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https://doi.org/10.5194/os-2020-55
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-2020-55
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 26 Jun 2020

Submitted as: research article | 26 Jun 2020

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This preprint is currently under review for the journal OS.

Seasonal variability of the Atlantic Meridional Overturning Circulation at 11° S inferred from bottom pressure measurements

Josefine Herrford1, Peter Brandt1,2, Torsten Kanzow3, Rebecca Hummels1, Moacyr Araujo4, and Jonathan V. Durgadoo1,2 Josefine Herrford et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
  • 2Christian-Albrechts-Universität zu Kiel, Kiel, Germany
  • 3Alfred Wegener Institute, Bremerhaven, Germany
  • 4Department of Oceanography Federal University of Pernambuco, Recife, Brazil

Abstract. Bottom pressure observations on both sides of the Atlantic basin, combined with satellite measurements of sea level anomalies and wind stress data, are utilized to estimate variations of the Atlantic Meridional Overturning Circulation (AMOC) at 11° S. Over the period 2013–2018, the AMOC and its components are dominated by seasonal variability, with peak-to-peak amplitudes of 12 Sv for the upper-ocean geostrophic transport, 7 Sv for the Ekman and 14 Sv for the AMOC transport. The observed seasonal cycles of the AMOC, its components as well as the Western Boundary Current as observed with current meter moorings are in general good agreement with results of an ocean general circulation model. The seasonal variability of zonally integrated geostrophic velocity in the upper 300 m is controlled by pressure variations at the eastern boundary, while at 500 m depth contributions from the western and eastern boundaries are similar. The model tends to underestimate the seasonal pressure variability at 300 and 500 m depth, slightly stronger at the western boundary. In the model, seasonal AMOC variability at 11° S is governed by the variability in the eastern basin. Here, long Rossby waves originating from equatorial forcing are known to be radiated from the Angolan continental slope and propagate westward into the basin interior. The contribution of the western basin to AMOC seasonal variability is instead comparably weak as transport variability due to locally forced Rossby waves is mainly compensated by the Western Boundary Current. Our analyses indicate, that while some of the uncertainties of our estimates result from the technical aspects of the observational strategy or processes being not properly represented in the model, uncertainties in the wind forcing are particularly relevant for AMOC estimates at 11° S.

Josefine Herrford et al.

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Data sets

Bottom Pressure Recorders used to estimating seasonal AMOC variability at 11° S. J. Herrford, P. Brandt, and G. Krahmann https://doi.pangaea.de/10.1594/PANGAEA.907589

Josefine Herrford et al.

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Short summary
The Atlantic Meridional Overturning Circulation (AMOC) is an important component of the climate system. Understanding its structure and variability is a key priority for many scientists. Here, we present the first estimate of AMOC variations for the tropical South Atlantic – from the TRACOS array at 11° S. Over the observed period, the AMOC is dominated by seasonal variability. We investigate the respective mechanisms with an ocean model and find different wind-forced waves to play a big role.
The Atlantic Meridional Overturning Circulation (AMOC) is an important component of the climate...
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