14ka B.P. 以来巴里坤湖区有机碳同位素记录及古气候变化研究

通过有机碳同位素（δ13Corg.），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 δ13Corg. 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C3植被为主，干湿变化是导致δ13Corg. 值波动的主要因素，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δ13Corg. 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（7.2~5.0ka 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.）δ13Corg. 值开始逐渐偏正，表明气候开始变干； 1.5ka B.P. 至今的 δ13Corg. 值则是在-24‰ ~-23‰ 间频繁波动，反映了该时段气候的不稳定性。

PALEOCLIMATE CHANGE RECORDED BY SEDIMENT ORGANIC CARBON ISOTOPES OF LAKE BARKOL SINCE 14ka B.P.

In this study, we reported the records of isotopic compositions of total organic carbon(δ13Corg.), media grain size and magnetic susceptibility in BLK-1 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 38~63μm quartz particles. The ages of sampled horizons were derived by liner interpolation, which were 0.14±0.02ka B.P. at 0.1m, 0.28±0.02ka B.P. at 0.2m, 4.08±0.26ka B.P. at 0.6m, 8.43±0.58ka B.P. at 1.6m, and 13.9±0.89ka B.P. at 2m, respectively. The δ13Corg. 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 C3 plants. According to the analyses of the chronology, the δ13Corg., the media grain size and the magnetic susceptibility. The vegetation type in this region could be considered as pure C3 plants Therefore, the variation of δ13Corg. 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 δ13Corg., media grain size and magnetic susceptibility values were the highest(-21.5‰, 300~500μm, and 25×10-7m3/kg respectively), suggesting an extremely dry regional climate condition. 2)8.4~7.2ka B.P., the δ13Corg. 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)7.2~5.0ka B.P., the δ13Corg. 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 δ13Corg. values increased slightly, indicating that the Lake Barkol was gradually shrinking. 5)1.5ka B.P. to present, the δ13Corg., 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 δ13Corg. values in a lakeshore profile can be used for inferring paleoclimate information.