Great Lakes Seminar Series: Allison Steiner

The Laurentian Great Lakes can influence regional climate and chemistry through a variety of mechanisms, and I’ll discuss these chemistry-climate interactions from the perspective of what goes up (e.g., water via evaporation, aerosols via lake spray) versus what comes down (e.g., aerosol deposition of nutrients, precipitation). From the climate perspective, we analyze the atmospheric moisture budget in the Great Lakes region using reanalyses and future climate model data to develop a process-level understanding of the precipitation seasonality. We identify the lakes not only as a source of moisture, but also in generating localized moisture flux convergence/divergence patterns that affect the seasonality of the water cycle. Despite differences in historical simulations from the Coupled Model Intercomparison Project (CMIP6) data archive, common patterns of change are present in the future projections of the atmospheric water budget. Specifically, summer drying and winter/spring wetting by mid-century is consistent across models, indicating a shift in the precipitation seasonal cycle towards colder months, while evapotranspiration magnitudes revealed unambiguous increases throughout the year in all models. Overall, the atmospheric transport of moisture is the primary driver of future precipitation changes, with an amplification of the moisture flux convergence seasonal cycle in future climate model simulations. From the atmospheric chemistry perspective, I’ll discuss the role of the lakes as a source or sink for chemical constituents in the atmosphere. Emissions of lake spray aerosol (LSA) can be a regional source of aerosol, and including LSA in regional chemistry models increases aerosol pH in the Great Lakes region and enables the partitioning of nitrate to the aerosol phase. Overall, this suggests that LSA should be included in regional assessments of atmospheric chemistry and air quality. The deposition of atmospheric aerosols is a source of phosphorus to the Great Lakes region, and while this contribution is small compared to surface runoff, it has not been well-constrained. We quantify the phosphorus deposition to the Great Lakes using a combination of ground-based measurements and models across the region, and highlight uncertainties in this atmospheric source of phosphorus.

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