论文部分内容阅读
On the basis of multi-proxy analysis on TOC, TN, C/N, organic δ13C and grain size, sedi- ment record from Qinghai Lake provides evidences of stepwise-patterned climatic change since 16 ka BP. Results show that Qinghai Lake underwent six environmental stages. From 16.2 to 14.3 ka BP and from 4.0 to 2.1 ka BP, the organic δ13C value was controlled by the concentration of atmospheric CO2. Relative higher organic δ13C values occurred between 14.3 to 10.4 ka BP indicative of water hardness decrease resulted from melting ice water, corresponding to two intervals of C/N peak values to the B?ling and Al- ler?d warm periods in Europe respectively. From 10.4 ka BP, Qinghai Lake entered the Holocene and the climate was warm and a little dry. The Megathermal appeared at about 6.7 ka BP when the vegetation around the lake transformed into a forest. Between 6.3 ka BP and 4.0 ka BP, the temperature decreased and δ13C value was controlled by the expansion of C3 plants and the retreat of C4 plants in river catchment. Since 4.0 ka BP, the climate gradually became cold and dry. From 2.1 ka BP, the cold-dry climate and human activity resulted in an abrupt increase in C/N with deceased δ13C value; meanwhile, many coarse grains appeared in sediments.
On the basis of multi-proxy analysis on TOC, TN, C / N, organic δ13C and grain size, sediment record from Qinghai Lake provides evidences of stepwise-patterned climatic change since 16 ka BP. Results show that Qinghai Lake underwent six From 16.2 to 14.3 ka BP and from 4.0 to 2.1 ka BP, the organic δ13C value was controlled by the concentration of atmospheric CO2. Relative higher organic δ13C values occurred between 14.3 and 10.4 ka BP indicative of water hardness ice water, corresponding to two intervals of C / N peak values to the B? ling and Al- ler? d warm periods in Europe respectively. From 10.4 ka BP, Qinghai Lake entered the Holocene and the climate was warm and a little dry. The Megathermal was at about 6.7 ka BP when the vegetation around the lake transformed into a forest. Between 6.3 ka BP and 4.0 ka BP, the temperature decreased and δ13C was controlled by the expansion of C3 plants and the retreat of C4 plants Since 2.1 ka BP, the cold-dry climate and human activity resulted in an abrupt increase in C / N with deceased δ13C value; in sediments.