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

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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.