Collaborative Research: Reconstructing river discharge and hydrologic variability in Panama via coral geochemistry: Implications for management of the Panama Canal award

Rivers and hydrology play a critical role in tropical ecosystems. They impact aspects of climate, help to sustain life, and influence societal needs such as drinking water, food security, and economics. In Panamá, a specific concern is the impact of rainfall on the functioning of the Panamá Canal. Rainfall and river discharge (Q) are strongly linked in Panamá, and they play a crucial role in the sustained success of the canal. Rainfall totals across Panamá consistently place it in the top five countries for annual rainfall, but when major droughts occur, the Panama Canal Authority places restrictions on ship traffic to conserve water so that the canal can continue to operate. Panamá has a well-known seasonal variability in precipitation, with a wet season that lasts from about May through November. However, little is known about rainfall variation on longer time scales, on the order of decades or centuries. In addition, it is not clear how El Niño events may influence Panamanian rainfall, though there are suggestions of a relationship between El Niño strength and drought severity. These questions are hard to address because instrumental data, particularly river discharge records, are short and often unreliable ? we need a longer-term perspective. The chemistry of coral skeletons can preserve records of climate conditions and climate variability; these chemical records are called climate proxies. This project will use coral climate proxies to reconstruct hydrologic variability along the Pacific Coast of Panamá over the past ~300 years at near-monthly resolution. The final product will be a multi-coral, multi-proxy record that can be used to identify the frequency and strength of events such as droughts or El Niño. This project includes support for 8 female undergraduates and 1 Ph.D. student. Results from this project will be incorporated into a teaching workshop for middle and high school educators and will also be shared with water resource managers in Panamá.

Many tropical nations are subjected to intense variation in precipitation with extreme seasonality. Meridional migration of the Intertropical Convergence Zone (ITCZ) is largely responsible for this variability, with northward movement during the boreal summer and a southward shift during the austral summer. In the Pacific, El Niño and other less well constrained decadal and century-scale modes of ocean- atmosphere variability also dictate regional climate. In Panamá, a country whose rainfall and river discharge (Q) are tightly coupled, understanding hydrologic variability is of the utmost importance when considering the potential impacts on the Panamá Canal, whose functioning relies solely on hydraulic head differences between the canal locks and the Gatun Lake reservoir. Therefore, the probability of anomalous hydrologic conditions, such as drought and flooding, must be well defined. However, the lack of long instrumental records of tropical hydrology (i.e.; rainfall and Q) limits our ability to develop a rigorous understanding of drought and flood recurrence intervals. These issues raise the following questions: 1) What is the relationship between El Niño Southern Oscillation and droughts and flooding in Panamá? 2) Can we identify droughts and flood years that are not related to El Niño? And 4) Has there been multi-decadal or long-term secular changes in Q in Panamá and what climatic processes are involved? Preliminary results indicate that barium/calcium (Ba/Ca) time-series data from a coral core collected in 1984 at Secas Island in the Gulf of Chiriquí (GoC) along the Pacific Coast of Panamá has a remarkably strong correlation with Q from two major nearby rivers. Given these encouraging results, we will be completing the Ba/Ca analyses of the Secas Island core back to 1707 CE and to analyze a new GoC coral core collected in 2018. The final near- monthly resolved composite Ba/Ca record of Q will extend from 2018 to 1707 CE. By pairing Ba/Ca and ?18O on the same 1mm samples we can separately evaluate salinity and sea surface temperature changes in the GoC over the last 311 years. These paleo-Q and salinity reconstructions will provide a comprehensive history of Panamanian hydroclimate that can be exploited to track protracted deviations from average conditions.

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.