Bridging Timescales of Climate and Vegetation Change Effects on Denudation: A Coupled Modeling Approach

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This proposal is a continuation of our work conducted in EarthShape phase 1. Our phase 1 research quantifies how climate and vegetation changes since the Last Glacial Maximum to present impacted topography and erosion rates in the EarthShape study areas. We found significant changes in vegetation and erosion over the last 21 ka, and a non-linear response and thresholds in erosion to vegetation cover change. Based on these results, the dramatic environmental and tectonic changes of the Cenozoic motivate us in this second phase to bridge across longer (million year) timescales to evaluate larger magnitude climate change effects on vegetation related weathering and erosion in the Chilean Coastal Cordillera. We do this by testing the overarching hypothesis that if atmospheric CO2 levels and warmer and wetter paleoclimate in the Cenozoic (Eocene-Oligocene boundary) decreased by an order of magnitude to lower values towards present then: (1) This change would drive a marked decrease in plant productivity and vegetation cover over the Cenozoic, and (2) The vegetation changes would fundamentally alter erosion rates and plant-facilitated weathering would decrease. Thus, present day topography may contain a strong imprint of past vegetation processes. Our exploration and evaluation of this hypothesis will build upon our own and others technical achievements of the first phase. We will apply a coupled dynamic vegetation (LPJ-GUESS) and a landscape evolution (LandLab) model that will be driven by predicted paleoclimate changes (ECHAM5) over the last 34 Ma. Integral and cutting edge to our approach is linking the vegetation and landscape evolution models to calculate changes in biotic (plant facilitated) and abiotic weathering. From this, we will: a) evaluate how transient vegetation changes influence catchment denudation rates, topography, and deep weathering; b) identify the sensitivity of vegetation modulated erosion and weathering to changes in paleo atmospheric CO2, precipitation, and temperature, and c) integrate existing phase 1, and new phase 2 soil, geochemical (denudation rate), geologic, and ecologic data from other projects into our modeling framework.