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

Abstract

Records of vascular plant leaf wax δ 13C 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 C 24–C 32 n-alkanoic acids, which originate from vascular plant leaf waxes. Differences in δD between C 16–C 18 and C 24–C 30 n-alkanoic acid homologues suggest a marine source for the shorter chain lengths and a terrestrial source for the longer chains. Both the δ 13C 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 δ 13C, which is a proxy for C 3 versus C 4 plant type, indicates that C 3 plants predominated in this area of the tropics during warm and wet periods, such as the Bølling/Allerød and the early Holocene, and C 4 plants proliferated during cooler and more arid periods, such as the Glacial and Younger Dryas. The biomarker δ 13C record agrees with pollen data from Cariaco Basin sediments, confirming that leaf wax compounds preserved in marine sediments can accurately record terrestrial vegetation changes.