过去一百年济州岛西南泥质区有机质来源变化的多参数指标研究

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是一种传统的区分海洋沉积有机质来源的指标,基于总有机碳与总有机氮的比值。BIT(Branched andIsoprenoid Tetraether index)和TMBR(Terrestrial and Marine Biomarker Ratio)是近年提出的用于指示陆源有机质相对贡献的新指标,二者具有明确的陆源及海源端元值。BIT指标是基于陆地土壤厌氧细菌生标Branched GDGTs与泉古菌生标Crenarchaeol的比值,TMBR指标是基于陆源高等植物生标和海源藻类生标的比值。本文利用C/N、BIT和TMBR指标,对济州岛西南泥质区DH11站位过去一百年以来陆源有机质和海源有机质的相对贡献进行了定量评估。总有机碳(TOC)、陆源和海源生物标志物的分析结果显示:近50a来,该站位的总有机质、海源有机质和陆源有机质的沉积通量(Mass Accumulation Rates,MARs)一直在增加。C/N指标通过二元混合模型的计算结果显示陆源有机质占总沉积有机质的比例在0.22～0.30之间,BIT与TMBR指示的陆源有机质贡献分别在0.05～0.11,0.08～0.22之间,所得相对贡献的差异主要是由不同指标的指示意义不同造成的。3种指标的结果表明该研究海域海源有机质在沉积有机质中占据主导地位。另外,从1950s开始陆源有机质的相对贡献呈现下降趋势,这说明海源有机质沉积通量增加的比例大于陆源有机质,这可能是由东亚季风、黑潮、河流输入、大气沉降和人类活动等多重因素引起的。

C/N ratio of total organic matter is a traditional indicator for distinguishing organic matter sources, while both BIT （Branched and Isoprer/oid 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 Cheiu 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 in- creasing MOM contribution for site DH11 during the past 50 years.