Pacific Ocean

May 13, 2013, 7:33 pm
Content Cover Image

Image of dolphins on the Pacific Ocean. (By The New Mikemoral, via Wkimedia Commons)

The world’s largest body of water, the Pacific Ocean, covers about one third of the Earth’s surface. This massive ocean is double the size of the Atlantic and contains twice its volume of water. The area of the Pacific Ocean, without its surrounding seas, is 165 million square kilometres. With the Seas of Japan and Okhotsk, the Bering, Celebes, Coral, East China, Sulu and Yellow Seas, its total area exceeds 179 million square kilometres. All of the continental land masses on the planet could be placed in the Pacific Ocean, and there would still be room left over.

Location

 

The Pacific Ocean stretches from Antarctica’s Ross Sea to the Bering Sea off Alaska. Its widest point occurs at approximately 5°N latitude where it reaches from the coast of Columbia on the east to the Malay Peninsula on the west. To the north, the Pacific Ocean is connected to the Atlantic via the Bering Strait at the Arctic Ocean. To the south it joins the Atlantic via the Drake Passage and Strait of Magellan between South America and Antarctica. The Pacific Ocean joins the Indian Ocean via the Strait of Malacca, and is separated from it by the chain of islands that extends from Sumatra to Australia. Canada’s Pacific coast, which stretches for 29,489 kilometres, makes up 11% of Canada’s total coastline.

Islands

More islands are found in the Pacific than in all of the other oceans combined. Most of these 25,000 islands are huddled near the equator, between the 30°N and 30°S latitudes. Those found to the west including Taiwan, the Philippines, Indonesia, New Guinea and New Zealand, which arise from continental plates. Other South Pacific islands are either volcanic in origin, like the Polynesian islands or are coral islands like those of Micronesia. Canada’s Pacific islands like the Queen Charlotte Islands, the Juan de Fuca Islands, the small Gulf Islands, and the very large Vancouver Island all arise from the Canadian section of the Pacific continental shelf.

Basins

An ocean basin is a large and deep depression that gradually slopes towards the seafloor, forming the shape of a basin. The Pacific basin is divided into East and West Basins. A large ridge called the East Pacific Rise that runs from the Gulf of California to the southernmost tip of South America is responsible for this division. The eastern Pacific Basin runs along the entire length of the Americas: from Alaska to Tierra del Fuego. The continental shelf associated with this long stretch of land is steep, and forms the eastern boundary of the East Pacific Basin.

Pacific Water Properties

The Pacific Ocean extends from the Arctic to the Antarctic. This vast area helps explain why there are such huge variations in the properties of the Pacific Ocean.

Salinity

Three major factors influence salinity (salt concentration) in Pacific Ocean waters: precipitation, evaporation and winds. Precipitation brings freshwater into the ocean, diluting its salt concentration. The rate of evaporation from the ocean’s surface waters is also important because it removes water molecules, leaving the salt behind. In regions where the evaporation is high, due to winds and high temperatures, the concentration of salt in the water increases. As a result, areas of water exposed to the strong trade-winds generally have higher salinity values.

The salinity of ocean water is measured in parts per thousand. High salinity values are over 35 parts per thousand, while values below this are considered low. Around the equator, where there is large amounts of rainfall, surface salinity rarely exceeds 34 parts per thousand. The lowest salinity occurs in the extreme northern regions of the Pacific, near the Bering Sea, where concentrations are often less than 32 parts per thousand.

Temperature

 

Currents regulate the temperature of the North Pacific Ocean. Warm waters enter the Northern basin along the Canadian west coast via the Kuroshio (Japan) current, which originates in the Sea of Japan. This current is, in turn, warmed by the easterly North Equatorial Current, which runs in a westward direction from about 5ºN latitude. Meanwhile, the California Current runs along the North American west coast, and carries cold water away from the North Pacific into the South Pacific Basin.

Generally, ocean waters are layered, with each layer having a different temperature. The bottom layers of the ocean are considerably colder – near freezing – than the surface layers. The surface layer of the Pacific Ocean waters ranges from about 300 to 900 metres thick. This warm layer is shallower along the coasts of North America than in the central and western regions of the Pacific. Along Canada’s west coast, the surface temperatures of the Pacific Ocean rarely get warmer than 15ºC.

The ocean temperatures in the North Pacific tend to be warmer than those in the South Pacific. This seems strange because the surface waters in the South Pacific are definitely warmer. However, because the ratio of land to sea area is greater in the North Pacific, the cumulative amount of cold deep water is less. In other words, the average temperature of waters in the North Pacific is warmer because there are more coastal areas. Also, the deep currents coming up from Antarctica into the South Pacific bring intensely cold waters with them. By contrast, most of the cold outflow from the Arctic Ocean enters the Atlantic Ocean via a strong current known as the Transpolar Drift.

Pacific Ocean Floor

The Pacific Ocean covers a huge part of the earth's surface and underneath all that water are some of the most interesting geographical features around. The deepest part of the ocean, submarine ridges that make Everst seem like a mere hill, and gigantic basins that could easily swallow North America all contribute to this collection of wonders.

Submarine Ridges

Although the Pacific Ocean has an average depth of about 4,000 metres, there are shallower regions. Lying approximately 2,000 kilometres off the North American coast is the East Pacific Rise. This oceanic ridge rises about 2 kilometres from the ocean floor, and stretches from the Gulf of California to the southernmost tip of South America. Submarine ridges owe their formation to the movement of the continental plates. As these plates slowly move away from each other, they leave gaps in the earth’s crust. This allows molten rock from beneath the earth’s crust to move up into the gap, forming a new part of the ocean floor. As the molten rock seeping through these gaps is under some pressure, it spews upward, forming a ridge. This upward movement formed the East Pacific Rise, which separates the Pacific Ocean into its East and West Basins. This large ridge reaches the edge of the North American Continental Plate at the Pacific-North American plate boundary.

Continental Shelfs

Canada’s Pacific coast lies on the edge of a continental shelf that reaches an average depth of about 200 metres, but is very steep and narrow. In most regions the Pacific Shelf is less than 45 kilometres wide, and it only rarely reaches its maximum width of 95 kilometres. It can be divided into 3 regions: the Queen Charlotte Shelf, Queen Charlotte Sound, and the Vancouver Island Shelf.

The Queen Charlotte Shelf is a narrow section of the Pacific continental shelf that ranges from 7-30 kilometres in width. This region lies west of the Queen Charlotte Islands in northern British Columbia. Beyond the shelf, the continental slope plunges steeply, dropping to a depth of about 2500 metres where it meets the Pacific Ocean’s abyssal plains. Beyond the Queen Charlotte Shelf is a large seamount – an underwater volcanic rise that has a height of over three kilometres. Called the Bowie Seamount, this structure lies over 200 kilometres west of the coast of the Queen Charlotte Islands and rises from the flat abyssal plain to within 37 metres of the ocean surface. The continental shelf around the area of Queen Charlotte Sound, just south of the islands, is considerably wider, reaching out to sea as far as 95 kilometres. The Vancouver Island Shelf ranges from 20 to 80 kilometers in width. Glaciers have gouged deep depressions in some parts of this shelf leaving several basins – sloping circular pits – and troughs, which are longer, steeper and more flat-bottomed than basins.

Pacific Basins

The East Pacific Rise forms the seaward edge, while the Pacific Coastal Shelf forms the landward edge, of the East Pacific Basin. The Pacific Basin is a large and deep depression that gradually slopes towards the seafloor, forming the shape of a basin. There are two sub-basins that lie along Canada’s Pacific coast: the northern Hectate Strait is formed by a depression in the Queen Charlotte Continental Shelf, that ranges from 200 - 400 metres deep. This region is bounded by the coast of northern British Columbia, and the Queen Charlotte Islands. The more southern Strait of Georgia is formed in the Vancouver Island Shelf, and has an average depth of about 155 metres. This Strait lies in between Vancouver Island and the most southern point of British Columbia. The American coastal shelf is a large continental shelf that extends from the mainland of North and South America, steeply sloping towards the Pacific Ocean Floor.

Sedimentation

Off the eastern coast of the Pacific Ocean, the sediments on the ocean floors are almost entirely pelagic. This means that they are not derived from materials swept from the land, but rather from the remains of planktonic organisms that once inhabited the surface waters of the ocean. The immense size of the Pacific Ocean, and the fact that a very small land area actually drains into its waters, account for the almost exclusively oceanic origins of its sediments.

Pacific Ocean Currents

Strong and predictable winds, like the trade winds, are one of the major forces which drive the Pacific currents. Winds are particularly important in driving surface currents, while deep-water currents are driven by convection, which results from temperature differences between water layers. Convection occurs when ocean water heats up and becomes less dense, and rises. This water moves above the cooler water, and gives off its heat to the surrounding environment. As it cools, it begins to sink, and the process is repeated. Convection results in a continual circulation of ocean water.

Driving Forces of Currents

There are many factors that determine the speed of a current, as well as its route. Winds have the most important influence on the flow of currents, but tides, precipitation, evaporation rates, shape of the ocean floor, and inflow from rivers and adjacent seas are also important. The waters of the north Pacific Ocean move in a general east to west direction, in response to the predominant trade winds. The general westerly movement of the Pacific waters around the equator forms the North and South Equatorial Currents, belts of water moving approximately parallel to the equator, which lie about 15° latitude on either side of it. Between these two currents, the Equatorial Countercurrent flows to the east.

Measuring the Flow of Currents

To measure the speed of currents, oceanographers have planted – or moored – instruments in the water that can calculate the rate of water movement at various times during the day. Other instruments known as drifters float on the surface and determine the paths and direction of the water. Aside from their speed, ocean currents are also measured by their rate in flow of millions of cubic metres per second. To put this into perspective, consider the outflow of water from the Mediterranean Sea into the North Atlantic Ocean. Flow from the Mediterranean Sea into the Atlantic Ocean occurs at a rate of 1 to 3 million cubic metres per second. By comparison, South America’s Amazon River discharges 0.2 million cubic metres per second. The large, fast Gulf Stream Current moves at a rate of 150 million cubic metres per second; that’s equivalent to 30,000 Olympic sized pools full of water being emptied every second! The Pacific equivalent to the Gulf Stream is the Kuroshio Current, which originates in the Sea of Japan, and carries a volume of 50 million cubic metres per second – about 500 times the volume of water flowing out of the great Amazon river.

North Pacific Currents

A clockwise circulation of water, known as the North Pacific Gyre generally dominates the North Pacific. This pattern of circulation is comprised of several smaller – but no less important – currents, the Kuroshio Current, the Alaskan Current, the Californian Current and the North Equatorial Current. The North Equatorial Current moves northeastward along the Philippine Islands, and eventually forms the Kuroshio Current (also called the Japan Current). This warm, saline current warms the shores of the western Pacific, and eventually moves eastward beyond Japan. Some branches of the Kuroshio pass north of the Hawaiian Islands, while others come to within 1000 kilometres of North America. These branches of the Kuroshio are moved by strong westerly winds that push the water into one large current, the North Pacific. This current heads towards North America from the Sea of Japan, and branches into the northward moving Alaskan Current, while the remainder forms the southward moving California Current. The California Current flows southeast off the British Columbia coast towards the Baja Penninsula, and brings cold water to these southern shores. Once it reaches this region of Mexico, it turns sharply west, and forms part of the North Equatorial Current.

El Niño

Every few years unusually warm currents occur in the South Pacific Ocean off South America. This rise in temperature is due to a relaxation of the trade winds that move the ocean waters throughout the globe. Without the trade winds, the surface water’s rate of evaporation declines and heat loss slows. With the cooling of the South Pacific disrupted, unusually high temperatures occur along the coastal shores of Chile all the way up to Ecuador. Called El Niño, this periodic increase in temperature fluctuates from a small increase in temperature (2-3ºC) to a large one (8-10ºC). A strong El Niño can influence climate worldwide! For example, 1997 - 1998 were predominated by a very strong El Niño. In North America, the effects of El Niño were felt most in winter with warmer temperatures than usual in the north, and colder temperatures than usual in the south. In years like these, cyclones and hurricanes develop in response to the high ocean temperatures, which in turn release more heat and humidity into the surrounding climate system. These systems then move up the coasts, affecting weather in both North and South America.

The most intense El Niño of the last century occurred in 1982-1983. Around this time, the surface water temperatures of the South Pacific rose about 10ºC higher than normal. The effects were devastating – drought in Australia, flooding in Chile and typhoons in the South Pacific Islands. The Canadian west coast felt the effects of this El Niño as well, experiencing unusually stormy weather throughout the entire winter.

La Niña

La Niña, the ‘kid sister’ of El Niño, is a weather phenomenon characterized by colder Pacific Ocean currents that result in cooler global climate patterns. The effects of La Niña are opposite to those of El Niño. They do not produce the same destructive weather patterns as El Niño, but they do leave their mark, often causing droughts and very cold North American winters.

North Pacific Tides

The Pacific Ocean is in a constant state of flux. While winds and currents make waves, the sun and moon interact to cause daily fluctuations in ocean levels. The sun and moon both pull the surface of the earth towards them, and oceanic waters are particularly affected by this attraction. The gravitational pull on the oceans causes water to bulge towards the orbiting moon. The varying position of the moon creates high and low tides. The tidal bulge created when ocean waters are pulled toward the moon is the high tide. Between each high tide, there is a low tide. As the moon rotates around the earth each day, water is displaced from the side of the earth facing the moon and also from the side of the earth facing away from the moon. The bulging of the waters on both sides of the earth occurs in response to the moon’s orbit. Because each orbit takes 24 hours and 50 minutes, there are usually two high tides and two low tides each day. However, because each orbit takes slightly longer than 24 hours, the timing of the high and low tides shift each day. There is also variation in the tidal range. When the sun and moon are aligned – during the full moon and new moon – the gravitational pull on the earth’s water is greater, causing very high tides and very low tides called spring tides. By contrast, when the moon and the sun are not aligned – in the first and third quarter of the lunar cycle – their gravitational forces partially cancel each other out, and the tidal range is less. These tides are called neap tides.

Queen Charlotte Shelf

Tidal ranges and patterns vary along the coast. Over most of the world’s coastal regions, the difference between water levels at high and low tide – the tidal amplitude or range – averages 2 metres. The tides along the Pacific coast range in amplitude from 2.5 metres to about 4 metres. In the northern region of the coast, off the Queen Charlotte Islands, the shelf is steep relative to the other shelves of the Pacific region. This steep shelf limits the amplitude of the tides to 2 metres. When tides run into deep continental shelves, their rate of movement is increased due to the lack of friction along the shore. This results in an even dispersal of energy as the water rushes in, and a smaller tidal amplitude than in shallower areas where the energy is concentrated into a smaller volume. However, to the east of the Queen Charlotte Islands lies the Hectate Strait, bordering the British Columbia mainland, which is considerably shallower than the shelf to the west of the islands. Therefore, in this region the tidal range is around 3-5 metres. These high tides create whirlpools and turbulent waters that have generated the complex and rugged ocean floor and coastline in this region.

Queen Charlotte Sound

The continental shelf of Queen Charlotte Sound has an average depth, so the tidal amplitude is close to the usual value of 2.5 metres. However, the ocean floor in this region is complex, with deep basins, shallow banks and channels. This complexity causes turbulent waters and whirlpools to appear with each incoming tide. These rough waters batter the coasts of the Queen Charlotte Islands, giving them their characteristic rugged appearance.

Vancouver Island

The region of the Pacific continental shelf off Vancouver Island is relatively shallow. The gradual slope of the shelf in this region produces the highest tidal range on Canada’s Pacific coast with amplitudes up to 4 metres.

Further Reading

Glossary

Citation

Hebert, P., & Ontario, B. (2013). Pacific Ocean. Retrieved from http://www.eoearth.org/view/article/155111

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