Optimizing the Simulation of Atmospheric Dust Concentrations and Investigating its Impact on the Asian Monsoon during the Miocene.

Abstract

The Middle Miocene Climate Optimum (16.75-14.5 Ma) serves as a valuable comparison for future climate scenarios due to its elevated CO₂ levels, but its climate state was also shaped by unique non-CO2 forcings, including dust aerosol concentrations. While dust accounts for considerable regional radiative forcing that mediates monsoon dynamics, its representation in paleoclimate models is poorly understood, creating uncertainty in climate sensitivity estimates and resulting hydroclimate responses. In this study, we focus on the Miocene dust emission parameterization in a climate model, the Community Earth System Model in version 1.2.2 (CESM1.2.2). We conducted sensitivity experiments to investigate how different parameterizations of soil erodibility affect dust concentrations and thereby impact Miocene hydroclimate. We analyzed two sensitivity experiments: one with topography-based soil erodibility (TopoS) and the other with uniform erodibility (UniformS). By comparing annually and seasonally averaged outputs, we quantified the effects of increased dust levels on the Asian Monsoon. Our results show that TopoS produces a higher dust burden on average over a region covering South Asia, the Middle East, and the western Tibetan Plateau. Regions with higher dust burden generally correspond to less precipitation, and regions with lower dust burden generally correspond to more precipitation.  Additionally, we observed a relationship between changes in dust burden and the surface energy balance, with cooler temperatures and reduced net radiation for TopoS compared to UniformS. These findings show that more realistic soil erodibility maps are essential for simulating dust's climatic impact, thus improving the accuracy of paleoclimate simulations.