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date: 23 January 2019

Quaternary Climate Variation in Southern Africa

This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Climate Science. Please check back later for the full article.

Quaternary paleoclimate reconstructions in tropical-subtropical southern Africa (taken here as approximately south of latitude 17 oS) require both knowledge of the key relevant elements of the atmospheric and climate systems over the subcontinent and a realistic assessment of the possibilities and limitations of the proxy data sources in the region. Orbital forcing and southern hemisphere ocean temperature changes are widely considered as primary drivers of temporal and spatial changes in the relative influence of different components of the circulation system (tropical Indian ocean monsoon, tropical Atlantic moisture, and temperate westerlies) that in turn drive precipitation distributions, amounts, and seasonality. Major debates in recent decades have focused on the timing and extent of aridity and humidity shifts, and the relative contribution of temperate and tropical sources of precipitation during the last approximately 100,000 years, notably at the Last Glacial Maximum (LGM) and during the Holocene climate optimum.

Many of the debates and uncertainties that have emerged are also a function of proxy data sources: where they are located, how they are interpreted, and their resolution. Extrapolation of data from marine core and high resolution terrestrial records to subregions where proxies are sparse, low resolution, or difficult to transform from environmental to climatic signals, may have oversimplified representation of the spatial variability of past climates in a region where variability is a norm today. Particular issues occur in, but are not confined to, the southern African interior, which to date has largely been devoid of reliable precipitation proxies, and where available proxies provide reconstructions of physical changes in landscape systems that can prove difficult to translate to high precision hydrological and rainfall records. Elsewhere, developments in interpreting palynological and isotope records have led to reanalysis of past simple interpretations of hydrological fluxes in the last 50,000 years. Now, a suite of new isotopic proxies derived from previously under-investigated areas or innovative biological and sedimentary sources, and a more realistic interpretation of existing records are generating a suite of testable hypotheses regarding Late Quaternary hydrodynamics. These include establishing the degree of cooling in mountainous regions and clarifying the northerly extent of temperate westerly moisture penetration during cold phases, as well as establishing the contribution of tropical Atlantic moisture to interior wetting and associated feedback mechanisms.