Subject: What is the coldest ocean water temperature?

A student of mine watched an episode of "The Blue Planet" on Animal Planet that concerned the deep 
ocean. The next day he asked me how the ocean water could be so cold and not freeze. I assumed he 
meant a few degrees below celsius and began talking about freezing point depression. He asserts that the 
program said that the coldest ocean temperatures are -40 degrees Celsius. I cannot find any information 
on the web or in books to support this, but he insists that the program said -40. I think he means -4. How 
cold is the coldest ocean water?

Re: What is the coldest ocean water temperature?