Scientific Glossary

Glossary of terms and abbreviations relevant to the International Seabed Authority and the documents it produces

Please note that this is a constantly evolving document.

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Title
Habitat	The environment occupied by an organism.
Hadal	The deepest part of the oceans below a depth of 6000m.
Hadalpelagic	Synonymous with hadopelagic.
Hadopelagic	Referring to the deepest region of the pelagic environment below 6000m. Synonymous with hadalpelagic. Occurs below theabyssopelagic where depths allow. {Figure}.
Halocline	A layer of water in which there is a steep gradient in salinity with depth. Compare to nutricline, pycnocline and thermocline.
Hawaii Ocean Time-series	A project with scientists making repeated observations of the hydrography, chemistry and biology at a station north of Hawaii since October 1988. The objective of this research is to provide a comprehensive description of the ocean at a site representative of the central North Pacific Ocean. Abbreviated to HOT.
HEBBLE	High Energy Benthic Boundary Layer Experiment (North Atlantic Ocean)
Herbivore	An organism that feeds on plants. Compare to carnivore.
Heterotroph	An organism which cannot synthesize its own organic material so obtains it through food. Compare to Autotroph
Heterotrophic	Pertaining to a heterotroph. Compare to autotrophic
High-Performance Liquid Chromatography	A quantitative method for identifying, purifying and analyzing compounds that are dissolved in solution. Abbreviated to HPLC.
Holoplankton	Permanent members of the plankton. Compare to meroplankton.
HOT	Hawaii Ocean Time-series.
HPLC	High-Performance Liquid Chromatography.
Hydrodynamic	Referring to any event related to the movement of water.
Hydrology	The scientific study of water and water masses.
Hydrothermal	Relating to hot water or the action of such water. The water is often heated by magma or in association with magma.
Hydrothermal Vents	Synonymous with active sulphides.
Hyperthermophiles	Archaea and Bacteria that grow optimally at temperatures in the range of 95°C to 110°C and can survive to temperatures close to 120°C.
Hypoxic	Low concentration of oxygen. Compare to oxic and anoxic.