Collaborative Research: Testing the hypothesis of an orbital forcing of southwestern North America climate over the past 500,000 years

长期以来，气候科学家一直证明，地球的轨道变化对冰河时代的兴衰有着强大的控制作用。30年前，来自内华达州魔鬼洞的一项标志性气候记录似乎表明，大盆地美国西部大盆地的气候与轨道节奏不同步，在冰川时期之后变暖，比地球轨道变化预期的要早。现在，新的证据表明，大盆地的气候变化与轨道变化是同步的，并表明在过去17.5万年的夏季，随着到达北半球的太阳辐射量的增加，气候变暖和变冷。来自大盆地洞穴的放射性测年石笋有可能将这一记录追溯到50万年前。这些洞穴沉积物记录了洞穴遗址上方和上风向大范围内的气候变化。因此，它们非常适合于测试对大盆地气候的轨道控制，并将允许与太平洋的海洋表面温度记录和魔鬼洞方解石记录进行比较。该项目还将促进根据已知的未来轨道变化对美国西南部进行长期气候预测。将在该项目过程中检验的主要假设是，西南部的古气候变化是由Milankovitch(轨道)强迫通过北半球夏季日照的变化改变东北太平洋地区的大气环流动力学来实现的。研究小组将对大盆地地区洞穴中的石笋进行高分辨率的氧同位素分析，并确定氧同位素的变化是否与过去50万年来北半球夏季日照的变化一致。氧同位素分析将在内华达大学拉斯维加斯分校进行，铀不平衡测年将在新墨西哥大学进行。研究团队将包括几名学生，他们既来自领先的机构，也来自本科服务机构--康奈尔学院(爱荷华州)。研究人员和学生还将制作洞穴教育材料，与当地洞穴组织和政府机构分享。

Climate scientists have long documented the strong control of Earth's orbital variations on the waxing and waning of the ice ages. Thirty years ago, an iconic climate record from Devils Hole, Nevada, seemed to suggest that Great Basin the climate of the Great Basin of the western United States was out of step with the orbital rhythm, warming after glacial periods before what would be expected from changes in the Earth's orbit. Now new evidence places Great Basin climate variations back in synchrony with orbital variations, and shows that climate warmed and cooled with the amount of solar radiation reaching the northern Hemisphere during summer over the last 175,000 years. Radiometrically-dated stalagmites from Great Basin caves have the potential extend the record back to 500,000 years before present. These cave deposits record variations in climate in a broad region over and upwind of the cave sites. As such, they are ideally suited to test for an orbital control on Great Basin climate, and will allow comparison to sea surface temperature records in the Pacific Ocean, and to the Devils Hole calcite record. This project will also facilitate long-term climate projections for the southwestern United States based on known future orbital variations. The overarching hypothesis that will be tested in the course of this project is that southwestern paleoclimatic change was paced by Milankovitch (orbital) forcing, through changes in northern hemisphere summer insolation altering atmospheric circulation dynamics over the northeastern Pacific Ocean region. The research team will generate high-resolution oxygen isotope analyses of precisely-dated stalagmites from caves across the Great Basin region, and determine whether or not oxygen isotope variations align with variations in northern hemisphere summer insolation over the past half million years. Oxygen isotopic analyses will be carried out at the University of Nevada Las Vegas, and uranium disequilibrium dating at the University of New Mexico. The research team will include several students from both lead institutions as well as an undergraduate-serving institution, Cornell College (Iowa). The researchers and students will also create cave educational materials for sharing with local caving groups and governmental agencies.