Oxygen minimum zone in the North Atlantic south and east of the Cape Verde Islands

• Published in: Journal of Geophysical Research
• Main Authors: Stramma, Lothar, Brandt, Peter, Schafstall, Jens, Schott, Friedrich, Fischer, Jürgen, Körtzinger, Arne
• Format: Article in Journal/Newspaper
• Language: English
• Published: AGU (American Geophysical Union) 2008
• Subjects: Antarctic; Antarc*; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/5037/; https://oceanrep.geomar.de/id/eprint/5037/1/55_Stramma_2008_OxygenMinimumZoneInThe_Artzeit_pubid9059.pdf; https://doi.org/10.1029/2007JC004369

The open-ocean oxygen minimum zone (OMZ) south and east of the Cape Verde Islands is studied from CTD hydrography, ADCP velocities, Argo float trajectories, and historical data, with a focus on the zonal supply and drainage paths. The strongest oxygen minimum is located north of the North Equatorial Countercurrent (NECC) at about 400 to 500-m depth just above the boundary between Central Water and Antarctic Intermediate Water (AAIW). It is shown that the NECC, the North Equatorial Undercurrent at 4 to 6°N, and a northern branch of the NECC at 8 to 10°N are the sources for oxygen-rich water supplied to the OMZ in summer and fall. A weak eastward NECC at 200-m depth also exists in winter and spring as derived from Argo floats drifting at shallow levels. Historical oxygen data from 200-m depth confirm this seasonality showing high (low) oxygen content in summer and fall (spring) within the supply paths. Compared to the strong oxygen supply at 150 to 300-m depth, the ventilation of the OMZ at 300 to 600-m depth is weaker. Westward drainage of oxygen-poor water takes place north of the Guinea Dome, i.e., north of 10°N, most pronounced at 400 to 600-m depth. In July 2006 the total eastward transport of both NECC bands above σ θ = 27.1 kg m−3 at 23°W was about 13 Sv (1 Sv = 106 m3 s−1). About half of this water volume circulates within the Guinea Dome or recirculates westward north of the Guinea Dome.