Millenial Scale Weak Monsoon Intervals over India (WeakMonsoons)

印度夏季风（ISM）对全球气候变化非常敏感。现代气候观测表明，主要是印度洋表面温度调节了印度大陆的降雨强度和季节持续时间。基于过去季风变化的多种古气候记录，并得到地球系统模拟的支持，在轨道和亚轨道时间尺度上，季风变率必须被视为对高纬度和低纬度气候变化、大气和海洋环流以及温室气体浓度和冰盖生长或融化变化的响应。这些过程的重要性仍然存在广泛的争论，但往往存在争议。在严重洪水事件及其对数百万人和经济福祉的破坏性影响的印象下，这些研究中的大多数也在地质时间尺度上解决了季风降水增强间隔的原因。然而，最近古气候重建的重点是面向季风降水非常少的时期，即所谓的弱季风间歇期（WMIs）。而在更长的时间尺度上，由于缺乏高分辨率的晚第四纪ISM降水时间序列，WMIs的强迫机制尚不清楚。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，生成印度过去百年来降雨变化的新记录，这些有机化合物被运送到孟加拉湾的海洋沉积物中并沉积下来，最近在IODP 353 Leg U1446站点进行了钻探。主要目标是确定末次冰期和全新世期间对外部和内部气候强迫的水文响应的大小，并更好地确定导致印度降雨变率的最重要控制机制。

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.