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

先前在山间盆地和邻近的变质核杂岩中发现的稳定同位素古气候代用物的研究表明，北美西部的地形发育是历时性的，在大约5000万年前首先在不列颠哥伦比亚省获得高海拔，并在大约4000万年前波及到内华达州。稳定同位素研究表明，存在快速而大的同位素变化，这种变化不可能仅仅是由于地表隆起造成的，因此需要气候控制。本研究旨在验证这样一种假设，即地形的发展和可能的区域尺度地表高程（由构造驱动）通过积极干扰大气水汽输送和/或稳定性而达到了导致快速气候和降水变化的阈值。为了验证这一假设，研究小组采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内从山间盆地收集稳定的同位素数据，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，以限制盆地集水区的地形起伏和造山发育；(3)对盆地进行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；(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，作为解释观测到的稳定同位素信号的一种方式。目的是区分两种明显不同的构造模型，这两种模型都与当前的数据集一致。一是在始新世至渐新世建立了由中高程低起伏景观到高海拔景观北向南隆起的动态地形。另一种是低起伏、高海拔的内华达平原从北向南崩塌，形成了一个与平均海拔较低但起伏明显较高的地区。这一建议解决了古气候分析中的一个基本问题。快速气候变化的原因。有人提出，随着全球变暖的加剧，一旦达到临界阈值，地球可能会经历气候体制的快速重组。在地球明显变暖和二氧化碳浓度较高的时期，识别这些快速的气候变化，对于我们了解地球如何？美国气候在变暖期间的表现。研究小组通过稳定的同位素分析确定了美国西部的一些地区，这些地区记录了地球明显变暖时（5000万到4000万年前）气候的快速变化。然而，导致这些气候变化的原因尚不清楚。通过将全球气候模型与同位素古降水测量相结合，就有可能评估导致这些快速气候变化的原因。具体来说，该项目将测试它们是否代表了对山脉上升或大规模气候重组的区域反应。

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.