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Climate Dynamics

, Volume 43, Issue 11, pp 2999–3024 | Cite as

Oxygen variance and meridional oxygen supply in the Tropical North East Atlantic oxygen minimum zone

  • J. HahnEmail author
  • P. Brandt
  • R. J. Greatbatch
  • G. Krahmann
  • A. Körtzinger
Article

Abstract

The distribution of the mean oceanic oxygen concentration results from a balance between ventilation and consumption. In the eastern tropical Pacific and Atlantic, this balance creates extended oxygen minimum zones (OMZ) at intermediate depth. Here, we analyze hydrographic and velocity data from shipboard and moored observations, which were taken along the 23°W meridian cutting through the Tropical North East Atlantic (TNEA) OMZ, to study the distribution and generation of oxygen variability. By applying the extended Osborn–Cox model, the respective role of mesoscale stirring and diapycnal mixing in producing enhanced oxygen variability, found at the southern and upper boundary of the OMZ, is quantified. From the well-ventilated equatorial region toward the OMZ core a northward eddy-driven oxygen flux is observed whose divergence corresponds to an oxygen supply of about 2.4 μmol kg−1 year−1 at the OMZ core depth. Above the OMZ core, mesoscale eddies act to redistribute low- and high-oxygen waters associated with westward and eastward currents, respectively. Here, absolute values of the local oxygen supply >10 μmol kg−1 year−1 are found, likely balanced by mean zonal advection. Combining our results with recent studies, a refined oxygen budget for the TNEA OMZ is derived. Eddy-driven meridional oxygen supply contributes more than 50 % of the supply required to balance the estimated oxygen consumption. The oxygen tendency in the OMZ, as given by the multidecadal oxygen decline, is maximum slightly above the OMZ core and represents a substantial imbalance of the oxygen budget reaching about 20 % of the magnitude of the eddy-driven oxygen supply.

Keywords

Oxygen minimum zone Tropical North East Atlantic Oxygen variance Eddy ventilation Oxygen supply Oxygen budget 

Notes

Acknowledgments

This study was supported by the German Science Foundation as part of the Sonderforschungsbereich 754 “Climate-Biogeochemistry Interactions in the Tropical Ocean”. We thank Marcus Dengler and Tim Fischer for helpful discussions, Sven-Helge Didwischus for post-processing of the velocity sections and Andreas Pinck for the development and the maintenance of the optode oxygen loggers.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • J. Hahn
    • 1
    Email author
  • P. Brandt
    • 1
  • R. J. Greatbatch
    • 1
  • G. Krahmann
    • 1
  • A. Körtzinger
    • 1
  1. 1.GEOMAR Helmholtz-Centre for Ocean Research KielKielGermany

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