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

气候科学家们早就记录了地球轨道变化对冰期盈亏的强烈控制。30年前，内华达州魔鬼洞的一份标志性气候记录似乎表明，美国西部大盆地的气候与轨道节奏不一致，在冰川期之后变暖，而地球轨道的变化是意料之中的。现在有新的证据表明，大盆地的气候变化与轨道变化是同步的，并表明在过去的17.5万年里，随着夏季到达北半球的太阳辐射量的增加，气候变暖或变冷。来自大盆地洞穴的石笋经放射性测定年代，有可能将记录时间延长到距今50万年前。这些洞穴沉积物记录了洞穴遗址上方和逆风的广阔地区的气候变化。因此，它们非常适合测试对大盆地气候的轨道控制，并将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。该项目还将根据已知的未来轨道变化，促进对美国西南部的长期气候预测。在这个项目的过程中将要验证的首要假设是，西南古气候变化是由米兰科维奇（轨道）强迫所主导的，通过北半球夏季日照的变化改变了东北太平洋地区的大气环流动力学。研究小组将对大盆地地区洞穴中精确测定年代的石笋进行高分辨率氧同位素分析，并确定氧同位素的变化是否与过去50万年北半球夏季日照的变化一致。氧同位素分析将在拉斯维加斯内华达大学进行，铀不平衡定年将在新墨西哥大学进行。研究小组将包括来自两所主要院校以及一所本科院校康奈尔学院（爱荷华州）的几名学生。研究人员和学生还将制作洞穴教育材料，与当地洞穴团体和政府机构分享。

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.