The tropical North East Atlantic (TNEA) is characterized by an oxygen minimum zone (OMZ) that is located at intermediate depth (300m – 700m) and latitudinally spreads between the oxygen-rich equatorial Atlantic and the Cape Verde Frontal Zone at about 20°N. Recent studies have shown that local oxygen fluctuations and the associated ventilation of the TNEA OMZ are mainly caused by diapycnal mixing and mesoscale eddies. Zonal currents additionally ventilate the TNEA by advecting oxygen-rich water from the well-ventilated western boundary eastwards. The spatial and temporal variability of these zonal currents is thought to contribute to the oxygen variability in this regime.
An intense measurement program along 23°W cutting through the TNEA OMZ has been executed during recent years. Moored observations and repeat ship sections were performed with CTD/O2 (conductivity, temperature, depth, oxygen) and current measurements. Here, we analyze the spatial and temporal variability of the zonal currents in the TNEA at intermediate depths and discuss their respective role for the spatial and temporal oxygen variability as well as the ventilation of the OMZ. Particularly, the observed annual cycle of the North Equatorial Undercurrent (NEUC) at 5°N, which is several cm/s at intermediate depth, causes phase-shifted (zonal velocity leading oxygen) annual oxygen fluctuations in a range of about 10 µmol/kg. In general, time-varying zonal currents advect oxygen eastwards that is meridionally redistributed by mesoscale eddies. The overall effect of those currents for the ventilation of the OMZ is discussed
