The ocean covers approximately 71 percent of the world’s surface and holds 97 percent of all water on the planet. Technically, there is just one continuous world ocean that wraps around the globe, but this is generally broken up into five separate oceans – the Arctic, Atlantic, Indian, Pacific, and Southern oceans – which also include various seas, gulfs, and bays. The ocean plays a crucial role in regulating the world’s climate, however human activity is accelerating global warming with disastrous consequences for life both above and below the water’s surface. It is often claimed that we know more about space than about the oceans, and while this is very unlikely to be true, it does allude to the fact that there is still much to be learned - further exploration may unlock new information about out our oceans and how they work, and could be the key to tackling some of the greatest challenges facing humanity today.
The oceans and marine life
The largest ocean, by far, is the Pacific, which makes up roughly one third of the world’s surface and contains almost half of all water on the planet. The Atlantic and Pacific oceans are often divided into North and South, although the South Pacific alone is almost as large as the entire Atlantic. The Pacific is also surrounded by the Ring of Fire, named so as it contains around two-thirds (up to 1,000) of the world’s volcanoes, and roughly 90 percent of the world’s earthquakes take place along this belt. The deepest naturally occurring point in the world’s surface, Challenger Deep, can be found at the edge of the Pacific tectonic plate, almost 11 kilometers (6.8 miles) below sea level in the Mariana Trench.
99 percent of the earth’s biomass is found on land, in the form of plants - fauna does not thrive underwater in the same way as sunlight generally cannot penetrate deep enough for photosynthesis to occur. In terms of wildlife, 80 percent of species live on land, while 15 percent live in the ocean, and five percent in freshwater. Yet, when we look at animal biomass alone, over three-quarters is found underwater – however, this is skewed by the fact that the vast majority of underwater life is made up by plankton. These often-microscopic organisms also play a crucial role in sustaining life on the planet, and phytoplankton (plants) live near the water’s surface and use photosynthesis to produce around half of the oxygen in our atmosphere (the other half is produced by flora on land).
Most statistics relating to marine life are estimates, as extreme pressure and virtual absence of light, along with technological limitations, meant that deep sea (1.8km below sea level) exploration was impossible for most of human history. Water pressure rises by approximately one bar every 10 meters of depth, and reaches more than 16,000 PSI (1.1 tons per cm²) at the deepest point. For these reasons, it was assumed that the deep ocean was largely devoid of life, but scientists now believe that may not be the case, and that the deep ocean may be home to an array of wildlife that obtains sustenance from organic matter that falls from the surface.
Currents and the Global Conveyor Belt
Surface currents are largely driven by wind, through the Coriolis Effect. This where air with low pressure is pushed away from the equator, while air with high pressure is pushed away from the poles - then, because of the earth’s rotation, winds move in a circular pattern, spinning clockwise in the northern hemisphere and anticlockwise in the southern hemisphere. These winds drive the world’s five oceanic gyres, which are large currents that carry water around the parameters of the Indian Ocean, and the Atlantic and Pacific oceans on either side of the equator.
In contrast, deep sea currents are largely caused by thermohaline circulation, which is the balance between waters of differing temperatures (thermo) and salinity (haline). Cold water is denser than warm water, and density also increases with salinity – this means that cold and salty water is much heavier, and gravity causes it to sink below warmer waters. Deep sea currents carry around 90 percent of global water, but do not exist independently from the surface, and these currents combine to form a network that stretches around the world and forms the Global Conveyor Belt.
Temperature regulation and global warming
This conveyor system plays a key role in determining regional and seasonal climates - a notable example is the North Atlantic Drift, which brings warm water from the Gulf of Mexico across the North Atlantic to Europe - this is credited as a major reason why European winters are much milder than other regions on similar latitudes. For example, Lisbon and New York are similar distances from the equator and are both on the coast, but average January temperatures are -1°C in New York, while Lisbon’s are around 11.5°C.
The acceleration of climate change, caused by greenhouse gases released form human activity, is most impactful in the atmosphere - yet it affects all layers of the earth’s surface. Polar waters tend to have high salinity, as salt is expelled from water as it freezes, and this is a crucial part of the global conveyor belt – as atmospheric temperatures rise and the ice caps melt at unprecedented rates, they release larger amounts of fresh water into these areas of the ocean, which is gradually offsetting the traditional thermohaline balance. The repercussions of this are that the conveyor system may slow, or even come to a halt, and the climates and weather systems on which life on earth depends upon may disappear or change. Scientific consensus on exact details or timeframes remain unclear, yet most climate scientists believe that if global warming continues at its current level, then its effects on the ocean and currents will have disastrous consequences for life on earth.
Additionally, many of the least developed countries (who bear the least responsibility for historical carbon emissions) are the most at-risk to oceanic changes - rising sea levels threaten the very existence of many small island nations, and, globally, 10 percent of the population live in coastal areas within 10 meters of sea level. Sea levels do not only rise due to the melting of ice caps, but also as rising temperatures are causing ocean waters to expand on such a large scale.
Along with their role in regulating the natural world, oceans have also helped to shape humanity’s development, by providing access to food, travel, trade, and tourism. Today, roughly 37 percent of the world live in coastal communities, and these are often nutritionally or economically dependent on the seas. Sea food is the largest source of animal protein in the world, and makes up over 50 percent of protein intake in some of the least developed nations – however, industrial fishing practices have resulted in overfishing, which threatens the long-term sustainability of fish as a food source in some regions. The primary human use for the oceans today is shipping – around 90 percent of all international trade is conducted via sea.
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