Question

This is a physical chemistry question.

Due to the ocean's depth, the layer of water at the surface of the ocean is warmer than the water at the bottom. Heating of the upper layer of water occurs due to the absorption of solar radiation. If we could use the Earth as a heat engine, how much work could be done in 1 year? State all assumptions and data used for your determination.

Answer 1

Ocean temperature (both vertical and horizontal) varies at places and it may due to many factor like season change. In general, ocean temperature depends on amount of the solar radiation (sun energy) absorbed. Another important factor may be the location of ocean. Like, tropical oceans receive a lot of direct overhead sunlight for a longer time of year. Hence, the water is warm. In polar regions, summer is the time to receive sunlight, and even then, it is never directly overhead, so water in these places tends to be cold. The amount of sunlight that hits the temperate regions (between the tropics and the poles) 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.

Water warms up more slowly than air but can hold more heat – water needs 4 times as much energy to raise its temperature by 1ºC as the same mass of air does. So the ocean plays an important part in taking up energy from the Sun and stopping the Earth getting too hot.

It also varies from top to bottom, giving a vertical structure to most of the ocean. There is an upper layer of water, up to 200m deep, that is warmed by the Sun and has the same temperature from top to bottom. Below that is a layer called the thermocline, reaching down in places to 1000m, which is colder at the bottom than at the top. The deep ocean below the thermocline, making up 80% of the ocean, is the same very cold temperature throughout.

Water expands when it warms up and heat energy makes its molecules move around more and take up more space. Because the molecules are more spread out, the density goes down. When water cools, it contracts and becomes denser.

Temperature and salinity both affect the density of water, resulting in water moving up or down through the ocean layers and moving as currents around the ocean.

If earth could be used as an engine, to a very great extend the ocean floor temperature can exceed.