PANAMA HYDROLOGY AND EASTERN PACIFIC INTERTROPICAL CONVERGENCE ZONE (ITCZ) RESPONSE TO ENSO AND VOLCANIC ERUPTIONS SINCE THE EARLY 1700S

The Intertropical Convergence Zone (ITCZ) is a narrow band of high rainfall and atmospheric convection in the tropics that contributes ~30% of total global precipitation. Seasonal and interannual changes in the ITCZ control tropical precipitation and surface hydrology across wide areas. Despite the importance of the ITCZ to tropical hydrology, there remains significant uncertainty about the mechanisms that control the position of the ITCZ and the origin of decadal and interannual ITCZ variability. The Gulf of Chiriquí in western Panamá offers a unique setting to monitor changes in Eastern Pacific ITCZ activity over the last 3 centuries due to the high correlation between near-monthly resolved coral skeletal Ba/Ca measurements and seasonal changes in local river discharge (Q). Here we present a partially replicated coral Ba/Ca reconstruction of seasonal changes in ITCZ-related river discharge into the Gulf of Chiriquí Panamá extending from 1719 to 2018 CE. In addition to recording La Niña flooding and El Niño droughts and some annual or biannual droughts following volcanic eruptions, our results also document decadal-scale droughts from 1808-1818 and 1974-1992 CE coincident with sequential and very large (VEI ³6) volcanic eruptions. These results support simulations and document for the first time in a paleo-archive, volcanic aerosol effects on interannual and decadal changes in the eastern Pacific ITCZ position. Our results identify tropical volcanism, in addition to ENSO, as a key factor for eastern Pacific ITCZ dynamics with implications for managing regional water resources in Panamá including the economically important Panamá Canal. The volcanic eruptions that correlate with interannual and decadal-scale droughts in Panamá were located in both hemispheres, yet the eastern Pacific ITCZ response to the inter-hemispheric volcanic aerosol forcing was always to shift south and/or weaken. Thus, our Gulf of Chiriquí coral Ba/Ca reconstruction of Panamá hydrology and eastern Pacific ITCZ position/intensity also appears to confirm simulations (i.e.; Schneider et al., 2014, Nature v.513) showing that the ITCZ mean latitudinal position is a function of both the cross-equatorial energy transport where it shifts towards the warming hemisphere, but also the net energy input to the equatorial atmosphere.