Großelindemann, Hendrik (2024) Long-term Variability of Agulhas Leakage and its Embedding into the Global Overturning. (Master thesis), Christian-Albrechts-Universität, Kiel, Germany, 38 pp.

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Abstract

The Agulhas Leakage (AL) 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 AL variability has been linked to AMOC variability. The AL is expected to
increase under a warming climate due to a shift in the Southern Hemisphere westerlies,
which could further influence the AMOC dynamics. This study investigates the AL
transport variability on long time scales in the pre-industrial and under a warming climate
and its relation to the AMOC. It uses a high-resolution configuration of 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, which resolves the necessary spatial
scales. The simulated AL 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 AL is shown,
meaning that an increase of the Agulhas Current transport leads to an increase in AL.
Furthermore, the salt flux associated with the AL influences AMOC dynamics through
the salt-advection feedback by reducing the AMOC’s freshwater transport at 34°S. In a
warming climate, the AL transport was indeed found to increase due to strengthened and
southward shifting winds while the Agulhas Current transport was found to decrease.
Consequently, a larger fraction of the Agulhas Current will flow into the Atlantic Ocean
rather than being recirculated into the Indian Ocean. The increase in AL is accompanied
by a higher salt flux into the Atlantic Ocean, which destabilises the AMOC within the
salt-advection-feedback. But whether and to what extent this additional salt advected
to the North Atlantic could also dampen an AMOC weakening induced by increased
meltwater input under climate change still needs further research.

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