Azores Current
The Azores Current is the northern branch of the subtropical gyre in the North Atlantic Ocean.
The current moves in a generally eastward to southeastward direction, originating in the vicinity of Newfoundland's Grand Banks, the point at which the Gulf Stream divides into two branches.
This current conveys approximately 15 Sv of water along 35-40o N to the western part of the gyre, i.e. the Canary Current.(Alves et al. 2002)
Hydrography
To first order, the Azores Current (AzC) and its associated thermohaline front are in geostrophic balance. This marine current divides fresher and colder waters of north and northeastern origin from warm and more saline water masses at the south (mainly the 18 degree Celsius mode water). The AzC is the northern border of the subtropical gyre and acts as a continuous link to the southeastern branch of Gulf Stream.
Where the Grand Banks of Newfoundland serves as the nominal point of origination of the Azores Current, the the northern current divide turns into the North Atlantic Current, and the southern branch becomes the Azores Current.
The AzC feeds the C+anary Current, that in turn connects with the westwards North Equatorial Current (or Cape Verde Current), which closes the gyre when it merges with the Gulf Stream. The AzC is a quasi-permanent feature throughout the year, centred between 33 and 35 degrees N, with a variable eastward to southeastward transport, ranging from about nine Sverdrup (Sv) in winter (one Sv=106 m3/s), 12 Sv in summer, to about 19 Sv in spring.
According to Jia, the efflux of highly saline water from the Alboran Sea subelement of the Mediterranean Sea serves to augment the strength of the Azores Current.
Marine Ecology
According to Fernandez and Pingree, a close linkage exists between the STF-Azores Current physical feature and high levels of chlorophyll a in the Azores Current. A high resolution survey showed chlorophyll a fluorescence associated with the southern frontal boundary (consisting of chain forming diatoms and flagellates) and with the Azores Current (composed of cells in the less than two micrometers size-class), respectively. Primary production rates measured in the frontal high-chlorophyll region (> 1 mg C per cubic meter h−1) were significantly elevated in comparson to prior data collected in the same locale in late spring and summer and about two times higher than modelling estimates for the region. The large spatial extension of the biological signature associated with the STF-Azores Current system suggests that carbon fixation within the frontal structure could be significant for regional carbon budgets of the subtropical northeast Atlantic Ocean.
Climate Implications
Many climatological studies suggest the AzC is a shallow baroclinic feature no deeper than 1000 m. Surface mean speeds reach 30 to 40 centimeters per second (cm/s), decreasing to some five cm/s at about 700 meters in depth. Unstable wavelengths ranging from 200 up to 400 kilometers or more may occur in the AzC system. Energetic time cycles between 20 and 120 days have been observed.
Further Reading
- Peter Saundry. 2011. Seas of the world. Topic ed. C.Michael Hogan, Ed.-in-Chief Cutler J.Cleveland. Encyclopedia of Earth
- Emilio Fernández and Robin D. Pingree. 1996. Coupling between physical and biological fields in the North Atlantic subtropical front southeast of the Azores. Deep Sea Research Part I: Oceanographic Research Papers. Volume 43, Issue 9, September 1996, Pages 1369-1393
- R.D.Pingree, C.Garcia-Soto and B. Sinha. 1999: Position and structure of the Subtropical/Azores Front region from combined Lagrangian and remote sensing (IR/altimeter/SeaWiFS) measurements. Journal of the Marine Biological Association of the United Kingdom, 79, 769-792.
- Physical Oceanography Index. Encyclopedia of Earth
- A. Sy. Investigation of large–scale circulation patterns in the central North Atlantic: The North Atlantic Current, the Azores Current, and the Mediterranean Water plume in the area of the Mid–Atlantic Ridge. Deep–Sea Res., 35:383–413, 1988.
- A. L. New, Y. Jia, M. Coulibaly, and J. Dengg. On the role of the Azores Current in the ventilation of the North Atlantic Ocean. Progr. Oceanogr., 48:163–194, 2001.
- T.M.Özgökmen., E.P. Chassignet and C.G.H. Rooth, 2001: On the Connection between the Mediterranean Outflow and the Azores Current. Journal of Physical Oceanography 31, 461–480.
- Mario Alves, Fabienne Gaillard, Michael Sparrow, Michaela Knoll, and Sylvie Giraud. Circulation patterns and transport of the Azores Front–Current system. DSR II, 49:3983–4002, 2002.
- Peter Saundry. 2011. Seas of the World. Topic ed. C.Michael Hogan. ed.-in-Chief Cutler J.Cleveland. Encyclopedia of Earth. National Council for Science and the Environment. Washington DC
- Y. Jia., 2000. Formation of an Azores Current due to Mediterranean overflow in a modeling study of the North Atlantic. Journal of Physical Oceanography 30, 2342–2358.
