
The Alaska Current is a southwestern shallow warm-water current alongside the west coast of the
North American continent beginning at about 48-50°N. The Alaska Current produces large clockwise eddies at two sites: west of the
Haida Gwaii
Haida Gwaii (; / , literally "Islands of the Haida people"), previously known as the Queen Charlotte Islands, is an archipelago located between off the British Columbia Coast, northern Pacific coast in the Canadian province of British Columbia ...
("
Haida Eddies") and west of
Sitka, Alaska
Sitka (; ) is a municipal home rule, unified Consolidated city-county, city-borough in the southeast portion of the U.S. state of Alaska. It was under Russian America, Russian rule from 1799 to 1867. The city is situated on the west side of Ba ...
("Sitka Eddy").
Track
The Alaska current results from the northward diversion of a portion of the
North Pacific Current
The North Pacific Current (sometimes referred to as the North Pacific Drift) is an ocean current that flows west-to-east between 30th parallel north, 30 and 50th parallel north, 50 degrees north in the Pacific Ocean. The current forms the souther ...
. The North Pacific Current provides energy for the
California Current
The California Current () is a cold water Pacific Ocean ocean current, current that moves southward along the western coast of North America, beginning off southern British Columbia and ending off southern Baja California Sur. It is considered an ...
and the Alaska Current. It forms a part of the Alaska Current and continues into the Alaskan Stream, which begins near
Kodiak Island and flows southwestward along the
Alaska Peninsula
The Alaska Peninsula (also called Aleut Peninsula or Aleutian Peninsula, ; Sugpiaq language, Sugpiaq: ''Aluuwiq'', ''Al'uwiq'') is a peninsula extending about to the southwest from the mainland of Alaska and ending in the Aleutian Islands. T ...
. A part of the Alaskan Stream turns southward and becomes part of the recirculation of the North Pacific Ocean Current, thus completing the loop of the Alaska Gyre.
Physical properties
The
Gulf of Alaska
The Gulf of Alaska ( Tlingit: ''Yéil T'ooch’'') is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the ...
coastal area includes the offshore Alaska Current, Alaskan Stream, Alaska Coastal Current and some eddies. In the eastern part of the Gulf of Alaska, the Alaska Current flows counterclockwise, and it is relatively wide (> 100 km)
meander
A meander is one of a series of regular sinuous curves in the Channel (geography), channel of a river or other watercourse. It is produced as a watercourse erosion, erodes the sediments of an outer, concave bank (cut bank, cut bank or river cl ...
ing and slow (3–6 m/min). The water of Alaska Current is characterized by temperatures above 39 °F (4 °C). Usually, the Alaska Current contains large
mesoscale vortices, which help to transfer energy and water from the ocean boundary into the interior of ocean. It turns into the Alaska Stream west of Kodiak Island where it becomes narrows (< 60 km) and its speed increases (1 m/s). The Alaska Coastal Current is located in the inner third of the continental shelf and it is driven by along-shore winds and freshwater influx. It has a typical width of about 30 km, the depth is 100–200 m, and the velocity is > 1 m/s. The mean transport is about 0.6
Sv and its seasonal variation is about 0.2 Sv.
Winds and
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
can both affect the Alaska Current. Winds are
downwelling along the coastal area most of the year, which helps to keep the
density contrast between central Gulf of Alaska water and fresher, lower density water on the shelf. The coastal current in the Gulf of Alaska is strongly
baroclinic. Precipitation and coastal runoff reduce the water density on the shelf. Due to the baroclinic density field, the Alaska current is highly sheared vertically, and the cross-current
density gradient is reflected by the offshore salinity gradient. The surface salinities are less than 30 PSU (Practical Salinity Unit) at the coastal areas, more than 31 PSU on the shelf, and more than 32.5 PSU in the central Gulf of Alaska. The mean transport of the baroclinic current near Kodiak Island in the western gulf of Alaska is approximately 10 Sv in the upper 1500 m.
The Alaska Current, together with the Gulf of Alaska, has an impact on the
climate system
Earth's climate system is a complex system with five interacting components: the Atmosphere of Earth, atmosphere (air), the hydrosphere (water), the cryosphere (ice and permafrost), the lithosphere (earth's upper rocky layer) and the biosphere ( ...
of the
southwestern United States
The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural list of regions of the United States, region of the United States that includes Arizona and New Mexico, along with adjacen ...
, including seasonal rainfall and snow. It has been shown that
El Niño
EL, El or el may refer to:
Arts and entertainment Fictional entities
* El, a character from the manga series ''Shugo Chara!'' by Peach-Pit
* Eleven (''Stranger Things'') (El), a fictional character in the TV series ''Stranger Things''
* El, fami ...
affects the west coast through atmospheric as well as oceanic route. During an El Niño, surface transport in the Alaska Gyre strengthens. In the Alaska Current system, 7– 8 months after El Niño occurred on the equator, an anomaly of subsurface temperature larger than 1.5 °C was found along the coast.
Productivity
Despite the dominance of downwelling-favorable winds, the water overlying the northern coast of the Gulf of Alaska has achieved high biological
productivity
Productivity is the efficiency of production of goods or services expressed by some measure. Measurements of productivity are often expressed as a ratio of an aggregate output to a single input or an aggregate input used in a production proce ...
. Several physical processes enhance its nutrient supply and
primary productivity
Primary or primaries may refer to:
Arts, entertainment, and media Music Groups and labels
* Primary (band), from Australia
* Primary (musician), hip hop musician and record producer from South Korea
* Primary Music, Israeli record label
Works
* ...
. Nutrients can be transported to the northern part of the Gulf of Alaska through
advection
In the fields of physics, engineering, and earth sciences, advection is the transport of a substance or quantity by bulk motion of a fluid. The properties of that substance are carried with it. Generally the majority of the advected substance is a ...
, river discharge,
estuarine circulation, tidal mixing, mesoscale eddy formation and transport, sediment resuspension, the relaxation of summer downwelling winds,
Ekman transport
Ekman transport is part of Ekman motion theory, first investigated in 1902 by Vagn Walfrid Ekman. Winds are the main source of energy for ocean circulation, and Ekman transport is a component of wind-driven ocean current. Ekman transport occurs w ...
of surface water from the central Gulf of Alaska basin onto the shelf during winter. This is important for
marine mammal
Marine mammals are mammals that rely on marine ecosystems for their existence. They include animals such as cetaceans, pinnipeds, sirenians, sea otters and polar bears. They are an informal group, unified only by their reliance on marine enviro ...
s, fish and birds. The productivity in the Alaska Current System supports some of the nation's largest fisheries and large numbers of birds and mammals.
Effects of climate change
Current climate models predict that the climate in the Gulf of Alaska will change drastically in the coming decades. The northern Gulf of Alaska maintains an efficient ecosystem, but the distribution and abundance of living marine resources are expected to be significantly affected by changes in water temperature, changes in
sea ice
Sea ice arises as seawater freezes. Because ice is less density, dense than water, it floats on the ocean's surface (as does fresh water ice). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world' ...
coverage, and
ocean acidification
Ocean acidification is the ongoing decrease in the pH of the Earth's ocean. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. Carbon dioxide emissions from human activities are the primary cause of ...
.
The mean
sea surface temperature
Sea surface temperature (or ocean surface temperature) is the ocean temperature, temperature of ocean water close to the surface. The exact meaning of ''surface'' varies in the literature and in practice. It is usually between and below the sea ...
is expected to increase. Model projections indicate that most of the North Pacific will have warmed by an average of 1.2-1.8 °C by 2050. Precipitation is likely to increase, and the amount of rainfall will exceed the amount of snowfall.
Glaciers
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
near the northern coast of the Gulf of Alaska are melting at an unprecedented rate. Climate models predict that by 2050, glacial river runoff from Alaska rivers will increase by 40%. More precipitation and glacial melting will add more fresh water to coastal areas, which will strengthen the baroclinic structure on the
continental shelf
A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...
. Coastal regions around Alaska are experiencing the most rapid and extensive ocean acidification.
Higher ocean acidity can damage
shellfish
Shellfish, in colloquial and fisheries usage, are exoskeleton-bearing Aquatic animal, aquatic invertebrates used as Human food, food, including various species of Mollusca, molluscs, crustaceans, and echinoderms. Although most kinds of shellfish ...
and certain types of
plankton
Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...
, and fewer plankton means less food available to support for fish and some other species.
See also
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References
{{Ocean
Climate of Alaska
Currents of the Pacific Ocean
Water in Alaska