Identifying orbital- and sub-orbital-scale controls on the Asian summer monsoon: a 500,000 year hydroclimate record from Nam Co, Tibet [NamCore-UK]

青藏高原位于喜马拉雅山脉以北，是一个面积很大的地区，海拔超过4公里。它被称为“第三极”，因为它拥有仅次于北极和南极的第三大冰川冰量，而且它是一个已经经历了持续的全球气候危机影响的地区。青藏高原和相关的冰川冰对许多邻近的亚洲国家也具有重大意义，是许多主要河流系统的源头，为数亿人供水，以及沉积物，形成了几个大型三角洲，是数千万人的家园。青藏高原在印度夏季风大气环流系统中也起着重要作用，传统上认为太阳对高海拔地区的加热会建立一个低压圈（即，向上流动的热空气），从印度洋吸入较潮湿的空气团，然后在印度次大陆上降下季节性季风雨福尔斯。然而，对亚洲季风系统的控制及其复杂性仍然缺乏详细的了解，需要更多的知识来了解该地区气候在全球变暖导致的未来气候变化情景下将如何发展。是在历史和地质的过去调查这样的系统，即通过重建过去的气候（称为古气候），一个常用的说法是“过去是现在的关键”。为了能够调查古气候，有必要拥有一个信息档案和一种重建关键古气候参数的方法，后者被称为基于代理的方法，因为人们测量的是保存在档案中的东西（代理），它表现出与感兴趣的关键参数的关系。大陆湖泊沉积物是一个重要的档案，本项目将利用来自西藏高原纳木错湖的此类材料。此前对该湖的调查显示，湖底埋有约700米的沉积物，预计这些沉积物可以追溯到距今约100万年前。纳木错湖沉积物档案的重大国际价值于二零二零年夏季获国际研究小组认可，并获国际大陆钻探项目（ICDP）拨款150万美元，该国际机构目前拥有21个成员国（包括英国）。中国科学院青藏高原研究所也已承诺提供额外的90万美元资金（中国北京），进一步证实了这一大型国际研究项目的重要性。纳木错沉积物档案将在2023年夏季通过位于驳船顶部的钻井平台取芯进行恢复，驳船将漂浮在湖面上，该方法已成功应用于许多其他ICDP湖泊钻探项目。一旦从湖底回收湖泊沉积物，将对它们进行大量的生物、化学和物理测量，以解决纳木错沉积物档案将允许解决的基本科学问题。这一由英国自然资源研究中心资助的项目，包括ICDP主要项目的两个支持者，将：1）为湖泊取芯作业提供额外资金; 2）应用基于化学的测年技术，以便确定回收沉积物的年龄;（3）完成湖泊沉积物化学代用指标的测定，特别是重点是提高对青藏高原水平衡的理解，以及它与印度夏季风控制的关系。

The Tibetan Plateau, located north of the Himalaya mountain range, is a large geographical area with an elevation greater than 4 km above sea-level. It is called "The Third Pole" because it has the third highest glacier ice volume after the Arctic and Antarctic, and it is a region that is already experiencing the effects on the ongoing global climate crisis. The Tibetan Plateau and associated glacier ice also have great significance for many neighbouring Asian countries, being the source of many of the major river systems supplying water to 100s of millions of people, as well as sediment that builds several mega-deltas that are homes to 10s of millions of individuals. The Tibetan Plateau also plays a major role in the Indian summer monsoon atmospheric circulation system, with the Sun's heating of the high-altitude region traditionally thought to set up a low-pressure cell (i.e., upward flowing heated air), into which wetter air masses are drawn from the Indian Ocean, from which seasonal monsoonal rain then falls over the Indian sub-continent. However, there remains a lack of detailed understanding of the controls on, and the complexity of, Asian monsoon systems, and additional knowledge is required in relation to how climate in this region will develop under future climate-change scenarios that will result from ongoing global warming.One way to gain an improved understanding of natural Earth systems, such as the Indian summer monsoon, is to investigate such systems in the historical and geological past, i.e. by the reconstruction of past climate (called palaeoclimate), one commonly used statement being "the past is the key to the present". To be able to investigate palaeoclimate it is necessary to have an archive of information and a means to reconstruct key palaeoclimate parameters, the latter termed a proxy-based approach because one measures something preserved in the archive (the proxy) that exhibits a relationship with the key parameter of interest. Continental lake sediments are one important archive and this project will utilise such materials from lake Nam Co on the Tibetan Plateau. Prior investigations of this lake have shown there is around 700 metres of sediment buried below the lake floor and it is expected that these sediments extend back to around one million years before present. The significant international value of the Nam Co lake sediment archive was recognised in summer 2020 by panels of international researchers who awarded US$1.5M from the International Continental Drilling Project (ICDP), an international agency currently with 21 member countries (including the UK). An additional US$0.9M funding also has already been committed by the Institute of Tibetan Plateau Research, Chinese Academy of Science (Beijing, China), further confirming the significance of this large-scale international research project.The Nam Co sediment archive will be recovered during summer 2023 by coring from a drilling rig sitting on top a barge that will float on the lake surface, an approach that has been applied successfully to many other ICDP lake drilling projects. Once the lake sediments have been recovered from below the lake floor they will be subject to numerous biological, chemical and physical measurements, in order to address the fundamental science questions that the Nam Co sediment archive will allow to be addressed. This UK NERC-funded project, including two of the proponents of the main ICDP project, will: 1) contribute additional funding to the lake coring operations; 2) apply chemistry-based dating techniques, so that the ages of the recovered sediments can be determined; 3) complete chemical proxy measurements on the lake sediments for palaeoclimate reconstruction, specifically with a focus on improving understanding of the water balance on the Tibetan Plateau and how that relates to controls on the Indian summer monsoon.