277 GLOSSARY GLOSSARY recirculates exhaled breathing gas. Red tide: An extremely heavy bloom of plankton or algae. Refraction: The bending of rays of light when they pass from a medium of one density into a medium of a different density. Resuscitation: The combination of external cardiac compressions and artificial respiration. Reverse block: A condition existing when the pressure in the middle ear exceeds the ambient pressure. Reverse thermocline: An abrupt transition from a colder layer of water to a warmer layer of water, where the colder layer is shallower than the warmer layer. Rip current: A strong, narrow current moving away from shore and formed when water in a surf zone is funneled through a narrow gap. S Saturation: A state existing when the tension of a gas in a liquid reaches a value equal to the partial pressure of the gas outside the liquid. Scrolling: A feature of a dive computer in which no-decompression limits for various depths are displayed sequentially and repeatedly. Scuba: Self-contained underwater breathing apparatus. Seiche: The oscillation of the surface of a lake or a landlocked sea and caused by wind blowing over the water. Seismic waves: Giant waves resulting from underwater earthquakes and mistakenly referred to as “Tidal waves” and “Tsunamis.” Semi-closed scuba: A system in which a portion of the exhaled breath is retained within the system and rebreathed. Shared Air Ascent: An ascent made where two divers share an air source. Set and drift: The direction and velocity of a current. Silent bubbles: Microscopic bubbles formed within the body as a result of decompression and theorized to contribute to the larger bubbles which cause decompression sickness. Single-hose regulator: A regulator with a single hose joining the first and second stages. Slack water: The period of time existing at high or low tide during which tidal current is at a minimum. Solid, Liquid, Gas: The three fundamental states of matter. Specific gravity: The density of a specific substance compared with that of pure water. Specific heat: The ratio of the amount of heat transferred to raise a unit mass of a substance one degree to that required to raise a unit mass of pure water one degree. Spilling breakers: A form of surf where waves break far from shore on a shallowly sloping bottom and continue to break to the beach. Spring tides: Tides with the greatest range between high water and low water. Stage: A pressure-reduction step in a regulator or compressor. Stipes: Strands of kelp. Stress: A physical and emotional state that evokes effort on the part of an individual to maintain or restore equilibrium. Submersible pressure gauge: An instrument to measure cylinder pressure while submerged.
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