Late Holocene isotope hydrology of Lake Qinghai, NE Tibetan Plateau: effective moisture variability and atmospheric circulation changes

A sub-centennial-resolution record of lacustrine carbonate oxygen isotopes (δ<sup>18</sup>O<sub>C</sub>) from the closed-basin Lake Qinghai on the NE Tibetan Plateau shows pronounced variability over the past 1500 years. Changes in δ<sup>18</sup>O<sub>C</sub> in hydrologically closed lakes are often interpreted in terms of changing effective moisture. Under this interpretation our record would imply increasing effective moisture during the Little Ice Age (LIA) compared to the Medieval Warm Period (MWP). However, independent evidence from other archives strongly suggests the Asian summer monsoon was stronger during the MWP and weakened during the LIA. Controls other than effective moisture (the balance of water inputs over evaporative loss) must therefore have contributed to the δ<sup>18</sup>O<sub>C</sub> values. We propose the LIA signal in Lake Qinghai resulted from a reduction in evaporation caused by colder air temperatures, coupled with a decrease in oxygen isotope composition of input waters as a result of an increase in the relative importance of westerly-derived precipitation. Our results caution against simplistic interpretations of carbonate oxygen isotope records from hydrologically closed lakes and suggest all possible controlling factors must be taken into account in order to avoid misleading palaeoclimatic reconstructions

Grain size of Lake Qinghai sediments: Implications for riverine input and Holocene monsoon variability

Grain-size compositions of lake sediments can provide direct information on changes in transporting mechanism and sedimentary environment. Various grain-size parameters have been employed to reconstruct hydrological conditions within the lake and dust influx from outside the lake. Here we present the grain-size results of a 5-m core retrieved from Lake Qinghai, northeastern Tibetan Plateau in order to address the links between Holocene depositional process and climatic change. Our results indicate that two parameters (skewness and grain-size ratio of 8-50/2-8 mu m) are sensitive to hydrodynamic changes in Lake Qinghai, which are further linked to the strength of the Asian summer monsoon. Variations of these two parameters reveal that summer monsoon intensity weakened gradually from early to late Holocene, superimposed by persistent centennial variability with dominant periods at 0.35, 0.23 and 0.12 kyr. Comparison of grain-size variations with solar activities and North Atlantic cooling events reveals that solar forcing likely plays an important role in driving centennial monsoon variability. (C) 2016 Elsevier B.V. All rights reserved