| A | B |
|---|
| SONAR | A system that determines the distance of an object under water by recording echoes of sound waves; gets its name from Sound Navigation and Ranging. |
| CONTINENTAL SHELF | A gently sloping, shallow area of the ocean floor that extends outward from the edge of the continent. |
| CONTINENTAL SLOPE | An incline leading down from the edge of the continental shelf. |
| SEAMOUNT | A mountain on the ocean floor that is completely underwater. |
| ABYSSAL PLAIN | A smooth, nearly flat region of the deep ocean floor. |
| MID-OCEAN RIDGE | The undersea mountain chain where new ocean floor is produced; a divergent plate boundary. |
| TRENCH | A deep canyon on the ocean floor. |
| PLANKTON | Tiny algae and animals that float in water and are carried by waves and currents. |
| NEKTON | Free-swimming animals that can move throughout the water column. |
| BENTHOS | Organisms that live on the bottom of the ocean or another body of water. |
| FOOD WEB | The pattern of overlapping food chains in a habitat or ecosystem. |
| INTERTIDAL ZONE | The area that stretches from the highest high-tide line on land out to the point on the continental shelf exposed by the lowest low tide. |
| ESTUARY | A coastal inlet or bay where fresh water mixes with salty ocean water. |
| BRACKISH | Water that is partly salty and partly fresh, characteristic of estuaries. |
| SUNLIGHT ZONE | The zone in which photosynthesis occurs. 90% of all marine life lives here. |
| OPEN-OCEAN ZONE | The area of the ocean beyond the edge of the continental shelf. |
| TWILIGHT ZONE | Only a small amount of light is here, not enough for photosynthesis. |
| MIDNIGHT ZONE | It is entirely dark here. The water pressure is extreme, and the temperature is near freezing. |
| BIOLUMINESCENCE | The production of light by living things. |
| HYDROTHERMAL VENT | An area where ocean water sinks through cracks in the ocean floor, is heated by the underlying magma, and rises again through the cracks. |
