Articles | Volume 14, issue 1
https://doi.org/10.5194/cp-14-73-2018
https://doi.org/10.5194/cp-14-73-2018
Research article
 | 
16 Jan 2018
Research article |  | 16 Jan 2018

Hybrid insolation forcing of Pliocene monsoon dynamics in West Africa

Rony R. Kuechler, Lydie M. Dupont, and Enno Schefuß

Abstract. The Pliocene is regarded as a potential analogue for future climate with conditions generally warmer-than-today and higher-than-preindustrial atmospheric CO2 levels. Here we present the first orbitally resolved records of continental hydrology and vegetation changes from West Africa for two Pliocene time intervals (5.0–4.6 Ma, 3.6–3.0 Ma), which we compare with records from the last glacial cycle (Kuechler et al., 2013). Our results indicate that changes in local insolation alone are insufficient to explain the full degree of hydrologic variations. Generally two modes of interacting insolation forcings are observed: during eccentricity maxima, when precession was strong, the West African monsoon was driven by summer insolation; during eccentricity minima, when precession-driven variations in local insolation were minimal, obliquity-driven changes in the summer latitudinal insolation gradient became dominant. This hybrid monsoonal forcing concept explains orbitally controlled tropical climate changes, incorporating the forcing mechanism of latitudinal gradients for the Pliocene, which probably increased in importance during subsequent Northern Hemisphere glaciations.

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Short summary
Measuring deuterium and stable carbon isotopes of higher plant wax extracted from marine sediments offshore of Mauritania, we recovered a record of hydrology and vegetation change in West Africa for two Pliocene intervals: 5.0–4.6 and 3.6–3.0 Ma. We find that changes in local summer insolation cannot fully explain the variations in the West African monsoon and that latitudinal insolation and temperature gradients are important drivers of tropical monsoon systems.