SES-02. Soil temperature calibration and paleoaltimetry of the Tibetan Plateau

Abstract
We seek to improve and understand the relationship between temperature and elevation in the Tibetan Plateau to constrain past surface elevations in this region. We measured air and soil temperatures from an altitudinal transect (from ~400 m to ~4000 m) on the northeastern margin of the Tibetan Plateau. These measurements were taken from July 2019 to July of 2020 in soils at 10 cm and 50 cm below the surface and at ~1.5 m in the air at 18 sites. Our temperatures combined with surface and air temperatures from Chinese meteorological stations in the same latitude band show dTs/dz = –4.0°C/km, where Ts = soil temperature and z = elevation, and dTa/dz = –3.5°C/km, where Ta = air temperature. The difference between soil and air temperature increases at ~0.5°C/km of elevation. We also sampled soil from 10 cm and 50 cm depth at the same sites where we measured temperatures, and we analyzed branched Glycerol Diakyl Glycerol Tetraethers (brGDGTs) in these soils. These brGDGTs are bacterial lipid biomarkers that, with empirical correlation with modern temperature, allow estimates of past temperatures of material preserved in sedimentary archives. We present a preliminary soil and air regional temperature calibration compared with the existing global calibrations. We compare how well these calibrations estimates modern temperatures in our altitudinal transect and in ~15 sedimentary samples from ~22 – 33 Ma.