Propagation of a dead-zone eddy in the tropical North Atlantic Ocean

The upper clip shows the eastern part of the tropical North Atlantic Ocean, with the African Coast on the right and the Cape Verde Islands in the centre. The white cross north of the islands marks the location of the Cape Verde Ocean Observatory (CVOO) mooring where the researchers observed the low-oxygen eddies.

The moving black circle indicates an eddy that, when it was observed at the mooring during February 2010, had very low oxygen concentrations. It formed near the West African coast and then moved slowly to the west due to the Earth’s rotation (the track is seen as an evolving blue line).

The colours in the upper plot represent sea level anomalies, which are also indicative of the direction of water rotation: red is for higher than mean sea surface and anticyclonic eddies, blue means lower sea level anomaly and is indicative of cyclonic eddies. Flow at the surface is represented by grey arrows.

The lower panel shows the oxygen concentration at 40 m depth at the CVOO mooring over a similar time period. Typical concentrations are close to saturation (5 to 6 ml/l). When the dead-zone eddy arrives at the CVOO, the oxygen measured at that location drops abruptly. After the passage, oxygen concentrations at the CVOO return to standard values.

Credit: Florian Schütte/GEOMAR

• ‘Dead zones’ found in Atlantic open waters (30 April 2015)

• Original video (218.1 MB, 49 s, format)
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