Moisture source variability in Central America over the past 1200 years

Abstract Central American precipitation is vital to agricultural and economic stability, but poorly constrained past hydroclimate variability limits future forecasts. Here, we reconstruct 1,200 years of precipitation and atmospheric circulation from sedimentary plant wax hydrogen isotope ratios and XRF spectroscopy from Lake Izabal, Guatemala. Warm intervals (e.g., the Medieval Climate Anomaly; MCA) were dry with ²H-depleted precipitation, whereas the cooler Little Ice Age (LIA) was wetter and precipitation was ²H-enriched—opposite to the conventional “amount effect.” We interpret this pattern as reflecting shifts in dominant moisture sources. Specifically, during the MCA, the Intertropical Convergence Zone (ITCZ) was in a northern position, while the Caribbean Low-Level Jet (CLLJ) strengthened and shifted south, reducing 2 H-enriched Caribbean input while comparatively increasing 2 H-depleted Pacific-sourced moisture. During the LIA, a northern CLLJ and southern ITCZ enhanced Caribbean-sourced precipitation, relative to precipitation sourced from the Pacific. Our results demonstrate the potential of isotopic proxies to reconstruct past changes in atmospheric circulation and moisture-source variability, and highlight the role of Atlantic-Pacific moisture balance in shaping regional isotopic signatures.