Collaborative Research: Response of the Tropical Pacific to the Abrupt Climate Change Event 8,200 Years Ago

8200年前，冰川融水灾难性地涌入拉布拉多海，扰乱了大西洋环流，使北大西洋地区陷入一个多世纪的寒冷状态，并影响了全球气候。一些气候模型表明，由于这种扰动，广大的热带雨带可能会向南移动，这对于理解如果海洋变暖破坏海洋环流，未来气候将如何变化具有重要意义。然而，对82000年前热带地区降雨的重建很少，这使得基于模型的预测很难得到证实。为了弥补这一数据缺口，该项目将根据位于现代热带雨带南北边缘的帕劳和Galápagos的湖泊沉积物的化学变化重建热带太平洋的降雨变化。这项研究将包括气候模型模拟，阐明帕劳和Galápagos预计的降雨量变化，这是对北大西洋融水增加的反应，其规模与8200年前的事件估计的规模相似。将在科斯雷（密克罗尼西亚）为密克罗尼西亚高中教师举办一个讲习班，并举办一次体验式学习讲习班。来自华盛顿大学的学生将与高中教师合作，根据他们的经验进行实地练习和创建课程活动。降雨将由来自帕劳和Galápagos湖泊的放射性碳定年沉积物中微藻脂质甾醇的氢同位素比率重建。对氢同位素信号的区域性质的信任将通过测量、沉积物岩心、湖泊和岛屿的复制来实现。所有9个沉积物岩心，长度在2-15米之间，都已收集，其中大多数具有初始放射性碳年代学。每个岩心的厚度在50 ~ 250 cm之间，时间分辨率为25 ~ 40年。每个岩心中剩下的全新世时期的氢同位素数据将以250-500年的分辨率产生，以便将8200年前的任何一次旅行置于整个全新世的背景下。对这些降雨重建的解释，包括它们的全球背景，将通过同位素支持的群落地球系统模型的模拟得到帮助，该模型采用了现实的拉布拉多海融水通量。由于热带太平洋降雨对淡水强迫的响应模式差异很大，我们的降雨重建将为这些模式提供一个关键的基准，并有助于约束热带对AMOC突然中断的响应机制。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

A catastrophic outburst of glacial meltwater into the Labrador Sea 8,200 years ago disrupted Atlantic Ocean circulation, plunging the North Atlantic region into cold conditions for more than a century and impacting climate globally. Some climate models indicate that the vast tropical rain bands may shift south in response to such a perturbation, which has important implications for understanding how the climate might change in the future if a warming ocean disrupts ocean circulation. Yet few reconstructions of rainfall exist from the tropics that span the 8,2000-year-ago time interval, making it difficult to confirm the model-based predictions. To remedy this data gap this project will reconstruct rainfall changes in the tropical Pacific from chemical variations in lake sediments in Palau and the Galápagos that lie on the northern and southern edges of the modern tropical rain band. The research will include climate model simulations elucidating the rainfall changes expected in Palau and the Galápagos in response to a meltwater addition to the North Atlantic similar in size to that estimated during the 8,200-year-ago event. A workshop will be held for Micronesian high school teachers along with an experiential learning coarse in Kosrae (Micronesia). Students from the University of Washington will work with high school teachers and conduct field exercises and create curricular activities based on their experiences. Rainfall will be reconstructed from hydrogen isotope ratios of the microalgal lipid dinosterol in radiocarbon-dated sediments from lakes in Palau and the Galápagos. Confidence in the regional nature of the hydrogen isotope signals will be achieved through replication of measurements, sediment cores, lakes, and islands. All nine sediment cores, which range in length from 2-15 m, have been collected, and most have initial radiocarbon chronologies. A temporal resolution of 25-40 yr is proposed for the 7,000-9,000-year-ago interval of each core, which ranges in thickness from 50-250 cm. The remainder of the Holocene period in each core will have hydrogen isotope data produced at 250-500-yr resolution in order to place any of the 8,200-yr-ago excursions in the context of the full Holocene. Interpretations of these rainfall reconstructions, including their global context, will be aided by simulations with the isotope-enabled Community Earth System Model forced with realistic meltwater fluxes to the Labrador Sea. Because models diverge widely in their response of tropical Pacific rainfall to freshwater forcing, our rainfall reconstructions will provide a critical benchmark for these models and help constrain the mechanisms by which the tropics respond to abrupt AMOC disruptions.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.