| A rare but important terrain feature found in the abyssal and hadal zones is the hydrothermal vent. |
| This is because abyssal and hadal waters are the reservoir for the salts from decomposed biological materials that settle downward from upper zones, and the lack of sunlight prevents their uptake by photosynthesis. |
| CeDAMar scientists have demonstrated that some abyssal and hadal species have a cosmopolitan distribution. |
| Waters deeper than 6,000 m are treated separately as the hadal realm by ecologists. |
| Another unusual feature found in the abyssal and hadal zones is the cold seep, sometimes called a cold vent. |
| They occur at abyssal and hadal depths, either burrowing or surface-dwelling, and are important elements of the midoceanic rift fauna. |
