HOLOCENE PALEOCLIMATE INTERPRETED BY STABLE CARBON AND OXYGEN ISOTOPES OF OSTRACODS FROM XIADA CO LAKE ON THE TIBETAN PLATEAU

Insights into climate changes that have occurred over the past 10,000 years in Asia may be found in the multiple glacial lakes that occur in Tibetan Plateau (TP). A small core from one of these lakes, Xiada Co Lake, located in the western region of the TP was recovered to investigate the ostracod fauna and stable isotope values of sediments and ostracod (Crustacea: Ostracoda) shells. The δ¹⁸O values provide insights into the temperature variations and the δ¹⁸O of lake water. The δ¹³C values provide insights to the surrounding vegetation.

Samples were taken every 2 cm from the 274 cm core, from which, species of ostracods belonging to three genera were identified. Limnocythere inopinata is known from southern and eastern regions of the TP, while the two other species (Leucocythere dorsotuberosa and Subulacypris sp.) are mostly found in the southern TP around Nam Co Lake. Stable C and O isotopic values were obtained from the analysis of Leucocythere dorsotuberosa, Subulacypris sp., and unconsolidated sediments. The analysis resulted in δ¹³C ranging from -3.5‰ to 1.9‰ VPDB for the ostracods and 3.2‰ to 4.1‰ VPDB for the sediments. δ¹⁸O ranged from -0.7‰ to 5.2‰ VPDB for the ostracods and -5.6‰ to -0.8‰ VPDB for the sediments.

L. inopinata has been identified in many Tibetan Plateau lakes, however, from these samples, it was not the dominant ostracod species. The largest presence of the three species in the samples was of L. dorsotuberosa. Multiple generations were observed from both L. dorsotuberosa and Subulacypris in the samples. On average δ¹³C is more enriched in Subulacypris sp., and δ¹⁸O is comparable between the two species with Subulacypris sp. being slightly more enriched by 0.1‰. These differences could be the result of vital effects. All ostracods have greater δ¹⁸O values than lake sediments. Whereas, the sediment samples are more enriched in δ¹³C than both species.

The overall enriched δ¹⁸O of both ostracod and sediments suggest evaporative conditions. The TP has undergone significant changes over the past 10,000 years, which includes increases and decreases in precipitation and evaporation as a result of shifts in the Indian and East Asian monsoon systems. This preliminary study contributes information for the western end of the TP and can result in a better understanding of how regional climate shifted in this area.