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The Effect of Oil Spills on Oceans

Published on Sep 05, 2023


Ocean water is made up of 96.5% water (H20, an oxide of hydrogen) and 3.5% solids. The main chemical ingredient in these solids is salt (sodium chloride, NaCl), a simple chemical compound found in the tissue of all living organisms. Other chemicals include Magnesium, Sulfate, Calcium, Potassium, Carbon, Bromine, Boron, Strontium, Fluorine and ions of Nitrogen. Since most scientists agree that life began in the sea, it is not surprising that a number of these chemicals (Magnesium, Sulfate, Calcium, Potassium, Carbon and the Nitrogen ions) are essential to life.

Physical Properties

Density: One of the most important physical properties of ocean water is its weight, or density. Which depends on two things – temperature and salinity.

The density of ocean water ranges from 1.026 to l.028 grams per centimetre.

High-salinity seawater is denser than low-salinity seawater. Cold seawater is denser than warm seawater.


Salinity is the amount of salt that’s dissolved in an ocean's water – and it's different in different places.

The salinity of ocean water varies between 3.0 and 3.7 percent, so it averages out at about 3.5%.


The temperature of ocean water is highest at the Equator (where it is warmed by the Sun) and coldest toward the poles.

There are three temperature zones in the oceans.

• The Surface Zone (which begins at the Earth's surface and goes down to about 400 meters) is 22 degrees Celsius on average.

• The Thermo cline (begins at about 400 meters and extends down to about 800 meters). Temperatures drop rapidly from warm surface conditions to frigid deep-water conditions.

• The Deep Zone (which starts at about 800 meters and extends down to the ocean floor). Temperatures hover just above the freezing point of water (0-4 degrees Celsius).

Petroleum (crude oil) properties

Chemical Properties

Petroleum is a complex mixture of paraffinic, naphthenic and aromatic hydrocarbons ranging in carbon number from C1 to >C60. Petroleum typically also contains smaller amounts of heteroatom compounds, metals and hydrogen sulfide.

Among these compounds, cyclic (aromatic) hydrocarbons that low boiling point are more dangerous, such as benzene, toluene and xylene. Naphthalene and Phenanthrene are more poisonous for fishes than the mentioned compounds. Aromatic compounds are more soluble in water than saturated hydrocarbons; therefore creatures may become poisoned without direct contact with the oil by the polluted water. Fortunately these compounds are volatile; their harmful effects will decrease with time.

Physical Properties

Petroleum is not a uniform substance since its physical properties vary from oilfield to oilfield and can even vary within wells at the same oilfield. At one extreme, it is a light, mobile, straw-colored liquid. At the other extreme, it is a highly viscous, semi-solid, black substance. The lower molecular weight components of petroleum possess moderate to high water solubility while higher molecular weight fractions tend to form emulsions in water.

Oil Spill Behavior

When oil is spilled in the ocean, it initially spreads in the water, depending on its relative density and composition. The oil slick formed may remain cohesive, or may break up in the case of rough seas. Waves, water currents, and wind force the oil slick to drift over large areas, impacting the open ocean, coastal areas, and marine and terrestrial habitats in the path of the drift.

Oil that contains volatile organic compounds partially evaporates, becoming denser and more viscous. A small percentage of oil may dissolve in the water. The oil residue also can disperse almost invisibly in the water or form a thick mousse with the water. Part of the oil waste may sink with suspended particulate matter, and the remainder eventually congeals into sticky tar balls. Over time, oil waste weathers and disintegrates by means of photolysis

Effects of Oil Spills on Marine Ecosystems

Environmental Effects

The impacts of oil pollution on marine ecosystem can be categorized into long term and short term effects. Suffocation cause by oil spills and oil poisoning are among the first group. Because oil floats on top of water, less light penetrates into the water, limiting the photosynthesis of marine plants and phytoplankton. Oil spills reduce oxygen absorption of the water, causing oxygen dissolution under oil spills to be even less than the deep sea levels.

Suspended oil can gain weight by bonding with minerals and settle on the sea floor and harm the ecosystem. Also causes sediments adherence to the sea floor, destabilizing plants. Usually it has been observed that sediments begin to move after oil settles on the sea floor.

Oil Spills Kill Birds

Oil-covered birds are practically a universal symbol of the environmental damage wreaked by oil spills. Any oil spill in the ocean is a death sentence for sea birds. Some species of shore birds may escape by relocating if they sense the danger in time, but sea birds that swim and dive for their food are sure to be covered in oil. Oil spills also damage nesting grounds, which can have serious long-term effects on entire species. They can even disrupt migratory patterns by contaminating areas where migrating birds normally stop.

By coating the feathers, oil not only makes it impossible for birds to fly but also destroys their natural waterproofing and insulation, leaving them vulnerable to hypothermia or overheating. As the birds frantically try to preen their feathers to restore their natural protections they often swallow some of the oil, which can severely damage their internal organs and lead to death.

Oil Spills Kill Marine Mammals

Oil spills frequently kill marine mammals such as whales, dolphins, seals and sea otters. The deadly damage can take several forms. The oil sometimes clogs the blowholes of whales and dolphins, making it impossible for the animals to breathe properly and disrupting their ability to communicate. Oil coats the fur of otters and seals, leaving them vulnerable to hypothermia.

Even when marine mammals escape the immediate effects, an oil spill can cause damage by contaminating their food supply.

Oil Spills Kill Fish

Oil spills often take a deadly toll on fish, shellfish and other marine life, particularly if large numbers of fish eggs or larvae are exposed to the oil.

Oil Spills Destroy Wildlife Habitat and Breeding Grounds

The long-term damage to various species, and to the habitat and nesting or breeding grounds those species depend upon for their survival, is one of the most far-reaching environmental effects caused by oil spills.

The severity of environmental damages caused by a particular oil spill depends on many factors, including the amount of the oil spilled, the type and weight of the oil, the location of the spill, the species of wildlife in the area, the timing or breeding cycles and seasonal migrations, and even the weather at sea during and immediately after the oil spill. But one thing never varies: oil spills are always bad news for the environment.

Oil Compound’s Effect on Animals

It's been proven that oil compounds will harm marine organisms even in low concentrations. Organisms accumulate oil compounds in their body through water, sediments and their food.

Oil compounds increase disease sensitivity in fishes and prevent growth of the phytoplankton. It's been estimated in oil spilled areas; about 70 years are required for marine life to completely restore. Decomposition of oil materials is done by bacteria but it's slow, especially in cold waters.

Experience has shown that in these assisted conditions animals restoration process will begin in a few months, but in natural process it takes one or two years. It has been observed that oil materials in sediments and cavities of sea floor will persist for 15 or more years.

The Dangers of Arctic Oil Drilling

The Arctic's extreme weather and freezing temperatures, its remote location and the presence of moving sea ice severely increase the risks of oil drilling, complicate logistics and present unparalleled difficulties for any clean-up operation. Its fragile ecosystem is particularly vulnerable to an oil spill and the consequences of an accident would have a profound effect on the environment and local fisheries.

The Arctic is home to four million people. It also houses a diverse range of unique wildlife: hundreds of species of seabirds, millions of migrating birds; 17 different species of whale live there. Mammals including Polar Bears, Arctic Foxes and various species of seal inhabit the Arctic at different points throughout the year. The impact of a spill on these communities and already vulnerable animal species would be devastating and long-lasting.

The US Geological Survey estimates that around 13% of the world's undiscovered oil could lie under the area north of the Arctic Circle Due to climate change, the Arctic sea ice is melting at an alarming rate each summer, allowing creeping industrialisation as companies and governments scramble for the region’s natural resources.

However, drilling in the Arctic presents, as even Cairn Energy admits, "significant challenges". Alongside the logistical nightmare of operating in such a hostile and remote region, oil rigs face an ever-present risk from huge icebergs and have to employ fleets of ships to drag them out of the way. Some of the icebergs are so big, though, that oil rigs are forced to stop drilling and move out of their way.

The Arctic drilling season is limited to a narrow window of a few months during the summer. In this short period of time, complete the huge logistical response needed to cap a leaking well would be almost impossible. If relief wells are left unfinished over the winter, oil could continue to gush out for up to two years. Yet despite these incredible risks oil companies continue to recklessly lobby governments to relax Arctic drilling safety rules.

In the Arctic´s freezing conditions, oil is known to behave very differently than in lower latitudes. It takes much longer to disperse in cold water and experts suggest that there is no way to contain or clean-up oil trapped underneath large bodies of ice. Toxic traces would linger for a longer period, affecting local wildlife for longer, be transported large distances by ice floes and leave a lasting stain on this pristine environment.

The oil industry cannot guarantee the safety of Arctic drilling and is recklessly putting profit before the environment. As Cairn's recent operations prove, the immense technical, economic and environmental risks of drilling in the Arctic just aren't worth it.