Biomarker evidence for late Miocene temperature and moisture from the Alagu planation surface, NE Tibetan Plateau

The late Miocene climatic change is critical to understanding the interactions among late Cenozoic global cooling, tectonic activity and the Asian monsoon system evolution. However, paleoclimate reconstruction is restricted to qualitative descriptions, and quantitative work is rare, which limits further study. Here, we reconstruct the late Miocene temperature and hydroclimate changes based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) and magnetic susceptibility evidence in the Alagu planation surface in the northeastern Tibetan Plateau (NE TP), which is at the junction of the zones of westerly and monsoonal influences. The following preliminary conclusions have been drawn: the late Miocene temperatures exhibit a near-linear decreasing trend, mainly in response to global sustained cooling rather than tectonic activity; while the humidity shows an increasing trend opposite to that of temperature. We regard the possible reason for the opposite evolution of the late Miocene temperature and moisture of the Alagu planation surface as the weakening East Asian summer monsoon (EASM) caused by global cooling, leading to westward monsoonal moisture transport and thereby enhancing precipitation.