Hydroclimatic changes over the past 900 years documented by the sediments of Tiewaike Lake, Altai Mountains, Northwestern China

The reconstruction of variations in effective moisture over the past millennium are important for assessing potential future climatic trends in environmentally-sensitive arid Central Asia (ACA), especially in the context of ongoing global warming. However, high-resolution time series reflecting past moisture variability in the region are scarce, thus preventing a full understanding of the hydroclimatic evolution. Here we present the results of multi-proxy analysis of a sediment core spanning the past 900 years from Tiewaike Lake in the Altai Mountains, northern Xinjiang. The climatic proxies measured include grain size, organic matter and carbonate content, C/N ratio, and the stable carbon isotope composition of bulk organic matter. The results show that over the past 900 years the climatic evolution of the study area can be divided into distinct hydroclimatic phases: the arid Medieval Climate Anomaly (MCA, ∼1090-1430 AD), the humid Little Ice Age (LIA, 1430-1940 AD), and the arid Current Warm Period (CWP, 1940-2012 AD). During the LIA, the water level at Tiewaike Lake was overall higher than during the other climatic intervals; in addition, the LIA climate was unstable and characterized by six intervals with the occurrence of heavy precipitation events on a multi-decadal timescale. A humid, unstable climate during the LIA is also suggested by climatic records from adjacent regions. Our results support the view that over the past millennium, on a multi-centennial timescale, the moisture variations in ACA were generally out-of-phase with those in the region affected by the Asian summer monsoon. The humid, unstable LIA climate in ACA may have been associated with changes in the North Atlantic Oscillation (NAO) index and/or with variations in solar irradiance.