Oceans, Seas, and Glaciers: Earth’s Water Systems
Oceans and Seas
Oceans are large bodies of water separating the continents. Planet Earth has five oceans; the largest is the Pacific, with its 180 million km2, larger in extent than all the continents combined. The other four are the Atlantic, Indian, Southern, and Arctic. Within the oceans, seas are areas near the coast, almost always located on the continental shelf.
Seafloor Relief
The average depth of the oceans is about four or five kilometers. This depth varies depending on the area:
- Continental Platform: This is the continuation of the continents under water, with depths ranging from 0 m on the coastline to about 200 m. It occupies about 10% of the ocean area and is an area of exploitation of oil resources, fisheries, among others.
- Slope: The area of steep slopes leading from the edge of the platform to the seabed. Creases appear, from time to time, submarine canyons carved by sediment that slide in large turbidity currents that fall from the platform to the seafloor.
- Seafloor: With a depth of between 2000 and 6000 meters, it occupies about 80% of the ocean area.
- Mid-Ocean Ridges: These are elongated seafloor surveys that run over more than 60,000 km. They have abundant volcanic and seismic activity because they correspond to areas of plate formation where the lithosphere is expanding the ocean floor.
- Abyssal Trenches: These are long, narrow areas where the seafloor drops to more than 10,000 m deep in places. They are particularly common at the edges of the Pacific Ocean. They have high volcanic and seismic activity because they correspond to areas where plates are subducted into the mantle.
Temperature
Oceans have a surface layer of warm water (12º to 30ºC), which reaches a varying depth up to about 400-500 meters. Below this layer, the water is cold with temperatures between 5º and -1ºC. The thermocline is the boundary between the two layers. The Mediterranean is an exception to this distribution because its deep water temperatures are around 13ºC. This is because the Mediterranean is almost isolated, contacting the Atlantic only by the Straits of Gibraltar, and this is just heating up around the water body. Also, the water is warmer in the equatorial and tropical zones and cooler near the poles and temperate zones.
Ocean Currents
The waters of the ocean’s surface are driven by prevailing winds, giving rise to surface currents. The rotation of the Earth to the east also influences the ocean currents; it tends to hold water against the coast west of the oceans. This effect may be represented by a bowl of water moving in one direction and noting that the water is somewhat delayed in the movement and stands up against the back wall of the container. This explains, according to some theories, why the strongest currents, such as the Gulf Stream in the Atlantic and the Kuroshio in the Pacific, are located in these zones.
This same effect of the Earth’s rotation explains the upwelling areas that are in the Eastern Pacific and Atlantic where cold, deep water flows towards the surface. This phenomenon is very important from an economic standpoint because the rising water carries nutrients to the surface, and in these areas, fishing is rampant. Fisheries in Peru, Gran Sol (Southern Ireland), or the African Atlantic were formed in this way.
In the oceans, there are also deep or thermohaline currents in the body of water located below the thermocline. In these, the water moves through density differences. The cooler or more saline water is denser and tends to sink, while the somewhat warmer or less saline water tends to rise. This creates vertical currents connected by horizontal movements to replace the water moved. In some areas, deep currents coincide with the surface, while others are on the counter. Ocean currents move large amounts of heat from equatorial to polar regions. United atmospheric currents are responsible for the temperature differences on Earth not being as strong as those they would on a planet with no atmosphere or hydrosphere. So, their influence on climate is remarkable.
Waves and Tides
Waves
Waves are formed by winds that sweep the surface of the water. They move water in a cylinder, without moving forward, but when they reach the coast and the cylinder touches the bottom, it starts rolling, just unbalancing the body of water, resulting in a breaking wave. Earthquakes on the seafloor sometimes cause huge waves called tsunamis.
Tides
Tides have a major influence on coastal organisms that have to adapt to very abrupt changes across the intertidal zone. These organisms must endure a few hours covered by seawater and whipped by the waves, followed by other hours without water or even in contact with fresh water if it rains. In addition, some coasts, due to their shape, have strong tidal currents when the waters rise and fall, which carry sand and sediment and remove the substrates in which living things live.
In the nearby coast, coastal currents often occur, varying according to the shape of the coast and the depths of the seabed. They have much interest in the formation of beaches, estuaries, and other coastal modeling forms. The energy released by continuous shock waves to the coast, tides, and currents is very important because they erode and transport coastal materials until they are sedimented in the most protected areas. They play a role in the formation of different types of coastal ecosystems: wetlands, beaches, shallow tidal flats, and dunes, among others. They also significantly affect the rivers leading to the location and nature of the rocks that form the coast.
Glaciers
Glaciers are large masses of ice that form when snow accumulates year after year without melting. Under pressure, the snow loses air, and milky ice is formed first, and then blue ice, clear as crystal. For glaciers to exist in an area, two conditions are required:
- Average temperatures must be low enough to allow snow to accumulate from one year to another. This occurs in equatorial areas from 5,000 m and in Antarctica to sea level. In the Iberian Peninsula, these conditions are only found in the Pyrenees, located more than 3,000 m above sea level.
- There must be enough rainfall. For example, there are places in northern Siberia that are very cold, but it rains so little that the snow cover rarely exceeds one meter high.
Periglacial Areas
Periglacial areas are the large areas surrounding the ice caps or that lie immediately beneath the areas of perpetual snow in the mountains. Its soil is permanently covered by ice but is frozen most of the year. This ground is called permafrost and is permanently frozen from a small depth. When spring thaws the outer layer, large pools form in which mosquitoes breed.
Water Pollution
Rivers, lakes, and seas collect the waste produced by human activity. While the natural water cycle has a great capacity for purification, the regenerative capacity of water is decreasing due to the amount of pesticides, chemical wastes, heavy metals, and radioactive waste, among others. The residues of these wastes can be found in varying amounts when analyzing the waters of the most remote corners of the world. Many waters are polluted to the point of making them dangerous for human health and harmful to life. With industrialization and economic development, the problem of pollution affects both developed and developing countries. Everyone has a share of responsibility for this problem; therefore, it is important to reflect and put into action ideas to improve environmental quality.