The Pacific Ocean
The Pacific Ocean
The Pacific Ocean is the largest ocean.
Oceans hold most of the Earth’s water.
Oceans regulate our climate and control our weather.
The largest living animal ever to have lived is the blue whale.
Many ocean fisheries have been overfished in the past 30 years.
Many animals can recover when human impacts on oceans are reduced.
Earth’s Largest Ocean
The Pacific Ocean covers one-third of the Earth’s surface. It is the largest and deepest ocean. Its 181 million square kilometer surface is greater than that of all the landmasses combined. The Pacific Ocean holds 714 million cubic kilometers of water with an average depth of 3940 meters. The deepest place on Earth is in the Mariana Trench where the sea floor is 11034 meters below the sea surface. From its base on the seafloor to the volcanic peak, Mauna Kea in the Hawaiian Island archipelago is taller than Mount Everest in the Himalayas. The most remote and isolated islands are the Hawaiian Chain.
Nine seas rim the Pacific Ocean basin. The Bering Sea, Sea of Okhotsk, and Sea of Japan are temperate waters in the north and northwest Pacific. The East China Sea, South China Sea, Java Sea, Arafura Sea, and South Coral Sea are in subtropical and tropical regions along the western Pacific. The Polar Sea lies along the shore of Antarctica.
Currents and tides
Equatorial surface currents follow the trade winds moving west in the Northern Hemisphere and east in the Southern Hemisphere. In temperate regions of the north Pacific, currents generally flow eastward. In the southern temperate region of the Pacific, currents generally flow westward. Large ocean gyres form between the temperate and equatorial currents. A slow moving deep ocean current connects all oceans. Marine animals use currents to aid travel through the oceans. Currents also create regions with an abundance of marine life including plankton, fish, birds and mammals. Pacific Ocean currents include the North Pacific Current, California Current, Kuroshio Current, North Equatorial Current, South Equatorial Current, Humboldt Peru Current and East Australian Current.
Tides rise and fall in rhythm to the movement of the moon and sun. Coastal areas can experience diurnal tides (1 high and 1 low in 24 hours), semi-diurnal tides (1 high and 1 low tides in 12 hours) or mixed tides (2 hi and 2 low tides with 1 high and low being greater). Around the world’s oceans, the tides dictate which marine animals and plants will be present on beaches.
El Nino & La Nina
El Nino and its opposite La Nina, are oceanographic events that alternate between periods of warm and cool water moving about the Pacific Ocean. In cold (La Nina) years, west flowing trade winds push warm surface water west toward southeast Asia to be replaced from the ocean depths by cool, nutrient laden waters rising to the surface off the South American coast. The nutrients are fertilizer for green surface dwelling plankton that bloom. Zooplankton flourish and become food for fish and other marine life. For reasons not well understood, the trade wind eases every few years so that warm water normally in the eastern Pacific returns to the South American coast triggering an El Nino. Nutrient-rich waters from the ocean depths off South America slow and marine life dies or migrates. The warming seawater triggers tornadoes in North America, and droughts in Indonesia, and southwest Africa.
Life in the Ocean
Plankton is the basis of the ocean food chain. They are tiny plants (phytoplankton) and animals (zooplankton) that spend most or all of their lives floating in the ocean. 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 live near the ocean surface. Zooplankton is found from sea surface to the ocean depths.
Marine algae (seaweeds) anchor to surfaces with a sucker-like attachment. There are green, brown and red algae. Seaweeds photosynthesize the sun’s energy and thereby are a source of food for grazing animals.
The 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. More….
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 the tuna, mullets, perch and smelts. Their name is derived from the short spines found in their fins. More…
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 ocean. More…
There are about 300 species of birds for which the ocean is their normal habitat and food source. Seabirds include the penguins, tubenoses, firgatebirds, gannets and boobies, pelicans and cormorants, gulls and terns, auks and some shorebirds. All species lay eggs in nests onshore, most have webbed feet, and they all eat sealife (fishes, squid, plankton and invertebrates). More…
The marine mammals include the dugongs & manatees, whales, dolphins & porpoises, seals, sealions & walruses, otters and bears. All living manatees and dugongs live in tropical or subtropical waters. The largest of the group was the se cow that was extirpated from temperate the north Pacific 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, sealions 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. More…
Ocean Ecology & Habitats
All life requires energy to live and reproduce and most energy is ultimately derived from the sun. Photosynthetic plants store the sun’s energy in their cells. Animals eat the plants or each other to obtain energy. A second source of energy is from deep ocean volcanic vents. Energy from the vents is consumed by bacteria that then eaten by other animals.
An estuary is where the ocean water is noticeably diluted by freshwater. Estuaries have an abundance of invertebrates particularly those with muddy substrates. They also harbour 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 neighbouring environments. Mangroves made up of a variety of tree and shrub species often arise in tropical estuaries.
Kelps are marine algae of which some species can grow to immense size in temperate oceans. They anchor 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.
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 by preying on one another. Birds and fish eat the invertebrates.
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.
Most corals can only grow where the water does not fall below 21C s they are mostly found in tropical waters. The oldest reefs are in the Indo-Pacific Region where over 2000 species of associated fish have been recorded. Coral reefs are 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.
The deep ocean is rich in species that can have evolved to live under high water pressure, 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 vertebrate on Earth are the bristlemouths found in the deep. Hydrothermal vents are openings in the Earth’s crust that 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.
Conserving the Ocean
The most important immediate action is to halt future damage to the marine environment. Then we need to preserve and restore important areas of the ocean and to use marine ecosystems sustainably.
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.