The Persian Gulf contains the warmest sea water in the world at 35 degrees Celsius. The Red Sea follows with a temperature of 32 degrees Celsius.
Sea water absorbs radiation from the sun. The Persian Gulf and the Red Sea are both near the equator and are thus exposed to more intense sun than other bodies of water.
Ocean temperatures are increasing due to global warming. After a 14-year stay in temperature, in 2014 the average ocean temperature increased 0.57 degrees Celsius higher than the previous yearly average.. This increase, originating in the North Pacific, broke 20th-century seawater temperature records.