Terrestrial n-alkanes and their carbon isotope records from the Hanon paleo-maar sediment, Jeju Island, Korea: Implications for paleoclimate and paleovegetation over the last 35 kyrs

Abstract

The carbon isotope of total carbon (delta C-13(org)), long-chain n-alkanes, and their compound-specific carbon isotope ratios (delta C-13(ALK)) were investigated in the Hanon paleo-maar sediment, Jeju Island of Korea to understand paleoclimate variabilities and their paleovegetation linkages. Based on the organic geochemical data (TOC (%), TN (%), and their delta C-13(org) and delta N-15), the core column stratigraphy was divided into three units, namely from the bottom to 14.5 ka (Unit I), from 14.5 ka to 3.01<a (Unit II), and from 3.0 ka to the core top (Unit III), respectively. In particular, delta C-13(org) showed marked fluctuation from -17.31%o to -28.68%o, suggesting different organic carbon sources. A relatively narrow range of variation in delta C-13(org) was observed in Unit III, and drastic changes in delta C-13(org) were observed from Unit I to Unit II. This may indicate a predominance of C-4 plants in Unit I, and drastic changes from terrestrial C-4 to C-3 in Unit II and predominance of C-3 plants in Unit III. The distributions of n-alkane were characterized by a continuous predominance of odd-numbered n-alkanes, particularly nC(29) and nC(31), and by high fluctuation of the total n-alkanes concentration. The average chain length (ACL), carbon preferences index (CPI), and paleoplant proxy (Paq) showed high fluctuation and glacial-interglacial variations with distinctive a high and low ratio at about 9.2 ka, corresponding to the switching points of delta C-13(org) and a high concentration of nalkane distribution. Individual n-alkane odd-numbered isotopes of delta C-13(Auc) ranged between -11.80%o in delta C-13n(21) and -34.93%o in delta C-13n(31), suggesting different sources of n-alkanes. The distribution of n-alkanes and their individual delta C-13(Auc), in particular delta C-13n(21), support paleovegetation changes, and their time dependent variations matched well with glacial-interglacial paleoclimate variations. Therefore, organic geochemical proxies recorded in Hanon paleo-maar sediment reflects paleoclimate variabilities as well as paleovegetation changes for the last 35 kyr in Jeju Island, Korea. (C) 2016 Elsevier Ltd and INQUA. All rights reserved.