278 NAUI Master Scuba Diver GLOSSARY Supersaturated solution: A solution holding more gas than is possible at equilibrium for a particular temperature and pressure. Surf: Breaking waves releasing their energy in shallow water. Surf beat: The periodic rise and fall in the height of waves and surf caused by the reinforcement or reduction of wave amplitude when two trains of waves approach an area at the same time. Surface equivalent: The effect that the partial pressure of a gas has on the body at depth in relation to an equivalent amount of gas at sea level, e.g., breathing 1% carbon monoxide at four atmospheres is the surface equivalent of breathing 4% carbon monoxide. Surface tension: The contractive forces at the surface of a liquid. Surf zone: That area in which the water within waves is moving forward with the waves in the form of surf. Surge: The back-and-forth sub-surface movement of water caused by waves passing overhead. Surging breakers: Surf formed by small swells approaching a very steep bottom. These waves slide up and down the steep incline with little or no foam production. Swash: The water on the face of a beach that washes back into the main body of water. Swells: The low, rounded form in which wave energy is transferred through water. T Tannin: A brownish chemical released by trees. Technical diving: Term that describes diving modes and techniques that are generally beyond the limits of traditional recreational diving. Thermocline: A horizontal, abrupt transition from a warmer layer of water to a colder layer of water. Tidal current: Movement of water produced by tidal changes. Tides: Periodic rising and falling of waters due to gravitational attraction of the sun and moon. Time to fly: The time before you are allowed to fly that is displayed on a dive computer. Trail line: A line with a float at the end extended behind a boat to assist divers in returning to the vessel if they should surface down current. Also called a “current line” or “tag line.” Trapdoor effect: The inability to equalize pressure in the middle ear because the opening to the eustachian tube leading to the middle ear is being held closed by ambient pressure. Trim: The control of an assumed position or body attitude. Trimix: A breathing gas consisting of a mixture of oxygen and two inert gases like helium and nitrogen. True North: A geographical location with reference to the earth’s axis rather than the magnetic poles and not the same as magnetic north. Tsunami: See Seismic Waves. Turbidity: A reduction in underwater visibility caused by suspended sediment. Two-hose regulator: A regulator with both stages and the exhaust valve in a single housing and with two hoses leading to a mouthpiece. U Unbalanced valve: A valve controlling high pressure in such a way that the pressure affects the force needed to open and close the valve.
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