A previous study of carbon isotopes in the sediments of a glacial lake in Costa Rica led to the hypothesis that changes in the migration of the intertropical convergence zone (ITCZ) over the course of the Holocene significantly affected the hydrology of the surrounding high-elevation paramo ecosystem. This hypothesis was based on millennial-scale changes in terrestrial n-alkane carbon isotope (d13C) values in a sediment core from Lago de las Morrenas 1, a tarn on the Chirripo massif of the Cordillera de Talamanca. Here we present terrestrial n-alkane hydrogen isotope (dD) data, a more direct proxy of ecosystem drought stress, from the same core. These new data support the previous hypothesis and confirm that the effects of millennial-scale ITCZ dynamics in the circum-Caribbean region were not restricted to tropical lowlands. In southern Central America, these dynamics may have played a fundamental role in millennial-scale fire dynamics in high-elevation paramo ecosystems. © 2013 Regents of the University of Colorado.