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High-latitude obliquity forcing drives the agulhas leakage

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Author(s): T. Caley | J.-H. Kim | B. Malaizé | J. Giraudeau | T. Laepple | N. Caillon | K. Charlier | H. Rebaubier | L. Rossignol | I. S. Castañeda | S. Schouten | J. S. S. Damsté

Journal: Climate of the Past Discussions
ISSN 1814-9340

Volume: 7;
Issue: 3;
Start page: 2193;
Date: 2011;
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ABSTRACT
The Agulhas Current (AC) transport of heat and salt from the Indian Ocean into the South Atlantic around South Africa (Agulhas leakage), has a profound role in the decadal variability of the Atlantic meridional overturning circulation (AMOC), which influences global climate. On glacial-interglacial timescales, paleostudies postulate that Agulhas leakage plays a decisive role for AMOC resumption during terminations (glacial-interglacial transitions). However, efforts to elucidate forcing mechanisms connecting Agulhas leakage with glacial-interglacial AMOC variability have been hampered due to a lack of climate records extracted from the area where the AC originates. Here we present 800-kyr sea surface temperature (SST) and salinity (SSS) records from the "precursor" region of the AC. These records contain strong obliquity-driven 41-kyr cycles, nearly in phase with changes in annual mean insolation and air temperature at high southern latitudes. In contrast, precession-driven cycles were negligible in our SST records, which is surprising given the low-latitude location of the Agulhas leakage. Together, this suggests that long-term Agulhas leakage dynamics are associated with a high latitude rather than a tropical climate forcing mechanism, probably by varying the position of the Southern Hemisphere subtropical convergence (STC) and its associated westerlies. We argue that during terminations stronger Agulhas leakage was triggered by increased obliquity exerting a positive feedback on the global climate system through modulating long-term AMOC variations.

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Tangokurs Rapperswil-Jona

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