High resolution Late-Holocene biomarkers records in southern continental shelf of the Korean peninsula: Implication for paleoclimate variations in East Asia

Abstract

High-resolution records for carbon isotopes of organic matter and n-alkane compounds were investigated in two gravity cores (SJP15-2 and SJP15-4) taken from the southern continental shelf of the Korean peninsula to evaluate the variation in influxes of terrestrial biomarkers and their linkage to paleoclimate and marine environmental changes since the last 4 kyr. The total organic carbon contents were < 1%, and the carbon isotope(d13Corg) ratio ranged from approximately −21‰ to -22‰ and, they did not highly fluctuate throughout the two cores. However, the vertical distributions of total terrestrial biomarkers, long-chain n-alkanes (nC25-35), and individual n-alkane compounds exhibited distinctive fluctuations. There are two switching points that discriminate patterns of excursion and distribution at ca. 2.5 ka, and 0.5 ka. Several n-alkane combined indices such as average chain length (ACL), carbon preference index (CPI), and paleovegetation index (Paq), were coincident with these switching points, implying that the supply of terrestrial biomarkers was strongly associated with environmental changes at the source area. In particular, the ratios of nC31/nC27 and nC31/nC29 show coincident excursion pattern with lower ratio between 3.0 ka and 1.8 ka, implying that this centinenal records was associated with wetter climate conditions, and thus paleovegetation and paleoclimate variation. Comparison with previous data of the detrital quartz from the East China Sea and aeolian dust in the Cheju (Jeju) Island, South Korea, and Dongge cave oxygen isotope records indicates strong synchronicity with paleoclimatic degredation, suggesting that paleoclimate system of the East Asian region may have influenced the sediment records of study area since the last 4 kyr. Therefore, our high-resolution n-alkane data are very useful for reconstructing past climatic records, and East Asian monsoon and regional records could be associated with the paleoclimate variations of the study area.