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

该项目旨在测试过去中美洲季风区域气候的气候强迫假设，包括海面温度、海洋环流、海因里希事件强迫和其他冰期-间冰期边界条件数据，这些数据来自墨西哥西南部的石笋三角洲氧-18，跨越几个冰川旋回。来自墨西哥JX洞穴的新概念证明石笋的时间跨度约为距今53,000至105,000年（BP），而来自墨西哥Sistema Huatla的新样本的时间跨度为115,000至340,000年BP。这些样品的初步数据偏离了平滑正弦轨道日照假设，而是显示出突发性阈值样行为，包括季风崩塌，明显与北大西洋海因里希事件一致，特别是在海洋同位素阶段（MIS） 5b的相对温暖区间。研究将集中在非冰期暖期（如MIS 5、7和9）的弱季风间断期，因为这些时间可能代表与人为气候变化引起的海洋环流减弱有关的未来干旱的古类似物。为什么要做这项研究，为什么是现在？流行的轨道季风假说描述了在轨道岁差（21,000年）时间尺度上夏季入射太阳辐射（日照）与区域季风强度之间的强正耦合关系。区域尺度季风强度与岩石层氧同位素值呈负相关关系，揭示了较长的季风古气候记录。轨道对季风的控制在东亚和南美季风系统中得到了强烈的表达，在这些系统中，洞穴氧同位素时间序列呈现出平滑的正弦变化，并以轨道日照为节奏。然而，在其他热带地区，轨道日照假说无法解释水文气候变化，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的古气候变化可以用轨道季风假说来解释。潜在的更广泛影响（bi）包括支持研究生培训，吸引内华达州历史上代表性不足的群体的学生，以及乔治亚州历史悠久的黑人学院和大学（HBCU）的学生。此外，研究人员还将在靠近Sistema Huatla的Plan Carlota的土著马萨特克社区参与洞穴科学研究，以及用西班牙语和马萨特科语制作洞穴教育海报。该项目对社会的直接潜在科学效益包括提高对极易受到气候变化影响的地区的热带水文气候变率的认识。这项研究的结果还可以帮助决策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。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。

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.