Collaborative Research: P2C2: Quantitative Reconstructions of Holocene Precipitation Changes Across Central America

该项目将对中美洲干旱的太平洋沿岸地区过去十年至百年时间尺度的降水变化进行定量评估。为应对未来气候变化，确定这一干旱敏感地区水资源可获得性的潜在变化是科学家和政策制定者的首要任务。例如，生活在中美洲“干燥走廊”的数百万人最近受到太平洋海面温度异常引发的干旱状况的影响。为了将最近的干旱情景放在更长期的角度来看，将利用湖泊沉积物地球化学记录和湖泊和气候模型模拟来重建过去的降雨量。该项目的成果将使人们能够更好地模拟、预测和缓解中美洲未来的干旱和水资源供应动态，以应对气候变化。这些数据将直接有助于SynTraCE-21工作组的工作，该工作组是过去负责进行代理数据模型比较的全球变化工作组之一。这项工作将有助于他们更好地了解气候系统对外部/内部强迫的反应，以及模型行为和限制。除了这笔赠款支持的美国科学家外，来自尼加拉瓜和墨西哥大学的独立资助的科学家以及牛津大学的一名博士生也参与了这一项目。该项目将沿着中美洲(危地马拉、萨尔瓦多、洪都拉斯和尼加拉瓜)的“干走廊”开发一条横断面上过去降雨量的详细定量重建。以前的工作记录了整个中美洲千年尺度的气候变化，这些变化与太阳辐射强迫的预期一致；然而，在这些较长期趋势上叠加的是较短期的变化，太平洋和大西洋盆地的海洋表面温度和大气可变性可以更好地解释这些变化。因此，需要更严格地了解全球海洋-大气系统的平均态变化可能引起的降水变化范围，以了解环加勒比区域水文气候变化的驱动因素。来自开阔和闭合盆地湖泊沉积岩心的稳定同位素(&amp；#948；18O)记录(使用放射性碳法测年)将使用最先进的同位素质量平衡模型进行解释，以重建近年度到十年尺度的全新世降雨量。元素地球化学与介形虫种类鉴定和18O测量相结合，将提供支持的替代数据。该项目将开发新的湖泊沉积物记录，以与热带太平洋和大西洋海洋-大气变化的替代重建和气候模型模拟进行比较，以便进一步评估这些系统在推动过去降雨变化方面的相对重要性。预计厄尔尼诺-南方涛动(ENSO)和北大西洋涛动(NAO)的不同平均状态变化结合在一起，将推动整个环加勒比区域降水的同步或(有时)反相模式。使用质量平衡模型解释开放和闭合盆地湖泊记录，将提供确定热带水文循环过去变化的有力手段；而对气候模型模拟结果的分析将为解释这些变化提供物理基础。此外，这项研究产生的古气候数据将为检验气候模式后播的准确性提供基准，从而为未来气候模式模拟中的参数修正提供基础。

This project will develop a quantitative assessment of past precipitation changes on decadal to centennial time-scales for the arid Pacific coast regions of Central America. Identifying the potential changes in water resource availability for this drought sensitive region in response to future climate change is a top priority for scientists and policy makers. For example, millions of people living in the 'dry corridor' of Central America have recently been affected by drought conditions triggered by anomalous Pacific Ocean sea surface temperatures. To put recent drought scenarios into a longer-term perspective, reconstructions of past precipitation amounts will be developed using lake sediment geochemical records and lake and climate model simulations. The results of this project will allow for better modeling, forecasting and mitigating of future drought and water availability dynamics in Central America in response to a changing climate. This data will contribute directly to the efforts of the SynTraCE-21 working group, which is one of the PAst Global changES working groups tasked with conducting proxy data model comparisons. This work will contribute to their objectives of better understanding the response of the climate system to external/internal forcing, as well as model behavior and limitations. Along with the U.S. scientists supported by this grant, independently supported scientists from Nicaraguan and Mexican universities are involved in the project, as is a PhD student from Oxford University.This project will develop detailed quantitative reconstructions of past precipitation amounts along a transect through the "dry corridor" of Central America (Guatemala, El Salvador, Honduras and Nicaragua). Previous work has documented millennial-scale shifts in climate across Central America that are consistent with expectations from solar insolation forcing; however, superimposed on these longer-term trends are shorter-term variations that are better explained by sea surface temperature and atmospheric variability in the Pacific and Atlantic basins. Hence, a more rigorous understanding of the range of possible precipitation changes resulting from mean-state variations in the global ocean-atmosphere system is needed to understand the drivers of hydroclimatic shifts in the Circum-Caribbean region. Stable isotope (δ18O) records from open and closed-basin lake sediment cores (dated using radiocarbon methods) will be interpreted using state-of-the-art isotope mass-balance models to reconstruct Holocene rainfall amounts at near-annual to decadal-scale resolution. Elemental geochemistry combined with ostracod species identification and δ18O measurements will provide supporting proxy data. This project will develop new lake sediment records to compare to both proxy-reconstructions and climate model simulations of tropical Pacific and Atlantic ocean-atmosphere variability in order to further evaluate the relative importance of these systems in driving past rainfall changes. It is anticipated that different mean state changes of the El Niño-Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) combined to drive either a synchronous or (at times) anti-phased pattern of precipitation across the Circum-Caribbean region. Interpreting the open- and closed-basin lake records using mass-balance models and will offer a robust means identifying past changes in the tropical hydrologic cycle; while analysis of climate model simulation output will provide a physical basis for explaining these changes. Furthermore, the paleoclimate data produced by this research will provide a benchmark for testing the veracity of climate model hindcasts and will therefore provide a basis for parameter refinement in climate model simulations of the future.