The water temperature at the bottom of the Mariana Trench is cold but not as cold as you might think it would be.
The temperature of the water at the bottom of the Mariana Trench ranges from 34 to 39 degrees F or 1 to 4 degrees C.
The thermocline also varies in thickness from about 1,000 feet to 3,000 feet and below that point water will cool off more slowly.