This glossary summarises terminology and acronyms commonly used within the mCDR sector. Though not exhaustive, the list has been compiled from many sources by partners within the SEAO2-CDR project and will be kept updated until the end of the project – please contact us to notify us of any significant absences or inaccuracies. 

 

Glossary

ALKALINITY – The ability of ocean water to neutralize acids. More alkalinity means the ocean can absorb and store more CO₂.

ARTIFICIAL DOWNWELLING (AD) – A method that pumps surface water down to deep waters to facilitate, or speed up, the transport of surface carbon to be stored in the deep ocean.

ARTIFICIAL UPWELLING (AU) – A method that pumps deep, nutrient-rich and CO2-rich water to the surface to stimulate the growth of tiny marine plants (phytoplankton) that absorb CO₂ from the atmosphere via photosynthesis.

BIOLOGICAL CARBON PUMP – A general term used to define the natural processes through which marine plants and animals convert CO₂ into organic matter, and some of that organic material sinks or is transported by fauna into deep marine environments where it can be stored for a long time.

BLUE CARBON – All biologically-driven carbon fluxes and storage in marine systems that are amenable to management. Actionable blue carbon ecosystems in climate mitigation policy include mangroves, seagrass beds, and tidal marshes, whereas seaweed forests are considered emerging blue carbon ecosystems. 

CARBON CAPTURE AND STORAGE (CCS) – A process whereby CO₂ is collected and stored in permanent (normally geological) reservoirs instead of being released into the atmosphere. 

CARBON SEQUESTRATION – Storage of CO₂ derived from carbon capture or carbon removal processes so that it isn’t released back into the atmosphere. 

CARBONATE CHEMISTRY – When CO2 dissolves into seawater it can form different inorganic chemical species. The chemical balance between these different types of dissolved inorganic carbon depends on how acidic the water is and affects how much CO₂ the ocean can absorb.

DIRECT AIR CAPTURE (DAC) – A technology that removes CO₂ directly from the air using special filters or chemical reactions. The captured CO2 must then be stored in permanent (geological) reservoirs to prevent release back into the atmosphere.

DIRECT OCEAN CARBON CAPTURE (DOCC) – A process that removes CO₂ directly from seawater, helping the ocean take in more CO₂ from the atmosphere. The captured CO2 must then be stored in permanent (geological) reservoirs to prevent release back into the atmosphere.

DISSOLVED INORGANIC CARBON (DIC) – A collective term that encompasses dissolved CO2 gas, carbonic acid (H2CO3), bicarbonate ion (HCO3–), and carbonate ion (CO32–), the chemical species of the seawater carbonate system that naturally store inorganic carbon in seawater.

EUTROPHICATION – A situation where too many nutrients in the water cause excessive growth of algae, which upon decay, can lead to low oxygen levels and harm marine life.

GEOLOGICAL SEQUESTRATION – Storing CO₂ underground in sediment or rock formations so it doesn’t return to the atmosphere.

GIGATON – A unit of mass equivalent to one billion metric tonnes. 

HYPOXIA – A condition where there is too little oxygen in the water, so the health of marine organisms is negatively affected and sensitive species may escape or die. 

MACROALGAE – Large algae in the ocean, like kelp or seaweed, that absorb CO₂ as they grow. Some approaches to CO₂ removal involve sinking macroalgae to deep waters to store carbon for a long time.

MARINE CARBON DIOXIDE REMOVAL (MCDR) – A general term for all ocean-based methods that remove CO2 from the atmosphere via increasing the capacity of seawater to absorb more CO2

MONITORING, REPORTING, AND VERIFICATION (MRV) – The process of tracking how much CO₂ is removed and making sure it stays stored as planned. Specific MRV may also be required for tracking environmental and ecological side effects. 

OCEAN ACIDIFICATION – The dissolution of CO₂ into seawater changes carbonate chemistry and makes the water more acidic (lower pH). Increasing ocean acidity beyond natural tolerances may harm marine life, especially shellfish and corals.

OCEAN ALKALINITY ENHANCEMENT (OAE) – A method that increases the ocean’s ability to absorb CO₂ by adding minerals or using electrochemical processes to make seawater more alkaline.

OCEAN FERTILIZATION (OF) - Addition of limiting nutrients (often iron) to stimulate growth of phytoplankton which remove CO2 from the water through photosynthesis. Sequestration of carbon occurs through subsequent aggregation and sinking of organic matter into deep water.

PHOTOSYNTHESIS – The process where plants, including tiny ocean algae (phytoplankton) and seaweed, use sunlight to take in CO₂, grow, and produce oxygen.

PHYTOPLANKTON BLOOM – A rapid increase in tiny marine algae, often stimulated by an increase in the availability of nutrients. These blooms absorb CO₂ but can also lower subsurface oxygen levels if sinking organic matter decays too quickly.

REMINERALIZATION – When dead plants, algae, animals, and organic detritus decay/breakdown in the ocean they release dissolved inorganic carbon and nutrients back into seawater. The deeper that this process happens within the ocean, the longer the carbon is likely to stay out of the atmosphere. 

RESPIRATION – The process by which organisms use oxygen and organic matter to produce energy and CO₂. This process transforms organic carbon to inorganic carbon and leads to accumulation of dissolved inorganic carbon in the ocean interior.

SEQUESTRATION DURABILITY – How long the stored CO₂ stays out of the atmosphere. Some methods store carbon for only a few years or decades, while others may keep it locked away for thousands of years.

TOTAL ALKALINITY (TA) – A measure of how much seawater can neutralize acids, which affects how much CO₂ it can absorb. Increasing alkalinity can help store more CO₂ in seawater.

UPWELLING – A natural process where deep, nutrient-rich and CO2-rich water rises to the surface, boosting marine life. Artificial Upwelling tries to replicate this process to increase CO₂ absorption via stimulating biological productivity.

 

 

 

Acronyms

AD                        Artificial downwelling

AU                        Artificial upwelling

CCU                      Carbon capture and utilisation

CCUS                    Carbon capture, utilisation and storage

CDR                      Carbon dioxide removal

DOCC                   Direct ocean carbon capture

EEZ                       Exclusive Economic Zone

EU                        European Union

GHG                     Greenhouse gas

IAM                      Integrated assessment model

IPCC                     Intergovernmental Panel on Climate Change

LCA                       Life cycle assessment

LULUCF                Land use, land-use change and forestry

mCDR                   Marine carbon dioxide removal

NET                      Negative emission technology

OAE                      Ocean alkalinity enhancement

OCDR                   Ocean-based carbon dioxide removal

OF                        Ocean fertilization

TRL                       Technical readiness level

UNFCCC               United Nations Framework Convention on Climate Change

VCM                     Voluntary carbon market