Eddies in the Gulf of Alaska

Image of the Month - March 2010

Sea Level Anomaly contours (for +10 cm) over year 2007 for two Gulf of Alaska eddies (one from the Kenai region, left the other, right, from the Sitka region), with starting and ending contours labeled and outlined in red, and the trajectory of the eddy center overlaid in black. (Credits University of California Santa Cruz)

 
Eddies are conveyors of many things in the ocean -- heat and nutrients among others. For a few years now mathematical techniques have been able to track and monitor these features in remotely sensed ocean datasets like sea surface height, in order to better understand their formation regions and transit pathways.

Gulf of Alaska's eddies tend to form in specific regions (for which they are later named), and move generally westward, along a corridor that runs parallel to the shelfbreak. Several warm eddies (anticyclonic eddies, seen as bumps on the sea level anomaly maps) are typically present at any given time in the Gulf of Alaska. These eddies form on or near the shelf, are about 80 to 200 km in diameter and extend to depths of 1500 m or below. Their core water is usually fresher, warmer, and more iron-rich than the ambient basin water in the same depth range.

Altimetry enables researchers to spot and monitor such ocean features. A better understanding of eddies, and their birth and movement, could improve our understanding the ocean.  An interesting area of current research is investigating the role of these eddies in transporting and mixing iron from the shelf to basin, substantially enhancing regional biological production.

Start (black triangles), end (red triangles), and interim (blue dots) locations of feature centers from an automated spotting and monitoring of the eddies (Blue stars mark the start locations of the two eddies mentionned above, green ones are other eddies, from the northwesternmost eddy generation region). Two clusters of black triangles are visible: one is off of the continental shelf in the southeast Gulf (the "Haida" formation region), and the other is in the northeast Gulf (the "Sitka" formation region). Haida eddies propagate both northwestward along the shelf break and often westward out into the central Gulf. While some Sitka eddies move into the interior of the Gulf, many propagate along the shelf break. There is almost no eddy in the interior of the western Gulf, which might be related to the chain of seamounts that cross the interior of the Gulf. (Credits University of California Santa Cruz)

See also:

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References:

  • Rovegno, P. S., C. A. Edwards, and K. W. Bruland (2009), Observations of a Kenai Eddy and a Sitka Eddy in the Northern Gulf of Alaska, J. Geophys. Res., 114, C11012, doi:10.1029/2009JC005451.
  • Henson, S. A., and A. C. Thomas (2008), A census of oceanic anticyclonic eddies in the Gulf of Alaska, Deep Sea Res. I, 55, 163– 176.