Oceans are vast bodies of water that cover roughly 70% of the earth. Seas are smaller and partially enclosed by land. The five oceans of the earth are in reality one large interconnected water body. In contrast, there are over 50 smaller seas scattered around the world.
Oceans cover 71% of the Earth's surface, and contain 97 percent of the planet's water. The Pacific Ocean is the largest ocean covering an area of 64,186,000 square miles and the Mediterranean Sea is the largest sea with an area of 1,144,800 square miles. In fact even the world’s smallest ocean Arctic Ocean (5,427,000 square miles) is larger than the Mediterranean.
List of oceans by size
- Pacific Ocean: 60,060,700 square miles
- Atlantic Ocean: 29,637,900 square miles
- Indian Ocean: 26,469,900 square miles
- Southern Ocean: 7,848,300 square miles
- Arctic Ocean: 5,427,000 square miles
Top 6 largest seas
- Mediterranean Sea: 1,144,800 square miles
- Caribbean Sea: 1,049,500 square miles
- South China Sea: 895,400 square miles
- Bering Sea: 884,900 square miles
- Gulf of Mexico: 615,000 square miles
- Okhotsk Sea: 613,800 square miles
The average depth in oceans is from 3,953ft to 15,215ft. Mariana Trench in the Pacific Ocean is the deepest, 36,200 ft deep. At 22,788 ft, the Caribbean Sea is the deepest sea. Most seas are much shallower.
Oceans and seas are home to rich and diverse marine life. The depth and distance from shore strongly influence the quantity and biodiversity of the plants and animals that live there. As seas are always near land marine life are abundant while oceans which are deeper and farther away from land have on few basic life forms like bacteria, microscopic plankton and shrimp.
Any water in a sea, ocean or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. Areas in the pelagic zone are distinguished by their depth and the ecology of the zone. It is further divided into:
- The epipelagic zone (sunlit) is closest to the surface and stretches down to around 200 m. An abundance of light allows for photosynthesis by plants and nutrients for animals like tuna external and sharks.
- The mesopelagic zone (twilight) begins at 200 m below the surface and reaches a depth of 1,000 m. There is a little light but not enough for photosynthesis to occur.
- The bathypelagic zone (midnight) follows, from 1000-4,000 m in depth. Bioluminescent organisms are found in this zone. Unique animals like the marine hatchet fish external and giant squid live in this zone, surviving mostly on the detritus that drifts down from the epipelagic zone.
- The abyssopelagic zone (lower midnight) is located from 4,000 m to directly above the ocean floor and is a completely dark area home to colorless and blind animals.
- The Hadopelagic zone is the deep water in ocean trenches. Some define the hadopelagic as waters below 6,000 m (19,685 ft), whether in a trench or not. Very little is known about this zone, and very few species are known to live here.
The bathypelagic, abyssopelagic, and hadopelagic zones have very similar characteristics. Because of this some marine biologists combine these three zones or at least combine the last two.
The Earth's climate is greatly affected by ocean currents which transfer cold or warm air to different coastal regions. To learn more about how the ocean affects the climate, watch the following video by NASA.