Temperature of Ocean Water

The Sun hits the surface layer of the ocean, heating the water up. Wind and waves mix this layer up from top to bottom, so the heat gets mixed downward too. The temperature of the surface waters varies mainly with latitude. The polar seas (high latitude) can be as cold as -2 degrees Celsius (28.4 degrees Fahrenheit) while the Persian Gulf (low latitude) can be as warm as 36 degrees Celsius (96.8 degrees Fahrenheit). Ocean water, with an average salinity of 35 psu, freezes at -1.94 degrees Celsius (28.5 degrees Fahrenheit). That means at high latitudes sea ice can form. The average temperature of the ocean surface waters is about 17 degrees Celsius (62.6 degrees Fahrenheit).

90 % of the total volume of ocean is found below the thermocline in the deep ocean. The deep ocean is not well mixed. The deep ocean is made up of horizontal layers of equal density. Much of this deep ocean water is between 0-3 degrees Celsius (32-37.5 degrees Fahrenheit)! It's really, really cold down there!

There is a neat program that is measuring the temperature and salinity of ocean surface waters around the world. The Argo program is deploying floats that measure salinity and temperature throughout the surface layer of the ocean. 3,000 floats will be deployed all over the ocean by 2003. Each float is programmed to sink 2,000 meters down, drifting at that depth for about 10 days. The float then makes its way to the surface measuring temperature and salinity the whole time. Data is sent to a satellite once the float reaches the surface, so that scientists have access to near real-time ocean data. Each float will last 4-5 years. At a greater depth, temperature and salinity measurements are often made with a CTD instrument, where the instrument is placed in the ocean water from a ship or a platform.