Last interglacial hydroclimatic changes in Southeast Africa and potential impact on early human migration

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Tropical Southeast Africa is generally considered to be strongly affected by hydroclimatic changes related to future global warming, but extent and socio-economic impact of these changes are still poorly understood. In this context, investigating regional hydroclimate variability and associated vegetation changes during the last interglacial, a time interval with higher temperatures than today, might provide important insights regarding possible future conditions. Furthermore, the last interglacial encompasses a key episode of hominin evolution, the migration of the first anatomically modern humans out of Africa. However, although the last interglacial therefore represents an important period for Southeast Africa, information about hydroclimatic variability in the region, its main control mechanisms and the consequences for early human migration is still relatively scarce. Within this project, marine sediments from IODP Site U1477 in the Mozambique Channel will be analysed in order to reconstruct terrestrial hydroclimate variability and associated changes in vegetation types in tropical Southeast Africa between ~150 and ~70 kyr BP. This will be accomplished by measuring the stable hydrogen (δD) and carbon isotope (δ13C) composition of long-chain n-alkanes (n-C27 to n-C33) that will be extracted from the sediments. These n-alkanes are major constituents of the epicuticular waxes of higher terrestrial plants and transported into the ocean by runoff from the adjacent Zambezi River. As the n-alkane δD primarily records amount-controlled changes in the δD of regional precipitation through time, it can be used to reconstruct past hydroclimate variability in the Zambezi River catchment. In addition, the n-alkane δ13C allows to trace past changes in the relative abundance of C3 (e.g. trees) and C4 plants (e.g. savanna grasses), because these plant types differ significantly in their δ13C values. Furthermore, also the concentration of the di- and tri-unsaturated homologues of the long-chain alkenone n-C37 in the IODP Site U1477 sediments will be analyzed. These organic components are synthesized by surface water-growing marine haptophyte algae and their ratio, known as the UK’37 index, is largely dependent on the sea surface temperature at the time of haptophyte growth, allowing to reconstruct past seas surface temperature variability in the southwestern Indian Ocean. Comparison of these data with other regional and global proxy records is expected to provide new information about hydroclimatic changes in Southeast Africa across the last interglacial and their main control mechanisms as well as the possible influence on the migration of early modern humans out of Africa.