Collaborative Research: Recovering Surface Uplift Histories and Climate Dynamics of the Cenozoic N. American Cordillera through Integrated Climate Modeling and Isotopic Studies

以前对山间盆地和邻近变质核杂岩中发现的稳定同位素古气候指标的研究表明，北美西部的地形是历时发展的，大约5000万年前首先在不列颠哥伦比亚省获得高海拔，大约4000万年前席卷内华达州。稳定同位素研究表明，有快速和大的同位素变化，不能仅仅由于地表抬升，需要气候控制。这项研究的目的是验证这样一种假设，即地形发展和可能的区域尺度地表高度(由构造驱动)达到了通过积极干扰大气水汽输送和/或稳定性而导致气候和降水快速变化的阈值。为了验证这一假设，研究小组使用了一种多学科的方法，其中包括：(1)在离散的时间间隔和广泛的地理区域收集山间盆地的稳定同位素数据，以便与气候模型的同位素结果进行比较；(2)测量碎屑矿物的冷却年龄，以努力限制盆地集水区内的地形起伏和造山；(3)盆地详细的沉积学和高分辨率地质年代学研究，以便将碎屑热年代学和稳定同位素分析置于适当的地质背景中；以及(4)利用全球和区域气候模式模拟不同地形/海拔情景下的气候条件和降水同位素，以此来解释观测到的稳定同位素信号。其目标是区分两种截然不同的构造模型，这两种模型都与当前的数据集相一致。一种是从始新世到渐新世，从中等海拔低起伏景观到高海拔景观由北向南隆起的动态地貌。另一种是低起伏、高海拔的所谓内瓦达普兰诺从北向南坍塌到与平均海拔较低但地形明显较高的地区。这一建议解决了古气候分析中的一个基本问题？气候快速变化的原因。有人提出，随着全球变暖加剧，一旦达到关键阈值，地球可能会经历气候制度的快速重组。在地球显著变暖和二氧化碳浓度较高的时期识别这些快速气候变化，对于我们理解地球在变暖期间的气候行为至关重要？S。研究小组通过稳定同位素分析确定了美国西部的地区，这些分析记录了当地球显著变暖时(5000万至4000万年前)的快速气候变化。然而，是什么导致了这些气候变化还不得而知。通过将全球气候模型与同位素古降水测量相结合，有可能评估造成这些快速气候变化的原因。具体地说，该项目将测试它们是否代表着对山脉上升或大规模气候重组的地区性反应。

Previous studies of stable isotopic paleoclimate proxies found in intermontane basins and adjacent metamorphic core complexes suggest that the topography of western North America developed diachronously, obtaining high elevations first in British Columbia at about 50 million years ago and sweeping into Nevada by about 40 million years ago. The stable isotopic studies show that there are rapid and large isotopic shifts that cannot be due to surface uplift alone and call for climatic controls. This research aims to test the hypothesis that relief development and possibly regional scale surface elevation (driven by tectonics) attained threshold values that caused rapid climate and precipitation shifts by actively interfering with atmospheric vapor transport and/or stability. To test this hypothesis, the research team is using a multi-disciplinary approach that involves: (1) collection of stable isotopic data from intermontane basins over discreet time intervals and over a wide geographic area so as to compare with isotope results from climate models; (2) measurement of cooling ages of detrital minerals in an effort to constrain relief and mountain building development within the basin catchments; (3) detailed sedimetological and high-resolution geochronologic studies in basins in order to place the detrital thermochronology and stable isotopic analyses in proper geologic context; and (4) simulation of climate conditions and isotopes of precipitation under different topographic/elevational scenarios using global and regional climate models as a way to interpret the observed stable isotope signals. The goal is to discriminate between two markedly contrasting tectonic models both of which are consistent with current data sets. One calls for the construction of dynamic topography from a moderate elevation low-relief landscape to a north-to-south swell of a high elevation landscape in the Eocene to Oligocene. The other is the north-to-south collapse of a low-relief, high elevation so-called Nevadaplano into region of similar to lower mean elevation but with significantly higher-relief.This proposal addresses a fundamental problem in paleoclimate analysis ? the cause for rapid climatic shifts. It has been proposed that with increased global warming the Earth may undergo rapid reorganization of climate regimes once critical thresholds are reached. Identifying these rapid climate changes during times when the Earth was significantly warmer and had higher concentrations of carbon dioxide is essential for our understanding of how the Earth?s climate behaves during warming episodes. The research team has identified areas in the American West through stable isotope analysis that record rapid climatic shifts when the Earth was significantly warmer (50 to 40 million years ago). What causes these climatic shifts is unknown, however. By combining global climate models with isotope paleo-precipitation measurements it is possible to assess what may have caused these rapid climate shifts. Specifically, the project will test whether they represent regional responses to the rise of mountains or large-scale reorganization of climate.