通过有机碳同位素(delta~(13)C_(org.)),磁化率和粒度的测定和分析,结合光释光年龄标定,对新疆巴里坤湖区滨湖相沉积物14ka B.P.以来delta~(13)C_(org.)值变化的影响因素及其反映的气候特征进行了研究。结果表明:在巴里坤湖区植被类型主要以C_3植被为主,干湿变化是导致delta~(13)C_(org.)值波动的主要因索,在末次冰消期至早全新世阶段(14.0~ 8. 4ka B.P.),巴里坤湖区周围冰川尚未融化,剖面delta~(13)C_(org.)值最为偏正,在-22到-21之间变化,暗示剖面处在干旱的气候条件下;进入全新世后,随着巴里坤山冰川的融化,湖区湿度增加,同位素值持续偏负,达到-23.5,同时中值粒径和磁化率同步降低;在中全新世阶段(7. 2 ~ 5. Oka B. P.)出现高湖面,同位素值达到-24左右,为剖面同位素值最低阶段;中晚全新世阶段(5.0~1.5ka B. P.)delta~(13)C_(org.)值开始逐渐偏正,表明气候开始变干;1.5ka B. P.至今的delta~(13)C_(org.)值则是在-24~-23间频繁波动,反映了该时段气候的不稳定性。
英文摘要:
In this study, we reported the records of isotopic compositions of total organic carbon (delta~(13)C_(org.)),media grain size and magnetic susceptibility in BLK-l core (43°37'09. 4"N,92°42'13. 1"E),taken from the ancient shoreline of Lake Barkol, Xinjiang, Northwest China. About 100 samples with a thickness of 2cm spanning the past 14ka B.P. were analyzed in this paper. The chronology was built on five Optically Stimulated Luminescence (OSL) dates from different depth using the 38~63mum quartz particles. The ages of sampled horizons were derived by liner interpolation, which were 0. 140. 02ka B.P. at 0.1 m, 0.280. 02ka B.P. at 0. 2m, 4. 080.26ka B.P. at 0.6m, 8.430.58ka B.P. at 1.6m, and 13.90.89ka B.P. at 2m, respectively. The delta~(13)C_(org.) values of BLK-1 section vary from -21. 6~-24.3,its mean value was -23. 3,indicated that the vegetation in the study area was dominated by C_3 plants. According to the analyses of the chronology, the delta~(13)C_(org.), the media grain size and the magnetic susceptibility. The vegetation type in this region could be considered as pure C_3 plants Therefore,the variation of delta~(13)C_(org.) values corresponded to wet/dry climate. The paleoclimate history of the Lake Barkol region during the last 14ka B. P. was revealed as 5 stages: 1) 14. 0 ~8. 4ka B. P.,the delta~(13)C_(org.),media grain size and magnetic susceptibility values were the highest (-21.5,300 ~500mum,and 25 x 10~(-7) m~3/kg respectively),suggesting an extremely dry regional climate condition. 2) 8. 4 ~7. 2ka B. P., the delta~(13)C_(org.) values suddenly decreased about 2 compared with stage 1, indicating a short dry to wet transition period as indicated by the significantly decreasing of all proxies. 3) 7. 2 ~ 5. Oka B.P.,the delta~(13)C_(org.) values slightly fluctuated around -24,the lake level expanded to the site of core BLK-1, suggesting a stable high lake level during this period,which is in good accordance with those of the adjacent region. 4) 5.0 ~ 1.5ka B.P.,the wet to dry climate transition period, the delta~(13)C_(org.) values increased slightly, indicating that the Lake Barkol was gradually shrinking. 5) 1.5ka B. P. to present, the delta~(13)C_(org.), grain size and magnetic susceptibility values fluctuated frequently, reflecting rapid climate changes in this period. The lake level dropped below the core site at 1. 5ka B.P., as a result of continuously enhanced evaporation. Overall, our research confirms that the variations of delta~(13)C_(org.) values in a lakeshore profile can be used for inferring paleoclimate information.