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(干旱和洪水)极端变化的影响。由于我们对控制过去变化的因素缺乏了解，预测非洲降雨变化的努力受到限制；例如，我们无法确定厄尔尼诺-南方涛动(ENSO)和印度洋偶极子(IOD)对非洲水文学的影响。当沃克环流和ENSO形成时，早更新世更温暖的条件提供了与未来非洲气候变化类似的条件。我们建议利用南非一种独特的每年层压50万年长的洞穴沉积物--布法罗洞穴流石来研究这些问题。基于我们以前对非洲降雨量的千年尺度记录，我们现在建议将替代分辨率扩大到波段厚度的年度和稳定同位素的十年。年度波段厚度计数和稳定同位素测量计划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异性的控制。根据初步的测年证据，布法罗洞穴流石记录涵盖了大约2.0-1.5 Ma的时间段，并跨越了热带地区最重要的气候转变之一，即1.8-1.7 Ma之间Walker环流的加强。因此，我们将能够描述在现代气候系统的这一基本特征建立之前、期间和之后南非降雨量的变化。它将使我们了解ENSO系统的演变和IOD的长期影响。这项研究将对过去的降雨变化提供新的见解，并将有助于我们对非洲未来降雨的预测。

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.