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The δ18O records of ostracode shells in sediments of core QH-2000 from Qinghai Lake can be used as a better proxy to reflect monsoon changes, Low monsoon precipitation between 17.5 and 11 cal. ka BP is indicated by positive #180 values averaging 2.37‰. A fast shift in #180 from positive at 11 cal, ka BP to negative at 10 cal. ka BP indicates sharp increase of monsoon precipitation. An interval of generally high monsoon precipitation is observed between 10 and 6 cal. ka BP with δ18O values averaging -2,15‰. Decrease of monsoon precipitation between 6 and 2.5 cal. ka BP is indicated by positive δ18O values. δ18O keeps positive values averaging 3.0‰ between 2,5 and 0 cal, ka BP suggesting low high monsoon precipitation. The climatic changes indicated by δ18O records of ostracode shells in sediments of core QH-2000 from Qinghai Lake and our broader regional comparison show that the climate in Qinghai Lake since the late Glacial is probably controlled by southwest monsoon other than southeast monsoon. [ABSTRACT FROM AUTHOR]

Based on the function relationship between the shell length of Limnocythere inopinata and the salinity of its living water in Tibetan Plateau lakes, the paleosalinty of Qinghai Lake in the past 900 years was reconstructed through the measurement of the adult body length of Limnocythere inopinata. Meanwhile, the paleosalinity sequence of Qinghai Lake during the same period was rebuilt by the Sr/Ca ratio of the shell of Eucypris inflata combined with the Sr/Ca ratio of living ostracod valves from the species of genus Eucypris inflata and the host water. The paleosalinity results obtained by two different methods were compared and assessed in this paper. To check the result, it was also contrasted with other historical climatic sequences of this area including tree ring and ice core. It was shown that the paleosalinity sequence rebuilt by adult ostracod body length had high reliability, and the paleosalinity reconstruction method by trace elements of ostracod shells was not suitable for Qinghai Lake. From the reconstructed paleosalinty sequence of Qinghai Lake, it can be found that low salinity during 1160-1290 AD showed the humid climate condition on the Mediaeval Warm Period in this area, while the high salinity during 1410-1540 AD, 1610-1670 AD and 17701850 AD which was corresponding to the three cold pulses of the Little Ice Age with a dry climate condition. And the high salinity in the latest several decades was consistent with recent warm and dry trends of the climate in this area. The good consistency of the reconstructed palaeosalinity sequence and the precipitation sequence in this area rebuilt by tree ring proves the reconstruction of past lake salinity is reliable. [ABSTRACT FROM AUTHOR]