AN ENVIRONMENTAL SEQUENCE REFLECTED BY MULTI-PROXIES OF CORE SEDIMENTS OF LAKE CHEN CO, SOUTHERN TIBET

The Tibetan Plateau is an ideal place for studies of past environmental. There are many places where ice cores, tree-ring series, lake cores, and hundreds years of historical documents can be collected. This study deals with a sediment core in the Lake Chen Co (28°53’-58’N, 90°28’35’E) in southern Tibet. The core was taken with a piston corer in 8 m of water, 800 m from the bank on a bottom slope of 1.5 percent It was divided into 216 1-cm-thick samples for analysis. The uppermost 30 cm of the core was selected for ²¹⁰Pb and ¹³⁷Cs analyses to calculate sedimentation rates. No radiocarbon ages are yet available, but the core is estimated to span 1400 years on the basis of the average sedimentation rate of 0.16 cm/a. All samples were analyzed for physical (magnetism and particle size), chemical (CaCO₃, trace elements, total organic carbon (TOC), ¹³C isotopic composition, hydrogen index (HI)), and biological (ostracod) properties. The analytical data indicate significant environmental change over the last 1400 years. Warm conditions from ca. AD 620 to AD 740 are shown by high ARM/*_lf, TOC, and HI, by low *¹³C, and by the ostracod assemblages. High CaCO₃ and Sr/Ba and low Fe/Mn suggest that this period was relatively dry. A second warm interval, from ca. AD 1120 to AD 1370, is inferred from high ARM/*_lf, TOC, and HI. This interval, however, may have been more humid, based on low CaCO₃ and Sr/Ba. High Fe/Mn and an increase in ostracod shells imply a larger and deeper lake. From ca. AD 1550 to AD 1690, cold, dry conditions are indicated by all of the proxies, for example low ARM/*_lf, TOC, and HI, and high CaCO₃ and Sr/Ba. Ostracod shells decrease rapidly during this interval. Warm conditions have prevailed since about AD 1900. We compared the record from Lake Chen Co with the records from ice cores, tree-rings, and historical documents and found good agreement among them. Interestingly, the warming stages coincide with times of prospering of the agriculturally based, Tibetan ethnical group. Relationships between human impacts and climate are worth pursuing at this site.

This work was supported by the China National (Grant no.: G19980408) and CAS (Grant no.: KZCX2-314) as well as CXIOG (Grant no.: CXIOG-A1-204) projects.