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

该项目旨在测试中美洲季风中过去区域气候的气候强迫假说，包括海表面温度、海洋环流、海因里希事件强迫和其他冰川-间冰川边界条件数据，对照来自墨西哥西南部的石笋三角洲氧气-18跨越几个冰川周期。来自墨西哥JX洞穴的新概念验证石笋覆盖了距今约53,000到105,000年的时间，而来自墨西哥Sistema Huatla的新样本跨越了115,000到34,000年。这些样本的初步数据偏离了光滑正弦轨道日照假说，而是显示了突然的门槛行为，包括明显与北大西洋Heinrich事件重合的季风坍塌，特别是在海洋同位素阶段(MIS)5b的相对温暖区间。这项研究将集中在非冰期暖期的弱季风间隔，如MIS5、MIS7和MIS9，因为这些时间可能代表着未来干旱的古类比，与人为气候变化导致的海洋环流预计减弱有关。为什么要进行这项研究？为什么是现在？盛行的轨道季风假说描述了轨道进动(21000年)时间尺度上的夏季入射太阳辐射(太阳辐射)与区域季风强度之间的强烈和正耦合关系。区域尺度季风强度与洞穴氧同位素值呈负相关，揭示了漫长的季风古气候记录。东亚和南美季风系统强烈地表现出对季风的轨道控制，那里的洞穴氧同位素时间序列表现出平滑的正弦变化，这种变化受轨道太阳辐射的影响。然而，在其他热带地区，轨道日照假说无法解释水气候变化，特别是在中美洲，那里的洞穴氧同位素与夏季日照无关。这种脱节表明，墨西哥南部和中美洲(中美洲)的古气候变化可能可以用轨道季风假说来解释。包括支持一项研究生培训，并让来自历史代表性不足群体的学生参与，包括在内华达州和佐治亚州的历史黑人学院和大学(HBCU)的福特谷州立大学。此外，研究人员将让Sistema Huatla附近Plane Carlota的Mazatec土著社区参与洞穴科学研究以及用西班牙语和Mazateco编写洞穴教育海报。该项目给社会带来的直接潜在科学利益包括：更好地了解一个非常容易受到气候变化影响的地区的热带水文气候变异性。这项研究的结果也可能有助于政策制定者了解过去突发事件的幅度和时间以及未来发生类似事件的可能性。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 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.