有机质饱和烃和δ^(13)C_(org.)记录的博斯腾湖早全新世晚期以来生态环境演变

ECOLOGICAL ENVIRONMENT CHANGE RECORDED BY SEDIMENT n-ALKANE ANDδ^(13)C_(org).OF LAKE BOSTEN SINCE LATE OF EARLY HOLOCENE

通过对新疆博斯腾湖湖芯沉积物中有机质饱和烃、有机质碳同位素组成(δ^(13)C_(crg))以及与前人得到的环境代用指标结果综合分析,重建了博斯腾湖从早全新世晚期以来古生态环境和湖泊水文的变化历史。结果表明,博斯腾湖大约在8130cal.a B.P.之前气候冷湿,湖泊不发育;约在8130~6400cal.a B.P.为暖湿的全新世适宜期,博斯腾湖流域降水和开都河径流量增加,湖泊水位上升外溢,水生植物及陆生植物发育;6400~5500cal.a B.P.左右冷湿,有效湿度较高,湖泊仍处于较高水位;5500~3000cal.a B.P.左右气候波动明显,为温干时期,而大约在4500—3900cal.a B.P.期间降温,为冷干环境;3000cal.a B.P.以来气温降低,2300~1250cal.a B.P.左右气温有所回升,大约自1250cal.a B.P.以来博斯腾湖地区自然环境逐渐干旱恶化,陆生植物发育较差,而湖泊中沉水植物发育较好。

Lake Bosten （41°56′～42°14′N,86°40′ ～87°26′E） is located in Xinjiang Province,Northwest China.In order to reconstruct changes of palaeoecological environment and hydrological characteristics of Lake Bosten since late of Early Holocene,a 9.53m-long core （41°56′33″N,86°45′52″E） called BOST2000 was obtained during a drill in 2000 from the lake using Wright piston drill.The whole core was divided into 467 samples based on an interval of 2cm.The chronology was established according to 14C-AMS data of four grass seeds and five leaves from BOST2000 and XBWu46,extending back to about 8500ca1.a B.P.The paper launched a investigation from 900cm to 0cm of the core which covered approximately from 8300cal.a B.P.to present.The total samples were analyzed for grain size.n-alkanes were analyzed using 8 samples which derived from 26～38cm,160～168cm,336～344cm,446～454cm,560～568cm,710～718cm,820～826cm,and 890～895cm.As the data of stable carbon isotope of bulk sediment organic matter （δ^13Corg） were deficient from 900cm to 950cm,we mainly discussed about 0～ 900cm which contained 439 samples.The data indicated that δ^13Corgranged from-30‰ to-20‰.The distribution of n-alkanes was also discussed in the paper,which showed the relative content of higher molecular weight n-alkanes and middle molecular weight n-alkanes were comparatively higher.The δ^13Corgand n-alkanes records of BOST2000 core showed five stages：（1） Before 8130cal.a B.P.δ^13Corgwas relatively light,higher molecular weight n-alkanes （C27,C29,and C31） which represented woody plants and middle molecular weight n-alkanes （C21 ～ C25） which represented aquatic plants were comparatively higher and dominated by higher molecular weight n-alkanes,which indicated that stage was cold and humid ; （2） During 8130～ 6400cal.a B.P.δ^13Corgfluctuated frequently between-28‰ ～-23‰.n-alkanes （C21 ～ C25） was dominated,which reflected the source of the organic matter was a mixture of terrestrial plants and aquatic plants.Paleocliamte was warm and wet during 8130 ～ 6400cal.a B.P.which belonged in the climate optimum in the Holocene.With increasing of precipitation and runoff in the Kaidu River,lake level expanded and overflew;（3） At the stage of 6400～5500cal.a B.P.middle molecular weight （C21 ～ C25） n-alkanes were primary,δ^13Corgchanged periodically from-28‰ to-25‰,the comparatively light δ^13Corgindicated emergent aquatic plants were dominated and no subemergent plants.It showed paleocliamte was cold and humid,lake-level was highfor low evaporation and high effective humidity; （4） During 5500～ 3000cal.a B.P.δ^13Corgranged from-30‰ to-23‰,at the scale of 3900 ～ 3000cal.a B.P.δ^13Corgreached a peak to-25‰,n-alkanes （C27,C29,and C31） and n-alkanes （C21 ～ C25） were in master status.At that stage paleoclimate was in the condition of mildness and dry but fluctuated frequently,especially during 4500cal.a B.P.to 3900cal.a B.P.paleotemperature dropped,which indicated the climate was dry and cold; （5） Since 3000cal.a B.P.,δ^13Corgwas comparatively heavy,which indicated dry climate that had a negative effect on terrestrial plants,middle molecular weight n-alkanes （C21 ～ C25）were dominated indicated less terrestrial plants similarly.The paleotemperature decreased in this stage,although paleotemperature rose a little during 2300 ～ 1250cal.a B.P.,and from that on,natural environment deteriorated with little terrestrial plants,but aquatic plants were flourishing.