Browsing by Author "Torres, Mark A"

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    Stochasticity, Stability, and Hysteresis in the Biogeochemical Cycling of Carbon and Silicon
    (2024-04-18) Hou, Yi; Torres, Mark A
    The cycling of elements between surface environments and the rock reservoir sets the chemistry of the atmosphere, natural waters, and soils. Carbon (C) and Silicon (Si) are particularly interesting as they are important in controlling our planet’s climate and habitability. However, the rates at which relevant biogeochemical processes drive and respond to environmental change remain uncertain. This thesis furthers the mechanistic understanding of two key processes, organic carbon (OC) burial and silicate weathering, to provide new, quantitative constraints on how biogeochemical cycles respond to environmental changes. Chapter one evaluates how OC burial is affected by sedimentation dynamics. Due to the internal dynamics in sedimentary systems, sedimentation rates at a discrete location appear virtually random. To investigate the previously unknown effect of this stochasticity on OC burial, reactive-transport modeling was coupled with statistical methods. The results show that this stochasticity alone can profoundly alter OC burial efficiencies and create autogenic signals independent of climatic or environmental forcings. Likely, these autogenic signals are prevalent in observed chemostratigraphic records. Chapter two demonstrates how silicate weathering responds to glaciation. A novel multi-proxy model was developed leveraging field observations. This model was used to constrain weathering flux changes over the past 10 ka in two Icelandic watersheds with different glacial histories. The results show a synchronous increase in weathering fluxes with the expansion of glaciers. This positive effect of glaciation on weathering my allow for rapid transitions between Earth’s glacial and interglacial (i.e. bistable) climate states. Chapter three examines the glacial control on secondary phase formation during silicate weathering. The extent of secondary clay formation in a recently deglaciated and a currently glaciated catchment was constrained by chemical, isotopic, and mineralogical compositions of river and suspended sediments. The observed spatial heterogeneity, modulated by landscape type, suggests that secondary clay formation depends on the history of glaciation and that the influence of glaciers on environmental processes persists beyond deglaciation.