Distribution Characteristics of Topsoil brGDGTs and Their Responses to Environmental Factors in the Southeastern Margin of the Tibetan Plateau

Key words: 
• Keywords: southeastern margin of the Tibetan Plateau /
• brGDGTs /
• modern processes /
• temperature /
• pH

Abstract: Abstract: [Objective] Glycerol dialkyl glycerol tetraethers (GDGTs) are chemically stable and can be preserved for long periods under natural conditions. Their composition and distribution show systematic responses to environmental conditions and have therefore been widely applied in recent years to paleoenviron-mental and paleoelevation reconstructions. The southeastern margin of the Tibetan Plateau is characterized by complex topography and highly variable climate, and the applicability of temperature and pH calibration equations developed from a single basin remains highly uncertain at the regional scale. Consequently, it is necessary to investigate the distribution patterns of branched GDGTs (brGDGTs) and their responses to temperature and pH across multiple basins in this region, to establish robust regional calibration equations that provide modern-process constraints for accurate quantitative reconstructions of regional paleotemperature and paleoelevation using sedimentary brGDGTs.[Methods] A total of 56 surface soil samples were collected from nine basins (Maqu, Gannan, Zoigê, Songpan, Nangqên, Leiwuqi, Gongjue, Mangkang, and Daocheng) on the southeastern margin of the Tibetan Plateau. brGDGTs were systematically analyzed and combined with instrumentally measured mean annual air temperature (MAAT) and mean annual precipitation (MAP) from meteorological stations, as well as measured soil pH data. Pearson correlation analysis was used to compare and evaluate published proxy indices, and stepwise regression was applied to develop regional calibration equations for temperature and pH.[Results] brGDGTs in surface soils of the study area are dominated by Ia, IIa, and IIIa, with 5-methyl brGDGTs accounting for the highest proportion. The regional MAAT calibration model established via stepwise regression shows high reconstruction accuracy within the low-temperature range (approximately ?4°C to 4°C). Among indices based on Tibetan Plateau surface soils, CBT'' exhibits the strongest correlation with measured pH.[Conclusions] The composition and distribution of surface-soil brGDGTs on the southeastern margin of the Tibetan Plateau are jointly controlled by temperature and pH, and global- or regional-scale calibration equations cannot be directly applied to this environment. The newly developed regional temperature and pH calibration equations show better applicability in high-altitude, cold environments. These results provide critical scientific constraints for developing and applying sedimentary brGDGTs to quantitatively reconstruct the evolutionary history of paleotemperature and paleoelevation on the Tibetan Plateau.