Explanation:

1. Ocean layers is roughly divided into 3 layers, warm, cool and cold. The third layer is very cold and extends upto deep ocean floor. Antarctic and Arctic latitudes, there is only one layer of cold water. Freezing point varies with salinity. Fresh water freezes at 0ºC whereas saline water freezes ~>2ºC. Sea ice formation removes freshwater from ocean, leaving behind more saline solution. Greater the salinity, greater the freezing point. Major source of temperature of oceanic water is the sun. 

2. The highest temperature is not recorded exactly at the equator, but a little north of it.

3. Below the thermocline, there is a rapid decrease in temperature with increase in depth.