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

热带东南非洲通常被认为受到与未来全球变暖相关的水文气候变化的强烈影响，但这些变化的程度和社会经济影响仍然知之甚少。在这种背景下，研究末次间冰期（一个温度高于今天的时间间隔）的区域水文气候变率和相关植被变化，可能为未来可能的条件提供重要的见解。此外，最后一次间冰期包含了人类进化的一个关键时期，即第一批解剖学意义上的现代人走出非洲的迁徙。然而，尽管末次间冰期因此代表了东南非洲的一个重要时期，但有关该地区水文气候变异、其主要控制机制和早期人类迁徙后果的信息仍然相对缺乏。在该项目中，将分析来自莫桑比克海峡IODP站点U1477的海洋沉积物，以重建热带东南部非洲在~150至~70 kyr BP之间的陆地水文气候变异和植被类型的相关变化。这将通过测量从沉积物中提取的长链正构烷烃（n-C27至n-C33）的稳定氢（δD）和碳同位素（δ13C）组成来完成。这些正构烷烃是高等陆生植物表皮蜡的主要成分，并通过邻近的赞比西河的径流进入海洋。正构烷烃δD主要记录了区域降水δD随时间的量控变化，可以用来重建赞比西河流域过去的水文气候变化。此外，正构烷烃δ13C可以追踪C3（如树木）和C4植物（如稀树草原草）相对丰度的过去变化，因为这些植物类型的δ13C值差异很大。此外，还分析了长链烯酮n-C37在IODP Site U1477沉积物中的二不饱和和三不饱和同源物的浓度。这些有机成分是由生长在地表水的海洋附生藻合成的，它们的比值，即所谓的UK ' 37指数，在很大程度上取决于附生藻生长时的海面温度，从而可以重建过去印度洋西南部海面温度的变化。将这些数据与其他区域和全球代用记录进行比较，预计将提供有关末次间冰期东南非洲水文气候变化及其主要控制机制的新信息，以及对早期现代人类迁出非洲的可能影响。

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.