GLOSSARY - Dive Atlas Of The World: An Illustrated Reference To The Best Sites - Jack Jackson

Dive Atlas Of The World: An Illustrated Reference To The Best Sites - Jack Jackson (2016)


Adjustable buoyancy life jacket (ABLJ) - Another name for a jacket style buoyancy compensator device (BCD).

Ahermatypic corals - Corals that do not have symbiotic algae present in the polyp tissue.

Algae - Simple photosynthetic plants.

Aqualung - Underwater breathing apparatus.

Atmosphere - The average pressure of the atmosphere at sea level. A unit of pressure of 14.7psi or 1 bar. The pressure underwater increases by one atmosphere for every 10m (33ft) of depth.

Atmospheres Absolute (ATA) - The sum of the atmospheric pressure and the hydrostatic pressure. In other words, the ATA or atmospheres absolute is the total weight of the water and air above divers.

Atoll - A group of reefs and islands that surround a central lagoon and drop away to deep water on their outer sides.

Bends - Term used for decompression sickness because sufferers bend the affected limb to ease the pain.

Bommie - There is no fixed definition for a bommie, it is mainly an Australian word for an undersea pinnacle, or coral head.

Bora - A strong northerly, squally wind which blows in the northern Adriatic.

Breathing loop (rebreather) - all the internal areas within which the diver’s breathing gases flow, including the counterlung, scrubber, breathing hoses and the diver’s lungs.

Buoyancy compensator device (BCD) - A device by which divers can adjust their buoyancy underwater or inflate as a life jacket when on the surface. A BCD is usually inflated by a direct-feed, (power-inflator) from the main scuba cylinder by way of the regulator first stage. However, a BCD may also be inflated by an emergency air cylinder or when on the surface by a cartridge of carbon dioxide, which can be used only once and then has to be replaced.

Buoyant ascent - A rapid emergency ascent following the inflation of a buoyancy compensator device or dry suit.

Caisson Workers Disease - Another name for decompression sickness because caisson workers doing underwater construction work in these watertight chambers suffered from it.

Carbon dioxide cartridge - A small cartridge of carbon dioxide (C02) used for one-off inflation of the BCD at the surface.

Cays - Islands formed by the accumulation of sand on a coral reef. These are distinct from islands that do not originate from reefs.

Certification card (‘C’-card) - An identification card that provides evidence that at one point the diver has passed certain performance standards of a recognized diving training agency. Some dive operators will also want to see your latest diving logbook to check your experience since qualifying and whether you have had recent diving experience.

Chimney - A steep and narrow, almost perpendicular cleft in a reef-face.

Commensals - Organisms that live together without obvious mutual benefit.

Compressor - A multi-stage pump that is used to fill cylinders or air-banks with compressed air.

Console - A unit that is attached to the submersible pressure gauge to enable a collection of instruments to be mounted together.

Contents gauge - A submersible pressure gauge that indicates the amount of gas in the scuba cylinder by its pressure.

Coriolis Effect - The deflection of the path of a body due to the earth’s rotation, to the left in the southern hemisphere and to the right in the northern hemisphere.

Counterlung - the sealed flexible bag that inflates as the diver exhales and deflates as the diver inhales. In acting as a storage area for the diver’s breathing gases, the positioning of this bag within the breathing loop can greatly affect the breathing effort.

Cut-through-anything-shears - Shears that will cut through most fishing lines and nets, even thin steel ones.

Decompression dive - A dive which requires one or more decompression stops to release dissolved gases in a controlled fashion.

Decompression sickness (DCS) - A condition caused by the rapid release of pressure on ascent; nitrogen (or helium if used) in the blood and body tissues forms bubbles that can block the circulation.

Decompression stop - One or more pauses during the ascent to allow the excess nitrogen (or helium if used) in the body to dissipate.

Decompression table - A table of times and depths used to calculate the limits of safe diving and any required decompression stops.

Delayed deployment surface marker buoy - A surface marker buoy that is only deployed when required. These include rescue tubes or sausages.

Demand valve (DV) - Another name for a regulator because it only supplies breathing gas on demand.

Depth gauge - An instrument that shows the diver’s depth beneath the surface by measuring the water pressure.

Diluent (rebreather) - The gas used in a closed circuit rebreather to make up volume in the breathing loop as the diver proceeds to deeper depths and the gases in the breathing loop are compressed. Depending on the rebreather, and the type of diving, the gas used for diluent could be air, Nitrox, Trimix or even Heliox.

Direct-feed - Also called a power-inflator, a one-way valve connected to a low-pressure hose, which enables a supply of gas from the first stage of the regulator to inflate the buoyancy compensator device or dry suit.

Dive planner - A table of times and depths used to calculate the limits of safe diving, particularly on multiple dives.

Dive timer - A timing device that is activated either manually or when it becomes submerged so that divers know the elapsed time of a particular dive.

Diving logbook - a record of your dives that also acts as proof of what types of dives you have accomplished since qualifying.

Drop-offs - Steep slopes of 60-85°.

Dump valve - A valve used to vent (dump) gases from dry suits or BCDs.

Elapsed time - the time that has elapsed since leaving the surface.

Emergency cylinder - A small cylinder that is fitted to many BCDs for emergency inflation.

Encrusting corals - A coral colony that forms a thin layer over a substrate.

Enriched Air Nitrox (EANx) - Any mixture of oxygen and nitrogen which has more or less oxygen than found in normal air. However, the term usually describes those mixtures with a more than the normal amount of oxygen.

Family - A grouping of related genera with common characteristics.

First stage - The section of the regulator that reduces the pressure of the gases in the scuba cylinder to a pressure that the second stage requires.

Free ascent - A diver surfacing rapidly in an emergency, forcibly breathing out all the way to avoid a burst lung.

Fringing reef - A reef that fringes an island or coast.

Fully-closed circuit rebreather - Refer to Rebreather.

Ghibli - A hot dry southerly/southeasterly wind of north Africa.

Gondwanaland - A supercontinent thought to have existed in the southern hemisphere in Palaeozoic times, comprising the present Africa, South America, Australia, Antarctica, and the Indian peninsula.

Guyot - A seamount with a flat top.

Haboob - A violent and oppressive seasonal wind blowing in Sudan and bringing sand from the desert.

Helictites - Distorted forms of stalactites resembling twigs.

Heliox - A breathing mixture of gases consisting entirely of helium and oxygen. This is used to eliminate Nitrogen narcosis and to control the effects of oxygen toxicity, by eliminating the nitrogen and reducing the amount of oxygen in the breathing mix.

Hermatypic or reef-building corals - Corals with symbiotic algae present in the polyp tissue.

Invertebrate - An animal that does not have a backbone or spinal column.

Khamsin - An oppressive, hot southerly/southeasterly wind, which blows in Egypt at intervals for about 50 days in March, April, and May, and fills the air with sand from the desert (Khamsin means 50 in Arabic).

Knot - Unit of speed used in sea and air navigation, equal to one nautical mile per hour.

Latitude (geographical) - The angular distance in degrees, north or south, of any place on the earth’s surface from the equator, which is at latitude 0 degrees.

Levanter - A strong easterly wind in the Mediterranean that passes through the Strait of Gibraltar.

Longitude (geographical) - The angular distance of any place on the earth’s surface, east or west of the standard meridian of Greenwich (UK), it is measured in degrees up to 180° East or West.

Loraine Smith Effect - see Oxygen Toxicity.

Meridian (geographical) - One of the imaginary lines along the surface of the earth at right angles to the equator, which join the North and South Geographical Poles, designated by degrees of longitude from 0 degrees at Greenwich (UK) to 180 degrees East or West.

Mistral - A strong, cold northwest wind which blows through southern France into the Mediterranean, mainly in winter.

Mollusc - Any animal of the phylum Mollusca, e.g. limpets, snails, cuttlefish, oysters, mussels, etc., members of which have soft bodies and usually have hard shells.

Monofilament cutter - A tool specifically designed to cut through monofilament line or netting.

Mouthpiece - Section of a regulator or snorkel which fits into the diver’s mouth.

Nematocysts - stinging cells in jellyfish and other coelenterates that contain a coiled thread, often barbed or poisoned, that is ejected as a defence or to capture prey.

Nitrox - see Enriched Air Nitrox.

Non-decompression stop dive or No stop dive - A dive that does not require any decompression stops.

Normoxic - This is the term used to describe the normal mixture of gases found in the atmosphere.

Nautical mile - The length of one minute of latitude - in practice 1852m (6076ft).

Nitrogen narcosis - A condition affecting divers’ mental processes caused by excess nitrogen in their body tissues. The effects of Nitrogen narcosis on divers are similar to being drunk and increase with depth.

Octopus rig - A second regulator second stage that is used for sharing air with another diver.

0-ring - A synthetic rubber ring that fits in a groove and is used to form an airtight or watertight seal.

Oxygen Toxicity - Physiological damage resulting from breathing higher than normal partial pressures of oxygen. There are two primary types. That resulting from long exposures of elevated partial pressures of oxygen is called the Loraine Smith Effect or Pulmonary Oxygen Toxicity as the primary damage is to the lungs and airways. The other type results from short exposure to high partial pressures of oxygen and is called the Paul Bert effect or Central Nervous System Toxicity (CNS Toxicity) and is characterized by convulsions.

Palaeozoic - Relating to an era of geological time that began 600 million years ago, lasted about 375 million years, and was marked by the development of marine and terrestrial plants and animals.

Partial pressure - The pressure of a particular gas within a mixture of gases. It is commonly represented as ‘pp’ followed by the atomic symbol of the gas. The partial pressure of oxygen would be written as ppO2.

Paul Bert Effect - see Oxygen Toxicity.

Pinnacle - A relatively narrow, vertical structure forming a peak.

Pleistocene - Denoting the first epoch of the Quaternary period (the most recent period of geological time), which lasted about 990,000 years and was characterized by widespread glaciation in the northern hemisphere and the evolutionary development of man.

Power-inflator - refer to direct feed.

Rebreather - A self-contained device used to recirculate and regulate breathing gases for the purposes of extended diving times and quiet operation. In a fully closed-circuit rebreather this is accomplished by chemically removing carbon dioxide (scrubbing CO2), and adding oxygen as necessary to maintain a constant partial pressure of oxygen. This type of rebreather does not release any gases from the unit except under the conditions of ascending from depth. The advantage of this system is the greatest possible use of the oxygen carried, the disadvantage is the added complexity of the electronics and mechanics in the unit. In most semi-closed systems a portion of each breath is released to the water, the carbon dioxide is scrubbed from the remaining gases and a similar portion of new breathing gases are injected into the system.

Regulator - Another name for a demand valve. A mechanism which reduces the pressure of the gases in the scuba cylinder to the pressure of the water surrounding the body at the level of the diver’s lungs so that the gases can be inhaled by the diver.

Rescue tube - A highly-visible surface marker buoy in the shape of a tube or sausage that is only deployed when required.

Residual nitrogen - The amount of absorbed nitrogen that is estimated to remain in the diver’s body after a dive.

Sand chute - A sloping channel down a reef which acts as a conduit for falling sand and other debris.

Scrubber or CO2 scrubber - The part of a rebreather that removes carbon dioxide (CO2) by passing it through a chemical that absorbs it.

SCUBA - An acronym for Self Contained Underwater Breathing Apparatus.

Scuba cylinder valve - The valve on the scuba cylinder, which is attached either to the regulator or the compressor.

Seamount - A submarine mountain (submerged volcano) rising more than 1000m (3300ft) above the ocean floor. Flat-topped ones are called guyots.

Second stage - The section of the regulator which further reduces the pressure of gases from the first stage to the ambient pressure of water level with the diver’s lungs so that the gases can be breathed comfortably through the mouthpiece.

Semi-closed circuit rebreather - see Rebreather.

Shelf - A structure projecting almost horizontally from a reef face.

Shot line - A weighted line marking an object on the seabed or providing a guide for divers during descent or ascent.

Sirocco - A hot, oppressive, and often dusty or rainy wind which blows from the north coast of Africa over the Mediterranean and parts of southern Europe.

Stalactite - A conical or tapering formation that hangs from the roof of a cave, formed of calcite etc. deposited by water droplets that have percolated through the overlying limestone.

Stalagmite - A conical or columnar formation that rises from the floor of a cave, formed of calcite etc. deposited by water droplets falling from the roof or from stalactites.

Spur and groove - The classic formation of alternating spurs and grooves that are formed on an outer reef face by waves of the sea flowing in and then out again. The spur and groove system is formed by erosion.

Stabilizer (stab) jacket - Another name for a jacket-style buoyancy compensator device.

Surface marker buoy (SMB) - A floating buoy used by divers to mark their position.

Swim through - A hole formed by large boulders or eroded coral or rock through which people can swim.

Symbiosis - Two dissimilar organisms living in close physical association, where each benefits the other.

Tectonic Plates - Each of the several nearly rigid pieces of the outer portion of the earth, including the crust and the outermost mantle, thought to make up the earth’s surface and to be moving slowly relative to one another. Their boundaries are identified with seismic, volcanic, and tectonic activity.

Tethys Sea - A large sea that lay between Laurasia and Gondwanaland during late Palaeozoic times, i.e. before the continents reached their present positions.

Trimix - A breathing mixture of gases most often composed of oxygen, nitrogen and helium. The proportions of each gas are changed according to the requirements of the particular dive plan.

Vendaval - A strong westerly wind in the Mediterranean that passes through the Strait of


Walls - A reef wall that is near the vertical and may be either overhanging or undercut.

Zooxanthellae - Any of numerous yellow-brown algae or plants known as dinoflagellates present as symbionts in the cytoplasm of many marine invertebrates.