Congratulations to Hong Shen who defended her dissertation on Friday, July 31, 2020

Advisor: Chris Poulsen

Abstract:

Mountain building processes have profound impact on both local and large-scale hydrology and climate change, and climate change interacts with mountain growth to form feedbacks. Numerous effects have been given to study the mountain-climate interactions, primarily by linking climate with erosion and topography during the growth history of mountains. Establishing such linkages require understanding on climate responses to mountain growth, how to interpret the climate signals preserved in proxy records, and the control of climate on landscape evolution. In this dissertation, we conduct numerical simulations in the Himalayan-Tibet and Andean orogens to investigate climate and isotopic response to mountain growth and the linked behavior among climate, erosion and topography.

Chapter 2 studies the climatic and isotopic responses to the uplift of the Himalayan-Tibet orogen and evaluate the application of the Rayleigh distillation process in reconstructing past elevation using an isotope-enabled general circulation model. The results show that the Rayleigh distillation is only the dominant process in monsoonal regions in the Himalayas when topography is high. At low elevations, local surface recycling becomes the primary process. On the Tibetan Plateau, stable water isotopes are shown to be primarily controlled by sub-cloud evaporation. This chapter show that the processes controlling isotopes varies by location and mountain elevation and using stable water isotopes as an indicator might be inappropriate.

Chapter 3 focuses on the climate response the widening of the central Andes, its impact on hydrology and proxy records, and the comparison with uniform uplift. The results show similar response of orographic precipitation on the eastern flank of central Andes due to the widening and due to the uplift, and substantial drying on the western flank due to the widening but little change due to the uplift. This chapter opens the ground of interpreting the hydrology changes preserved in proxy records as signals showing a west-east expansion of the Andes.

Chapter 4 is a technical study presenting a coupling framework for simulating climate-erosion-topography interaction, and simulations in various climate regimes to explore the strength of this interaction at different locations. The results from the simulations show a general relationship of higher annual precipitation rates corresponding to higher discharge, more erosion, smaller slopes and lower elevation. This control is stronger in regions with heavier precipitation and when topography grows higher. This study highlights the mountain-climate interactions as a first-order control on mountain building process.

Collectively, these chapters improve our understanding on climate response to mountain growth, the interpretation of climate and hydrology signals in proxy records, and the control of climate change on shaping landscape through erosion.