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

人们普遍认为，热带东南非洲受到与未来全球变暖有关的水文气候变化的强烈影响，但对这些变化的程度和社会经济影响仍知之甚少。在这种情况下，调查区域水文气候变化和相关的植被变化，在最后一次间冰期，一个时间间隔，温度高于今天，可能会提供重要的见解，未来可能的条件。此外，最后一次间冰期包含了古人类进化的一个关键阶段，即第一批解剖学上的现代人类从非洲迁徙出来。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化、其主要控制机制和早期人类迁移后果的信息仍然相对缺乏。在本项目中，将对莫桑比克海峡IODP U1477站点的海洋沉积物进行分析，以重建约150和约70 kyr BP之间热带东南非洲陆地水文气候变化和相关的植被类型变化。这将通过测量将从沉积物中提取的长链正构烷烃（n-C27至n-C33）的稳定氢（δ D）和碳同位素（δ 13 C）组成来实现。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径流进入海洋。由于正构烷烃δ D主要记录了区域降水δ D随时间的变化，因此可用于重建赞比西河流域过去的水文气候变化。此外，正构烷烃δ 13 C可以追踪C3（例如树木）和C4植物（例如稀树草原草）相对丰度的过去变化，因为这些植物类型的δ 13 C值显着不同。此外，还将分析IODP站点U1477沉积物中长链烯酮n-C37的二和三不饱和同系物的浓度。这些有机成分是由地表水生长的海洋附着藻类合成的，它们的比例被称为UK '37指数，在很大程度上取决于附着藻类生长时的海面温度，从而可以重建印度洋西南部过去的海面温度变化。这些数据与其他区域和全球代理记录的比较，预计将提供新的信息，在东南非洲的水文气候变化的最后一个间冰期及其主要控制机制，以及早期现代人类的迁移出非洲的可能影响。

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.