Alaska Current
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 Eddies") 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 provides energy for the California Current 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. 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
Winds and precipitation 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.[4]
The Alaska Current, together with the Gulf of Alaska, has an impact on the
Productivity
Despite the dominance of downwelling-favorable winds, the water overlying the northern coast of the Gulf of Alaska has achieved high biological productivity. Several physical processes enhance its nutrient supply and primary productivity. 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 mammals, 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.[5]
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.[6]
The mean
See also
- Ocean current – Directional mass flow of oceanic water generated by external or internal forces
- Ocean gyre – Any large system of circulating ocean surface currents
- Physical oceanography – Study of physical conditions and processes within the ocean
- Gulf of Alaska – Arm of the Pacific Ocean
- California Current – Pacific Ocean current
References
- ^ McKinnell, S.M.; Dagg, M.J. (2010). "Marine Ecosystems of the North Pacific Ocean 2003-2008" (PDF). PICES Special Publication 4.
- ^ "Alaska Current | current, Gulf of Alaska". Encyclopedia Britannica. Retrieved 2021-05-15.
- ^ Stone, R.P.; Shotwell, S.K. (2007). "State of deep coral ecosystems in the Alaska Region: Gulf of Alaska, Bering Sea and the Aleutian Islands" (PDF). N: Lumsden SE et Al., Eds. The State of Deep Coral Ecosystems of the United States. NOAA Technical Memorandum CRCP-3. Silver Spring, MD.
- ^ ISBN 9780128130827.
- .
- .
- ^ a b "A climate science regional action plan for the Gulf of Alaska" (PDF). August 2017.
- ^ "CLIMATE CHANGE IN THE GULF OF ALASKA".
- Environmental Protection Agency. August 2016.