The temperature of ocean water also varies with depth. In the ocean, solar energy is reflected in the upper surface or rapidly absorbed with depth, meaning that the deeper into the ocean you descend, the less sunlight there is. This results in less warming of the water. Ocean temperatures don't cool at night, nor do they warm during the day. When the sun goes down, air temperatures cool. When the sun rises, air temperatures warm. Pacific Ocean temperatures lag about three months behind the hottest or most direct sun's energy. Water gets colder with depth because cold, salty ocean water sinks to the bottom of the ocean basins below the less dense warmer water near the surface.

Ocean temperatures don't cool at night, nor do they warm during the day. When the sun goes down, air temperatures cool. When the sun rises, air temperatures warm. Pacific Ocean temperatures lag about three months behind the hottest or most direct sun's energy. The heat that the ocean absorbs is mixed with the lower water quickly. That mixing spreads the heat around. At night, while the land cools off quickly, the water at the surface is kept warmer because the water is mixed around with the warmer water underneath. Water gets colder with depth because cold, salty ocean water sinks to the bottom of the ocean basins below the less dense warmer water near the surface. The temperature of ocean water also varies with depth. In the ocean, solar energy is reflected in the upper surface or rapidly absorbed with depth, meaning that the deeper into the ocean you descend, the less sunlight there is. This results in less warming of the water.The temperature never fluctuates far from a chilling 39°F (4°C). The pressure in the bathypelagic zone is extreme and at depths of 13,100 feet (4,000 meters), reaches over 5850 pounds per square inch. The correct answer is 20°C. The temperature difference between upper layers and deeper layers of the ocean for setting up an OTEC power plant should be 20°C. Since ocean thermal energy is generated due to a difference in temperatures, for an OTEC plant to be installed, a temperature difference of 20oC is required. The temperature can be colder than the freezing temperature of fresh water (0˚C) because the dissolved salts in seawater lower the freezing point. The lowest ocean surface temperatures are found near the North Pole and near Antarctica. Inland areas usually have greater temperature extremes from day to night and from season to season because land absorbs and loses heat energy more quickly than water. Locations near the ocean or other large bodies of water usually have more moderate daily and seasonal temperatures. Water heats and cools more slowly than landmasses. Therefore, the coastal regions will stay cooler in summer and warmer in winter, thus creating a more moderate climate with a narrower temperature range. Temperatures in the oceans decrease with increasing depth. There are no seasonal changes at the greater depths. The temperature range extends from 30 °C (86 °F) at the sea surface to −1 °C (30.2 °F) at the seabed. Water gets colder with depth because cold, salty ocean water sinks to the bottom of the ocean basins below the less dense warmer water near the surface. It may be pointed out that maximum temperature of the oceans is always at their surface because it directly receives the insolation and the heat is transmitted to the lower sections of the oceans through the mechanism of conduction. Global mean sea surface temperature (SST) has increased since the pre-industrial era. The increase in SST has not been uniform in time or space, but there has been an average global increase of around 0.6°C over the last four decades.

The heat that the ocean absorbs is mixed with the lower water quickly. That mixing spreads the heat around. At night, while the land cools off quickly, the water at the surface is kept warmer because the water is mixed around with the warmer water underneath.The best time is when the tide has been low in the morning, and the incoming afternoon tide flows over the hot sands. If the timing is right, early evening with the tide now high and the sun setting over calm warm waters is hard to beat. Changes in sea surface temperature vary regionally. While most parts of the world's oceans have seen temperature rise, a few areas have actually experienced cooling for example, parts of the North Atlantic. Ocean temperature also doesn't vary much over a 24 hour period, less than 1 degree. So for those yet to experience a night-swim, because actual air temperature can drop, but the sea stays the same, the water may feel warmer at night. The temperature of ocean water varies by location both in terms of latitude and depth, due to variations in solar radiation and the physical properties of water. Since water has a high capacity to hold on to hea once heated it stays hot for a time, seasonal changes in ocean temperatures lag about 2 months behind land temperatures. So in temperate climates, the ocean is much warmer for swimming in the fall than in the spring. At night the sea is warmer than land since the heat capacity of water is higher than soil, which means the air above the sea is warmer and the air above land is cool. Water gets colder with depth because cold, salty ocean water sinks to the bottom of the ocean basins below the less dense warmer water near the surface. Temperatures in the oceans decrease with increasing depth. There are no seasonal changes at the greater depths. The temperature range extends from 30 °C (86 °F) at the sea surface to −1 °C (30.2 °F) at the seabed. The amount of sunlight that hits the temperate regions varies between summer and winter. The variation in solar energy absorbed means that the ocean surface can vary in temperature from a warm 30°C in the tropics to a very cold -2°C near the poles. Temperatures of 120 degrees Celsius (248 degrees Fahrenheit) are normally encountered at about 4,000 meters below the seafloor.