World of Earth Science | Oceans and Seas

Oceans are large bodies of saltwater connected together, unevenly covering 70% of the earth, and containing about 97% of Earth's water supply as salt water. The five major oceans, in descending order of size by area, are the Pacific Ocean (64 million square miles, about 165 million square kilometers), Atlantic Ocean (33 million square miles, about 85 million square kilometers), Indian Ocean (28 million square miles, about 70 million square kilometers), Southern Ocean (almost 8 million square miles, about 20 million square kilometers), and Arctic Ocean (5,000,000 square miles, almost 13 million square kilometers).

The Pacific Ocean is the largest ocean, covering about one third of the earth's surface, which is a bigger area than all of the continents combined. The Pacific Ocean is not only the home of the highest mountain on Earth (Mauna Kea, 33,476 ft, or 10,203 m), but also has the deepest trench (Mariana trench, 36,198 ft, or 11,033 m deep). The Atlantic Ocean is the second largest, covering 20% of Earth's surface. It is also the youngest among the five oceans, and it is the ocean where the most shipping occurs. The third largest ocean is the Indian Ocean, which provides an important trade route between Africa and Asia, and is home to the most expressed monsoon system. The next in size is the Southern Ocean, which surrounds Antarctica, and was officially named in the year 2000 by the International Hydrographic Organization. Finally, the Arctic Ocean is the smallest ocean of all five, but contains the widest continental shelf.

Seas are the smaller bodies of salt water connecting the oceans, which can be partially or entirely enclosed by land. Examples of seas adjacent to the oceans include the South China Sea (the largest sea), Caribbean Sea, Mediterranean Sea, Bering Sea, Gulf of Mexico, Hudson Bay, Gulf of California, Sea of Japan, and Persian Gulf. Examples of inland seas (or lakes) are the Caspian Sea, Sea of Galilee, or Dead Sea.

Earth's oceans and seas are unique in that there is no other planet in our Solar System that has liquid water on its surface. Life on Earth began in the oceans, and today they still are the home to some of the most spectacular wildlife in the world. Most of the oceans' wildlife is located in the upper ocean layers, which contain about two percent of the oceans' volume. The oceans also play a significant role in the earth's water cycle. Oceans are a large source of water vapor for the atmosphere, which is important in heat transportation in the atmosphere in the form of latent heat. Additionally, the oceans gather water at the end of the water cycle not only from precipitation, but also from surface runoff and return flow from rivers and as groundwater flows from land. The oceans are major reservoirs in the carbon cycle. In order to double the current atmospheric carbon dioxide, it would be necessary to release only 2% of the carbon currently stored in the oceans.

Oceans produce important and widespread effects on Earth's atmosphere, weather, and climate. Oceans and land exhibit different heating and cooling properties; solar energy penetrates deeper into water than into land, and water can circulate that absorbed heat easily into deeper layers. Because the specific heat of water (the amount of heat required to raise the temperature of one gram of water by one degree Celsius) is higher than that of land, it takes about five times more energy to warm up water by one degree Celsius than to equally heat a rock. Consequently, oceans not only warm more slowly than land, but also cool more slowly. Oceans, therefore, act as a giant heat reservoir, which heats the land during winter and cools it during summer, moderating the climate of the land located next to it.

Oceans not only moderate the climate of adjacent areas by absorbing and storing solar energy, they also distribute heat between lower and higher latitudes by a global, interconnected system of ocean currents. An example of the climatic effects of oceans on lands is the Gulf Stream, which is not only part of the heat redistributing process by carrying warm waters towards higher latitudes, but also brings mild air to the British Isles and Northwest Europe, causing a significantly milder climate than it would normally have according to its latitudes.

Interesting examples of the interaction between the oceans and the atmosphere are the El Niño and La Niña phenomena patterns. Along with the Southern Oscillation, El Niño and La Niña influence not only nearby areas in the Pacific Ocean, but effect the entire global climate system, along with the ecologies and economies of many countries worldwide, from New Zealand to the United States.

As the oceans and seas are a significant part of the atmosphere and the climate system with many interactions and feedback mechanisms, there is a recent debate about their role in anthropogenic climate change, and also about the possible consequences of climate change for the oceans. Rising sea levels could occur due to both the thermal expansion of the oceans, and from the partial melting of the polar ice because of global warming. Although there is a debate between scientists about the possibility and the intensity of this prediction, if rising sea levels happen at any level, it could be potentially devastating for many coastal cities around the world.