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Ocean Sci., 13, 531-549, 2017
https://doi.org/10.5194/os-13-531-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
06 Jul 2017
On the meridional ageostrophic transport in the tropical Atlantic
Yao Fu1, Johannes Karstensen1, and Peter Brandt1,2 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
2Christian-Albrechts-Universität zu Kiel, Kiel, Germany
Abstract. The meridional Ekman volume, heat, and salt transport across two trans-Atlantic sections near 14.5° N and 11° S were estimated using in situ observations, wind products, and model data. A meridional ageostrophic velocity was obtained as the difference between the directly measured total velocity and the geostrophic velocity derived from observations. Interpreting the section mean ageostrophy to be the result of an Ekman balance, the meridional Ekman transport of 6. 2 ± 2. 3 Sv northward at 14.5° N and 11. 7 ± 2. 1 Sv southward at 11° S is estimated. The integration uses the top of the pycnocline as an approximation for the Ekman depth, which is on average about 20 m deeper than the mixed layer depth. The Ekman transport estimated based on the velocity observations agrees well with the predictions from in situ wind stress data of 6. 7 ± 3. 5 Sv at 14.5° N and 13. 6 ± 3. 3 Sv at 11° S. The meridional Ekman heat and salt fluxes calculated from sea surface temperature and salinity data or from high-resolution temperature and salinity profile data differ only marginally. The errors in the Ekman heat and salt flux calculation were dominated by the uncertainty of the Ekman volume transport estimates.

Citation: Fu, Y., Karstensen, J., and Brandt, P.: On the meridional ageostrophic transport in the tropical Atlantic, Ocean Sci., 13, 531-549, https://doi.org/10.5194/os-13-531-2017, 2017.
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Short summary
Meridional Ekman transport in the tropical Atlantic was estimated directly by using observed ageostrophic velocity, and indirectly by using wind stress data. The direct and indirect methods agree well with each other. The top of the pycnocline represents the Ekman depth better than the mixed layer depth and a constant depth. The Ekman heat and salt fluxes calculated from sea surface temperature and salinity or from high-resolution temperature and salinity profile data differ only marginally.
Meridional Ekman transport in the tropical Atlantic was estimated directly by using observed...
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