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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

Hyun, Sangmin, Shin, Kyung-Hoon, Lee, Suk-Chang, Chang, Se Won, Nam, Seung-Il
Quaternary international 2017 v.441 pp. 89-100
C3 plants, C4 plants, alkanes, carbon, nitrogen, paleoclimatology, sediments, stable isotopes, stratigraphy, South Korea
The carbon isotope of total carbon (δ¹³Corg), long-chain n-alkanes, and their compound-specific carbon isotope ratios (δ¹³CALK) 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 δ¹³Corg and δ¹⁵N), the core column stratigraphy was divided into three units, namely from the bottom to 14.5 ka (Unit I), from 14.5 ka to 3.0 ka (Unit II), and from 3.0 ka to the core top (Unit III), respectively. In particular, δ¹³Corg showed marked fluctuation from −17.31‰ to −28.68‰, suggesting different organic carbon sources. A relatively narrow range of variation in δ¹³Corg was observed in Unit III, and drastic changes in δ¹³Corg were observed from Unit I to Unit II. This may indicate a predominance of C4 plants in Unit I, and drastic changes from terrestrial C4 to C3 in Unit II and predominance of C3 plants in Unit III. The distributions of n-alkane were characterized by a continuous predominance of odd-numbered n-alkanes, particularly nC29 and nC31, and by high fluctuation of the total n-alkanes concentration. The average chain length (ACL), carbon preferences index (CPI), and paleo-plant 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 δ¹³Corg and a high concentration of n-alkane distribution. Individual n-alkane odd-numbered isotopes of δ¹³CALK ranged between −11.80‰ in δ¹³ⁿC21 and -34.93‰ in δ¹³ⁿC31, suggesting different sources of n-alkanes. The distribution of n-alkanes and their individual δ¹³CALK, in particular δ¹³ⁿC21, 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.