Pollutants (substances that cause pollution) enter the ocean through accidents, carelessness, and the deliberate dumping of wastes. The ocean can absorb some types of pollutants in certain quantities because of its great size and the natural chemical processes that occur within it. But people continue to introduce more and more pollutants into the sea. The ocean will not be able to absorb it all. The ocean provides us with many necessities, and it helps keep our environment healthful. It is therefore extremely important that we work to control ocean pollution.
Most oil pollution enters the ocean from oil spills on land or in rivers used to transport petroleum. Oil also seeps into the ocean from cracks in the sea floor as part of a natural process. When tankers running aground spill oil, currently deposit about 37 million gallons of oil into the ocean every year. The largest amount of oil entering the ocean through human activity is the 363 million gallons that come from industrial waste and automobiles. When people pour their used motor oil into the ground or into a septic system, it eventually seeps into the groundwater. Coupled with industrial waste discharged into rivers, oil becomes part of the run-off from waterways that empty into the ocean.
All of this oil affects ocean ecosystems. When an oil spill occurs in the ocean, the oil may spread across miles of open water and up onto beaches, littering them with tar balls. The intertidal zones-coastal areas that are the habitat for fish, birds, and other wildlife-are often the most vulnerable. Animals may perish when the oil slicks their fur or downy feathers, decreasing the surface area so they are no longer insulated from the cold water. Or the animals may ingest the oil, then become sick or unable to reproduce properly.
Scientists and engineers have devised several methods to clean up oil spills. One method involves placing a ring of floating devices around the spill to prevent it from spreading. Pumps or skimming devices then collect the oil, which floats on the surface of the water. Oil may also be recovered by placing sheets or particles of floating, oil-absorbing material on the ocean surface. Burning the oil cleans a spill, but it produces air pollution. Detergents help break up spills, but they may cause additional harm to marine life.
The deliberate dumping of waste products into the sea is another major source of ocean pollution. Such products include industrial wastes and sewage. Industries dump chemicals, animal and plant matter, and other pollutants. Sewage systems carry human wastes, ground-up garbage, and water used for bathing and laundering to the sea. Waste treatment plants remove some of the most poisonous wastes from sewage, but most treated sewage still contains material harmful to the ocean.
Plastics dumped into the ocean form an especially damaging group of pollutants because they do not break down easily. Sea birds, turtles, seals, whales, and other marine animals eat plastic nets, bags, and packing material. Animals that mistake plastic items for food die of starvation if the plastic blocks the digestive system. Tiny plastic pellets also litter the ocean. These pellets tend to float on the ocean surface, where they disrupt the environment of microscopic, surface-dwelling organisms.
By the late 1980's, an estimated 16 billion pounds (6.4 billion kilograms) of plastic was being dumped into the ocean annually. The figure includes plastic trash discarded from ships and fishing vessels. In December 1988, an international treaty banning the dumping of plastics from ships and other vessels went into effect. Russia, the United Kingdom, the United States, and several other countries have ratified the treaty.
The different sources of ocean noise, as ship engines, machinery,acoustic
deterrents (pingers) for aquaculture, aircraft (supersonic planes), personal
watercraft (jet skis, leisure craft) prevent the good communication between
marine mammals. Ambient noise in the oceans has risen 10 decibels between
1950 and 1975. A 900% increase in 25 years.
We humans are continuously increasing the noise we produce in the world's oceans and seas, slowly destroying the ability of marine mammals to communicate, echolocate for food, find their mates, and sing their songs. We could reduce ocean noise by making ships much quieter if their engines were better engineered and maintained, and mounted on vibration-absorbing blocks. Propellers can be designed to be more efficient and quieter. Military vessels, such as submarines where quietness is essential, are virtually silent. Similar considerations could reduce the mechanical noises produced by activities such as oil exploitation and seismic surveys.