NSF Award
2303487
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. <br/><br/>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.<br/><br/>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.<br/><br/>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.<br/><br/>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.<br/><br/>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.
