Age model, lipids, and iron/calcium-ratios of sediment core GeoB9307-3

Hide Intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast Africa since the Last Glacial Maximum, about 20,000 years ago. In particular, the relative importance of atmospheric and oceanic processes is not firmly established. Southward shifts of the intertropical convergence zone (ITCZ) driven by high-latitude climate changes have been suggested as a primary forcing, whereas other studies infer a predominant influence of Indian Ocean sea surface temperatures on regional rainfall changes. To address this question, a continuous record representing an integrated signal of regional climate variability is required, but has until now been missing. Here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro-climatology in southeast Africa during rapid climate changes over the past 17,000 years. Our results are based on a reconstruction of precipitation and river discharge changes, as recorded in a marine sediment core off the mouth of the Zambezi River, near the southern boundary of the modern seasonal ITCZ migration. Indian Ocean sea surface temperatures did not exert a primary control over southeast African hydrologic variability. Instead, phases of high precipitation and terrestrial discharge occurred when the ITCZ was forced southwards during Northern Hemisphere cold events, such as Heinrich stadial 1 (around 16,000 years ago) and the Younger Dryas (around 12,000 years ago), or when local summer insolation was high in the late Holocene, i.e., during the last 4,000 years.

围绕着约2万年前末次冰盛期（Last Glacial Maximum）以来热带及亚热带东南非洲水文变化的气候机制，学界始终存在激烈争论。尤为关键的是，大气与海洋过程的相对重要性尚未得到明确证实。此前有研究提出，由高纬度气候变化驱动的热带辐合带（intertropical convergence zone, ITCZ）南移是主要的强迫因子；而另有研究则认为印度洋海表温度对区域降雨变化起主导作用。为解答这一科学问题，亟需能反映区域气候变率综合信号的连续记录，但此类记录迄今仍付阙如。本研究表明，在过去1.7万年的快速气候变化阶段，北半球高纬度冷事件通过远程大气强迫作用，似乎是东南非洲水文气候的主要驱动因子。本研究的结论基于对降水与河流径流变化的重建，该重建数据取自赞比西河（Zambezi River）河口附近海域的海洋沉积物岩芯，其位置处于现代季节性热带辐合带迁移的南界附近。研究结果显示，印度洋海表温度并未对东南非洲水文变率起到主导调控作用。相反，当北半球冷事件（如约1.6万年前的海因里希冷期1（Heinrich stadial 1）和约1.2万年前的新仙女木事件（Younger Dryas））迫使热带辐合带南移时，或是在全新世晚期（即过去4000年）当地夏季太阳辐射较高的阶段，东南非洲便会出现降水充沛、陆地径流丰富的时期。