Zhongping Lai

Holocene climate and landscape change in the northeastern Tibetan Plateau foreland inferred from the Zhuyeze Lake record

Pollen and grain-size data from the Holocene Zhuyeze Lake record in arid Central Asia were re-assessed and combined with new ostracod species assemblage data to improve inferences of the lake history and controlling climate conditions. Zhuyeze Lake was a perennial freshwater–oligohaline lake since its establishment ca. 13 cal. ka BP. The lake level fell below the position of the QTL02 section site at 2.1 cal. ka BP after the beginning of the Han Dynasty, and we assume that significantly intensified land use upstream of Zhuyeze Lake was at least partly causing the lake-level decline. Most stable lake conditions and lowest salinities were recorded in the mid Holocene between 7.5 and 5.5 cal. ka BP, providing additional evidence for the inference of the highest moisture availability in the mid Holocene in arid Central Asia. The most striking feature of analyses of grain-size and ostracod data is the inference of more or less unchanged lake levels and lake water chemistry during a period of aeolian sand accumulation in the lake between 7.8 and 7.5 cal. ka BP. Similar conspicuous and apparently contemporaneously formed sand layers were recorded in other sections in the ancient lake basin and farther upstream, and mobilization of aeolian sands must have occurred for a few hundred years in the region. Indications for the 8.2 ka event from our section and other climate records in Central and eastern Asia support the hypothesis that a short-lived cold-dry climate initiated the increased activation of aeolian sands which was later on gradually enhanced as a result of burial of previously vegetated land by dunes and sand sheets. Further work is required to determine the regional extent of sand mobilization at ca. 7.5 cal. ka BP in the northeastern Tibetan Plateau foreland and to examine the timing and controls of the self-enhancing aeolian sand mobilization, vegetation degradation and subsequent recovery.

Reply to comment by Zhang (2014): The Shell Bar in the Qaidam Basin: fluvial or lake deposit, and OSL versus 14C age data

Zhang’s (2014) comments on the formation and age of the Shell Bar in the Qaidam Basin go far beyond our specific Shell Bar papers (Lai et al. 2014; Mischke et al. 2014) and include questions about a number of other lake basins in China. Although we disagree with many of Zhang’s comments about these other basins (e.g. the Qinghai Lake Basin), we cannot hope to address them all here, so we stick to several main points. First, we address specific comments about the Shell Bar, including: (1) Shell Bar sediments, (2) geomorphological history and implications, (3) Corbicula shells as a major Shell Bar constituent, and (4) OSL age data. Second, we address what is surely the more scientifically important, and as yet unsettled issue at the core of the debate, i.e. the relative reliability of OSL versus radiocarbon dating for shoreline sediments in the range from MIS 5 to early MIS 3.