Late quaternary climate and sedimentary history derived from N-alkanes, alkenones and bulk organic carbon analyses in Fujian coast, China

Abstract

Late Quaternary is an important period for paleoclimate study due to the boom of human civilization and thus its influence on climate conditions of the present interglacial period. In this study, a 52 m long borehole was drilled in a coastal embayment of Fujian, China, within which a thick marine layer from 16.05 to 32.60 m is found. Bulk organic geochemical analyses, containing total organic carbon content (TOC), carbon isotope ratio (δ13C), alkenones and n-alkanes, were analyzed for the whole core. Organic carbon isotope ratios (δ13C) of the sediment layers vary between -22.1‰ and -32.9‰, with higher values in the two marine sequences and lower in the two aquatic sequences. In the thick marine sequence, the δ13C is relatively stable, and it becomes gradually enriched from the base upwards and depleted rapidly at the top, indicating a full cycle of marine transgression and regression. The n-alkanes exhibit a similar trend, with several indexes, i.e., maximum concentration (Cmax), carbon preference index (CPI), average chain length (ACL), terrestrial-aquatic ratio (TAR), Paq and C31/(C29+C31). These results suggest the control of EAM and sea-level change in the sedimentary processes. Analysis on alkenones shows sea surface temperature (SST) variations as well as sea-level oscillations in the study site.