Investigating southern African Holocene climate - bridging from the early Holocene to today

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Due to its position between the subtropical and the temperate zone, southern African climate is highly sensitive to climatic variabilities, as is evident also in the present 3-year drought. Climate variability is characterized by changes in strength and position of the temperate Westerlies, Inter-Tropical Convergence Zone (ITCZ), and Congo Air Boundary (CAB), as well as by Sea Surface Temperature (SST) variabilities. The complexity of the climate system is also evident in the isotope signal of Holocene proxy records, which shows, even over small distances, high regional climate variability. The extent to which Holocene rainfall variability of southern Africa is linked to the coupling between northern and southern hemispheric climate, local insolation or SST, is not fully understood yet. A crucial question for improved understanding of Southern African climate variability of past and present days is the interplay between Benguela and Agulhas current dynamics, related ocean SSTs), the strength and position of ITCZ and CAB, and the extent of summer and winter rainfall dominated areas. Summer and winter rainfall regimes are most likely not independent of each other. A connection between summer and winter rains might exist through land – atmosphere feedback mechanisms. With this project we aim at improving the understanding of the processes that governed past and present climate variability of southern Africa and at explaining the isotopic signal of proxy records, which are altered by surface evaporation and terrestrial water flows. For this purpose we will perform, on the one hand, highly resolved global coupled model simulations for different time slices to investigate the influence of ocean – -atmosphere interactions. This part of the study will be complemented by atmosphere-only sensitivity experiments to isolate the effects of single factors contributing to Holocene climate evolution. As a methodological innovation we will, on the other hand, implement the so-called tagging of stable water isotopes in the atmospheric and terrestrial compartments of a regional climate model. The combination of stable water isotope modelling with atmospheric and terrestrial water tagging from the major moisture source regions, i.e. Indian and Atlantic Ocean, offers the unique opportunity not only to investigate differences in proxy records, but also to analyze changes in atmospheric dynamics and land – atmosphere feedback mechanisms that influence southern African climate dynamics on a regional scale. With this approach, for the first time, a technique only recently developed in present-day atmospheric modelling will be implemented and extended to answer open questions in climate research. For the interpretation of model results and proxy records and for an analysis of the added value of high-resolution climate modelling for past climates, we will use the most recent southern African Holocene proxy records.