Collaborative Research: P2C2--What is the Driver of Orbital-Scale Central American Monsoon Variations? Tests of the Insolation and Sea Surface Temperature Hypotheses

该项目旨在从危地马拉加勒比海沿岸的一个洞穴中产生跨越最后一次冰川时期(14万年或更长时间)的轨道-时间尺度洞穴群同位素记录。雷伊·马科斯洞穴提供了概念验证数据，可以根据理想的地球化学特征和平衡同位素值获得高精度的铀系年龄。来自过去15,000年的石笋的初步数据显示，中美洲季风在大约9,200年前增强，与加勒比海海洋表面温度(SST)和危地马拉陆地表面温度上升相一致。强烈而稳定的季风是全新世其余部分的特征，与从卡里亚科盆地推断的日照减少而导致的全新世季风减弱形成对比。研究人员假设，对中美洲季风的主要强迫是SST变化，轨道辐射是次要的，不太重要。该项目将使对SST和轨道强迫假设在轨道时间尺度上的新测试成为可能。此外，这项工作将记录过去气候事件的时间和持续时间，如当前和最后一次间冰期，海因里希体育场引起的千年尺度变化的影响，大西洋经向翻转环流的变化，以及丹斯加德/奥施格事件从高到低纬度的表现。概念验证数据有别于其他区域记录，这些区域记录记录了与轨道和北大西洋起源的千年变异性的联系，例如来自墨西哥的中美洲季风的喷发旋涡记录和来自加勒比盆地的海洋沉积物。重建季风行为的区域异质性突出表明，需要在轨道时间尺度上提供更多高分辨率和精确年代的加勒比海斜坡记录。这些解释将与CMIP 5/6和PMIP 3/4模式运行的模式结果进行比较，以更深入地了解支配中美洲季风的主要机制以及外部强迫和内部产生的变率的相对作用。潜在的更广泛的影响包括加深对自然气候变异性的理解；编制与洞穴有关的教育材料；培训两名来自代表性较低的少数民族的研究生，掌握双语(英语/西班牙语)技能，以促进在中美洲的工作；这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project aims to generate orbital-timescale speleothem isotopic records spanning the last glacial period, 140,000 years or longer, from a cave on the Caribbean coast of Guatemala. Rey Marcos cave has yielded proof-of-concept data that allows for high-precision Uranium-series ages resulting from ideal geochemical characteristics and equilibrium isotopic values. Preliminary data from a stalagmite spanning the last 15,000 years shows that the Central American monsoon strengthened at approximately 9,200 years ago coincident with increased Caribbean Ocean sea surface temperatures (SSTs) and land surface temperatures in Guatemala. A strong and stable monsoon characterizes the rest of the Holocene in contrast to the monsoon weakening over the Holocene arising from decreasing insolation inferred from the Cariaco Basin. The researchers hypothesize that the dominant forcing on the Central American monsoon is SST change and that orbital insolation is a secondary and less important forcing.The project will enable a new test of the SST versus orbital forcing hypotheses on orbital timescales. Further, the work will document the timing and duration of past climate events like the current and last interglacials, the influence of millennial-scale variability arising from Heinrich stadials, changes in the meridional overturning circulation of the Atlantic Ocean, and high-to-low latitude manifestations of Dansgaard/Oeschger events. The proof of concept data differ from other regional records which have documented links to orbital and North Atlantic sourced millennial variability, such as speleothem records of the Mesoamerican monsoon from Mexico and marine sediments from the Cariaco Basin. The regional heterogeneity in reconstructed monsoon behavior highlights the need for additional high-resolution and precisely dated records from the Caribbean slope on orbital timescales. The interpretations will be compared with model output from the CMIP 5/6 and PMIP 3/4 model runs to gain deeper insights about the dominant mechanisms governing the Central American monsoon and about the relative role of externally-forced and internally-generated variability.The potential Broader Impacts include furthering the understanding of natural climate variability; development of educational materials related to caves; training of two graduate students from underrepresented minorities with bi-lingual (English/Spanish) skills to facilitate work in Central America; and stakeholder participation with the local Guatemalan communities hosting the cave sites.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.