过去5000 a以来抚仙湖沉积物有机质碳同位素的古环境指示意义

Paleoenvironmental significance of organic carbon isotope in lacustrine sediments in Lake Fuxian during the past 5 ka

通过测定抚仙湖沉积物全有机样品的稳定碳同位素组成(δ^(13)C_(org))、总氮、总有机碳含量指标并计算碳氮比值,对过去5000 a以来抚仙湖沉积物有机质来源、δ^(13)C_(org)的影响因素及其所指示的古环境意义进行分析.结果表明:在过去的5000 cal a BP里,抚仙湖沉积物有机质主要来源发生明显变化,沉积物有机质输入由内源水生生物和陆生C_3植物共同输入(5000-2300 cal a BP阶段)转变为以内源沉水植物、浮游植物和藻类等输入为主(2000 cal a BP至今阶段);有机质来源发生变化是造成抚仙湖沉积物δ^(13)C_(org)值变化的主要原因;2000 cal a BP以来,陆源有机质输入的锐减与人类活动的影响密切相关;在2300-2000 cal a BP阶段,抚仙湖沉积物δ^(13)C_(org)值的快速变化可能指示了抚仙湖流域的古环境在这一时期经历了快速变化的气候事件.

We measured several indexes including the stable organic carbon isotope （δ18Corg ）, the total nitrogen content, the total organic carbon content and the ratio of carbon and nitrogen content of bulk sediments in Lake Fuxian to exploring the sources of or- ganic matters in sediments and the paleoenvirnnmental significance of δ18Corg during the last 5 ka. The results showed the organic matter inputs from both the terrestrial C3 plants and the aquatic organisms as the main source to the lake sediments have greatly changed during the period of 5000-2300 cal a BP, and changed to the only aquatic input （ submerged plants, phytoplankton and algae） since 2000 cal a BP. δ18Corg values of bulk sediments in Lake Fuxian were mainly affected by different organic matter in- puts. Rapid changes of the δ18Corg values during the stage of 2300-2000 cal a BP may indicate that the paleoenvironment of Lake Fuxian basin has experienced a rapid chmate event.