Palaeoclimate dynamics within the Summer Rainfall Zone of South Africa

Abstract

South Africa has a particularly spatially heterogeneous climate driven by a complex set of ocean-atmospheric factors. This results in three distinct regions of rainfall seasonality: the summer- (SRZ), winter- (WRZ) and year-round (YRZ) rainfall zones. Even within these zones there is considerable spatio-temporal variability in precipitation patterns, especially in the SRZ which covers the largest terrestrial area. Over the past several thousand years the position of the boundaries of the southern extent of the SRZ have shifted due to the influences of major climate systems, as well as changes in the characteristics of the adjacent oceanic currents. Here we use the Modern Analogue Technique on a new synthesis of pollen records from across the SRZ to quantitatively reconstruct four climate variables (Mean Temperature of the Coldest month, Mean Temperature of the Warmest Month, Mean Summer Precipitation and Winter Climatic Moisture Index), over the past 36,000 years. The climate variables and number of analogues used were selected after thorough examination of the modern dataset. The results provide evidence for three key features: first, an early deglaciation following a cold, dry and prolonged Last Glacial Maximum. Second, a clear manifestation of the African Humid Period in the north-eastern part of the zone, supported by reconstructed sea surface temperatures. And third, a short-lived cold period at around 10 cal kyr BP, which may have been obscured by larger statistical errors in past studies. As it is still mostly within the margin of error for our study, this period requires further study. Our results show that the technique can be used successfully on large and diverse compilations of South African records, improving comparability with other regions.