117-11 Using plant wax hydrogen isotope ratios to reconstruct Central American moisture source variability over the past 1,200 years

Abstract:

Accurately attributing the drivers of isotopic variability is particularly important in regions like Central America, where multiple moisture pathways intersect and their relative influence shifts through time. To improve predictive modeling efforts, a more complete characterization of the factors that influence regional isotope-based records is required. To address this need, we reconstructed 1,200 years of precipitation and circum-Caribbean atmospheric circulation using 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 attribute this to 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 the contribution of ²H-enriched Caribbean moisture while increasing the relative contribution of ²H-depleted Pacific moisture. During the LIA, a northern CLLJ and southern ITCZ enhanced Caribbean-sourced precipitation. Our results highlight that Atlantic-Pacific moisture-source balance exerts a primary control on regional isotopic signatures, demonstrating the potential of isotopic proxies to reconstruct past moisture-source variability.

Geological Society of America Abstracts with Programs. Vol. 58, No. 5, 2026

doi: 10.1130/abs/2026AM-21255

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.