通过对浙江余杭北湖桥钻孔(简称BHQ孔)沉积物中总有机碳(TOC)和碳同位素(delta~(13)C_(org))的分析,结合碳氮比(C/N)、粒度参数、年代和孢粉资料,探讨了研究区域早中全新世期间气候演变规律。结果表明,BHQ孔所在区域早中全新世期间,环境变化可以划分为3段:①11.4~8.7 ka B.P.,delta~(13)C_(org)在-27.24~-23.4范围内波动升高,TOC含量(0.19%~0.69%)呈显著增加趋势,指示气候由冷干逐渐转向温湿。②8.7~8.0 ka B.P.,TOC含量偏低,delta~(13)C_(org)(-24.91~-22.93)较为偏正,指示气候呈冷干温湿温干。③8.0~4.2 ka B.P.,TOC含量(0.18%~2.18%)和delta~(13)C_(org)(-26.33~-19.09)变化频繁且幅度较大,但整体上TOC含量偏高,delta~(13)C_(org)偏负,指示该段时期内气候总体呈暖湿特征,且存在不同尺度的冷暖波动。其中在8.0~5.7 ka B.P.期间,TOC含量(0.43%~2.18%)明显偏高,delta~(13)C_(org)(-25.79~-23.15)明显偏负,指示气候温暖湿润,对应于区域全新世大暖期;此外本段时期内还记录到5.5 ka B.P.和4.2 ka B.P.两次冷事件。由此表明湖沼相沉积物TOC及delta~(13)C_(org)可以记录降水量和温度的变化状况,能有效指示古气候的变化规律,同时研究结果初步揭示了浙北地区早中全新世期间气候演变特点。
英文摘要:
The study area is situated in the southwest of Hangjiahu plain, where the surface water system is developed and most rivers originate from Tianmu mountain and Mogan mountain in the northwest of Zhejiang. The sediment samples were collected from a core drilled at the Beihuqiao (BHQ) of Yuhang town, where the location is 30°22.443' N, 119°56.237' E. The BHQ core is 19.0 m in length, and core sediments are composed of homogeneous gray, clayey silt and silt with a little carbonate nodules except for an intercalation of silty sand in the lower part. No disturbance was observed in the whole core. The part (4.775~19.0 m) of the core was sampled at 2.5 cm increments. Four bulk samples were collected for AMS radiocarbon dating from the organic-rich sediments. And 136 samples were chosen for TOC and delta~(13)C_(org) analysis at about 10 cm intervals. Combined with the proxies of grain size parameters, pollen data, C/N radio and age data, and contrasted with researches of surrounding areas, TOC and delta~(13)C_(org) in organic matter, BHQ core in Zhejiang province are analyzed to interpret the basic environmental information and climate changes during the Early-Middle Holocene. Results reveal that the paleoclimate changes in Hangjiahu plain during the Early-Middle Holocene which can be divided into three periods: (1)11.4~8.7 ka B.P.. Organic carbon isotope increased in the range of -27.24 to -23.4 and TOC content increased obviously in the range of 0.19% to 0.69%, indicating that the cold-dry climate turned gradually to warm and humid in this period. (2)8.7~8.0 ka B.P.. Compared with the last stage, TOC turned to be negative and fluctuated between 0.2%~1.33%, delta~(13)C_(org) fluctuated slightly between -24.91~-22.93 and tended to be positive. As a whole, the climate was dry, and presented cold-dry to humid and warm-dry trend. (3)8.0~4.2 ka B.P.. The major characteristic of the climate in the northern of Zhejiang province was warm and humid, however, some cold-dry events also happened at different time scales in this period. And during the period, TOC and delta~(13)C_(org) fluctuated in 0.18%~2.18% and -26.33~-19.09 ranges, respectively. Especially during 8.0~5.7 ka B.P., TOC content improved obviously in 0.43%~2.18% and delta~(13)C_(org)tended to be negative in -25.79~-23.15, which indicated the Holocene Megathermal emerged in this region. Meanwhile, there were two cold events occurred in about 5.5 ka B.P. and 4.2 ka B.P.. During these two periods, TOC tended to down and delta~(13)C_(org) had a positive fluctuation, and they also corresponded with the contemporaneous pollen data and grain sizes parameters. Combined with multiple climatic proxies of BHQ core and the results of correlation analysis between these proxies, the BHQ core sediments provide a reliable basis interpretation of palaeoclimate. TOC and delta~(13)C_(org) of BHQ core can be good proxies of paleoclimate in this research zone and indicate the changes of precipitation and temperature respectively. At the same time, this study also effectively suggests the evolution law of paleoenvironment in the northern of Zhejiang province during the Early-Middle Holocene.