Millenial Scale Weak Monsoon Intervals over India (WeakMonsoons)

印度夏季风(ISM)高度多变，对全球气候变化敏感。现代气候观测表明，印度洋表面温度主要影响印度大陆的降雨强度和季节持续时间。根据过去季风变化的多种古气候记录，并在地球系统模型的支持下，轨道和亚轨道时间尺度的季风变化必须被视为对高、低纬气候变化、大气和海洋环流以及温室气体浓度和冰盖增长或融化的变化的反应。这些过程的重要性仍然存在广泛的争论，但往往是有争议的。鉴于严重洪灾事件及其对数百万人和经济福祉的破坏性影响，这些研究大多探讨了季风降水间歇性增加的原因，也是在地质时间尺度上。然而，最近古气候重建的重点是季风降水非常少的时期，即所谓的弱季风间隔(WMI)。在千年时间尺度上，WMI对应于北半球高纬度突发性寒冷气候周期，但在较长的时间尺度上，由于缺乏ISM降水的高分辨率晚第四纪时间序列，WMI的强迫机制尚未得到很好的理解。该项目旨在利用来自陆地植物的特定有机化合物的氢和碳同位素比率，对印度上空过去几百年的降雨量变异性产生新的记录，这些有机化合物被运输到孟加拉湾的海洋沉积物中并沉积在海洋沉积物中，最近在IODP LEG 353，U1446站点钻探。主要目标是确定在最后一次冰期和全新世期间对外部和内部气候强迫的水文反应的大小，并更好地确定对印度上空降雨量变化负责的最重要的控制机制。

The Indian Summer Monsoon (ISM) is highly variable and sensitive to global climate change. Modern climate observations suggest that mainly Indian Ocean surface temperatures modulate rainfall intensity and seasonal duration over the Indian continent. Based on the manifold paleoclimatic records for past monsoon changes and supported by earth system modelling monsoon variability at orbital and suborbital timescales must be considered as a response to changes in high and low latitude climate change, in atmosphere and ocean circulation, as well as in greenhouse gas concentrations and ice-sheet growth or melt. The importance of theses processes is still extensively, but often controversely, debated. Under the impression of severe flooding events and their devastating impact on millions of people and economic well-being most of these studies have addressed the causes for intervals of enhanced monsoonal precipitation also at geological time scales. However, more recently the focus of paleoclimate reconstructions is oriented towards periods of very low monsoonal precipitation, so-called Weak Monsoon Intervals (WMIs). At millenial timescales WMIs correspond to abrupt cold climate periods characteristic for northern hemishere high latitudes, However, as for the longer timescales, the forcing mechanisms of WMIs are not well understood due to the scarcity of high-resolution Late Quaternary time series of ISM precipitation. This project aims to generate a new record of past multi-centennial variability in rainfall over India using hydrogen and carbon isotope ratios of specific organic compounds from land plants, transported to and deposited in marine sediments in the Bay of Bengal and recently recently drilled at IODP Leg 353, Site U1446. The main objectives are the determination of the magnitude of hydrological responses to external and internal climate forcing during last Glacial and Holocene and to better identify the most importcontrol mechanisms responsible for rainfall variability over India.