Oceans

Oceans
Location	Earth
Type	Saltwater
Primary inflows	Rivers, underwater springs
Primary outflows	Evaporation, water cycle
Catchment area	Global
Basin countries	Worldwide
Surface area	Approximately 361 million square kilometers
Average depth	Average: 3,688 meters
Max. depth	10,994 meters (Mariana Trench)
Water volume	Approximately 1.332 billion cubic kilometers
Shore length1	377,000 kilometers
Islands	Thousands
Settlements	Coastal cities worldwide
1 Shore length is not a well-defined measure.

The oceans cover about 71% of the Earth's surface and are a major component of the planet's hydrosphere. Comprising the largest habitat on Earth, oceans are integral to life, influencing the weather and climate patterns, supporting a diverse range of biomes and ecosystems, and providing vital resources including food, minerals, and energy.

Composition and characteristics

Oceans are primarily composed of salt water with an average salinity of about 3.5%. This salinity can vary in different areas due to the influx of freshwater from rivers, rainfall, and melting ice. The oceans are also rich in minerals and provide habitats through various physical features such as coral reefs, seamounts, trenches, and volcanic islands.

Ocean zones

The ocean can be divided into different zones:

• The Epipelagic zone (sunlight zone) extends from the surface to about 200 meters. It is where most of the visible light exists and photosynthesis can occur.
• The Mesopelagic zone (twilight zone) stretches from 200 meters to 1,000 meters. Light diminishes significantly in this zone, and the pressure increases.
• The Bathypelagic zone (midnight zone) ranges from 1,000 meters to 4,000 meters. It is characterized by complete darkness and very high pressures.
• The Abyssopelagic zone and Hadalpelagic zone are deeper still, with the latter found in deep oceanic trenches.

Marine life

Oceans are home to a diverse array of marine life, from microscopic plankton to the largest mammals on Earth, such as the blue whale. Marine organisms play crucial roles in the biogeochemical cycles that regulate the Earth's environment.

Human interaction

Human activities impact the oceans through fishing, marine pollution, and the extraction of marine resources. Climate change also affects ocean temperatures, sea levels, and ocean currents, which in turn affect global climate systems.

Conservation

Efforts to conserve and sustainably manage the oceans include marine protected areas, regulations on overfishing, and initiatives to reduce marine pollution. International agreements such as the United Nations Convention on the Law of the Sea (UNCLOS) play a crucial role in the governance of global ocean resources.

See also

• Marine biology
• Oceanography
• List of seas