南日群岛东部海域岩芯沉积物有机碳含量和δ^(13)C_(TOC)值的变化特征及古气候环境意义

Total organic carbon,organic carbon isotope and paleoclimatic significance of sediments core in the eastern Nanri Islands

2008年在南日群岛东部海域用钻机采集长度为1 004 cm的岩芯样品,测试沉积物中总有机碳(TOC)含量、稳定碳同位素比值(δ13CTOC)、碳氮比值(C/N)、碳酸盐含量以及14C数据,分析其垂直剖面上的变化特征,阐明其沉积环境和古气候的指示意义.沉积物TOC含量变化范围为0.44%~0.74%,垂直剖面上总体显示出末次冰期和全新世中期TOC含量较高,全新世早期相对稳定,而全新世中后期TOC波动范围明显增大.C/N值在5.3~14.9之间变化,平均值为8.1;δ13CTOC值范围为-23.07‰^-21.04‰,表明沉积物中的有机质以海洋自生为主,同时混有部分陆源有机质.碳酸盐含量在3.3%~10.9%之间.TOC含量、C/N比值、δ13CTOC值在岩芯垂直剖面上具有很好的相关性.14C测年数据以及各要素测值在垂直剖面上的变化特征表明:自11 250 aBP以来该海域附近古气候有可能经历了以下4个演化阶段:①11 500~9 000 aBP期间气候寒冷、海平面下降,采样点可能为浅水区或潮间带;②9 000~8 000 aBP期间为升温期,气候由寒冷转向温暖;③8 000~4 300 aBP期间,为相对稳定的暖湿期,在后期气候出现小幅的波动;④4 300 aBP至今,气候进入明显的周期性波动期,暖湿和干冷气候多次交替变化;4 300~3 000 aBP期间为相对寒冷的时期;3 000~1 800 aBP期间为较稳定温暖期,1 800~1 000 aBP期间气温快速降低,标志着研究区进入一个新的寒冷阶段,但是自1 000 aBP以来,气候又再次出现转暖的趋势.

The sediment cores were collected using drilling rig in 2008 at sites TS located in the eastern Nanri Islands. According to the characteristics of total organic carbon（TOC）,organic carbon isotope values（δ13CTOC）,inorganic carbon content,C / N and14C age in the sediment core,the depositional environment and paleoclimate changes of this area since the last glacial were analyzed. TOC in sediment varied from 0. 44% to 0. 74%. TOC content was relatively high during the last glacial and interim Holocene,and varied little in Early Holocene and the range variation increased in late Holocene. The C / N values varied from 5. 3 to 14. 9,with average value 8. 1, δ13CTOCvalues varied from- 23. 07‰ to- 21. 04‰,suggesting that the contents of organic matter in the sediment are mainly controlled by marine origin. The inorganic carbon content varied from 3. 3% to 10. 9%. The results show that the δ13CTOC,TOC and C/N in core have a good relation with climate changes.Based on14C age and above comprehensive analysis,it can be concluded that the paleoclimate of the study area has four stages as follows since 11 250 aBP.（1） 11 500 ～ 9 000 aBP：during this stage the climate was cold and dry,the sea level descended,and the sampling site could be intertide;（2） 9 000 ～ 8 000 aBP：this stage the climate had been changing from cold to warm;（3） 8 000 ～ 4 300 aBP：the climate was stable and warm and wet in this period,the climate appeared slight fluctuation in the late of period;（4） since 4 300 aBP：an instable stage since 4 300 aBP is suggested by the dramatic variation of all proxies; ① a short cold stage occurred at 4 300 ～ 3 000 aBP; ② the stage between 3 000 ～ 1 800aBP,the climate is stable and warm; ③ the climate became cold the period of 1 800 ～ 1 000 aBP; ④ the temperature have increased since the 1 000 aBP.