Isotopic records of tropical vegetation and climate change from terrestrial vascular plant biomarkers preserved in Cariaco Basin sediments

Records of vascular plant leaf wax δ13C and δD were generated from terrestrial biomarkers preserved in Cariaco Basin marine sediments, and were found to parallel known regional millennial-scale climate changes between the late Glacial and Preboreal periods. The terrestrial biomarkers used consisted of C24–C32 n-alkanoic acids, which originate from vascular plant leaf waxes. Differences in δD between C16–C18 and C24–C30 n-alkanoic acid homologues suggest a marine source for the shorter chain lengths and a terrestrial source for the longer chains. Both the δ13C and δD leaf wax records exhibited enrichment during the late Glacial and Younger Dryas and relative depletion during the Bølling/Allerød and Preboreal periods. δD likely records the hydrogen isotopic composition of plant growth water, and thus may act as a proxy for local aridity. In agreement with Cariaco Basin sediment grey scale records, the δD record suggests that the late Glacial and Younger Dryas were more arid than the Bølling/Allerød and Preboreal periods. n-Alkanoic acid δ13C, which is a proxy for C3 versus C4 plant type, indicates that C3 plants predominated in this area of the tropics during warm and wet periods, such as the Bølling/Allerød and the early Holocene, and C4 plants proliferated during cooler and more arid periods, such as the Glacial and Younger Dryas. The biomarker δ13C record agrees with pollen data from Cariaco Basin sediments, confirming that leaf wax compounds preserved in marine sediments can accurately record terrestrial vegetation changes.