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。科学家和决策者的首要任务是确定这个干旱敏感地区水资源可用性的潜在变化，以应对未来的气候变化。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条件的影响。为了从更长远的角度看待最近的干旱情景，将利用湖泊沉积物地球化学记录和湖泊和气候模式模拟来重建过去的降水量。该项目的成果将有助于更好地模拟、预测和缓解中美洲未来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，该工作组是负责进行代理数据模型比较的过去全球变化工作组之一。这项工作将有助于他们更好地理解气候系统对外部/内部强迫的响应，以及模式行为和局限性的目标。除了获得这笔资金支持的美国科学家之外，来自尼加拉瓜和墨西哥大学的独立科学家也参与了该项目，其中包括牛津大学的一名博士生。该项目将对中美洲“干旱走廊”（危地马拉、萨尔瓦多、洪都拉斯和尼加拉瓜）的横断面上过去的降水量进行详细的定量重建。以前的工作记录了中美洲地区千年尺度的气候变化，这与太阳日照强迫的预期一致；然而，叠加在这些较长期趋势之上的是较短期的变化，这些变化可以更好地用太平洋和大西洋盆地的海表温度和大气变率来解释。因此，需要更严格地了解由全球海洋-大气系统平均状态变化引起的可能降水变化的范围，以了解环加勒比地区水文气候变化的驱动因素。来自开放和封闭盆地湖泊沉积物岩心的稳定同位素（δ18O）记录（使用放射性碳方法定年）将使用最先进的同位素质量平衡模型进行解释，以近年至十年尺度的分辨率重建全新世降雨量。元素地球化学结合介形虫物种鉴定和&amp；#948；18O测量将提供支持的代理数据。该项目将开发新的湖泊沉积物记录，与热带太平洋和大西洋海洋-大气变率的代理重建和气候模式模拟进行比较，以进一步评估这些系统在驱动过去降雨变化方面的相对重要性。预计厄尔尼诺Niño-Southern涛动（ENSO）和北大西洋涛动（NAO）的不同平均状态变化共同驱动了加勒比海周边地区的同步或（有时）反相降水模式。利用质量平衡模型解释开放和封闭盆地的湖泊记录，并将提供一种确定热带水文循环过去变化的有力手段；而对气候模式模拟结果的分析将为解释这些变化提供物理基础。此外，本研究产生的古气候数据将为检验气候模式预测的准确性提供基准，从而为未来气候模式模拟的参数改进提供基础。

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.