Establishing a Chronology of Late Quaternary Glacial Advances in the Tropical American Cordillera

近几十年来，热带地区在过去和未来气候变化中的作用引起了人们的极大关注，但关于热带地区与中高纬度地区之间的气候联系仍存在争议。热带山地冰川是高度敏感的气候指标，过去冰川波动留下的冰川地貌为古气候趋势及其强迫机制提供了关键证据。传统上，很难确定冰川地貌的年代，因此准确地将年龄分配给它们记录的气候阶段和事件一直不太成功。宇宙核素定年的最新发展已经彻底改变了过去冰川动力学的地貌研究，现在提供了一种可靠的手段来限制冰川冰碛和其他特征的形成年龄。在这个项目中，研究人员将为美国科迪勒拉地峡部分的中美洲南部的塔拉曼卡科迪勒拉建立一个长期的冰川年代学。该年代学将通过对哥斯达黎加Chirripó地块的两个山谷中三个冰碛复岩的代表性冰碛和基岩露头的36Cl表面暴露定年来确定，并使用为此目的已经收集的60个样本。待开发的年代学将揭示美国科迪勒拉地峡部分的冰川推进是否与其他地方的冰川推进同步，该地区受太平洋和加勒比海的影响比其北部或南部地区更强烈。先前的研究表明，晚第四纪冰川的推进以明显不同的温度和湿度条件为特征，但冰川阶段只是相对的。通过将这些重建固定在时间上，宇宙起源定年将使研究人员能够将塔拉曼卡山脉的古气候趋势与冰川地貌、花粉组合、同位素记录和其他新热带地区及其他地区的气候代用物记录的古气候趋势进行比较。作为中美洲地峡部分最高和最大的山脉，哥斯达黎加的塔拉曼卡山脉保存了冰川记录，这对了解美洲的古气候和冰川推进的时间至关重要。这个项目将填补沿美国科迪勒拉横断面冰川年代学的知识空白。结果将有助于理解新热带海洋对流层的过去动态，以及中美洲南部更新世的气候。通过提高对该地区过去气候动态的科学认识，该研究有助于模拟和预测未来全球气候变化。对冰川期气候的了解也与了解生物地理格局以及新热带生态系统中高度物种多样性的起源和维持有关。这项研究将为田纳西大学的研究生和本科生以及当地学校6-12年级的学生提供教育机会，这些学校的教师和研究生将在课堂上进行科学推广。通过国际推广工作，该项目还将帮助教育公园警卫、导游和游客了解塔拉曼卡山脉的冰川和气候历史。

The role of the tropics in past and future climate change has garnered significant attention in recent decades, but debate still exists over climatic linkages between the tropics and the middle and high latitudes. Glaciers in tropical mountains are highly sensitive indicators of climate, and the glacial landforms left behind by past glacier fluctuations provide key evidence of paleoclimate trends and their forcing mechanisms. Traditionally, it has been difficult to date glacial landforms, so accurately assigning ages to the climate stages and events they record has been less than successful. The recent development of cosmogenic nuclide dating has revolutionized geomorphic investigation of past glacial dynamics and now provides a reliable means to constrain the formation ages of glacial moraines and other features. In this project, investigators will develop a long-term glacial chronology for the Cordillera de Talamanca of southern Central America, in the isthmian portion of the American Cordillera. The chronology will be established using 36Cl surface exposure dating of representative moraines and bedrock outcrops from three moraine complexes in each of two valleys of the Chirripó massif in Costa Rica, using 60 samples already collected for this purpose. The chronology to be developed will reveal whether glacial advances in the isthmian portion of the American Cordillera, which is more strongly influenced by the Pacific Ocean and Caribbean Sea than areas to the north or south, were synchronous with glacial advances elsewhere. Previous work reconstructing glacier extents from moraine complexes at the study site revealed that Late Quaternary glacial advances were characterized by distinctly different temperature and moisture conditions, but the glacial stages were only dated relative to each other. By anchoring these reconstructions in time, the cosmogenic dating will allow the researchers to compare paleoclimate trends in the Cordillera de Talamanca with those recorded by glacial landforms, pollen assemblages, isotope records, and other climate proxies elsewhere in the neotropics and beyond.As the highest and largest mountain range in the isthmian portion of Central America, the Cordillera de Talamanca of Costa Rica preserves glacial records important to understanding paleoclimate and the timing of glacial advances in the Americas. This project will fill a knowledge gap in glacial chronologies along the transect of the American Cordillera. Results will contribute to understanding of the past dynamics of the neotropical marine troposphere, and of Pleistocene climates in southern Central America. By improving scientific understanding of past climate dynamics in this region, the research can assist in modeling and anticipating future global climate change. Knowledge of glacial-age climates is also relevant to understanding biogeographic patterns and the origin and maintenance of high species diversity in neotropical ecosystems. The research will provide educational opportunities for graduate and undergraduate students at the University of Tennessee, and for grades 6-12 students in local schools in whose classrooms faculty and graduate students will conduct scientific outreach. Through international outreach efforts, the project will also help educate park guards, guides, and tourists on glacial and climate history in the Cordillera de Talamanca.