The drivers of late Quaternary climate variability in eastern South Africa

Abstract

Abstract. The scarcity of continuous, terrestrial, palaeoenvironmental records in eastern South Africa leaves the evolution of late Quaternary climate and its driving mechanisms uncertain. Here we use a ~ 7-m long core from Mfabeni peatland (KwaZulu-Natal, South Africa) to reconstruct climate variability for the last 32 thousand years (ka BP). We infer past vegetation and hydrological variability using stable carbon (𝛿13Cwax) and hydrogen isotopes (𝛿Dwax) of plant-wax n-alkanes and use Paq to reconstruct water table changes. Our results indicate that late Quaternary climate in eastern South Africa did not respond directly to orbital forcing nor to changes in sea surface temperatures (SSTs) in the western Indian Ocean. The arid conditions evidenced at Mfabeni during the Last Glacial Maximum (LGM) are a consequence of both low SSTs and an equatorward displacement of the southern hemisphere westerlies due to increased Antarctic sea ice extent. The increased humidity at Mfabeni between 19–14 ka BP likely resulted from decreased Antarctic sea ice which led to a southward retreat of the westerlies and increased the influence of the moisture-bearing tropical easterlies. Between 14–5 ka BP, when the westerlies were in their southernmost position, local insolation became the dominant control, leading to stronger atmospheric convection and an enhanced tropical easterly monsoon. Generally drier conditions persisted during the past c. 5 kyrs, but were overlain by high amplitude, millennial-scale environmental variability, probably resulting from an equatorward return of the southern hemisphere westerlies and heightened ENSO activity. Our findings stress the influence of the southern hemisphere westerlies in driving climatological and environmental changes in eastern South Africa.

Vegetation state changes in the course of shrub encroachment in an African savanna since about 1850 CE and their potential drivers

“…This technique enables the reconstruction of tropical plant diversity at high taxonomic resolution (Boessenkool et al, 2014;Bremond et al, 2017). Further, fire dynamics and its impact on savanna vegetation can be reconstructed from sedimentary charcoal (Colombaroli, van der Plas, Rucina, & Verschuren, 2018;Gillson & Ekblom, 2009), while carbon (δ 13 C) and deuterium (δD) isotope compositions of plant-wax n-alkanes can be used to reconstruct vegetation structure and hydrological variability (Garcin et al, 2018;Miller et al, 2019;Walther & Neumann, 2011). In addition, grain-size analyses of lake sediments are useful to reconstruct sediment mobility in savanna landscapes and to identify soil erosion (Walther & Neumann, 2011).…”