperature.
isotope, isotopic	Atoms of an element that have different numbers of neutrons, and therefore different atomic masses than the atoms of other isotopes of the same element. See CC7.
jelly, jellies, jellyfish	Gelatinous holoplankton of the class Scyphozoa, Phylum Cnidaria. Also called "jellyfish."
jet stream	Easterly-moving air mass at an altitude of about 10 km that can have speeds exceeding 300 km·h–1. Jet streams follow a meandering path in the mid latitudes and influence how far polar air masses extend into lower latitudes.
jetty	Elongated structure built outward from the shore into a body of water to protect a harbor or a navigable passage from accumulation of sand transported by longshore drift.
joule	Unit of energy equal to the energy expended in 1 s by an electrical current of 1 ampere with a potential difference of 1 volt.
kelp	Various species of large brown algae (Phaeophyta).
kinetic energy	Energy of an object in motion. Kinetic energy increases as the mass of the object or the speed of the object in motion increases. Compare to potential energy.
krill	Common name applied to euphausiids, members of an order of the subphylum Crustacea, phylum Arthropoda.
lagoon	Shallow estuary or area of ocean adjacent to the shore but partly or completely separated from the open ocean by an elongated, narrow strip of land such as a reef or barrier island.
Langmuir circulation	Cellular water circulation set up by strong winds that blow consistently in one direction. The cells are arranged in alternating clockwise and counterclockwise helical spirals aligned parallel to the wind direction.
larva, larvae	Animal embryo that lives free from its parents before assuming the adult form.
laser	Abbreviation for “light amplification by stimulated emission of radiation.” Instrument that generates a very intense, extremely narrow beam of light of a single wavelength
latent heat of fusion	For 1 g of a substance at its melting point temperature, the quantity of heat energy that must be added to convert it from solid to liquid (or that must be removed to convert the liquid to solid) without changing the temperature.
latent heat of vaporization	For 1 g of a substance at its boiling point temperature, the quantity of heat energy that must be added to convert it from liquid to gas (or that must be removed to convert the gas into liquid) without changing the temperature or pressure.
lava	Fluid magma that emerges from an opening in the Earth’s surface, or the same material after it cools and solidifies.
leach, leaching	To dissolve constituents of solids by passing (filtering) a fluid (usually water) through cracks or pores in the solid or sediment.
leeward	The direction toward which the wind is blowing or the waves are moving. The term usually applies to the sheltered downwind or downcurrent side of a barrier or landmass. Compare to windward.
levee	Low ridge that forms the sides of a river channel. Levees may be human-made or natural (created by sediment deposition during flooding).
lichens	Organisms that are a mutualistic relationship of fungi with algae or cyanobacteria. The algae (or cyanobacteria) are protected by the fungi, which depend on the algae to produce food by photosynthesis.
light-limited	Pertaining to the condition in which the rate of production of organic matter by a phototrophic organism or population of organisms is inhibited by the absence of sufficient light energy when all other requirements for an increase in the rate of production are met.
limestone	Sedimentary rock composed of at least 50% calcium or magnesium carbonate. Limestone may be either biogenous or hydrogenous.
limiting nutrient	Nutrient present at such a low concentration that its lack of availability reduces the rate of growth or prevents the growth of phytoplankton (or other primary producers).
limpets	Mollusks of the class Gastropoda, phylum Arthropoda, that have a low conical shell and adhere to a substrate where they are covered by the shell.
lipids	Fats. Lipids are among the principal structural components of living cells.
lithogenous	Pertaining to material derived from the rock of continents and islands and transported to the ocean by wind or running water. The term is usually applied to sediments that have a high proportion of mineral grains of terrestrial origin. Compare to biogenous, cosmogenous, and hydrogenous
lithosphere, lithospheric	Outer layer of the Earth. The lithosphere includes the crust and the part of the upper mantle that is fused to the crust. It is the layer that is broken into the lithospheric plates.
lithospheric plates	Sections of the Earth’s lithosphere that are separated from each other by boundaries at which the adjacent sections move in relation to each other.
littoral zone	To biological oceanographers, the benthic zone between the highest and lowest normal water marks reached by the tide. To geological oceanographers, the zone between the seaward boundary of land vegetation (or the base of a cliff if present) and the point where the seafloor reaches a depth at which sediment is no longer disturbed by waves.
longshore bar	Sand mound that extends generally parallel to the shoreline a short distance offshore. The bar may be submerged or exposed, especially at low tide, and is created by sand accumulated by wave action.
longshore current	Current that flows in the surf zone and parallel to the shore. Longshore currents are created by breaking waves.
longshore drift, littoral drift	Sediment transport along the beach within the region from the breaker zone to the top of the swash line. Longshore drift is associated with the long-shore current. Also called “littoral drift.”
low-tide line	Lowest point on the shore that is not covered by water at low tide. Compare to high-tide line.
low-tide terrace	Flat section of the foreshore that lies seaward of any scarp and on which most wave energy is dissipated.
low-tide zone	Zone of the shore that is mostly covered with water and lies between the highest (neap) low-tide line and the lowest (spring) low-tide line. Compare to high-tide zone and middle-tide zone.
lunar month	Interval between successive times when the moon and sun are both directly overhead at a specific line of longitude at a specific time of day. The time interval between two successive full moons (or new moons), approximately 291/2 days.
macroalgae, macroalga	Algae that have massive forms, easily seen by the naked eye. Macroalgae are generally attached to the substrate. Compare to microalgae.
magma	Molten rock.
magmatic arc	Line of volcanic islands formed on the nonsubducting plate parallel to and near an oceanic convergent plate boundary.
magnetic anomaly	Local variation of the Earth’s magnetic field caused by variable magnetization of minerals in the Earth’s crust.
manganese nodule	Lump of hydrogenous mineral consisting primarily of oxides of iron and manganese. Manganese nodules are scattered in groups over some parts of the ocean floor.
mangrove	Group of tropical plant species that grow in low marshy areas at latitudes below about 30°. Mangroves have extensive root systems and produce much organic detritus to create a unique coastal environment for marine life.
mantle	1. The layer of the Earth between the core and crust. 2. In certain mollusks, including clams, mussels, and oysters, the part of the animal’s body that secretes shell materials.
marginal sea	Semi-enclosed body of water adjacent to a continent.
marine mammals	Members of the class Mammalia, subphylum Vertebrata, phylum Chordata, that live some or all of their life in the ocean. Warm-blooded animals that have mammary glands and hair, and that bear live young.
maximum sustainable yield	Maximum quantity of fish that can be harvested annually while still allowing the population to be sustained by reproduction. See CC16.
meander, meandering	Sinuous curve or turn in a current (of any fluid such as air, river water, ocean water, or magma).
meroplankton	Planktonic larval forms of organisms that become members of the benthos or nekton when they become adult. Compare to holoplankton.
mesoplates	Hypothesized segments of the Earth’s mid-depth mantle that may move relative to each other below the crustal tectonic plates. Three major mesoplates have been proposed: Hawaiian (mostly beneath the oceanic plates of the Pacific), Tristan (beneath most plates of the Atlantic and Indian Oceans), and Icelandic (beneath Eurasia, the northernmost Atlantic Ocean, and the Arctic Ocean).
metamorphosis, metamorphose	1. Change of form of an organism, usually as it passes from one life stage to another, similar to the change from caterpillar to butterfly. 2. Change in the mineral composition of rocks after their initial formation.
methane hydrates	Ice-like solids formed in sediments or sedimentary rock layers by the trapping of methane gas in the crystalline lattice of water at high pressures and low temperatures. At atmospheric pressure, they are unstable and release their methane.
microalgae, microalga	Algae that are sufficiently small that they cannot be seen easily by the naked eye unless present in high concentrations. Most microalgae are single-celled, and they may be benthic or planktonic. Compare to macroalgae.
microbial	Organisms too small to be seen with the naked eye (about 1 mm or 100 µm).
micronutrient	An element or compound, including certain trace metals and vitamins, that is essential to the life processes of some species of organisms and that is present in seawater at concentrations substantially lower than those of nitrogen and phosphorus compounds.
middle-tide zone	Zone between the high-tide zone and the low-tide zone that is usually covered by water but is exposed to the atmosphere during all or most low tides.
mixed layer	Surface layer of ocean water that is mixed by wave and tide motions. As a result of the mixing, this layer has relatively uniform temperature and salinity.
mixed tide	Tide that has two high and two low tides each tidal day, with the two highs and/or the two lows being markedly different in height. Compare to diurnal tide and semidiurnal tide.
mollusks	Members of a phylum (Mollusca) of soft unsegmented animals that usually are protected by a calcareous shell and use a muscular foot for locomotion. Mollusks include snails, mussels, clams, chitons, and octopi.
mutagens, mutagenic	Chemical compounds that can cause mutations in organisms that are exposed to them. Compare to carcinogens and teratogens.
neap tide	Tide that has the smallest range within a lunar month. Neap tides occur twice during the month, when the moon is at its first and third quarters. Compare to spring tide.
nebula, nebulae	Cloud of interstellar gas and dust, often illuminated by stars.
nekton	Pelagic animals that are active swimmers and thus can overcome currents and determine their position in the ecosystem. Nekton include fishes, marine mammals, and squid.
niche	Range of environmental characteristics within which a particular species can survive and reproduce. The term is often used to include the function of the organism itself in the ecosystem.
node	Point on a standing wave where there is no (or minimal) vertical motion. Compare to antinode.
nonindigenous species	Species that is imported, accidentally or deliberately, to an ecosystem in which it is not present naturally.
nonpoint source	Source of pollution other than discharge pipes of industry and sewage treatment plants. Nonpoint sources include storm drains, street runoff, runoff from agricultural land, deposition of air pollutants, acid rain, and many other widely dispersed sources.
nudibranchs	Sea slugs. Members of the class Gastropoda, phylum Mollusca, that have no protective covering as adults.
nutrient	Any organic or inorganic compound that is used by plants, algae or photosynthetic bacteria in primary production. The most important nutrients include nitrogen and phosphorus compounds.
nutrient-limited	Pertaining to the condition in which the rate of growth of an organism or population of organisms, generally the production of organic matter by a photosynthetic organism or populations of organisms, is inhibited by the absence of a sufficient supply of one nutrient element (often nitrogen or phosphorus) when all other requirements for an increase in the rate of growth or production are met.
oceanic convergent plate boundary	Region where two lithospheric plates converge, each of which has oceanic crust at its margin. Compare to oceanic ridge.
oceanic plateau	Small area where the seafloor is raised a kilometer or more above the surrounding oceanic crust. Oceanic plateaus are extinct volcanoes, old oceanic ridges, or fragments of continents.
oceanic ridge	Linear undersea mountain range that marks a tectonic plate boundary where two lithospheric plates diverge. Oceanic ridges extend through all the major oceans. Compare to oceanic convergent plate boundary.
omnivores, omnivorous	Animals that feed on both on other animals and plants, algae or photosynthetic bacteria. Compare to carnivores and herbivores.
ooze	Sediment that contains at least 30% skeletal remains of marine organisms. Ooze may be siliceous or calcareous, and it may be diatom ooze, foraminiferal ooze, radiolarian ooze, or pteropod ooze, depending on the organisms that are the major contributors to the sediment.
orbital velocity	For an orbiting object (or particle within a wave), the speed of movement (distance covered per unit time) in the orbital path. See CC12.
osmoregulation	Ability of an organism to adjust its internal salt concentration independently of the external salinity.
osmosis	Passage of water molecules from a solution of lower solute concentration into a solution of higher solute concentration through a semipermeable membrane that separates the two solutions.
osmotic pressure	Measure of the tendency for osmosis to occur. The pressure that must be applied to a solution to prevent water molecules from passing into it through a semipermeable membrane that has pure water on the other side.
outfall	Pipeline that extends from the shore across the seafloor. An outfall carries liquid waste some distance offshore, where it is discharged from the submerged end of the pipe.
overfishing, overfished	Harvesting a fish species at a rate exceeding the maximum harvest that would still allow a stable population to be maintained by reproduction.
oviparous	Pertaining to animals that release eggs that develop and hatch outside the body. Compare to ovoviviparous and viviparous.
ovoviviparous	Pertaining to animals that incubate eggs inside the reproductive tract (usually the mother’s) until they hatch. Compare to oviparous and viviparous.
oxygen demand, oxygen-demanding	Quantity of oxygen that is needed to decompose organic matter or oxidize chemicals in an ecosystem. Waste materials often increase the natural oxygen demand.
ozone	Form of oxygen in which the molecule has three oxygen atoms.
ozone layer	Region of the atmosphere between about 15 and 30 km altitude in which there is a natural high concentration of ozone. Ozone in this layer absorbs much of the ultraviolet radiation from the sun.
paleomagnetism, paleomagnetic	The record of the past orientation of the Earth’s magnetic field incorporated in rocks during their formation.
parasites	Organisms that take their food and nutrients from the tissues of another organism. Parasites benefit from the host, but the host is disadvantaged.
parasitism	Symbiotic relationship in which the parasite harms the host from which it takes its nutrition.
partial tides	Harmonic components comprising the tide at any location. The periods of the partial tides are derived from the various components of the periodic motions of the Earth, sun, and moon in relation to one another.
partially mixed estuary	Estuary in which a distinct low-salinity layer moves seaward over a distinct higher-salinity layer that moves landward, but with a vertical gradation of salinity between the layers due to substantial vertical mixing. Compare to salt wedge estuary and well-mixed estuary.
passive margin	A continental margin that is not significantly deformed by tectonic processes, because the margin is located away from the edge of a lithospheric plate.
pathogen, pathogenic	Any microscopic organism that causes disease.
PCBs	Polychlorinated biphenyls, a group of industrial chemicals with a variety of uses. PCBS are toxic and mutagenic, they are not readily biodegraded, and they may be biomagnified.
pelagic	Pertaining to the open-ocean water environment.
petroleum hydrocarbons	Organic compounds that are present in petroleum and that consist predominantly of carbon and hydrogen. Extremely large numbers of different compounds are present in any petroleum sample.
phosphorite nodule	Lump composed primarily of phosphate minerals. Phosphorite nodules are scattered throughout certain parts of the ocean floor.
photic zone	Upper part of the ocean in which solar radiation is of sufficient intensity to enable phototrophy to occur. Compare to aphotic zone.
phytoplankton	Plankton that photosynthesize. Includes algae and photosynthetic bacteria. Compare to zooplankton.
pinnipeds	Members of a suborder (Pinnipedia) of marine mammals. Includes sea lions, seals, and walrus.
planetary vorticity	Rate of rotation of a fluid (ocean water or atmospheric air) due to the rotation of the Earth.
plankton, planktonic	Organisms that drift passively or swim weakly and are dependent on currents to determine their location. Most plankton are microscopic forms.
plate tectonics, plate tectonic	Initially a theory that the lithosphere is divided into plates that are moving relative to each other across the Earth’s surface. Now the term refers to the processes affecting plate motions and the effects of these motions.
pollution, pollute	Addition of substances to or alteration of the ocean ecosystem in a way that is deleterious to the ocean ecosystem or its resources. Compare to contaminant.
polyaromatic hydrocarbons, PAHs	Organic compounds present in organisms and petroleum, and created by the burning of fossil fuels that have carbon atoms arranged in ring structures. PAHs include the more toxic and carcinogenic compounds in petroleum.
polyp	Single individual of a cnidarian colony or a solitary attached cnidarian that has a central mouth fringed with many small tentacles.
pore water	Solution present between the mineral grains of a sediment or rock.
potential energy	Energy that is the result of the relative position of an object, such as the energy of a compressed coil spring or of an object that is placed at the top of a slope. In each case, the potential energy can be released and converted to kinetic energy by releasing the object.
pressure gradient	Pressure (P) variation on a horizontal surface. A gradient can be straight or curved. The steepness of the gradient is measured as difference in pressure per unit distance within the gradient (e.g., δP·km^–1).
primary production	The process of synthesis of organic material by phototrophic or chemosynthetic autotrophs. The term is sometimes used to mean primary productivity.
primary productivity	Rate of production of organic matter by autotrophs, measured as the quantity (usually mass) of organic matter synthesized by organisms from inorganic substances within a given volume of water or other habitat in a unit of time.
progressive wave	Wave in which the waveform progressively moves. Compare to standing wave.
prokaryotes	Organisms (single-celled or multicelled) whose cells are not surrounded by a membrane and that do not have a discrete nucleus and other subcellular compartments. Archaea and bacteria are prokaryotes. Compare to eukaryotes.
protists	Members of the kingdom Protista. Protists are those eukaryotes that are not animals, plants, or fungi.
protozoa, protozoan	Single-celled animals that have a nucleus confined within a membrane.
pteropods	Members of an order of pelagic animals of the class Gastropoda, phylum Mollusca, in which the foot is modified for swimming and the shell may be absent.
radioactive, radioactivity	Pertaining to a property of certain elements, or isotopes of an element, whose atomic nuclei are unstable and can spontaneously disintegrate and emit ionizing radiation.
radioisotope	Radioactive isotope of an element that may also have nonradioactive isotopes.
radiolaria, radiolarian, radiolarian	Planktonic and benthic protozoa of the phylum Sarcodina that are protected by shells that are usually siliceous.
radionuclides	Nuclei of radioactive atoms.
reef	Rocky elevation of the seafloor whose upper part is at depths of less than about 20 m. The term is often restricted to such areas that pose a hazard to navigation.
reef flat, reef terrace	Platform of coral fragments and sand that is relatively exposed at low tide. Also called “reef terrace.”
refraction, refract, refracted	Process by which part of a wave is slowed, causing the wave to bend as it passes from one zone to another in which it travels at a different speed. Refraction occurs as a water wave enters shallow water, or as a sound wave or light wave crosses an interface between two fluids or crosses a thermocline or halocline.
relict sediment	Sediment that was deposited under a set of environmental conditions that have since changed, but has not been buried by more recent sediment.
reptiles	Species of the class Reptilia, subphylum Vertebrata, phylum Chordata. Reptiles breathe air and are cold-blooded. The few marine species include turtles and sea snakes.
residence time	Average length of time that a particle of any substance spends in a defined part of the ocean. See CC8.
residual current	Current that remains after the reversing tidal current components have been subtracted. Residual current is indicative of the mean drift after multiple tidal cycles.
restoring force	Force that tends to restore a disturbed ocean surface to a flat configuration.
resuspend, resuspended	To lift particles off the sediment surface (by currents) or the ground (by winds) on which they have been temporarily deposited. Particles become suspended sediment and airborne dust in water and air, respectively.
rhodopsin	A group of proteins found in various bacteria and archaea (and the human eye) that are light sensitive and in some species are to gather light energy in phototrophy.
rift zone	Zone where the Earth’s crust is being torn apart. Rift zones are often elongated and may be locations where tectonic plates are separating.
rip current	Fast, narrow surface or near-surface current that flows seaward through the breaker zone at nearly right angles to the shore. Rip currents are the seaward return flow of the water piled up on the shore by incoming waves.
rocky intertidal zone	Zone of a rocky coastline between the high- and low-tide lines.
runoff	Freshwater that is returned to the ocean or to a river after falling on the land as rain or snow.
salinity	Measure of the quantity of dissolved salts in ocean water. Salinity is defined in terms of the conductivity of the water relative to the conductivity of a defined salt solution. Salinity has no units but is approximately equal to the weight in grams of dissolved salts per kilogram of seawater.
salps	Members of a genus of pelagic tunicates (subphylum Vertebrata) that are cylindrical and transparent.
salt marsh	Relatively flat area of the shore where fine sediment is deposited and salt-tolerant grasses grow.
salt wedge estuary	Estuary, normally deep, that has a large volume of freshwater flow separated by a sharp halocline from a lower wedge-shaped layer of seawater that moves landward. Compare to partially mixed estuary and well-mixed estuary
sand dune	Rounded mound or hill of sand on the back-shore formed by accumulations of windblown sand. Sand dunes may have rooted vegetation.
saturation pressure	Maximum amount of water that can remain in the vapor phase in air at a particular pressure and temperature expressed as a partial pressure of water vapor (the pressure if only the water vapor were present).
saturation solubility, soluble solubility	Concentration of a dissolved substance when no more of the substance can be dissolved in the solvent.
scarp	Linear, steep or nearly vertical topographic feature that separates areas of gently sloping or flat surfaces. Compare to berm.
scatter, scattered	Reflection of light or sound in random directions, generally by particles suspended in a fluid. Compare to backscatter.
scavengers, scavenge	Animals that feed on dead organisms.
school, schooling	Aggregation of fishes, squid, or crustaceans that is organized to remain together as the organisms move.
scuba	Abbreviation for “self-contained underwater breathing apparatus,” the means by which humans descend beneath the sea surface carrying their own source of air to breathe.
sea cucumbers	Members of the class Holothuroidea, phylum Echinodermata.
sea fans	Corals whose colonies grow out from a point of attachment to the substrate in a form resembling an intricate fan. Sea fans belong to the order Alcyonacea.
sea grasses	Any of several species of rooted plants of the class Angiosperma that grow predominantly in marshes and shallow-water lagoons.
sea stars	Animals of the class Anthozoa, phylum Cnidaria, that have a number of radial arms, on the underside of which are numerous tube feet to provide locomotion. The mouth is on the underside at the center. Many sea stars prey on mollusks.
sea urchins	Animals belonging to the class Echinoidea, phylum Echinodermata. Sea urchins have a fused test (external calcified covering) and well-developed spines.
seafloor spreading	Process producing oceanic crust by upwelling of magma along the axis of the oceanic ridges.
seamount	Individual peak of seafloor topography that rises more than 1000 m above the ocean floor.
seawall	Wall built parallel to the shore to protect the shore from erosion by waves.
sedimentary arc	Chain of low sedimentary islands formed at some oceanic convergent plate boundaries between the boundary and the magmatic arc.
sedimentation	Accumulation of particles on the seafloor by progressive deposition of particles from the suspended sediment to form sediments.
sedimentation rate	Rate of accumulation of sediments, normally measured in millimeters of sediment thickness per thousand years in the open ocean.
seismograph	Instrument that detects and records earthquake waves that have traveled through the Earth from an earthquake focus.
semidiurnal tide	Tide with two high and two low tides each tidal day, with the two highs and the two lows being equal or almost equal to each other in height. Compare to diurnal tide and mixed tide.
sensible heat	Heat that, when added to or removed from a substance, changes the temperature of that substance.
sewage sludge	Solids or slurry remaining after sewage wastewater has been treated. Sewage sludge contains pathogens, trace metals, nutrients, and other contaminants.
shallow-water wave	Wave whose wavelength is at least 20 times the depth of water beneath it. Compare to deepwater wave and intermediate wave.
shear stress	Resistance (friction) that develops at the interface between two fluids that are moving in relation to each other.
shelf break	Depth at which the gradual seaward slope of the continental shelf steepens appreciably, defining the boundary between the continental shelf and the continental rise.
shelf valley	Valley in the seafloor topography that cuts across the continental shelf. Shelf valleys are usually “drowned river valleys.”
shellfish	Animals of the phylum Crustacea or Mollusca that have hard outer shells. The term generally is applied to species that are valuable for human consumption.
shoal	Shallow place in a body of water that presents a hazard to navigation. Shoals are often in the form of a sandbank or sandbar whose surface may be exposed when the tide is low.
shore	Zone between the highest level of wave action during storms and the lowest low-tide line.
shoreline	Line that marks the intersection of the water surface with the shore. The shoreline migrates up and down as the tide rises and falls. Compare to coastline.
siliceous	Pertaining to material containing abundant silica.
sill	Submarine ridge that separates the deeper parts of two adjacent ocean basins. Sills are often present at the mouths of fjords and other coastal embayments or at the entrances to marginal seas.
slack water	The time when the current speed is zero as a reversing tidal current changes direction.
slump	Collapse of a mass of earth or sediments from the sides of sloping topography, and movement of this mass downward on the slope.
soft corals	Species of corals that do not secrete massive calcareous skeletons and do not have zooxanthellae.
solar wind	A stream of charged subatomic particles (mainly protons and electrons) that flows outward from the sun and other stars.
solstice	Time of year when the sun is directly over one of the tropics. Solstices occur on June 20 or 21 when the sun is over the Tropic of Cancer in the Northern Hemisphere and on December 21 or 22 when the sun is over the Tropic of Capricorn in the Southern Hemisphere. Compare equinox.
sonar	Abbreviation of “sound navigation and ranging,” a method by which sound pulses can be used to measure the distance to objects in the ocean.
sorted	Describing the range of grain sizes in a sediment. Well-sorted sediment consists of grains that have a restricted range of grain sizes.
sounding	Measuring the depth of water beneath a ship.
spatial	Pertaining to the location of points in three-dimensional space. The term is used in the same way that temporal is used with respect to points in time.
spawn	To produce eggs, which may be laid in one location or dispersed in the water.
species	Population of organisms whose members interbreed under natural conditions and produce fertile offspring and that is reproductively isolated from other such groups.
species succession	Sequence of dominance by different species of phytoplankton during seasonal changes, especially in mid-latitude marine ecosystems.
spit	Narrow strip of land, commonly consisting of sand deposited by longshore currents, that has one end attached to the mainland and the other terminating in open water.
sponges	Animals of the phylum Porifera, most of which are microscopic but build massive colonies. Sponges are filter feeders.
spore	Small reproductive body that is highly resistant to decomposition but is capable of growing and metamorphosing to produce an adult form either immediately or after a prolonged interval of dormancy.
spreading cycle	Period during which the continental crust on the Earth’s surface is broken into a number of pieces that move apart on their lithospheric plates. Spreading cycles are preceded and followed by a period when the continents are brought together.
spring tide	Tide that has the greatest range within a lunar month. Spring tides occur twice during the month, when the moon is new and when it is full. Compare to neap tide.
standing stock	Biomass of a population present at any given time.
standing wave	Waveform that oscillates vertically without progressive movement. Compare progressive wave.
storm surge	Temporary rise of sea level above its normal height as a result of wind stress and reduced atmospheric pressure during storms.
stratification, stratified	Layering of fluids according to density. Stratification is stable when density decreases continuously (but not necessarily uniformly) with distance from the Earth’s center.
subduction, subducted	Process by which one lithospheric plate descends beneath another.
subduction zone	Area in which a lithospheric plate is descending into the asthenosphere.
sublittoral zone	Benthic environment extending from the low-tide line to a depth of 200 m.
submarine canyon	Steep, V-shaped canyon cut into the continental shelf or slope.
submersible	Undersea vehicle with an enclosure that has an atmosphere in which human passengers can be transported.
subtropical gyre	Circular current system centered in the subtropical high-pressure region of each major ocean basin, driven by the trade winds and westerly winds. The subtropical gyres rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.
subtropical high	One of several regions of semipermanent high atmospheric pressure located over the oceans between 20° and 40° of latitude in both the Northern and Southern hemispheres of the Earth—associated with the downwelling zone of the Hadley cells.
supernova, supernovae	Violent explosion of a star that is many times more massive than our sun. The exploding star may become temporarily extremely bright. Matter is thrown off into space at high velocity and high energy during the explosion, and the star collapses to become either a neutron star or a black hole.
superplume	Massive upwelling of warmer mantle material that arises from extended areas near the Earth’s core. There are thought to be two such superplumes on the present-day Earth. They may each feed numerous hot spots.
supersaturated	An unstable condition in which the concentration of a dissolved substance (or of water vapor in air) is greater than the saturation solubility. The substance (or water vapor) may not precipitate unless provided with nuclei (such as suspended particles or dust) on which to deposit.
supralittoral zone	Splash or spray zone above the spring high-tide shoreline.
surf	Turbulent foam produced by breaking waves. The term is also used to mean “surf zone.”
surf zone	Region between the shoreline and offshore in which most wave energy is released by breaking waves.
surface microlayer	Thin (about 0.1 mm thick) layer that covers the entire ocean surface and has different properties than the underlying water has. Often called a “slick.”
surface tension	Tendency for the surface of a liquid to contract because of the attractive forces between its molecules.
survival niche	Range of environmental variables within which the individuals of a species can survive. Compare to fundamental niche.
suspended sediment	Small solid particles that sink slowly or are maintained in suspension and distributed in the water column by turbulence.
suspension feeders, suspension-feeding	Animals that feed by capturing or filtering suspended particles from the water column. Compare to filter feeders.
swash	Water that washes up over exposed beach as waves break at the shore.
swell	Smoothly undulating ocean wave that is the result of wave dispersion and that is transported with little energy loss across great stretches of ocean.
swim bladder	Gas-containing flexible organ in many fish species that aids in attaining neutral buoyancy.
symbiosis, symbiotic	Association between two species in which one or both benefit. A species in such an association that does not benefit may be harmed or may be unaffected by the association.
synoptic	Describing measurements made simultaneously at many different locations.

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