February 2, 2018 @ 12:00 pm - 1:00 pm CST
GIESS – Departmental Research in Earth, Environmental and Planetary Sciences
Seminar Topic: Earth Covering
Loredana Suciu: “Eulerian chemical transport models underpredict plume chemistry in young fire plumes: insight from a small prescribed-fire in South Carolina (U.S.) using CMAQ simulations”
Wildfires and prescribed burning are important sources of particulate and gaseous pyrogenic organic carbon (PyOC) emissions to the atmosphere. These emissions impact atmospheric chemistry, air quality and climate, but the spatial and temporal variabilities of these impacts are poorly understood, primarily because small and fresh fire plumes are not well predicted by Eulerian chemical transport models due to their coarser grid size. Generally, this results in underestimation of downwind deposition of particulate matter, hydroxyl radical reactivity, secondary organic aerosol formation and ozone (O3) production. However, such models are good for simulating multiple atmospheric processes that could affect the lifetimes of PyOC emissions over large spatiotemporal scales, allowing us to evaluate their impacts and study paleoclimate-fire interactions. Lagrangian reactive plumes models could be used to trace fresh emissions at the sub-grid level of the Eulerian model but they require background chemistry predicted by the Eulerian models to simulate the interactions of the plume material with the background air during plume aging. By coupling the two models, the physico-chemical evolution of the biomass burning plumes can be tracked from local to regional scales. In this context, we primarily validated the coarser scale chemistry by comparing it with airborne plume measurements from a small prescribed-fire. We found that the Eulerian model alone consistently underpredicts 1-h average concentrations of formaldehyde, methanol and O3, and does not follow the non-linear trend exhibited by the measured chemistry in the plume. We also found that submicron particulate organic carbon underpredicts anhydrosugars (PyOC markers); this could be partially explained by the missing chemistry of these species in the chemical mechanism.
Hehe Jiang: “Continental Arcs as Both Carbon Source and Sink in Regulating Long Term Climate”
Abstract: Hehe Jiang, Cin-Ty A. Lee
The long-term variability of atmospheric pCO2 is determined by the balance between the rate of geologic inputs of CO2 (e.g., magmatic/metamorphic degassing, carbonate weathering) and the rate of carbonate precipitation driven by silicate weathering. The Late Cretaceous-Early Cenozoic was characterized by elevated atmospheric pCO2 and greenhouse climate, likely due to increased magmatic flux from continental arcs. However, it has been suggested that continental arc magmatism is accompanied by rapid uplift and erosion due to magmatic/tectonic thickening of the crust, thus continental arcs likely enhance the chemical weathering flux, in turn increasing the carbon sink. To assess the contribution of continental arcs to global carbon inputs and sinks, we conducted a case study in the Cretaceous Peninsular Ranges batholith (PRB) and associated forearc basin in southern California, USA, representing one segment of the Cretaceous Cordillera arc-forearc system. Arc magmatism occurred between 170-85 Ma, peaking at 100 Ma, but erosion of the arc continues into the early Eocene, with forearc sediments representing this protracted arc unroofing. During magmatism, we estimate up to 5 km elevation increase due to magmatic thickening, and the CO2 degassing flux from the PRB was at least ~5-25*105 mol·km-2·yr-1. By calculating the depletion of Ca and Mg in the forearc sediments relative to their arc protoliths, we estimate the silicate weathering/carbonate precipitation flux to be ~106 mol·km-2·yr-1 during Late Cretaceous magmatism, decreasing to ~105 mol·km-2·yr-1 by the Early Eocene. We show that in continental arcs, the CO2 degassing flux is comparable to CO2 consumption driven by silicate weathering in the arc. However, after magmatism ends, a regional imbalance arises in which the arc no longer contributes to CO2 inputs but continued silicate weathering of the arc drives carbonate precipitation such that the arc indirectly becomes CO2 sink. We propose that the development of continental arcs increases weatherability through mountain building processes, and therefore may increase the strength of the global negative feedback between silicate weathering and climate.
Lunch served on the patio at 11:30 AM