ABSTRACT

This project will develop a quantitative assessment of past precipitation changes on decadal to centennial time-scales for the arid Pacific coast regions of Central America. Identifying the potential changes in water resource availability for this drought sensitive region in response to future climate change is a top priority for scientists and policy makers. For example, millions of people living in the 'dry corridor' of Central America have recently been affected by drought conditions triggered by anomalous Pacific Ocean sea surface temperatures. To put recent drought scenarios into a longer-term perspective, reconstructions of past precipitation amounts will be developed using lake sediment geochemical records and lake and climate model simulations. The results of this project will allow for better modeling, forecasting and mitigating of future drought and water availability dynamics in Central America in response to a changing climate. This data will contribute directly to the efforts of the SynTraCE-21 working group, which is one of the PAst Global changES working groups tasked with conducting proxy data model comparisons. This work will contribute to their objectives of better understanding the response of the climate system to external/internal forcing, as well as model behavior and limitations. Along with the U.S. scientists supported by this grant, independently supported scientists from Nicaraguan and Mexican universities are involved in the project, as is a PhD student from Oxford University.

This project will develop detailed quantitative reconstructions of past precipitation amounts along a transect through the "dry corridor" of Central America (Guatemala, El Salvador, Honduras and Nicaragua). Previous work has documented millennial-scale shifts in climate across Central America that are consistent with expectations from solar insolation forcing; however, superimposed on these longer-term trends are shorter-term variations that are better explained by sea surface temperature and atmospheric variability in the Pacific and Atlantic basins. Hence, a more rigorous understanding of the range of possible precipitation changes resulting from mean-state variations in the global ocean-atmosphere system is needed to understand the drivers of hydroclimatic shifts in the Circum-Caribbean region. Stable isotope (δ18O) records from open and closed-basin lake sediment cores (dated using radiocarbon methods) will be interpreted using state-of-the-art isotope mass-balance models to reconstruct Holocene rainfall amounts at near-annual to decadal-scale resolution. Elemental geochemistry combined with ostracod species identification and δ18O measurements will provide supporting proxy data. This project will develop new lake sediment records to compare to both proxy-reconstructions and climate model simulations of tropical Pacific and Atlantic ocean-atmosphere variability in order to further evaluate the relative importance of these systems in driving past rainfall changes. It is anticipated that different mean state changes of the El Niño-Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) combined to drive either a synchronous or (at times) anti-phased pattern of precipitation across the Circum-Caribbean region. Interpreting the open- and closed-basin lake records using mass-balance models and will offer a robust means identifying past changes in the tropical hydrologic cycle; while analysis of climate model simulation output will provide a physical basis for explaining these changes. Furthermore, the paleoclimate data produced by this research will provide a benchmark for testing the veracity of climate model hindcasts and will therefore provide a basis for parameter refinement in climate model simulations of the future.

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