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，是一个海拔超过4公里的大地理区域。它被称为“第三极”，因为它的冰川冰量仅次于北极和南极，是一个已经受到持续的全球气候危机影响的地区。青藏高原及其相关的冰川冰对许多亚洲邻国也具有重要意义，因为它是为数亿人供水的许多主要河流系统的源头，同时也是形成几个巨型三角洲的沉积物，这些三角洲是数千万人的家园。青藏高原在印度夏季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形成一个低压单元（即向上流动的热空气），从印度洋吸引来的潮湿气团进入该低气压单元，然后从该低气压单元向印度次大陆降下季节性季风性降雨。然而，对亚洲季风系统的控制和复杂性仍然缺乏详细的了解，并且需要更多的知识来了解由于持续的全球变暖而导致的未来气候变化情景下该地区的气候将如何发展。提高对自然地球系统（如印度夏季季风）的理解的一种方法是在历史和地质上研究这些系统，即通过重建过去的气候（称为古气候），一种常用的说法是“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，因为人们测量的是档案中保存的东西（代理），它与感兴趣的关键参数有关系。大陆湖泊沉积物是一个重要的档案，本项目将利用青藏高原纳木错湖的这些材料。先前对这个湖的调查表明，在湖底下埋有大约700米的沉积物，预计这些沉积物可以追溯到距今100万年左右。2020年夏天，国际研究人员小组认可了纳木湖沉积物档案的重要国际价值，他们从国际大陆钻探项目（ICDP）获得了150万美元的奖金，该项目是一个国际机构，目前有21个成员国（包括英国）。另外，中国科学院青藏高原研究所（中国北京）也已承诺提供90万美元的额外资金，进一步证实了这一大型国际研究项目的重要性。南错沉积物档案将于2023年夏季通过漂浮在湖面上的驳船上的钻井平台取芯进行回收，这种方法已成功应用于许多其他ICDP湖泊钻井项目。一旦从湖底下回收湖泊沉积物，将对它们进行大量的生物、化学和物理测量，以便解决南错沉积物档案所能解决的基本科学问题。这个由英国nerc资助的项目，包括ICDP主要项目的两个支持者，将：1)为湖泊取心作业提供额外资金；2)应用化学测年技术，确定回收沉积物的年龄；3)完成湖泊沉积物的化学代用测量，用于古气候重建，特别是侧重于提高对青藏高原水平衡及其与印度夏季风控制的关系的理解。

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.