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Eddies and an extreme water mass anomaly observed in the eastern south Pacific at the Stratus mooring
Author(s) -
Stramma Lothar,
Weller Robert A.,
Czeschel Rena,
Bigorre Sebastien
Publication year - 2014
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2013jc009470
Subject(s) - eddy , ocean gyre , water mass , anticyclone , mooring , geology , sea surface height , mode water , thermocline , oceanography , anomaly (physics) , climatology , subtropics , sea surface temperature , meteorology , turbulence , geography , physics , condensed matter physics , fishery , biology
In the tropical eastern South Pacific the Stratus Ocean Reference Station (ORS) (∼20°S, 85.5°W) is located in the transition zone between the oxygen minimum zone (OMZ) and the well‐oxygenated subtropical gyre. In February/March 2012, extremely anomalous water mass properties were observed in the thermocline at the Stratus ORS. The available eddy oxygen anomaly was −10.5 × 10 16 µmol. This anomalous water was contained in an anticyclonic mode‐water eddy crossing the mooring site. This eddy was absorbed at that time by an anticyclonic feature located south of the Stratus mooring. This was the largest water property anomaly observed at the mooring during the 13.5 month deployment period. The sea surface height anomaly (SSHA) of the strong mode‐water eddy in February/March 2012 was weak, and while the lowest and highest SSHA were related to weak eddies, SSHA is found not to be sufficient to specify the eddy strength for subsurface‐intensified eddies. Still, the anticyclonic eddy, and its related water mass characteristics, could be tracked backward in time in SSHA satellite data to a formation region in April 2011 off the Chilean coast. The resulting mean westward propagation velocity was 5.5 cm s −1 . This extremely long‐lived eddy carried the water characteristics from the near‐coastal Chilean water to the open ocean. The water mass stayed isolated during the 11 month travel time due to high rotational speed of about 20 cm s −1 leading to almost zero oxygen in the subsurface layer of the anticyclonic mode‐water eddy with indications of high primary production just below the mixed layer.