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

由于位于亚热带和温带之间，南部非洲的气候对气候变化高度敏感，这一点也从目前的三年干旱中可见一斑。气候变化的特征是温带西风、热带间辐合带(ITCZ)和刚果空气边界(CAB)的强度和位置的变化，以及海表面温度(SST)的变化。气候系统的复杂性也从全新世替代记录的同位素信号中可见一斑，这表明即使在很小的距离内，区域气候变异性也很高。非洲南部全新世降雨量的变化在多大程度上与南北半球气候、当地日照或SST之间的耦合有关，目前尚不完全清楚。要更好地了解南部非洲过去和现在的气候变化，一个关键问题是本格拉和阿古拉斯洋流动态之间的相互作用、相关的海洋海温、热带气旋和热带气旋的强度和位置、以及夏季和冬季降雨占主导地位的地区的范围。夏季和冬季的降雨机制很可能并不是相互独立的。夏季和冬季降雨之间的联系可能是通过陆地-大气反馈机制而存在的。通过这个项目，我们的目的是改善对支配南部非洲过去和现在气候变化的过程的理解，并解释受地表蒸发和陆地水流影响的替代记录的同位素信号。为此，一方面，我们将对不同时间片进行高分辨率全球耦合模式模拟，以研究海-气相互作用的影响。这项研究的这一部分将由仅针对大气的敏感性实验来补充，以分离对全新世气候演变有贡献的单一因素的影响。另一方面，作为一项方法创新，我们将在区域气候模型的大气和陆地部分实施所谓的稳定水同位素标记。稳定的水同位素模拟与印度洋和大西洋等主要水分源区的大气和陆地水标记相结合，不仅提供了独特的机会，不仅可以调查替代记录中的差异，而且还可以分析在区域范围内影响南部非洲气候动态的大气动力学和陆地-大气反馈机制的变化。通过这种方法，一种在当今大气建模中最近才发展起来的技术将第一次得到实施和推广，以回答气候研究中的公开问题。为了解释模型结果和替代记录，并分析过去气候的高分辨率气候模拟的附加值，我们将使用最新的南部非洲全新世替代记录。

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.