Influence of Orbital Forcing on ENSO variability - new insights from an annually laminated speleothem

未来的气候变化情景表明，非洲大陆将越来越容易受到降雨极端变化（干旱和洪水）的影响。预测非洲降雨量变化的努力受到限制，因为我们对控制过去变化的因素缺乏了解;例如，描述厄尔尼诺-南方涛动（ENSO）和印度洋偶极子（IOD）对非洲水文的影响。更新世早期较温暖的条件下，当步行者环流和厄尔尼诺/南方涛动成为建立提供了一个类似的未来非洲气候变化。我们建议调查这些问题，利用一个独特的每年层压50万年长的洞穴存款从南非-布法罗洞穴流石。在我们以前的千年尺度记录的非洲降雨量的基础上，我们现在建议扩大代理分辨率，以每年的波段厚度和稳定同位素的十年。年度谱带厚度计数和稳定同位素测量方案将产生前所未有的长度和时间分辨率的降雨记录，使我们能够调查从年际到轨道的一系列时间尺度上对非洲降雨变化的控制。布法罗洞穴的流石记录涵盖了大约1950年的时间段。根据初步测年证据，该时间范围为2.0-1.5 Ma，并跨越了热带地区最重要的气候转变之一，即1.8至1.7 Ma之间的步行者环流的加强。因此，我们将能够在现代气候系统的这一基本特征建立之前、期间和之后，监测南非降雨量的变化。它将使我们了解ENSO系统的演变和IOD的长期影响。这项研究将为过去的降雨量变化提供新的见解，并将有助于我们预测非洲未来的降雨量。

Future climate change scenarios suggest the African continent will become increasingly susceptible to extreme changes in rainfall (droughts and flooding). Attempts to predict rainfall variability in Africa have been limited by our poor understanding of what controls past variability; for example characterising the influence of El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) on African hydrology. The warmer conditions of the early Pleistocene when the Walker Circulation and ENSO become established offer an analogue to future African climate variability. We propose to investigate these issues by utilising a unique annually laminated half a million year long speleothem deposit from South Africa - the Buffalo Cave flowstone. Building on our previous millennial scale record of African rainfall, we now propose to expand proxy resolution to annual for band thickness and decadal for stable isotopes. The program of annual band thickness counting and stable isotope measurement will generate a rainfall record of unprecedented length and temporal resolution, enabling us to investigate the controls on African rainfall variability at a range of timescales from inter-annual to orbital. The Buffalo Cave flowstone record covers the time period ca. 2.0-1.5 Ma, based on preliminary dating evidence, and crosses one of the most important climate transitions in the Tropics, the intensification of the Walker circulation between 1.8 and 1.7 Ma. We will thus be able to characterise changes in South African rainfall before, during and after the establishment of this fundamental feature of the modern climate system. It will allow us to understand the evolution of the ENSO system and the long term influence of the IOD. This research will provide new insights into rainfall variability in the past, and will aid our predictions of future rainfall in Africa.