Even on the calmest of days the ocean is never still, how and why do these huge bodies of water move?
Waves are familiar to everyone. Most waves are created by wind, as a breeze blows over water, the surface tension breaks and ripples are created, the wind pushes the back of the ripples and eddies form at the front. The particles of water are pushed into a circular movement that reinforces the shape of the wave. Waves may look like a movement of water, but actually they are a movement of energy and have very little forward movement of the water particles themselves. Once a wave makes contact with the seabed, friction slows the bottom of the wave, but the crest continues at the same speed and then spills over and releases its energy onto the shore. The profile of the seabed determines if a wave surges, plunges or spills.
The size of the wave is determined by the fetch or distance, over which the wind is blowing.
The highest wave ever recorded was 34 m. Sea going folk will be familiar with the Beaufort Scale, a standard invented by British admiral Sir Francis Beaufort that shows the relationship between waves, sea conditions and wind velocity.
Tsunamis are giant waves created by earthquakes, volcanic eruptions or mudslides. They are shock-waves that may travel up to 700kph, they are insignificant in deep water but once they reach shore their speed builds enormous waves of great height and energy.
Tides are caused by the gravitational pull of the Moon and the Sun combined with the centrifugal force of the Earth’s rotation. The Moon’s gravitational force pulls the ocean towards it, so the oceans facing the Moon develop a bulge. At the same time at the opposite side of the Earth the centrifugal force pulls water in the opposite direction and forms another bulge of water. These bulges are high tides, and areas which lose water to the bulges experience low tides. Twice every month at new and full moon the sun and moon’s gravitational forces act together and create higher tides (spring tides) and when the moon is waxing or waning the forces are weaker so we experience lower tides (neap tides).
Currents are oceanic rivers created by global wind systems and the Coriolis effect (the effect of Earths rotation, which causes particles in move slightly to the right in the Northern Hemisphere, and slightly to the left in the Southern Hemisphere). There are fast warm water currents moving from tropics to poles eg Gulf Stream and slow cold water currents moving from poles to tropics eg Humbolt current.
Gyres are areas of the ocean where the spiralling movement of the ocean creates a centre higher than the surrounding oceans. They tended to be areas of flotsam and jetsam, but now they have become gigantic floating garbage patches. Gyres that may be twice the size of Great Britain are simply jammed with floating bottles, plastics, TVs, cigarette lighters, disposable products, containers and a huge accumulation of plastic rubbish that wreak havoc on wildlife.
It is now estimated that there are approximately 13,000 pieces of plastic litter on every square km of the ocean’s surface, this is in addition to the 70% of plastics that sink to the bottom of the ocean where the pollution is unseen. Millions of seabirds, marine mammals and other ocean wildlife are killed by plastic annually. Biodegradable plastic is not the answer because although it breaks down into smaller pieces under UV light, it still remains plastic and still poses a threat to wildlife and the environment. 80% of litter in the oceans is washed in from land, so do please do your bit to protect the oceans, don’t litter and remember the three Rs – reduce, re-use and recycle.