Collaborative Research: Are Amazonian and Andean ecosystems close to a tipping point?

合作研究：亚马逊和安第斯生态系统是否已接近临界点？

• 批准号: 2029615
• 负责人: Liviu Giosan
• 金额: $ 13.13万
• 依托单位: Woods Hole Oceanographic Institution
• 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: 2021-06-01 至 2024-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2029615&HistoricalAwards=false
• 关键词: Collaborative; Research; Amazonian; Andean; ecosystems

Amazonian rainforests are famous for the immense biological and cultural diversity they support. These forests are also a vital part of global recycling of freshwater, and their loss has implications for food security for millions of people as well as global climate dynamics. Climate change is threatening these systems and there are concerns that as temperatures rise and rainfall becomes less reliable, these forests might be replaced by low-diversity grasslands. However, it is unclear what level of climate change might trigger a forest-to-grassland transition. Paleoecology can provide information about biological diversity in the past, and how biodiversity patterns changed during past warming events. This research project will investigate two periods of climate warming, one that lasted from about 8000 to 5000 years ago, and another even warmer time that lasted from 128,000 to 120,000 years ago. Ancient lakes build up sediments through time, and by taking a drill-core down through the sediment the history of the region can be captured in the lake mud. The researchers will analyze the fossil and chemical content of lake sediment cores from seven locations in the Amazon and Andes to establish how much the climate changed in the past, and whether those changes were enough to induce a shift from forest to grassland. By looking at a range of locations that vary in moisture, from very wet to quite dry, and degree of warming, the researchers will estimate how close the modern rainforest is to a forest-to-grassland transition. Additionally, new interactions between the collaborating research groups will include a co-taught paleoecology/paleoclimatology course, a sponsored category in a local film festival, and training of at least 10 undergraduates, two doctoral students, and one postdoctoral researcher. The research will address a number of hypotheses relating to climate-vegetation responses such as flickering, teleconnections, ecosystem buffering, and tipping points. By using organic geochemical data to estimate paleotemperature, leaf wax isotopes to estimate precipitation, sediment chemistry to characterize droughts, fossil pollen to reconstruct vegetation, and charcoal to reconstruct fire frequency, the researchers will investigate ecosystem change under conditions as much as 2 degrees C (4 degrees F) warmer than the present. The Last Interglacial will provide an index of scale of change in traits, fire prevalence and community composition in a climate 1-2 degrees C warmer than modern. In the directly-dated Holocene, the data will assess sub-decadal variance in ecosystem indicators, and allow rates of change to be investigated. Currently, no high-resolution records of Amazonian temperature exist, so the novel approach of separating climatic change from that of ecological proxies will be transformational for quantitative neotropical paleoecology.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.

亚马逊雨林因其支持的巨大生物和文化多样性而闻名。这些森林也是全球淡水循环的重要组成部分，它们的消失对数百万人的粮食安全以及全球气候动态产生影响。气候变化正在威胁这些系统，人们担心，随着气温上升和降雨变得不那么可靠，这些森林可能会被低多样性的草原所取代。然而，目前尚不清楚什么程度的气候变化可能会引发森林向草原的转变。古生态学可以提供有关过去生物多样性以及过去变暖事件期间生物多样性模式如何变化的信息。该研究项目将调查两个气候变暖时期，一个持续约8000至5000年前，另一个更温暖的时期持续128,000至120,000年前。古老的湖泊随着时间的推移积累了沉积物，通过在沉积物中钻取岩心，可以在湖泥中捕捉到该地区的历史。研究人员将分析亚马逊和安第斯山脉七个地点的湖泊沉积物核心的化石和化学成分，以确定过去气候变化的程度，以及这些变化是否足以导致从森林到草原的转变。通过观察一系列湿度变化（从非常潮湿到非常干燥）以及变暖程度的地点，研究人员将估计现代雨林距离森林向草原过渡的距离。此外，合作研究小组之间的新互动将包括共同教授古生态学/古气候学课程、当地电影节的赞助类别，以及对至少 10 名本科生、两名博士生和一名博士后研究员的培训。该研究将解决一些与气候植被反应有关的假设，例如闪烁、遥相关、生态系统缓冲和临界点。通过使用有机地球化学数据来估计古温度、叶蜡同位素来估计降水量、沉积物化学来表征干旱、化石花粉来重建植被、木炭来重建火灾频率，研究人员将调查在高达 2 摄氏度的条件下的生态系统变化（ 4 华氏度）比现在温暖。最后一次间冰期将提供比现代气候温暖 1-2 摄氏度时特征、火灾发生率和群落组成变化规模的指数。在直接年代的全新世中，数据将评估生态系统指标的亚年代际变化，并允许研究变化率。目前，尚不存在亚马逊温度的高分辨率记录，因此将气候变化与生态指标分开的新方法将对定量新热带古生态学产生变革。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准。