The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 70. 8% of the surface of Earth and contains 97% of Earth's water. Another definition is 'any of the large bodies of water into which the great ocean is divided'. Separate names are used to identify five different areas of the ocean: Pacific (the largest) Atlantic, Indian, Southern (Antarctic), and Arctic (the smallest). Seawater covers approximately 361, 000, 000 km2 (139, 000, 000 sq mi) of the planet. The ocean is the principal component of Earth's hydrosphere, and therefore integral to life on Earth. Acting as a huge heat reservoir, the ocean influences climate and weather patterns, the carbon cycle, and the water cycle. Oceanographers divide the ocean into different vertical and horizontal zones based on physical and biological conditions. The pelagic zone consists of the water column from surface to ocean floor throughout the open ocean. The water column is further categorized in other zones depending on depth and on how much light is present. The photic zone includes water from the surface to a depth of 200 m, where photosynthesis can occur.