Response of terrigenous weathering to the African monsoon during the penultimate deglaciation and the last interglacial period

Abstract. Climates of the last interglacial period (i.e., marine isotope stage 5e; MIS 5e) were associated with hydrographic, ecological, and human expansions across northern Africa. Model simulations and geological proxy data for northern subtropical latitudes resolve a dry penultimate deglaciation (Heinrich stadial 11; HS11) followed by an abrupt increase of African rainfall that predates the orbital insolation maximum of early MIS 5e. These climate changes have been attributed to the equatorward displacement and rebound of the tropical rainbelt in response to glacial reorganizations of Atlantic meridional overturning circulation (AMOC). In this paper, we examine MIS 5e and HS11 paleoenvironments by using X-ray fluorescence measurements to construct a Rb/Sr proxy record of terrigenous delivery to marine core site VM 30-40 (0o 12’ S, 20o 09’ W, 3,706 m depth) of the Atlantic Ocean. The geochemical timeseries was inferred to represent continental weathering influenced by the African monsoon evolving over the last ~260 kyr of the Quaternary. Peak Rb/Sr values were observed at the most recent and penultimate glacial maxima, attributed to different modes of continental weathering or perhaps dissolution of Sr-bearing phases by corrosive deep waters. Spectral coherency results and filtering of the Rb/Sr timeseries demonstrate an absence of obliquity yet a predominance of a precession signal that shares the best phase relationships with March-April-May insolation at the equator. This vernal signal is interpreted to indicate that the terrigenous fraction of the core had low-latitude source areas, where the monsoonal cycle is most sensitive to insolation changes about the equinoxes. These data also show a wet climate during HS11 that progresses towards peak conditions at ~127 ka, nearly coinciding with the insolation maximum of early MIS 5e. We interpret that latitude plays an important role in determining the outcomes of AMOC forcing, with the low-latitude terrigenous sources differing from the northern subtropics because the former was into the (equatorward) direction of rainbelt displacement. Lastly, these results suggest a very limited role for obliquity-controlled paleoenvironmental changes within Middle Stone Age habitats and may support previous interpretations that social networks were enhanced between the west and north African regions during times of increased rainfall forced by precession-modulated insolation.