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  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 region of marine organisms. The ability to harvest 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 the 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: the Yellow Sea and the East China Sea, the Okhotsk Sea, the Oyashio Current System, the Kuroshio Current System, the Bering Sea, the Alaska Current System, and the California Current System; not all are part of the North Pacific Gyre. This gyre occupies approximately 7.7 million square miles (20 million square kilometers), with a clockwise circular pattern. The Aleutian Islands 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 semi-enclosed 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 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: the Tsushima current, the Yellow Sea Warm Current (YSWC), and the broader influence of the Kuroshio Current.

Due to its jagged coastline and many islands scattered around its 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 in the Yellow Sea. 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, fifty halophytes (salt-tolerant species), 500 marine invertebrates, and approximately 389 vertebrate species. Among them, 166 zooplankton and 276 resident fish species have been reported 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 semi-enclosed marginal sea bounded by Russia to the north and west and Japan to the south, with an area of 611,000 square miles (1,583,000 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 Kuril Islands and the Kamchatka Peninsula. Seasonal changes are distinctive, and ice can typically be found from November through 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 sixty-two 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 the semienclosed sub-Arctic 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 fifteen species of squid. Of these, at least forty species are of some commercial importance, and catches are dominated by walleye pollock (Gadus chalcogrammus), flatfish (Pleuronectidae), Pacific cod (Gadus macrocephalus), crab (Paralithodes spp. and Chionoecetes 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 fish such as capelin (Mallotus villosus), eulachon (Thaelichthys 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 not well-known, but it is likely dominated by lantern fish (Myctophidae, in particular Stenobrachius leucopsarus) and deep-sea smelts (Bathylagidae).

Scientists have reported long-term declines in sea ice, although the eastern Bering Sea has shown a steady increase in ice extent since 2018. The Bering Sea’s ice extent varies seasonally, usually reaching its maximum in March or April and declining through spring and early summer. However, 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, and the lowest on record to that point. By 2022, the Bering Sea’s ice cover reached its greatest extent for early to mid-February since 2013, when it covered more than 327,000 square miles (846,000 square kilometers), exceeding the 1981–2010 mean. In 2023, Arctic sea ice reached its annual minimum at 4.23 million square kilometers on September 19, ranking sixth lowest in the satellite record.

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. The Bering Sea’s seasonal ice cover is extremely important for regional climate regulation, marine ecosystems, and local livelihoods. It insulates ocean waters during winter, while algae growing on the ice’s underside in spring initiates a chain of biological productivity. The extent of this ice is shaped by strong northerly winds, which can expand the cover, and long-term variability in the northern Pacific Ocean. This activity can influence patterns over decades, and these dynamics highlight the delicate balance required to maintain the ecological and economic systems reliant on the ice.

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 three to 124 miles (five 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 waters. During the summer months, the ACC has local reversals and small eddies that concentrate plankton and small fish 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 (Delphinapterus leucas), killer whale (Orcinus orca), humpback whale (Megaptera novaengeliae), and sea otter (Enhydra lutris) are also found in the gulf. However, according to the National Oceanic and Atmospheric Administration, the once thriving population of beluga whales in the Cook Inlet had declined by 75 percent as of 2016. Scientists estimated there were only 269 whales left in 2018, and they estimated there were between 290 and 386 alive in the wild by 2023. The Cook Inlet beluga whale population remains endangered and has not shown significant recovery despite ongoing conservation and monitoring efforts.

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 sagax caerulea), Pacific hake (Merluccius productus), and Pacific herring (Clupea pallasii).

At the southern end, the northern anchovy (Engraulis mordax) and market squid (Doryteuthis 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. Research shows that persistent marine heatwaves in the eastern North Pacific through 2025 have become a major driver of ecosystem change, although strong coastal upwelling in the California Current has helped buffer some impacts. In general, biomass has been decreasing in the deepwater areas of the eastern and western North Pacific. Phytoplankton and zooplankton biomass have 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 the North Pacific Ocean coastal systems has declined. More than fifty species of marine mammals are found in the North Pacific. Although not all species are considered to be of commercial importance, the Steller’s sea cow (Hydrodamalis  gigas) is known to have been exploited to extinction before 1800, and the Japanese sea lion (Zalophus japonicus) was deemed extinct by 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, there have been significant losses of marine biodiversity.

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. Research suggests an increase in Arctic and Alaskan cyclones linked to warmer tropical Pacific waters, indicating changing storm patterns in the North Pacific.

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 patch contained about 79,000 metric tons of plastic. Significantly more encircled this mass. The organization began removing plastic with a system it devised, and by July 2022, it reported that it had extracted 220,462 pounds (100,000 kg). In 2023, The Ocean Cleanup removed over 8 million kilograms of trash from oceans and rivers, including a record 31,816 kg in a single trip.

A 2023 study revealed that plastics in the Great Pacific Garbage Patch (GPGP) serve as rafts for marine species, spreading them far from their habitats. The GPGP orbits around 32°N and 145°W and shifts seasonally. Its plastic composition is dominated by fishing-related debris. A 2018 study attributed 46 percent of its composition to nets and ropes.

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