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

建立美洲热带科迪勒拉地区晚第四纪冰川进展的年表

• 批准号: 1227018
• 负责人: Yingkui Li
• 金额: $ 20万
• 依托单位: University of Tennessee Knoxville
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1227018&HistoricalAwards=false
• 关键词: Establishing; Chronology; Late; Quaternary; Glacial

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.

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然存在争议。热带山区的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提供了古气候趋势及其强迫机制的关键证据。传统上，很难确定冰川地貌的年代，因此准确地确定它们记录的气候阶段和事件的年代并不成功。宇宙成因核素测年技术的最新发展为古冰川动力学地貌研究带来了革命性的变化，并为冰碛物的形成年代和其他特征的确定提供了可靠的手段。在这个项目中，研究人员将为中美洲南部的塔拉曼卡山脉制定一个长期的冰川年代学，该山脉位于美洲山脉的地峡部分。将使用哥斯达黎加奇里波加夫两个山谷中三个冰碛复合体的代表性冰碛和基岩露头的36 Cl表面暴露测年法确定年代，并使用为此目的收集的60个样品。将要制定的年代学将揭示美洲科迪勒拉地峡部分的冰川进展是否与其他地方的冰川进展同步，美洲科迪勒拉地峡部分比北部或南部地区更受太平洋和加勒比海的影响。以前的工作重建冰川范围从冰碛复合体在研究现场显示，晚第四纪冰川的进步的特点是明显不同的温度和湿度条件，但冰川阶段只相对于彼此的日期。 通过在时间上锚定这些重建，宇宙起源测年将使研究人员能够将塔拉曼卡山脉的古气候趋势与新热带地区及其他地区的冰川地貌，花粉组合，同位素记录和其他气候代理记录进行比较。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，对了解美洲的古气候和冰川前进的时间很重要。该项目将填补沿美国科迪勒拉山脉断面沿着冰川年表的知识空白。结果将有助于了解过去的动力学的新热带海洋对流层，更新世的气候在中美洲南部。通过提高对该地区过去气候动态的科学认识，这项研究可以帮助建模和预测未来的全球气候变化。冰川期气候的知识也与了解新热带生态系统中的地理格局以及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提供教育机会，并为当地学校的6-12年级学生提供教育机会，教师和研究生将在当地学校的教室里进行科学推广。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。