Reconstructions of Neotropical Hydroclimate: A Compound-Specific Deuterium Isotope Approach.

2020-01-17T16:14:05Z (GMT) by Genevieve Tyrrell
The hydrogen isotope composition of leaf wax (δDwax) has been found to successfully record the isotopic composition of precipitation (δDp) and as a result has been used extensively in palaeohydrological research. Although widely applied across the globe, δDwax records remain scarce within the tropics, most specifically in northern South America. To resolve this gap in the literature, the δDwax values of three sediment cores obtained from Colombia – two from the Amazon Basin and the third from the high-altitude Páramo ecosystem of the Andes - were analysed to reconstruct past rainfall in northern South America. In the Amazonian sites, microbial degradation limited the extent of palaeohydrological data obtained from the cores, providing a precipitation record for the past ~2000 years. The records showed increased precipitation during the Little Ice Age and Medieval Climate Anomaly, contradicting other northern South American records. In contrast, the high-Andean δDwax record spanned ~85,000 years. δDwax values decrease by ~4‰ during the Last Glacial Maximum suggesting the rainfall slightly increased during this time. Additionally, δDwax during the Younger Dryas increased suggesting a slight reduction in precipitation. δDwax values indicate the climate became progressively drier throughout the early-to-mid-Holocene, with the highest δDwax occurring at 4200 cal yr BP (the 4.2 event). This was then followed by a dramatic reduction in δDwax into the Late Holocene, before increasing again into the youngest 2000 cal yr BP of the record. Interestingly, higher precipitation, inferred through a decrease in δDwax, coincides with a southward displacement of the ITCZ during the LGM and the LIA. The records suggest that, in northern South America, ITCZ movements may not be the sole cause of changes in precipitation.