Why does temperature decrease with depth underwater?

[youngdylz]

Seems like an easy question yet I can't find an answer. Obviously the surface layer of the ocean gets more sunlight but I don't think that is the reason deep water is colder. The increase in pressure usually increases the temperature but this seems to be the exception. Thanks for taking the time to answer

 

[Bystander]

How does density depend upon temperature?

 

[youngdylz]

How does density depend upon temperature?

aha seems I was looking in all the wrong places. Thank you

 

[Vanadium 50]

Before asking why something is true, you should first ask if it is true. Your statement is true in the tropics. Is it true at the poles?