The Pacific Ocean

By Archives •  Updated: 07/15/22 •  10 min read

The Pacific is the biggest and deepest of Earth’s five oceans. It goes from the Arctic Ocean in the north all the way to Antarctica at the bottom. It’s got land around it on every side, including Asia and Australia in the west and America across from it to our east.

The Pacific is the biggest and deepest of Earth’s five oceans. It goes from the Arctic Ocean in the north all the way to Antarctica at the bottom. It’s got land around it on every side, including Asia and Australia in the west and America across from it to our east.

The Pacific can be further divided by the equator into northern (North Pacific) and southern (South Pacific) regions. The Pacific Ocean is the largest and deepest of the Earth’s oceanic divisions, covering an area of 165.2 million km2 (63.8 million sq mi).

To get an inkling of how vast this body of water is, it’s larger than Earth’s entire combined landmass and comprises 32% of Earth’s total surface area. Plus, only about 2.5% of the water on Earth is fresh water – the other 97.5% is saline.

Its mean depth is 13,000 feet, but Challenger Deep in the Mariana Trench, located in the western north Pacific, is the deepest point in the world, reaching a depth of 10,928 meters, or 35,853 feet. The Pacific also contains the deepest point in the Southern Hemisphere, the Horizon Deep in the Tonga Trench, at 35,509 feet). The third deepest point on Earth, the Sirena Deep, is also located in the Mariana Trench.

The Water Of The Pacific Ocean

Pacific Ocean located on globe map

Credit: CIA World Factbook

The volume of the Pacific Ocean, making up approximately 50.1 percent of the world’s oceanic water, has been estimated at some 714 million cubic kilometers (171 million cubic miles). The temperature of the water at the surface of the Pacific ocean can vary markedly, from −1.4 °C (29.5 °F), the freezing point of seawater, in the poleward areas to about 30 °C (86 °F) near the equator.

The motion of Pacific waters is generally clockwise in the Northern Hemisphere (the North Pacific gyre) and counter-clockwise in the Southern Hemisphere. The North Equatorial Current, driven westward along latitude 15°N by the trade winds, turns north near the Philippines to become the warm Japan or Kuroshio Current.

Salinity varies latitudinally. It reaches a maximum of 37 parts per thousand in the southeastern area. The water near the equator, which can have a salinity as low as 34 parts per thousand, is less salty than that found in the mid-latitudes because of abundant equatorial precipitation throughout the year.

The minimum counts of less than 32 parts per thousand are found in the far north as less evaporation of seawater takes place in these frigid areas.

Who Named the Pacific Ocean?

The eastern Pacific ocean was first sighted by Europeans in the early 16th century when Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama in 1513 and discovered the great “Southern Sea” which he named Mar del Sur.

The Pacific gets its modern-day name from the Latin Mare Pacificum, “peaceful sea”, which the Portuguese explorer Ferdinand Magellan dubbed it. Magellan and his crew were the first to cross the Pacific in recorded history. However, the first seaborne migration in human history is believed to be the Neolithic Austronesian expansion of the Austronesian peoples in c. 3000-1500 BCE. Austronesians came from the island of Taiwan where they invented the first maritime sailing technologies – outrigger boats, catamarans, lashed-lug boats, and the crab claw sail.

From around 1300 to 1200 BCE, a branch of the Austronesian migrations known as the Lapita culture reached the Bismarck Archipelago, the Solomon Islands, Vanuatu, Fiji, and New Caledonia. From there, they settled Tonga and Samoa by 900 to 800 BCE.

Some people also migrated back north in 200 BCE to settle the islands of eastern Micronesia (including the Carolines, the Marshall Islands, and Kiribati), mixing with earlier Austronesian migrations in the region. This remained the furthest extent of the Austronesian expansion into Polynesia until around 700 CE when there was another surge of island exploration. They reached the Cook Islands, Tahiti, and the Marquesas by 700 CE; Hawaiʻi by 900 CE; Rapa Nui by 1000 CE; and finally New Zealand by 1200 CE.

Life In The Pacific Ocean


Plankton is at the base of the ocean food chain. These are tiny plants (phytoplankton) and animals (zooplankton) that spend most or all of their lives floating in the Pacific ocean.


The Phycosphere: Ocean Bacteria and Phytoplankton.
Symbiodinium (in orange) is a species of single-cell, photosynthetic organisms that live in the ocean. Symbiodinium cells release metabolites into their surroundings and form a region around them called the “phycosphere”. Because marine bacteria (in green and cyan) utilize phytoplankton metabolites as a food source, the phycosphere represents a feasting ground for bacteria in the ocean. The marine bacteria in these images (Ruegeria pomeroyi) are engineered to fluoresce in different colors according to their metabolic activity. The gradient of fluorescence of bacteria (in response to the gradient of metabolites emanating from Symbiodnium cells) allows us to visualize the phycosphere. This image was taken with epifluorescence microscopy with a 100x objective.
Credit: Cherry Gao, ETH Zurich, CC-BY

Phytoplankton is mostly algae and zooplankton is the early stages of familiar seashore animals such as mussels, crabs, and snails as well as animals that live entirely as plankton. Phytoplankton requires light and therefore lives near the ocean surface. Zooplankton can be found from the sea surface to the ocean depths.

Marine Algae

Marine algae, commonly known as seaweeds, anchor to surfaces with a sucker-like attachment. There are green, brown, and red algae. Seaweeds photosynthesize the sun’s energy and from that are a source of food for grazing animals.

Marine Invertebrates

Invertebrates living in the ocean include corals, jellyfish, anemones, comb jellies, marine worms, mollusks (clams, octopus, and relatives), crustaceans (barnacles, crabs and relatives), and echinoderms (seastars and their relatives). The vertebrates include the sea squirts, fishes, reptiles, birds, and mammals.


The ocean is the realm of the fishes. They include the lampreys & hagfishes, sharks, rays & chimearas, bony fishes, and spiny-rayed fishes.

Lampreys and hagfish are ancient forms. The 1000 or so species of sharks, rays, and chimeras include the world’s largest fish – the whale shark – and the massive manta ray. The chimaeras are often found in the deep sea.

There are more species of bony fishes than any other vertebrate in the world. They include many familiar fishes such as eels, herrings, and catfish. More than 10,000 of the 13,000 or so spiny-rayed fish live in the marine environment and include familiar fish such as tuna, mullets, perch, and smelts. Their name is derived from the short spines found in their fins.


The marine reptiles include 8 species of marine turtles, many sea snakes, a lizard (marine iguana), and saltwater crocodiles. They are restricted to warmer waters of tropical and southern temperate oceans.


There are about 300 species of birds for which the ocean is their normal habitat and food source. Seabirds include the penguins, tubenoses, frigate birds, gannets and boobies, pelicans and cormorants, gulls and terns, auks, and some shorebirds.

All species lay eggs in nests on shore, most have webbed feet, and they all eat sea life (fishes, squid, plankton, and invertebrates).

Marine Mammals


Endangered Florida manatee (Trichechus manatus) Photo credit: Keith Ramos

The marine mammals include the dugongs & manatees, whales, dolphins & porpoises, seals, sealions & walruses, otters, and bears. All manatees and dugongs live in tropical or subtropical waters. The largest of the group was the sea cow that disappeared from the north Pacific Ocean in the 18th century.

Whales, dolphins, and porpoises have evolved to become entirely aquatic mammals. There are about 90 species worldwide. All but five river dolphins are marine species. The blue whale is the largest animal to have ever lived.

Seals, sea lions, and walruses (pinnipeds) are highly mobile and sometimes acrobatic animals in the ocean that come ashore to reproduce and rear their young. The otters include the sea otter and marine otter, and the polar bear.

Ocean Ecology

All life requires energy to live and reproduce. Most energy comes from the sun, which is the way photosynthetic plants store it – the plant’s cells turn sunlight into energy. Animals eat some of these plants or other animals to release that stored-up solar power in their cells.

Deep ocean volcanic vents are a second source of energy. Energy from the vents is consumed by bacteria that are then eaten by other animals.


An estuary is an area where an ocean’s water is noticeably diluted by freshwater. Estuaries have an abundance of invertebrates particularly those with muddy substrates.
They also harbor tremendous numbers of fish and birds at various stages of their lives.

Plants and animals must cope with changing saline conditions and so they tend to have fewer species than neighboring environments. Mangroves made up of a variety of tree and shrub species often arise in tropical estuaries.

Kelp Forests

Kelps are marine algae of which some species can grow to immense size in temperate oceans. They are anchored to the seafloor with a sucker and use a gas-filled float to rise into the sunlight. Kelp forests provide a source of food and shelter for fish and invertebrates.

Seagrass Meadows

Seagrasses are found throughout the world’s oceans along the fringe of the sea. They form extensive beds where the substrate is soft and water conditions are suitable.

Seagrass meadows are nurseries for many species of fish and provide habitats for invertebrates.

Mud and Sandflats

Muddy shores and sandy beaches provide habitats for many burrowing invertebrates and tremendous numbers of fish and birds. The invertebrates find food by filtering detritus from the water column, eating a thin layer of diatoms on the mud surface or preying on one another. Birds and fish eat the invertebrates.

Rocky Shorelines

Rock shores offer a strong footing for invertebrates that can anchor themselves. It is here that mussels and barnacles cling in vast numbers and marine algae form dense beds.

Species confined to the rock live in layers up and down the surface each dependent on the preferred duration of exposure to air and water.

Coral Reefs

Most corals can only grow in waters that do not fall below 21C so they are mostly found in tropical waters. The oldest reefs are in the Indo-Pacific region of the Pacific Ocean where over 2000 species of associated fish have been recorded.

Coral reefs are comprised of colonial animals with calcium carbonate skeletons. Successive generations have formed massive reefs some of which are hundreds of millions of years old. The Great Barrier Reef in Australia is the world’s largest coral reef.

Ocean Depths

The deep regions ocean are rich in species that can have evolved to live under high water pressure, with no light and cold ocean water. Food floats down from the surface or from seafloor vents. Some animals have evolved bioluminescent lights.

Crustaceans squid, corals, jellyfish, seastars, worms, and fish live in the depths. The most numerous vertebrates on Earth are the bristlemouths found in the deep.

Hydrothermal vents, openings in the Earth’s crust on the seafloor, emit mineral-rich water. Bacteria in the bodies of animals living around the vents derive energy from sulfides in the vent water. Tube worms form large clusters at some vents while others are surrounded by a mat of bacteria that are eaten by crabs.

Further Reading:

Butler, R.W. 2003. The Jade Coast: Ecology of the North Pacific Ocean. Key Porter Books.

Hutchinson, S. and L.E. Hawkins. 2008. Oceans: a visual guide. Firefly Books.

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