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Ocean Science An interactive open-access journal of the European Geosciences Union

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doi:10.5194/os-2016-98
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
09 Jan 2017
Review status
This discussion paper is under review for the journal Ocean Science (OS).
On the meridional ageostrophic transport in the tropical Atlantic
Yao Fu, Johannes Karstensen, and Peter Brandt GEOMAR Helmholtz Centre for Ocean Research 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 wind products, in-situ observations, 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. Wave-like structures exist in the ageostrophic velocity with 60–80 m vertical scale and large horizontal coherence, which are likely associated with near-inertial waves. The meridional Ekman transport estimated by integrating the ageostrophic velocity was 6.2 ± 2.3 Sv northward at 14.5° N and 11.7 ± 2.1 Sv southward at 11° S, which 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 top of the pycnocline well represents the penetration depth of the Ekman currents at both sections, which was typically 20 m deeper than the local mixed layer depth. We observed that in the meridional Ekman heat and salt flux calculation, using only the sea surface temperature and salinity data had a negligible impact on the resulting fluxes compared to using temperature and salinity profile data covering the Ekman layer. The errors in the Ekman heat and salt flux calculation were dominated by the uncertainty in the Ekman volume transport estimates.

Citation: Fu, Y., Karstensen, J., and Brandt, P.: On the meridional ageostrophic transport in the tropical Atlantic, Ocean Sci. Discuss., doi:10.5194/os-2016-98, in review, 2017.
Yao Fu et al.
Yao Fu et al.
Yao Fu et al.

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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. Top of the pycnocline represents the Ekman depth better than the mixed layer depth and a constant depth. Wave-like structures with large horizontal coherence were observed in the ageostrophic velocity, which are likely associated with near-inertial motions.
Meridional Ekman transport in the tropical Atlantic was estimated directly by using observed...
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