![Schematic of the Alaska Current](https://upload.wikimedia.org/wikipedia/commons/3/33/Schematic_of_the_Alaska_Current.jpg)
The Alaska Current is a southwestern shallow warm-water current alongside the west coast of the
North American continent
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
beginning at about 48-50°N. The Alaska Current produces large clockwise eddies at two sites: west of the
Haida Gwaii
Haida Gwaii (; hai, X̱aaydag̱a Gwaay.yaay / , literally "Islands of the Haida people") is an archipelago located between off the northern Pacific coast of Canada. The islands are separated from the mainland to the east by the shallow Heca ...
("
Haida Eddies
Haida Eddies are episodic, clockwise rotating ocean eddies that form during the winter off the west coast of British Columbia’s Haida Gwaii and Alaska’s Alexander Archipelago. These eddies are notable for their large size, persistence, and freq ...
") and west of
Sitka, Alaska ("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 a slow warm water current that flows west-to-east between 30 and 50 degrees north in the Pacific Ocean. The current forms the southern part of the North Pacific Su ...
. The North Pacific Current provides energy for the
California Current
The California Current is a cold water Pacific Ocean 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 Eastern bound ...
and the Alaska Current. It forms a part of the Alaska Current and continues into the Alaskan Stream, which begins near
Kodiak Island
Kodiak Island ( Alutiiq: ''Qikertaq''), is a large island on the south coast of the U.S. state of Alaska, separated from the Alaska mainland by the Shelikof Strait. The largest island in the Kodiak Archipelago, Kodiak Island is the second la ...
and flows southwestward along the
Alaska Peninsula. 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 east ...
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 of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank ( cut bank) and deposits sediments on an inner, convex ba ...
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. 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 under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
can both affect the Alaska Current. Winds are
downwelling
Downwelling is the process of accumulation and sinking of higher density material beneath lower density material, such as cold or saline water beneath warmer or fresher water or cold air beneath warm air. It is the ''sinking'' limb of a convecti ...
along the coastal area most of the year, which helps to keep the
density contrast Density contrast is a parameter used in galaxy formation to indicate where there are local enhancements in matter density.
:\Delta=\frac
It is believed that after inflation
In economics, inflation is an increase in the general price lev ...
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
In fluid dynamics, the baroclinity (often called baroclinicity) of a stratified fluid is a measure of how misaligned the gradient of pressure is from the gradient of density in a fluid. In meteorology a baroclinic flow is one in which the densi ...
. 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 Density gradient is a spatial variation in density over an area. The term is used in the natural sciences to describe varying density of matter, but can apply to any quantity whose density can be measured.
Aerodynamics
In the study of supersonic ...
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 having five interacting components: the atmosphere (air), the hydrosphere (water), the cryosphere (ice and permafrost), the lithosphere (earth's upper rocky layer) and the biosphere (living things). '' ...
of the
southwestern United States, including seasonal rainfall and snow. It has been shown that
El Niño
El Niño (; ; ) is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (approximately between the International Date ...
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 proces ...
. Several physical processes enhance its nutrient supply and
primary productivity
In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through c ...
. Nutrients can be transported to the northern part of the Gulf of Alaska through
advection, river discharge,
estuarine circulation, tidal mixing, mesoscale eddy formation and transport, sediment resuspension, the relaxation of summer downwelling winds,
Ekman transport of surface water from the central Gulf of Alaska basin onto the shelf during winter. This is important for
marine mammal
Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They are an informal group, unified only by their ...
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 coverage, and
ocean acidification
Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
.
The mean sea surface temperature 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 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. Coastal regions around Alaska are experiencing the most rapid and extensive ocean acidification.
Higher ocean acidity can damage
shellfish and certain types of
plankton
Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...
, 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