North Pacific Ocean

Category: Marine and Oceanic Biomes.

Geographic Location: Northern Hemisphere.

Summary: The North Pacific Ocean provides an assemblage of some of the most productive and diverse marine ecosystems in the world.

The Pacific Ocean is the world’s largest, coldest, and deepest ocean, covering approximately one-third of the Earth’s total surface. The Pacific Ocean is commonly divided into North and South Pacific segments. The North Pacific Ocean is a major world source of marine organisms. Harvest of these organisms plays an important role in the economies and international relations of bordering countries—and of the planetary food web. The region itself extends from the near-tropical waters off southern Japan to the Arctic waters of the Bering Sea.

The North Pacific Ocean is characterized by strong latitudinal gradients in surface temperature and salinity (high in the south and low in the north), multiple water masses, major oceanic gyres, mesoscale eddies of up to 124 miles (200 kilometers) across, and a complex bathymetry of deep trenches and remote seamounts. Climate-system variability around the world is intimately linked to the natural variability in this oceanic region.

High biological production is typical in the area, and it is responsible for major commercial fisheries of tuna and Pacific salmon. The North Pacific Ocean biome is also an important sink region for atmospheric carbon dioxide (CO₂), and therefore plays an important role in the ultimate fate of CO₂ on Earth.

Seven physically complex subregions are identified in the North Pacific Ocean: Yellow Sea and East China Sea, Okhotsk Sea, Oyashio Current System, Kuroshio Current System, Bering Sea, Alaska Current System, and California Current System. These seven subregions are part of the main gyre, the North Pacific Gyre. This gyre occupies approximately 7.7 million square miles (20 million square kilometers), with a clockwise circular pattern. The Aleutian Island chain constricts the main gyre, causing recirculation with two subgyres: the Western Subarctic and Alaskan gyres. These gyres and seas have distinct characteristics, often supporting different species and patterns of production.

Yellow Sea and East China Sea

The Yellow Sea is a shallow marginal sea with a surface area of 146,719 square miles (380,000 square kilometers) and an average depth of 144 feet (44 meters). It is broadly connected with the East China Sea to the south, and contains a semienclosed gulf in the north, the Bohai Sea. The People’s Republic of China, the Democratic People’s Republic of Korea, and the Republic of Korea are populations located on the Yellow Sea, making it one of the most densely populated regions in the world. Three main currents are found in the Yellow Sea: Kuroshio, Tsushima, and the Yellow Sea Warm Current (YSWC).

Due to its jagged coastline and many islands scattered around the shallow waters, the Yellow Sea has diverse marine habitats. Intertidal flats are the most significant type of coastal habitat, but mudflats, salt marshes, sandflats with gravel beaches, sand dunes, eelgrass beds, and mixed flats are also found. These habitats provide feeding, wintering, and summering grounds for migratory birds, and support important food resources and ecological niches for many species. Approximately 1,600 species have been reported from marine and coastal habitats in the Korean part of the Yellow Sea, including 400 phytoplankton, 300 marine macroalgae, 50 halophytes (salt-tolerant species), 500 marine invertebrates, and some 389 vertebrate species. Among them, 166 zooplankton and 276 fish have been reported as resident species in the Yellow Sea. Additionally, 100 commercial species have been identified in the region, comprising demersal fish (66 percent), pelagic fish (18 percent), cephalopods (7 percent), and crustaceans (7 percent).

Sea of Okhotsk

The Sea of Okhotsk is a semienclosed marginal sea bounded by Russia to the north and west and Japan to the south, with an area of 590,003 square miles (1,528,100 square kilometers), similar in magnitude to the Bering Sea. The bottom topography is rugged, featuring the deep Kuril Basin. The shelf zone occupies almost 40 percent of the total area, and is somewhat isolated from direct water exchange with the open ocean by the Kamchatka Peninsula. Seasonal changes are distinctive, and ice can be found from November (rarely, in October) to June. In March, the Sea of Okhotsk is mostly covered by ice, except near Kamchatka and the Kuril Islands.

Oyashio and Kuroshio

The Oyashio is the western boundary current of the sub-Arctic North Pacific, and it is characterized by low temperature, low salinity, and high nutrient concentrations. The eastward-flowing Oyashio forms the Subarctic Front (Oyashio Front), which is a distinctive temperature front. The Oyashio Front mixes with the Kuroshio Extension Front, where cold and warm waters mix and many mesoscale features are formed. This region is called the Kuroshio-Oyashio-Transition Zone (KOTZ), or mixed water region. The Oya­shio brings nutrient-rich water into the western North Pacific, resulting in high productivity in the confluence zone of the two currents.

Along the south side of the Japanese Archipelago flows the Kuroshio Current, a western-boundary warm current. The width of this current is about 62 miles (100 kilometers). The high temperature and high salinity qualities of Kuroshio water bring a high diversity of tropical marine life northward to the coastal area of the Japanese archipelago and off eastern Japan.

Although many species of invertebrates (such as corals) and vertebrates (such as butterfly fishes) can be found near the south coast of Japan, most of them cannot survive and reproduce in the coastal area because of the cold winter water temperatures and the low nutrient concentrations of the Kuroshio. Nutrient concentrations and biological production in the Kuroshio are much lower than in the cold western boundary Oyashio current. Nevertheless, the Kuroshio is a major spawning area for many species of pelagic fishes, such as Japanese sardine (Sardinops melanostictus) and Pacific saury (Cololabis saira), that have their nursery and feeding grounds in the Oyashio area.

Bering Sea

The North Pacific and Arctic Oceans are connected by a semienclosed sub-Arctic sea, the Bering Sea. Bounded by the Bering Strait to the north and the Aleutian archipelago to the south, the Bering Sea consists of a deep central basin, a northwestern shelf in the Gulf of Anadyr that reaches south along the Kamchatka Peninsula, and a broad eastern shelf that stretches from the Alaska Peninsula to Russia and the Bering Strait.

High biological productivity in the Bering Sea supports more than 400 species of fish and at least 15 species of squid. Of these, at least 40 species are of some commercial importance, and catches are dominated by walleye pollock (Theragra chalcogramma), flatfish (Pleuronectidae), Pacific cod (Gadus macrocephalus), crab (Paralithodes spp. and Chioenocetes spp.), rockfish (Sebastes spp.), and five species of Pacific salmon (Oncorhynchus spp.). Rich benthic communities with a large biomass and production of flatfish, Pacific cod, crab, and cephalopods are found in the broad shelves along the eastern and western margins of the Bering Sea.

Forage fishes such as capelin (Mallotus villosus), eulachon (Thalichthys acificus), Pacific sand lance (Ammodytes hexapterus), and juvenile walleye pollock and cephalopods can be locally abundant and provide important food sources to upper-trophic-level species. The surface waters of the central basin of the Bering Sea comprise important feeding areas for abundant Pacific salmon. The midwater community in the basin is poorly known, but it is likely dominated by lantern fishes (Myctophidae, in particular Stenobrachius leucopsarus), and deep-sea smelts (Bathylagidae).

Scientists have reported that the ice extent of the Bering Sea, which is heavily connected to the marine ecosystem around it, has been steadily decreasing. By April 2018, the National Aeronautics and Space Administration's (NASA) Earth Observatory found that the sea's covering of sea ice was drastically below the average for that point in the year. This unusual pattern of melting is likely to disrupt the blooms of phytoplankton, which will in turn negatively impact the marine life dependent upon them.

Alaska Currents

The Alaska Current System comprises the shoreward Alaska Coastal Current (ACC); the offshore Alaska Current (AC); and the Alaskan Stream, eddies, and meanders. Currents extend along the continental shelf and shelf break, reaching as far south as the mouth of the Columbia River and as far west as the Aleutian Islands. The eastern Gulf of Alaska reaches abyssal depths of 9,843 feet (3,000 meters) and plummets to 22,966 feet (7,000 meters) in the Aleutian Trench. The continental shelf has a total area of approximately 142,858 square miles (370,000 square kilometers), and ranges from 3 to 124 miles (5 to 200 kilometers) in width. Islands, banks, ridges, and numerous troughs and gullies cut across the shelf, resulting in a complex bathymetry that promotes exchange between shelf water and deeper waters.

The ACC distributes sub-Arctic plankton communities around the region and into protected inside waters. During the summer months, the ACC has local reversals and small eddies that concentrate plankton and small fishes in convergence zones for foraging fish, birds, and marine mammals. Species including the southeast Alaska Pacific herring (Clupea pallasii), pink salmon (Oncorhynchus gorbuscha), sablefish (Anoplopoma fimbria), Alaska rockfish (Sebastes spp.), Pacific Ocean perch (Sebastes alutus), northern rockfish (Sebastes polyspinus), tanner crab (Chionoecetes bairdi), and Dungeness crab (Metacarcinus magister) are of commercial and ecological importance.

Marine mammals such as the stellar sea lion (Eumetopias jubatus), beluga whale (Delhinapterus leucas), killer whale (Orcinus orca), humpback whale (Megaptera noraengeliae), and sea otter (Enhydra lutris) are also found in the gulf. However, according to the National Oceanic and Atmospheric Association, the once thriving population of beluga whales in the Cook Inlet had declined by 75 percent as of 2016.

California Current

The California Current is a year-round Equator-directed flow that extends 1,864 miles (3,000 kilometers) from the northern tip of Vancouver Island to Baja California Sur. Cool, fresh, and nutrient-rich water is carried through the California Current System. Fishery resources include invertebrate populations, especially in near-shore waters; groundfish populations along the continental shelf; and migratory pelagic species such as salmon (Oncorhynchus spp.), Pacific sardine (Sardinops caeruleus), Pacific hake (Merluccius productus), and Pacific herring (Clupea harengus).

At the southern end, the northern anchovy (Engraulis mordax) and market squid (Loligo opalescens) are important. This system also supports large and diverse seabird and marine-mammal populations.

Oceanic Biome Status

Throughout the North Pacific, annual rates of primary and secondary productivity are generally similar among regions. In general, biomass has been decreasing in the deepwater areas of the eastern and western North Pacific. Phytoplankton and zooplankton biomass has decreased in the northern part of the Oyashio Current and in the southern part of the California Current, but increased in the Yellow Sea and the coastal parts of the Gulf of Alaska.

Fish fauna of North Pacific Ocean coastal systems have declined. More than 50 species of marine mammals are found in the North Pacific. Although not all species are considered to be of commercial importance, the stellar sea cow (Hydroanalus gigas) is known to have been exploited to extinction before 1800, and the Japanese fur seal (Zalophus californianus japonicus) was deemed extinct in the 1970s.

The North Pacific Ocean is known to be one of the most productive and diverse marine ecosystems in the world. This region has witnessed a rapid increase in human population, with important technological, economic, and social transformations. Due to human pressures and the chemical deterioration of many regions in the North Pacific Ocean, significant losses of marine biodiversity have been caused.

Observing an area as large as the North Pacific Ocean is a significant task, resulting in a lack of information for many coastal regions. Scientific research on many fronts has addressed global warming and its potential effects on Pacific Ocean water-layer modalities, salinity, acidity, current structure and speed, atmospheric changes, seasonal “marching,” and island and shoreline effects—to say nothing of observations and theories on the climate-change impacts sustained by many affected marine species. Long-term monitoring programs in this ecosystem that sample physical and biological conditions are necessary to understand the long-term effects of global environmental changes and human activity.

A significant concern since its discovery in 1997, the Great Pacific Garbage Patch is a soup of plastic created by the North Pacific Subtropical Gyre currents. It consists of western and eastern patches of plastic chunks including microplastics, which have been found in the food chain and in the human body. An organization called the Ocean Cleanup estimated in 2018 that the main mass contained 174 million pounds (79 million kg) of plastic. Significantly more encircled this mass. The organization began removing plastic with a system it devised, and as of July 2022 reported it had extracted 220,462 pounds (100,000 kg).

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