How cold is it in the deep zone of the ocean generally? ____C

I was reading my book book but it doesn't give me what I'm looking for. My answer would be 2 degrees Celsius. If you find information on this could you please provide a link or resource.

Thank you.

Deep ocean water has a very low temperature, with a high of 1.6 °C

(not 4 degrees, because sea water is salty)

Its 4 degrees centigrade.This is because of the anomalous behaviour of water.Water is unusual as when it cools from say 10 degrees centigrade it contracts , and becomes more dense , this contraction with temperature continues until the water reaches four degrees centigrade and at this temperature water is at its most dense.Any further cooling of the water actually makes the water expand and so it becomes less dense.
So when water reaches four degrees centigrade it is at its most dense and so will sink , any water either warmer or colder will float so the surface temperature of water can vary but the water below quite a shallow depth will always be four degrees centigrade.
This is a vital fact that allows water not to freeze and allows marine life to survive winters , without this life as we know it would not exist !!.