Multi-Proxy Records of Terrestrial and Marine Organic Matter Sources in the Mud Area Southwest off Cheju Island over the Last 100 Years

C/N ratio of total organic matter is a traditional indicator for distinguishing organic matter sources,while both BIT(Branched and Isoprenoid Tetraether index) and TMBR(Terrestrial and Marine Biomarker Ratio) are new proxies for calculating relative contributions of terrestrial organic matter(TOM) and marine organic matter(MOM) in marine sediments.In this paper,these indicators are applied to evaluate the contributions of TOM and MOM during the past 100 years for site DH11 located in the Mud Area Southwest off Cheju Island.The mass accumulation rates(MARs) records of total organic carbon(TOC),terrestrial and marine biomarkers reveal a relatively stable trend of sedimentary organic matter before 1950s and an increasing trend of buried organic matter after the 1950s.The calculated TOM contribution using a binary mixture model based on C/N ratios varies from 0.22 to 0.30.The range of TOM contribution based on BIT and TMBR indices is 0.05 to 0.11 and 0.08 to 0.22,respectively.The differences of TOM contribution could be attributed to different sources of organic matters used in these indices.In addition,low TOM contributions indicate that MOM plays dominant role in sedimentary TOC at site DH11.The values of C/N ratio,BIT and TMBR indices were decreasing since 1950s,suggesting reduced TOM contribution,which is related to the larger increasing amplitude of MOM than TOM.Strengthened East Asian Winter Monsoon and Kuroshio and increased nutrient inputs could cause the increasing MOM contribution for site DH11 during the past 50 years.