Wet climate during the 'Little Ice Age' in the arid Tarim Basin, northwestern China

A relatively cold period, the 'Little Ice Age' (LIA), just prior to the current warm period, has been documented from many regions of the globe. However, hydrological changes (wet/dry conditions) during the LIA appear to be very different across different climatic regimes, suggesting that the position, strength and/or pattern of atmospheric circulation could have changed significantly in the past. Therefore, paleohydrological studies may have some implications for potential future hydrological changes in an anticipated warming world. In this study, we investigated hydrological changes over the last similar to 800 years in the arid Tarim Basin, northwestern China. We used carbon isotopes of plant remains (mainly leaves) from a 10.5 m long aeolian sand sediment section to evaluate changes in dry/wet conditions. The average value of carbon isotopes of plant remains during the LIA period (similar to AD 1490 to 1890) is -26.0%, ranging from -28.2% to -23.6%, much lower than values before (average of -24.3%, from -25.5% to -22.4%) and after this period (average of -22.8%, -24.6% to -21.6%). Although other environmental factors could also affect carbon isotopes to some degree, such consistent, large negative isotopic excursions of up to 6% strongly suggest a wetter climatic condition in the study area at that time, which is also consistent with two silty clay layers, indicating a wet depositional environment, found around ad 1560 and ad 1625 during the LIA period. This inference is consistent with previous studies suggesting a relatively wet period during the LIA in the Tarim Basin and possibly extending to the western central Asia region, but appears to be opposite to hydrological changes in regions that are today dominated by Asian monsoon systems. This pattern of regional hydrological changes may be related to possible changes in the trajectory or strength of the westerlies and/or the orographic effect in this region, as previous studies suggested.