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The oxygen minimum zone in the eastern North Atlantic south and east of the Cape Verde Islands

Journal of Geophysical Research (2008)
Stramma L, Brandt P, Schafstall J, Schott F, Fischer J and Körtzinger A
Doi: 10.1029/2007JC004369
Vol 113; Issue C4; pp. 1-15

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 degrees N, and a northern branch of the NECC at 8 to 10 degrees 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 degrees N, most pronounced at 400 to 600-m depth. In July 2006 the total eastward transport of both NECC bands above sigma(theta)= 27.1 kg m(-3) at 23 degrees W was about 13 Sv (1 Sv = 10(6) m(3) s(-1)). About half of this water volume circulates within the Guinea Dome or recirculates westward north of the Guinea Dome.

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