Epipelagic Zone Wind keeps this layer mixed and thus allows the sun's heat to be distributed vertically. The base of this mixing layer is the beginning of the transition layer called the thermocline. Mesopelagic Zone Because of the lack of light, bioluminescence begins to appear on organisms in this zone . The eyes on the fishes are also larger and generally upward directed, most likely to see silhouettes of other animals (for food) against the dim light. Bathypelagic Zone The temperature in the bathypelagic zone, unlike that of the mesopelagic zone, is constant. The temperature never fluctuates far from a chilling 39°F (4°C). The pressure in the bathypelagic zone is extreme and at depths of 4,000 meters (13,100 feet), reaches over 5850 pounds per square inch! Yet, sperm whales can dive down to this level in search of food. Abyssopelagic Zone The name (abyss) comes from a Greek word meaning "no bottom" because they thought the ocean was bottomless. Three-quarters of the area of the deep-ocean floor lies in this zone. Hadalpelagic Zone The temperature is constant, at just above freezing. The weight of all the water over head in the Mariana Trench is over 8 tons per square inch. Even at the very bottom, life exists. In 2005, tiny single-celled organisms called foraminifera, a type of plankton, were discovered in the Challenger Deep trench southwest of Guam in the Pacific Ocean. The deepest a fish have ever been found, Abyssobrotula galatheae, was in the Puerto Rico Trench at 8,372 meters (27,460 feet). |