Collaborative Research: Investigating Inter-Hemispheric Phasing of Tropical Andean Hydroclimate in Response to Holocene Orbital Forcing

合作研究：调查热带安第斯水文气候对全新世轨道强迫的响应的半球间相位

• 批准号: 2103072
• 负责人: Byron Steinman
• 金额: $ 9.61万
• 依托单位: University of Minnesota Duluth
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-15 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2103072&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigating; Inter; Hemispheric

The primary objective of this research is to investigate the mechanisms of tropical South American hydroclimate variably during the last 10,000 years (the Holocene). For more than two decades, latitudinal (north-south) changes in the position of the tropical rain belt (also referred to as the Intertropical Convergence Zone; ITCZ) in response to variations in the distribution of solar energy across the Earth’s surface have been viewed as the primary driver of tropical South American hydroclimate. A growing number of lake-level reconstructions from the tropical Andes, however, show that changes in Andean hydroclimate did not closely track long-term changes in solar energy. Instead, there were abrupt and marked changes between drought and pluvial (wet phases) conditions that lasted for centuries to millennia. How gradual changes in the global distribution of solar energy produced abrupt and long-lasting changes in tropical Andean hydroclimate remains an open question. Determining the mechanisms responsible for abrupt Andean climate changes in the past has profound implications for predicting the ways in which future climate change will impact this region which provides freshwater resources to over 350 million people across 11 countries. Because tropical climate variability directly impacts mid-latitude regions, including North America, this research will additionally provide critical insight into large-scale climate system interactions that will improve our understanding of how mid-latitude climate will change in the future.The researchers will investigate Holocene tropical Andean hydroclimate by conducting biological, geochemical, and sedimentological analyses of sediment from Lake Tota, a high-altitude lake in the eastern cordillera of the Colombian Andes. The researchers will use these data to develop proxy records of mean annual temperature (MAT), mean annual precipitation (MAP), the hydrogen isotopic composition of precipitation and lake water, and lake levels. Lake Tota was specifically selected for this work because previous geophysical and sediment core research shows that it contains a thick sequence of Holocene sediments that archive the aforementioned hydroclimate proxies and can be accurately dated with radiometric techniques. These data will provide insight on hydroclimate responses to external forcing in the understudied core ITCZ region of South America. Integrating the proxy data with lake and climate model simulations and existing paleoclimate records, the researchers will test the hypothesis that Holocene Andean effective moisture (the balance between precipitation and evaporation) was driven by MAP (as controlled by ITCZ dynamics) and mean annual evaporation (as controlled by MAT) responses to the hemispheric distribution of summer insolation and that Northern Hemisphere (NH) Andean effective moisture was generally anti-phased with the Southern Hemisphere (SH) Andes. For the NH, it is hypothesized that Andean MAP was slightly lower during the early Holocene when the ITCZ was at its northerly most position, increased during the early middle Holocene as the ITCZ migrated southward, and generally lessened as the ITCZ migrated further southward as summer insolation decreased in the NH and increased in the SH. Changes in MAE, as moderated by MAT, mitigated or enhanced changes in ITCZ-driven MAP, resulting in non-insolation-like effective moisture trends.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.

本研究的主要目的是研究过去10，000年（全新世）热带南美洲水文气候变化的机制。二十多年来，热带雨带（也称为热带辐合带; ITCZ）位置的纬度（南北）变化对地球表面太阳能分布变化的响应被视为南美洲热带水文气候的主要驱动力。然而，越来越多的来自热带安第斯山脉的湖面重建表明，安第斯山脉水文气候的变化并没有密切跟踪太阳能的长期变化。相反，干旱和多雨（潮湿阶段）条件之间发生了突然和显著的变化，持续了几个世纪到几千年。全球太阳能分布的逐渐变化如何导致热带安第斯水气候的突然和持久变化，仍然是一个悬而未决的问题。确定造成安第斯山脉气候突变的机制对预测未来气候变化将如何影响这一地区具有深远的意义，该地区为11个国家的3.5亿多人提供淡水资源。由于热带气候变化直接影响中纬度地区，包括北美，这项研究还将为大尺度气候系统的相互作用提供重要的见解，这将提高我们对未来中纬度气候如何变化的理解。研究人员将通过对托塔湖沉积物进行生物学，地球化学和沉积学分析，哥伦比亚安第斯山脉东部的一个高海拔湖泊。研究人员将利用这些数据来开发平均年温度（MAT），平均年降水量（MAP），降水和湖水的氢同位素组成以及湖泊水位的代理记录。托塔湖是专门为这项工作选择的，因为以前的地球物理和沉积物岩心研究表明，它包含了一个厚厚的全新世沉积物序列，这些沉积物保存了上述水文气候代理，并可以用放射性技术准确地测年。这些数据将提供深入了解水文气候响应的外部强迫在未充分研究的核心ITCZ地区的南美洲。将代用数据与湖泊和气候模型模拟以及现有的古气候记录相结合，研究人员将检验全新世安第斯山脉的有效湿度（降水和蒸发之间的平衡）由MAP驱动（受ITCZ动力学控制）和平均年蒸发量（由MAT控制）对夏季太阳辐射半球分布和北方半球（NH）安第斯山脉的有效湿度一般与南半球（SH）的安第斯山脉反相。对于NH，据推测，安第斯MAP略低，在全新世早期时，ITCZ是在其最北的位置，增加在早中全新世的ITCZ向南迁移，并普遍减少ITCZ进一步向南迁移的夏季日照减少在NH和增加在SH。MAE的变化，由MAT调节，减轻或增强了ITCZ驱动的MAP的变化，导致非日晒样有效湿度趋势。该奖项反映了NSF的法定使命，并被认为是值得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的支持。