Did Mid-Pleistocene biome shifts cause gully erosion in eastern South Africa?

Pleistocene climate change affects landscape stability in many ways and is reflected in sedimentary archives through phases of erosion, deposition and soil formation. Vegetation dynamics play a mediating role here: while established vegetation stabilizes the landscape when it’s within its climatic optimum, climate-induced vegetation shifts are characterized by ecological stress, turnover and the establishment of new vegetation forms, which promotes a phase of erosion. The landscape archive of Jojosi, KwaZulu-Natal, South Africa, is an exceptional site to better understand these dynamics. The site lies on the boundary between savanna and grassland, where a succession of sedimentary bodies indicates repeated phases of gully cut-and-fills since the Mid-Pleistocene.

We report on the results of several field campaigns in which we have stratigraphically correlated the Jojosi badlands, characterized them using geochemical and spectral properties, dated them using feldspar luminescence and measured their current erosion dynamics with UAV photogrammetry. Building on this, we used geostatistical models based on paleoclimate models to simulate the development of vegetation over the last 800,000 years. According to these models, the environmental conditions of the site oscillated back and forth between grassland and savannah over several climate cycles. The results suggest that past climate changes influenced the growing season length and fire regime, leading to non-linear, altitudinal shifts of the tree line, which promoted erosion and is reflected in the sedimentary succession. Our findings from the past allow to inform the future by inferencing our model to near-future climate scenarios to estimate related erosion risk.