A rapid growth of large amounts of micro- or macroalgae or cyanobacteria in water.

One of the two most abundant forms of calcium carbonate in the ocean. The other is calcite.

A measure of the thermodynamic tendency for the mineral calcium carbonate to form or to dissolve. The symbol Ω (omega) is often used as shorthand for "calcium carbonate saturation state". By convention, Ω is usually expressed with respect to aragonite, one of the two most abundant forms of calcium carbonate in the ocean. An aragonite saturation state (Ωar) greater than 1.0 indicates supersaturation, while values less than 1.0 indicate undersaturation with instability favoring dissolution. Recent research shows that calcifying organisms require Ωar well in excess of 1.0 to optimally produce shells or skeletons. Levels below 1.0 are considered corrosive, and skeletons and shells may be subject to dissolution.

The production and accumulation of calcium carbonate by living organisms to create hard body parts such as shells and skeletons.

Buffering is the resilience of seawater against changes in pH, or acidification. A well-buffered solution’s pH changes very little when an acid is added. Buffering capacity depends on a number of factors such as alkalinity, pH, temperature, and salinity.

A well-buffered solution’s pH changes very little when an acid is added.

Buffering describes the resilience of seawater against changes in pH, or acidification.

A well-buffered solution’s pH changes very little when an acid is added. Buffering capacity varies depending on factors such as alkalinity, pH, temperature, and salinity. Ocean waters of the U.S. Northeast tend to have poor buffering capacity because they are cold and relatively low in salinity. Consequently, these waters are more susceptible to acidification than other parts of the ocean where the water has a higher buffering capacity.

Any type of marine life that uses calcium carbonate in building its body.

One of the two most abundant forms of calcium carbonate in the ocean. The other is aragonite.

A chemical compound with the formula CaCO₃. It is a common substance and is the main component of shells of mollusks, sea urchins, and calcifying plankton. It is a minor albeit critical contributor to the carapaces of lobsters, clams, and shrimp. The two most abundant forms of calcium carbonate in the ocean are aragonite and calcite.

A measure of the thermodynamic tendency for the mineral calcium carbonate to form or to dissolve. The symbol Ω (omega) is often used as shorthand for calcium carbonate saturation state. By convention, Ω is usually expressed with respect to aragonite, one of the two most abundant forms of calcium carbonate in the ocean. An aragonite saturation state (Ωar) greater than 1.0 indicates supersaturation, while values less than 1.0 indicate undersaturation with instability favoring dissolution. Recent research shows that calcifying organisms require Ωar well in excess of 1.0 to optimally produce shells or skeletons. Levels below 1.0 are considered corrosive, and skeletons and shells may be subject to dissolution.

An acid that forms when carbon dioxide (CO₂) dissolves in water. The CO₂ can come from either the atmosphere or from the respiration of organic matter by marine life.

A decline in seawater pH that occurs because of high levels of respiration by marine life—typically bacteria involved in decomposition of algae. Respiration releases carbon dioxide into the water, which leads to formation of carbonic acid. Coastal acidification (CA) is often fueled by nutrients carried into the ocean by rivers, stimulating outbreaks of phytoplankton that subsequently decompose on or near the seabed. This phenomenon happens in coastal waters because that is where high nutrient levels and algal blooms occur. Coastal acidification is differentiated from ocean acidification (OA), which is a global-scale phenomenon of carbon dioxide from the atmosphere dissolving into the ocean. However, both CA and OA involve increases in carbon dioxide in the water.

Condition when aragonite saturation state in seawater is less than 1, when skeletons and shells of marine life may be subject to dissolution.

A phylum of bacteria that obtain their energy through photosynthesis. The name comes from the color of the bacteria. Also called blue-green algae or Cyanophyta.

A large gulf of the Atlantic Ocean on the east coast of North America. The landward boundary of the Gulf of Maine extends along the coast from Cape Cod, Massachusetts, through New Hampshire, Maine, and New Brunswick to Cape Sable at the southern tip of Nova Scotia. Georges Bank defines the seaward boundary of the Gulf of Maine.

A general term for the young life stages of some types of marine life such as lobster, crabs, fishes, and sea urchins. Larvae are often planktonic, meaning they drift in the ocean, even for species such as lobster, crabs, and urchins in which adults dwell on the seafloor.

A general term for large photosynthetic organisms including seaweeds (algae) and seagrasses.

The quantity of nutrients entering a water body or ecosystem from an external source in a given period of time.

A decline in seawater pH that occurs on a global scale and is caused primarily by carbon dioxide from the atmosphere entering the ocean. This leads to formation of carbonic acid. Ocean acidification (OA) is differentiated from coastal acidification (CA), which is a more localized phenomenon typically fueled by nutrients carried by rivers. However, both OA and CA involve increases in carbon dioxide in the water.

Ocean acidification (OA) is a global process that involves a reduction in the pH of the ocean. It is caused primarily by carbon dioxide from the atmosphere entering the ocean. Coastal acidification (CA) is a more localized, further reduction in pH. It is caused by high levels of respiration (typically by bacteria involved in decomposition), which releases carbon dioxide into the water. CA is often fueled by nutrients entering the water from land, stimulating outbreaks of phytoplankton that subsequently decompose on or near the seabed. CA happens in coastal waters because that is where high nutrient levels and algal blooms occur. The term ocean and coastal acidification (OCA) encompasses both the global and the local processes of acidification.

A number expressing the acid/base characteristic of a solution on a logarithmic scale, roughly equivalent to the negative logarithm of the hydrogen ion concentration. A pH of 7 is neutral. Lower values are more acidic, and higher values are more alkaline.

A process through which plants, algae, cyanobacteria, and some other organisms use light energy, normally from the sun, to convert carbon dioxide and water into carbohydrates, such as sugars. Oxygen is released as a product of photosynthesis by plants, algae, and cyanobacteria.

Microscopic, single-celled plants and other photosynthetic organisms that inhabit the upper, sunlit waters of the ocean.

A diverse category of tiny plants, animals, and bacteria that live suspended in the water column and are too small to swim against the current. There are two general types of plankton: Phytoplankton are microscopic, single-celled plants and other photosynthetic organisms that inhabit the upper sunlit waters of the ocean. Zooplankton are animals that live all or part of their life as plankton, suspended and drifting in the water; some zooplankton are the larvae (young) of animals such as lobsters, crabs, clams, sea stars, and sea urchins that live on the seabed as adults.

Small planktonic mollusks with winglike extensions to their bodies that they use for swimming. Pteropods build shells of aragonite and could be strongly affected by ocean and coastal acidification. They play a key role in the food web as a major food source for some zooplankton and higher predators, such as whales, birds, herring, and salmon.

The uptake of oxygen and the release of carbon dioxide by living organisms. Respiration by bacteria involved in the decomposition of algal blooms can contribute to coastal acidification. The carbon dioxide they release dissolves in the water and forms carbonic acid.

Ocean waters that lie above the continental shelf. Shelf waters are relatively shallow compared to the deep sea.

A process in which deep, cold water rises toward the surface of the ocean. 

A well-buffered solution’s pH changes very little when an acid is added.

A diverse group of animals that live all or part of their life as plankton, suspended and drifting in the water. Some zooplankton are the larvae (young) of animals such as lobsters, crabs, clams, sea stars, and sea urchins that live on the seabed as adults.

The symbol Ω (omega) is used by scientists as shorthand for "calcium carbonate saturation state". Ω is a measure of the thermodynamic tendency for the mineral calcium carbonate to form or to dissolve. By convention, Ω is usually expressed with respect to aragonite, one of the two most abundant forms of calcium carbonate in the ocean. An aragonite saturation state (Ωar) greater than 1.0 indicates supersaturation, while values less than 1.0 indicate undersaturation with instability favoring dissolution. Recent research shows that calcifying organisms require Ωar well in excess of 1.0 to optimally produce shells or skeletons. Levels below 1.0 are considered corrosive, and skeletons and shells may be subject to dissolution.