Distribution of GDGTs in lake surface sediments on the Tibetan Plateau and its influencing factors

Quantitative paleotemperature records are vital not only for verifying and improving the accuracy of climate model simulations, but also for estimating the amplitude of temperature variability under global warming scenarios. The Tibetan Plateau(TP) affects atmospheric circulation patterns due to its unique geographical location and high elevation, and studies of the mechanisms of climate change on the TP are potentially extremely valuable for understanding the relationship of the region with the global climate system. With the development of biomarker-based proxies, it is possible to use lake sediments to quantitatively reconstruct past temperature variability. The source of Glycerol Dialkyl Glycerol Tetraethers(GDGTs) in lake sediments is complex, and their distribution is controlled by both climatic and environmental factors. In this work, we sampled the surface sediments of 27 lakes on the TP and in addition obtained surface soil samples from six of the lake catchments. We analyzed the factors that influence GDGT distribution in the lake sediments, and established quantitative relationship between GDGTs and Mean Annual Air Temperature(MAAT). Our principal findings are as follows: the majority of GDGTs in the lake sediments are b GDGTs, followed by crenarchaeol and GDGT-0. In most of the lakes there were no significant differences between the GDGT distribution within the lake sediments and the soils in the same catchment, which indicates that the contribution of terrestrial material is important. i GDGTs in lake sediments are mainly influenced by water chemistry parameters(p H and salinity), and that in small lakes on the TP, TEX_(86) may act as a potential proxy for lake p H; however, in contrast b GDGTs in the lake sediments are mainly controlled by climatic factors. Based on the GDGT distribution in the lake sediments, we used proxies(MBT, CBT) and the fractional abundance of b GDGTs(f_(abun)) to establish calibrations between GDGTs and MAAT, respectively, which potentially provide the basis for paleoclimatic reconstruction on the TP.

Influence of temperature and turbidity on water COD detection by UV absorption spectroscopy

Ultraviolet(UV) absorption spectroscopy is used to detect the concentration of water chemical oxygen demand(COD). The UV absorption spectra of COD solutions are analyzed qualitatively and quantitatively. The partial least square(PLS) algorithm is used to model COD solution and the modeling results are compared. The influence of environmental temperature and turbidity is analyzed. These results show that the influence of temperature on the predicted value can be ignored. However, the change of turbidity can affect the detection results of UV spectra, and the COD detection error can be effectively compensated by establishing the single-element regression model.