The environmental conditions of MIS5 in the northern South China Sea, revealed by n-alkanes indices and alkenones from a 39 m-long sediment sequence

摘要

In order to reconstruct the environmental conditions of marine isotope stage (MIS) 5 in the coastal area of northern South China Sea, a sediment core was collected from the south coast of Hainan Island (18 degrees 16'57"N, 109 degrees 42'38"E), from which a thick marine mud unit (39 m) is found to be the deposit of MIS 5. According to the high abundance of alkenones, the thick mud sequence was deposited under marine conditions. The high TOC and n-alkanes concentrations (as normalized to TOC) suggest this was a period of high organic matter (OM) production, and the majority of OM came from terrestrial vascular plant sources. Comparatively, short chain n-alkanes (C18-22) and proportion of aquatic plant index (Paq) in the lower sub-unit appear higher than those in the middle and upper sub-units, suggesting a gradual increase in terrestrial OM supply throughout MIS 5e. The carbon preference index in long-chain n-alkanes (CPI25-33) implies high precipitation and/or temperature in this interval, whilst the average carbon length index in long-chain n-alkanes (ACL(25-33)) indicates a warm climate during MIS 5e. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.