Preprints
https://doi.org/10.5194/egusphere-2024-2288
https://doi.org/10.5194/egusphere-2024-2288
31 Jul 2024
 | 31 Jul 2024

Long-term Variability and Trends of Agulhas Leakage and its Impacts on the Global Overturning

Hendrik Grosselindemann, Frederic S. Castruccio, Gokhan Danabasoglu, and Arne Biastoch

Abstract. Agulhas Leakage transports warm and salty Indian Ocean waters into the Atlantic Ocean  and as such is an important component of the global ocean circulation. These waters are part of the upper limb of the Atlantic Meridional Overturning Circulation (AMOC), and Agulhas Leakage variability has been linked to AMOC variability. Agulhas Leakage is expected to increase under a warming climate due to a southward shift in the South Hemisphere westerlies, which could further influence the AMOC dynamics. This study uses a set of high-resolution pre-industrial control and historical and transient simulations with the Community Earth System Model (CESM) with a nominal horizontal resolution of 0.1° for the ocean and sea-ice and 0.25° for the atmosphere and land. At these resolutions, the model represents the necessary scales to investigate the Agulhas Leakage transport variability and its relation to the AMOC. The simulated Agulhas Leakage transport of 19.7 ± 3 Sv lies well within the observed range of 21.3 ± 4.7 Sv. A positive correlation between the Agulhas Current and the Agulhas Leakage is shown, meaning that an increase of the Agulhas Current transport leads to an increase in Agulhas Leakage. The Agulhas Leakage impacts the strength of the AMOC through Rossby wave dynamics that alter the cross-basin geostrophic balance with a time-lag of 2–3 years. Furthermore, the  salt flux associated with the Agulhas Leakage influences AMOC dynamics through the salt-advection feedback by reducing the AMOC’s freshwater transport at 34° S. The Agulhas Leakage transport indeed increases under a warming climate due to strengthened and southward shifting winds. In contrast, the Agulhas Current transport decreases, both due to a decrease in the Indonesian Throughflow as well as the strength of the wind-driven subtropical gyre. The increase in Agulhas Leakage is accompanied by a higher salt flux into the Atlantic Ocean, which suggests a destabilisation of the AMOC by salt-advection-feedback.

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Hendrik Grosselindemann, Frederic S. Castruccio, Gokhan Danabasoglu, and Arne Biastoch

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2288', Wilbert Weijer, 13 Aug 2024
  • RC2: 'Comment on egusphere-2024-2288', René van Westen, 24 Aug 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2288', Wilbert Weijer, 13 Aug 2024
  • RC2: 'Comment on egusphere-2024-2288', René van Westen, 24 Aug 2024
Hendrik Grosselindemann, Frederic S. Castruccio, Gokhan Danabasoglu, and Arne Biastoch
Hendrik Grosselindemann, Frederic S. Castruccio, Gokhan Danabasoglu, and Arne Biastoch

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Short summary
This study investigates Agulhas Leakage and examines its role in the global ocean circulation. It utilises a high-resolution earth system model and a pre-industrial climate to look at the response of Agulhas Leakage to the wind field and the Atlantic Meridional Overturning Circulation (AMOC) as well as its evolution under climate change. Agulhas Leakage influences the stability of the AMOC whose possible collapse would impact the global climate on the Northern Hemisphere.