Evolution of Pliocene-Pleistocene climate and vegetation in the Tropical Andes

500万到250万年前的上新世时期，经常被认为是全球气候与今天类似的最后一次。虽然大气中二氧化碳的浓度与今天相当，但地球的平均温度可能比现在高3摄氏度，这就提出了我们的气候系统对二氧化碳变化有多敏感的问题。此外，关于这些变暖的温度如何影响热带地区，包括降水和植被，还有相当多的争论。该项目重建了过去500万年来哥伦比亚热带安第斯山脉发生的环境变化，以测试全球气候转变、热带环境变化和山脉隆起之间的关系。这一倡议加强了美国和哥伦比亚科学家之间的美洲合作，促进了少数民族研究生、早期职业教师、来自低收入家庭和少数民族的本科研究助理的职业发展，并通过与哥伦比亚大学自然历史博物馆合作的双语活动，激励了小学和中学的贫困儿童。该项目通过重建晚中新世以来热带大陆气候变化，首次整合了湖泊沉积物和露头中基于生物标志物的气候和植被记录。利用分支GDGTs、植物蜡及其稳定同位素组成，以及保存在Sabana de Bogota（哥伦比亚）沉积物中的现有和新的花粉记录，对地表温度、植被和水文变化进行了限制：(a)来自已灭绝的Funza湖的Funza II （~70 ka至~3 Ma）沉积物岩芯；(b)晚中新世-更新世河流和湖泊沉积物的露头样品；(c)中新世晚期-上新世早期低海拔河流沉积。此外，沿着东部科迪勒拉干湿两侧的当代土壤样本将用于产生现代代理校准。该研究为确定中高纬度地区变暖时热带地区是否变暖提供了依据。这样的记录将填补上新世以来热带地区过去气候重建的空白，并将提供一个全面的气候框架，以更好地解释热带地区的植被变化。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Pliocene epoch, 5 to 2.5 million years ago, is often cited as the last time global climate resembled that of the present day. While the concentrations of atmospheric CO2 were comparable to those of today, Earth's mean temperature was likely ~3 degrees centigrade warmer, which raises questions about how sensitive our climate system is to CO2 changes. Additionally, there is considerable debate about how these warmer temperatures affected the tropics, including precipitation and vegetation. This project reconstructs environmental changes occurring in the tropical Andes of Colombia over the past 5 million years to test the relationships between global climate transitions, tropical environmental change, and mountain uplift. This initiative enhances Inter-American collaboration among US and Colombian scientists, fosters the career of a minority graduate student, an early career faculty, undergraduate research assistants from low-income families and minority groups, and inspires underprivileged children in elementary and middle schools through bilingual activities in collaboration with the CU Museum of Natural History.This project constitutes the first integration of biomarker-based climate and vegetation records in lake sediment and outcrops by reconstructing continental climate variability in the tropics since the late Miocene. Surface temperatures, vegetation, and hydrological changes are constrained using branched GDGTs, plant waxes, and their stable isotope composition, in addition to existing and new pollen records preserved in sediment from the Sabana de Bogota (Colombia): (a) the Funza II (~70 ka to ~3 Ma) sediment core from the extinct Funza Lake; (b) outcrop samples of Late Miocene-Pleistocene fluvial and lacustrine deposits; and (c) Late Miocene-Early Pliocene fluvial deposits at low-elevation sites. Additionally, contemporary soil samples along the wet and dry flanks of the Eastern Cordillera will be used to produce a modern proxy calibration. This study provides a foundation to determine whether the tropics were warmer when mid and high-latitude regions were warm. Such a record will fill a hole in reconstructions of past climate in the tropics since the Pliocene and will provide a comprehensive climatic framework to better interpret vegetation changes in the tropics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.