Collaborative Research: P4Climate--Testing Hypotheses of Mesoamerican Hydroclimate over the Last Several Glacial Cycles

该项目旨在测试气候强迫假设过去的区域气候在中美洲季风，包括海面温度，海洋环流，海因里希事件强迫，和其他冰川间冰期边界条件数据对石笋三角洲氧-18从墨西哥西南部跨越几个冰川周期。来自墨西哥JX洞穴的新的概念验证石笋涵盖了距今约53，000至105，000年的时间段（BP），而来自墨西哥Sistema Huatla的新样本跨越了115，000至340，000年BP。从这些样本的初步数据出发，从一个平滑的正弦轨道日射假设，而是显示突然的阈值样的行为，包括季风崩溃显然与海因里希事件在北大西洋，特别是在海洋同位素阶段（MIS）5 b相对温暖的间隔。 该研究将集中在弱季风间隔在非冰期温暖时期，如MIS 5，7，和9，因为这些时间可能代表未来干旱的古模拟与海洋环流的预计减弱，由于人为气候变化。为什么这项研究，为什么现在？流行的轨道季风假说描述了轨道岁差（21，000年）时间尺度上的夏季入射太阳辐射（日射）与区域季风强度之间的强烈正耦合关系。区域尺度季风强度与洞穴沉积物氧同位素值之间的负相关关系揭示了漫长的季风古气候记录。在东亚和南美季风系统中，洞穴沉积物氧同位素时间序列显示出受轨道太阳辐射影响的平滑正弦变化，强烈表现出对季风的轨道控制。 然而，在其他热带地区的轨道日射假说未能解释水文气候变化，特别是在中美洲，洞穴氧同位素不相关的夏季日射。 这种脱节表明，墨西哥南部和中美洲（中美洲）的古气候变化可能是由轨道季风假说解释的。包括支持研究生培训和吸引来自内华达州和州立大学历史上代表性不足群体的学生，这是一所位于格鲁吉亚的历史上的黑人学院和大学（HBCU）。此外，研究人员还将让Sistema Huatla附近的Plan Carlota中的土著Mazatec社区参与洞穴科学研究，以及用西班牙语和Mazateco制作洞穴教育海报。该项目对社会的直接潜在科学效益包括提高对该地区热带水文气候变化的理解，该地区非常容易受到气候变化的影响。这项研究的结果也可能有助于告知政策制定者关于过去突发事件的幅度和时间以及未来类似事件的可能性。该奖项反映了NSF的法定使命，并被认为值得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来支持。

This project seeks to test climate forcing hypotheses for past regional climate in the Mesoamerican monsoon that include sea surface temperature, ocean circulation, Heinrich event forcing, and other glacial-interglacial boundary condition data against stalagmite delta Oxygen-18 from southwestern Mexico spanning several glacial cycles. New proof-of-concept stalagmites from JX Cave, Mexico, cover a time period from approximately 53,000 to 105,000 years before present (BP), and a new sample from Sistema Huatla, Mexico spans 115,000 to 340,000 years BP. The preliminary data from these samples departs from a smooth sinusoidal orbital insolation hypothesis, and instead shows abrupt threshold-like behavior including monsoon collapses apparently coincident with Heinrich events in the North Atlantic, notably during the relatively warm interval of Marine Isotope Stage (MIS) 5b. The research will focus on weak monsoon intervals during non-glacial warm periods such as MIS 5, 7, and 9, because these times may represent paleo-analogs of future aridity associated with the projected weakening of ocean circulation due to anthropogenic climate change.Why this research and why now? The prevailing orbital monsoon hypothesis describes a strong and positively coupled relationship between summer incoming solar radiation (insolation) on orbital precession (21,000 year) timescales and regional monsoon strength. Long monsoon paleoclimate records are revealed in the inverse correlation between regional scale monsoon strength and speleothem oxygen isotope values. The orbital control on monsoons is strongly expressed in the East Asian and South American monsoon systems where speleothem oxygen isotope time series show smooth sinusoidal variations that are paced by orbital insolation. However, in other tropical areas the orbital insolation hypothesis fails to explain hydroclimate variations, notably in Central America, where speleothem oxygen isotope does not correlate to summer insolation. This disconnect suggests that paleoclimate variations in southern Mexico and Central America (Mesoamerica) may be explained by the orbital monsoon hypothesis.The potential Broader Impacts (B.I.) include supporting a graduate student training and engaging students from historical underrepresented groups students in Nevada and also at Fort Valley State University, an Historical Black College and University (HBCU) in Georgia. In addition, the researchers will involve the indigenous Mazatec community in Plan Carlota near Sistema Huatla in cave science research as well as the development of cave education posters in Spanish and Mazateco.Direct potential scientific benefits to society from this project include an improved understanding of tropical hydro climate variability in a region which is very vulnerable to climate change. The results of this research may also help to inform policy makers about the amplitude and timing of abrupt events in the past and the potential of similar events in the future.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.