Answer:
Abyssal plain
Step-by-step explanation:
Between 4000 to 6000 meters below the ocean, the abyssal zone exists which is salty (saltiness between 34.6 to 35 parts per thousand) and cold (temperature between 0 to 4 degree celcius)
Abyssal plain consists of uneven surface of oceanic crust covered by fine grain sediments such as clay and silt. They have major reserve of deep ocean biodiversity.