Holocene hydroclimate in highland Costa Rica: new evidence from hydrogen and carbon isotopes in n-alkanes of terrestrial leaf waxes in a 10 000-year sediment profile

We conducted compound-specific stable hydrogen (δD) and carbon (δ¹³C) isotope analysis on n-alkanes from terrestrial leaf waxes preserved in a 10 000-year sediment profile from Lago de las Morrenas 1 (9.4925° N, 83.4848° W, 3480 m), a glacial lake on the Chirripó massif of the Cordillera de Talamanca in Costa Rica. Our results demonstrate millennial-scale variations in hydroclimate across the Holocene, with drier than average conditions in the highlands during the early Holocene, but with gradually increasing precipitation; mesic conditions during the middle Holocene with a gradual drying trend; and highly variable conditions during the late Holocene. This general pattern is punctuated by several centennial-scale manifestations of global climate events, including dry conditions during the 8200, 5200 and 4200 cal a  bp events and the Terminal Classic Drought (1200–850 cal a  bp). Our δ¹³C analyses demonstrate that carbon isotope signals are responding to changes in hydroclimate at the site and reinforce prior interpretations of a stable páramo plant community that established following deglaciation and persisted throughout the Holocene. The shifts in hydroclimate inferred from analyses of n-alkanes in Lago de las Morrenas 1 sediments show correspondence with charcoal records in multiple lakes, with fires most common during drier intervals.