中文摘要：

文章对位于大兴安岭中北段四方山天池湖泊沉积物进行了多指标的分析,结果表明,15.4ka B.P.以来,TOC和TN含量变化较大,两者正相关（R=0.99）,TOC含量从冰期的1.60％逐渐上升到近代的34.40％,可能反映了湖泊有机质逐渐累积过程.TOC/TN比值的变化范围为10.4～18.8,平均值14.2;δ13Corg.值在-31.79‰～-22.51‰之间波动.四方山天池周边为森林,植被类型以C3植物占绝对优势,δ13Corg.值的变化可能主要受到有效降水量的控制.根据δ13Corg.的变化以及TOC、TOC/TN指标,本区域15.4ka B.P.以来的气候演化过程可以分为以下6个阶段：1）15.4～14.5kaB.P.,TOC含量低（1.60％ ～4.76％,平均值为2.95％）,TOC/TN比值在10.4～13.8之间,可能表明沉积物有机质主要来源于湖泊藻类和陆生C3植物的共同输入,且水生植物贡献比例较高,δ13Corg.值相对偏正,有效降水量低,气候冷干;2）14.5～12.7kaB.P.,与Bφlling-Allerφd暖期相对应,TOC含量和TOC/TN比值显著上升,且波动明显,并于13.6ka B.P.左右同时达到此阶段的最大值,可能指示沉积物有机质主要来源在13.6ka B.P.左右发生了从以陆生植物为主到湖泊藻类和陆生植物贡献相当的转变,δ13Corg.值整体偏负,并在14.4ka B.P.左右出现最负峰值（-31.79‰）,有效降水量有所增加,但也经历了明显的湿-千变化;3）12.7～11.3ka B.P.,此阶段对应新仙女木期,TOC含量稍有增加（6.33％ ～ 10.19％）,TOC/TN比值持续下降（平均值为13.7）,此时湖泊藻类和陆生C3植物对沉积物有机质都有贡献,但水生植物略多,δ13Corg.值严重偏负,有效降水量增加,气候冷湿;4）11.3～7.2ka B.P.,TOC含量有所增加且变化较大（8.49％ ～ 20.24％）,TOC/TN比值在11.5～18.4之间,沉积物有机质主要来源于陆生植物和湖泊藻类的共同输入,δ13Corg.值是整个剖面曲线上最为偏正的时期,气候升温明显,有效降水量减少,但也有冷暖-干湿波动;5）7.2～4.5k

英文摘要：

Lake Sifangshan （49°22＇32.97″N, 123°27＇49.90″E; altitude in 933m a.s. 1.）, a circle nearly dried up volcanic lake, located on the central-northern part of the Great Xing＇an Range, northeast of China, current northern margin of the East Asian summer monsoon. It is a particularly sensitive region to climate changes and was formed by volcanic eruptions during the Late-Pleistocene （0.128±0.01Ma）. A suite of cores were retrieved from Lake Sifangshan using piston corer in 2012. The cores were correlated using distinctive layers. Then a 482.5cm long sediment core recovered. The cores were split in half longitudinally, and one half of the core was used for geochemical analyses sampled at lcm interval （e.g. stable carbon isotope of bulk organic matter （813Corg.） , total organic carbon contents （TOC） and total nitrogen （TN） contents） to understand the process of changes in the climate condition during the last 15.4ka B.P. The results show a large variation in TOC and TN contents, they were positively correlated （R= 0.99）. TOC values may reflect the gradual accumulation of the organic matter in the lake sediment which change from the 1.60% during the last glacial period to 34.40% in Modern Time. The atomic rations of TOC to TN ranging from 10.4 to 18.8 with the average of 14.2, indicating the different contribution from algae and terrestrial plant during different climate stage. C3 plants account for absolute advantage in the forest around the Lake Sifangshan. Theδ13Corg.. values which is interpreted to reflect effective precipitation variations from -31.79‰ to -22.51‰ The process of the climate changes since 15.4ka B.P. can be divided into six stages according to the stable carbon isotope record of bulk organic matter, TOC content and TOC/TN. During 15.4-14.5ka B.P., TOC content is low （ 1.60% - 4.76% ）, TOC/TN values changes from 10.4 - 13.8 which may reflect that the original organic matter of the lake sediment was from algal in the lake and terrestrial C3 plants and th