Huangqihai Lake Sediment Organic Matter And Organic Carbon Isotope Paleoclimate Significance

Diverse lakes distributed in dtherent climatic zones and ecological environments archivedmuch useful information on environmental changes for the stUdy of past global changes and forthe understanding and prediction of possible trends of the changing envirOtuneflts in which llowwe are living. In the past tWo decades, orgedc carbon isotopic records from lake sediment cores.. 1were increasingly stUdied and used as a valuabIe environmental proxy indicating glacial-interglacial change in atmospheric pCO2, major fluctuations in catclunent vegetation, and changesin lake-level and regional temperafore.We have successfully recovered three sediment cores of ll m long each from the middle ofLake Huangqihai, Inner Mongolia. A multi-proxy aPproach was aPplied to the study of cores. IllAns thesis stUdy we report results from investigation on the records of orgedc maller (OM) andorganic carbon isotope (8"Corg) from core HQH4 and discuss environLmental implications of thetWo proxies from the shallow closed-drainage lake.Results suggest that the pre-Ho1ocene climate at Lake Huangqihai was cold and dry, asevidenced by the organic productivity distinctly lower than the Holocene (OM content is on' average l3 times lower). Correspondingly, the 8"Corg values of the pre-Holocene sediments are onaverage 2.77%0 higher than the Holocene. In addition, 8"Corg values from core HQH4 inverselycorrelate well with OM contents (r = 0.782). About 2%, negative shift in 8"Cors around the lateglacialnsolocene boundary is in a way related to rapid increase in the orghoc Productivity of thepaleo-lake. The substantial increase in primary productivity at the onset of the Holocene in LakeHuangqihai provides evidence fOr an abrupt warming at that time of the regional climate.Variation in 8"C.rg during the Holocene is characterized by both negative and positiveexcursions from the line of the average 8"Corg value of --26.4%,. These excursions may principallyreflect the magnitUde, timing and duration of certain condihons in productivity and OMpreservation, which in some way link to climate-induced lake-level fluctuations.While age data from the ongoing radiocarbon measurements is yet not available, varvecounting fOr the Holocene sediments of core HQH4 provides an average sedimelltation rate of0.805 mm/ear. Based on the data available, as presentCd above, environmentaI stapes from thepost-glacial lacustrine sequence thus are dishngUished. An attempt was made to correlatC these' stages with those from Northern Europe and from the sediment sechons around shore area Of LakeHuangqihai.