Oceans

Aquatic Habitats

Oceans of the World

Pacific Ocean

The Pacific Ocean is the largest of all the oceans and covers nearly one-third of the globe. All the continents could be placed into it with room left over! This is a very geologically active area with many volcanoes.

Atlantic Ocean

The Atlantic Ocean is considered a passive margin ocean with most of its geological activity centered along the Mid-Atlantic Ridge. Most of its coastal regions are low and geologically quiet. The Atlantic's major marginal seas include the Mediterranean Sea, the North Sea, the Baltic Sea, Hudson Bay, the Gulf of Mexico, and the Caribbean Sea. Its greatest depth is in the Puerto Rico Trench at 8,605 meters (28,231 feet).

Indian Ocean

The Indian Ocean is often thought of as a tropical ocean, however, it extends from India in the north, all the way to Antarctica in the south. It contains about 20% of the earth's water. It's deepest point is the Java trench at 7725 m.

Arctic Ocean

The Arctic Ocean is centered on the North Pole and is the smallest of the oceans. This ocean is unique in that it has permanent to semi-permanent ice.

Featured Resource

Google Earth: Oceans [Image: Google Earth]

Google Earth, a geographic mapping application powered by Google technology, has added the world's oceans to its user interface. Users can now plunge below the ocean's surface and virtually explore the ocean's varied underwater terrain. The Google Earth Oceans interface features videos and articles about marine science, as well as information about surfing, diving, and coastal travel locations.

Oceans

This image shows the abundance of life in the sea, dark blue represents warmer areas where there is little life due to lack of nutrients, and greens and reds represent cooler nutrient-rich areas.
[Photo: Seastar satellite, NASA]

Water in oceans accounts for 97.5% of the Earth's water budget, covering 71% of the world's surface. It is inhabited from its surface down to depths over 11,000 meters. The physical and chemical properties of oceans create a habitat suitable for a great diversity and abundance of organisms. Ocean temperature, which changes with depth, latitude and currents, regulates where marine life can live.

Waves, currents, tides, and upwellings move and mix ocean water, and aid in the migration of marine species. Waves breaking at the surface of the ocean mix oxygen and warm water into deeper zones. Currents, which are driven by differences in water density based on temperature and salinity, and by the "Coriolis Effect", created by the earth's rotation and atmospheric winds, move water at many different scales. Warm surface currents flow from the tropics to higher latitudes, and cold surface currents from polar and temperate latitudes flow towards the equator. In the Northern Hemisphere currents move clockwise, and in the Southern Hemisphere, they move counterclockwise. These large systems of rotating ocean currents are called gyres. A tide is a periodic oscillation of marine waters caused by the gravitational pull of the moon and the sun. The intertidal zone is defined by the water levels of the high and low tides. Upwelling is the movement of water from deep in the ocean into the surface waters. This is important because it is one of few ways to bring nutrient rich water into the photic zone.

Source:
Barnes, R.S.K. and R.N. Hughes. 1988. An Introduction to Marine Ecology. Blackwell Science Publications. Palo Alto, CA.

To find out more about oceans including their classification, habitats, and human impacts, follow the links below:

	Classification Learn about how oceans and marine environments are classified.
	Human Impacts (Accessible soon) Find out about how human activities can affect ocean habitats.
	Ocean Habitats Learn about the diverse habitats within oceans.

Aquatic Food Webs

Aquatic Food Webs [Image: US EPA]

Aquatic food webs are conceptual diagrams that demonstrate the flow of energy and nutrients in aquatic systems. Although the species that make up aquatic food webs will greatly vary depending on habitat type, the basic trophic levels or feeding levels of food webs are similar. Producers such as phytoplankton, aquatic plants, and algae use photosynthesis to convert sunlight and nutrients into living tissue. Primary consumers such as zooplankton and plant grazers eat producers. Secondary and tertiary consumers such as invertebrate predators, birds, fish, mammals, and humans eat lower-level prey items. Decomposers consume dead plants and animals, breaking organic matter down into nutrients. Since organisms seldom feed exclusively on another, several food chains are often woven together to form a "food web," a complex cycle of interconnected organisms and organic matter.

Explore the NBII Fisheries and Aquatic Resources Node's Aquatic Organisms section for more information about the wide variety of organisms that use the aquatic environment, ranging from endangered species to aquaculture.

Discover the NBII Bird Conservation Node's U.S. Fish and Wildlife Service Focal Bird Species, many of which are shorebirds, seabirds, and waterfowl that are important components of aquatic food webs.

Featured Marine Resource

[Image: NBII]

The NBII Marine Habitats Node provides access to information about marine habitats, including general information, coral reefs, federal management agencies, invasive species, plants and animals, and data. Key projects of the Marine Habitat Node include the Coral Reefs Project, which integrates coral reef datasets, maps, publications, fact sheets, images, and other information from a variety of partner organizations; and OBIS-USA, a one-stop source for biogeographic data collected from U.S. waters and oceanic regions which is part of the global Ocean Biogeographic Information System (OBIS).

Why is the ocean salty?

The ocean is salty because of the gradual concentration of dissolved chemicals eroded from the Earth's crust and washed into the sea. Solid and gaseous ejections from volcanoes, suspended particles swept to the ocean from the land by onshore winds, and materials dissolved from sediments deposited on the ocean floor have also contributed. Salinity is increased by evaporation or by freezing of sea ice and it is decreased as a result of rainfall, runoff, or the melting of ice.

The average salinity of sea water, 35 parts per thousand (ppt or o/oo), occurs at the Equator. But concentrations as high as 40 o/oo are observed in the Red Sea and the Persian Gulf. Salinities are much less than average in coastal waters, in the polar seas, and near the mouths of large rivers.

If the salt in the sea could be removed and spread evenly over the Earth's land surface it would form a layer more than 500 feet thick, about the height of a 40-story office building. The saltiness of the ocean is more understandable when compared with the salt content of a fresh-water lake. For example, when 1 cubic foot of sea water evaporates it yields about 2.2 pounds of salt, but 1 cubic foot of fresh water from Lake Michigan contains only one one-hundredth (0.01) of a pound of salt, or about one sixth of an ounce. Thus, sea water is 220 times saltier than the fresh lake water.

Why is the ocean salty?

The NBII Program is administered by the Biological Informatics Program of the U.S. Geological Survey

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