Spatial variability and the controlling mechanisms of surface sediments from Nam Co, central Tibetan Plateau, China

Sixty-six surface sediments were retrieved from Nam Co, central Tibetan Plateau, to evaluate the spatial variability of their distributions and controls across the entire lake. Grain size distribution, total carbon, total nitrogen, total sulfur, 210Pb and 137Cs activities, and carbon and oxygen isotopes of carbonate of the bulk sediments were analyzed, and the correlations among these variables, as well as water depth, were calculated. The results showed distinct spatial variability for all variables. The grain size distribution provides adequate information to reflect water energy levels within the lake. Based on these factors, the accumulation zone of Nam Co was distinguished from the erosional and transportation zones. The results indicate that the deep area (> 80 m) of the central main basin and the centre of the eastern small basin serve as the accumulation zones in Nam Co. Water depth is the most important factor influencing the distribution of the surface sediments because all variables show different distribution patterns in shallow and deep areas. Additionally, river input, sediment focusing, grain size effects, and heterogeneous physicochemical features of the lake water, as well as possible currents within the lake, also play different roles that affect surface sediment characteristics. Water depth noticeably affects grain size and the δ13C and δ18O values of carbonate sediment, implying that these proxies could be used as indicators of lake level change. These findings are of significance for palaeoenvironmental interpretations when using these proxies.