The Earth’s oceans house an enormous amount of energy—from waves, currents, deposits of petroleum under the seabed and more. In the US, more than one-fourth of the oil and gas produced each year comes from offshore sources.
Underwater petroleum and natural gas deposits were created millions of years ago when tiny sea plants and animals died and were turned into hydrocarbons (the stuff oil and gas are for the most part made of) by intense pressure and heat. These hydrocarbons seeped into empty spaces in the surrounding rocks, forming what are basically oil-soaked sponges. The oil is trapped inside by a layer of rock, salt or clay. Offshore drilling, which was first attempted in California in 1897, involves digging deep into wells in the seabed from rigs or platforms. Floating platforms or drillships are used to drill in deeper water, sometimes going 10,000 feet/3,048 meters under the water.
Nature also creates oil and gas seeps—oil that is naturally released from the sea floor and rises to the ocean surface. The largest seeps are off the coast of California. The natural gas evaporates at the surface, but the oil congeals there and turns into sticky tar that is carried by ocean currents to nearby beaches. These seeps have been occurring for thousands of years and were first noted in 1542 by explorer Juan Rodriguez Cabrillo, who saw oil floating on the waves. Early peoples living in the area, including the Native American Chumash tribe, used the tar for waterproofing boats and bottles, repairing bowls, making pipes and more. More than 1,200 natural seeps have been discovered near Santa Barbara, Calif., and the equivalent of between 130 and 150 barrels of oil seep to the surface every day.
The ocean floor also contains a huge reserve of energy-rich methane gas. Methane gas is usually the product of organic decay, including the decay of sea animal and plant remains. Under the pressure and in the cold temperatures of the ocean floor, the methane gas dissolves. The methane gas molecules are then encased with water molecules and bond together in crystal-like structures. In some places, a solid block of crystals—called methane hydrate—extends hundreds of meters under the sea floor. Scientists think an enormous amount of energy could be found in these crystals and in a huge deposit of methane gas trapped under the hydrate level. The problem is getting to this methane safely and economically—it’s very deep underwater and freeing the methane has the potential to cause negative environmental effects.
Solar energy is also important to discuss in relation to energy from the ocean, as most of the ocean’s energy comes from the sun. Ocean currents, winds and waves are all created by the sun’s radiant energy, and that solar power can also be used to create electricity. Some solar power systems have been created to generate power for navigation, radio communication and research at sea. The water close to the surface of the ocean, which the sun heats to a higher temperature than deep water, can also be used to create electricity through a process called ocean thermal energy conversion (OTEC). Though OTEC has great potentially, it is not currently a very energy-efficient or economical option.
Energy created by wind, waves and the tides are capable of creating electricity, too. Wind turbines can be installed on offshore drilling platforms that generate enough power to operate the equipment used for drilling. Waves can be used to spin turbines to create electricity, especially if they are forced into a narrow channel that increases their power and size. Tidal power can be used to generate electricity through a small dam called a tidal barrage that harnesses the outgoing tide to spin turbines. Tidal fences (a system of vertical-axis turbines through which water flows) and tidal turbines (essentially wind turbines with the blades being powered by water instead of wind) can also be used to generate electricity.