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: 2102919
• 负责人: Anders Noren
• 金额: $ 14.29万
• 依托单位: University of Minnesota-Twin Cities
• 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=2102919&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.

这项研究的主要目的是调查过去一万年（全新世）热带南美水文气候变化的机制。二十多年来，热带雨带（也称为全新世）位置的纬度（南北）变化。被称为热带辐合带；ITCZ），以响应地球表面太阳能分布的变化，被视为热带南美洲的主要驱动力然而，越来越多的热带安第斯山脉湖泊水位重建表明，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，干旱和雨季之间出现了突然而显着的变化。 ）持续了几个世纪到几千年的条件。全球太阳能分布的逐渐变化如何导致安第斯热带水文气候突然而持久的变化仍然是一个悬而未决的问题。该地区为 11 个国家的 3.5 亿多人提供淡水资源，因此，该研究对预测未来气候变化将如何影响具有深远影响。此外，还提供了对大规模气候系统相互作用的重要见解，这将提高我们对未来中纬度气候将如何变化的理解。研究人员将通过对湖泊沉积物进行生物、地球化学和沉积学分析来研究全新世热带安第斯水文气候托塔是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年平均气温（MAT）、年平均降水量（MAP）、降水和湖水的氢同位素组成的代理记录。托塔湖被专门选择用于这项工作，因为之前的地球物理和沉积岩芯研究表明，它包含厚厚的全新世沉积物序列，这些沉积物记录了上述水文气候指标，并且可以通过辐射技术准确测定年代。研究人员将深入研究南美洲核心 ITCZ 区域的水文气候对外部强迫的响应，将代理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有效水分（之间的平衡）的假设。降水和蒸发）由 MAP（由 ITCZ 动力学控制）驱动，年平均蒸发量（由 MAT 控制）对夏季日照的半球分布和北半球的响应(NH)安第斯山脉有效水汽与南半球(SH)安第斯山脉反相位。对于NH来说，在全新世早期当ITCZ位于最北位置时，安第斯山脉MAP略低，增加。中全新世早期，随着 ITCZ 向南迁移，并且随着 ITCZ 进一步向南迁移，北半球夏季日照减少，南半球日照增加，MAE 的变化如下：由 MAT 调节，减轻或增强 ITCZ 驱动的 MAP 的变化，从而导致非日晒样的有效湿度趋势。该奖项是 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。