Collaborative Research: Growth of the Tibetan Plateau and Eastern Asia Climate: Clues to Understanding the Hydrological Cycle

50年来，青藏高原一直被认为是扰动大气环流的最大地形特征。 它是一个理想的野外实验室，可以用来了解形成高地的地球动力学过程。 因此，高原的生长应该改变了大气环流，因此不仅在东亚区域气候上，而且在全球气候上写下了不断演变的古气候特征。 尽管最近有许多研究，我们仍然不知道青藏高原何时达到目前的规模，以及它如何扰乱大气环流。 该项目汇集了地球动力学家、大气科学家和古气候学家，对何时和如何进行多学科研究。该项目的主要目标之一是量化西藏通过地壳增厚、逆冲断层和褶皱、地壳内流动重新分配物质而增长的程度，或由较热的物质替换较冷的地幔岩石圈（均处于均衡平衡状态）。这样的量化将使我们在理解高原是如何形成的以及大陆岩石圈如何变形方面迈出一大步，这些都是地球动力学的前沿课题。要确定西藏是如何发展的，需要使用基本的野外方法和现代实验室技术，确定地壳缩短和增厚发生的时间，并使用新的同位素工具量化古海拔。然而，应用这种古高度测量技术不仅需要了解大气如何传输同位素，还需要了解过去不断变化的高地形如何影响地表温度。即使该项目？的重点仅仅是西藏的发展，这是研究的一个气象组成部分，特别关注东亚？的水循环，将是必要的。大多数大陆古气候指标被认为对降水比对温度更敏感，在未来气候的未知数中，水文循环尤为突出。 因此，一个主要的重点将是了解像西藏这样的高地形如何影响东亚，特别是中国的水文循环。这些研究将侧重于：（1）高原既是地形障碍物又是太阳辐射的汇，它如何影响大气环流;（2）大气如何输送稳定同位素（Δ 18 O和Δ D）;（3）高原如何影响中纬度气候变率，包括高原如何通过背风气旋形成而扬起和输送沙尘;（4）植被如何反馈大气环流和水文循环。 作为从发生在多万年的时间尺度上的地质过程到人类时间尺度上的地质过程的联系，主要研究人员计划进行研究，专门研究过去几十万年来的古降水，使用黄土沉积和洞穴沉积来量化古气候。

For fifty years, the Tibetan Plateau has been recognized as the largest topographic feature that perturbs atmospheric circulation. It serves as an ideal field laboratory for understanding the geodynamic processes that build high terrain. Accordingly, the growth of the plateau should have altered atmospheric circulation and therefore written an evolving paleoclimatic signature not only on eastern Asian regional climates, but on global climate as well. Despite many recent studies, we still do not know precisely when the Tibetan Plateau reached its current dimensions and how it perturbs atmospheric circulation. This project brings together geodynamicists, atmospheric scientists, and paleoclimatologists in a multidisciplinary study of the when and the how.One of the major goals of the project is to quantify the extent to which Tibet has grown by crustal thickening, by thrust faulting and folding, by flow within the crust that redistributes material there, or by replacement of cold mantle lithosphere with hotter material (all in a state of isostatic equilibrium). Such quantification will take big steps toward the understanding of how high plateaus are built and how continental lithosphere deforms, topics at the forefront of geodynamics. Determining how Tibet has grown will require determining when crustal shortening and thickening occurred, using basic field methods and modern laboratory techniques, and quantifying paleoaltitudes with new isotopic tools. Applying such paleoaltimetric techniques, however, requires an understanding not only of how the atmosphere transports isotopes, but how the evolving high terrain affected surface temperatures at times in the past. Even if the project?s focus were solely on how Tibet has grown, a meteorological component of the study, focused particularly on eastern Asia?s hydrological cycle, would be necessary. Most continental paleoclimatic indicators are thought to be more sensitive to precipitation than to temperature, and among the unknowns of future climate, the hydrological cycle stands out. Accordingly, a major focus will be on understanding how high terrain like Tibet affects the hydrological cycle of eastern Asia, and China in particular. These studies will focus on: (1) how the plateau, as both a topographic obstacle and a sink for solar radiation, affects atmospheric circulation; (2) how the atmosphere transports stable isotopes (ä18O and äD); (3) how it affects mid-latitude climate variability, including how, via lee cyclogenesis, it lofts and transports dust, and (4) how vegetation feeds back on atmospheric circulation and the hydrological cycle. As links from geologic processes occurring at multi-Myr time scales to those on human time scales, the Principal Investigators plan studies that specifically examine paleoprecipitation over the past few hundred thousand years, using both loess deposition and speleothems that quantify paleoclimate.