The carbon balance of Lake Superior: Modeling lake processes and understanding impacts on the regional carbon budget

The North American Carbon Program (NACP) intends (1) to develop quantitative scientific knowledge, robust observations, and models to determine emissions and uptake of CO2, CH4 and CO, changes in carbon stocks, and factors regulating these processes for North America and adjacent ocean basins; and (2) to develop the scientific basis for full carbon accounting on regional and continental scales. The Laurentian Great Lakes cover 25% of the land area of the 8 Great Lakes states, and CO2 emission and seasonal cycling from them may be comparable to local terrestrial ecosystems. Though their contributions to the regional carbon balance may be significant, these fluxes are currently poorly understood. CO2 fluxes from Lake Superior are of particular interest because they may directly impact observations at nearby AmeriFlux towers, yet due to the current lack of quantification, Lake Superior fluxes are presently neglected in analysis of these data. Motivated by the need for improved knowledge of Great Lake CO2 fluxes, this project will couple an ecosystem-carbon module with an existing hydrodynamic model of Lake Superior. This model will lead to estimates of the air-water CO2 fluxes and their spatial and temporal variability. New observations to improve knowledge of carbon cycling in winter and to constrain the model will also be obtained. With model output, the impact of Lake Superior CO2 fluxes on observations at AmeriFlux towers and on the regional carbon budget will be evaluated. The five key research questions are: 1. What is the magnitude of the air-water carbon flux in Lake Superior? 2. How are the fluxes influenced by variability in the physical climate? 3. How does Lake Superiors carbon cycle behave in winter? 4. What are the most important uncertainties in the Lake Superior carbon budget? 5. How do Lake Superior carbon fluxes impact the regional carbon budget? This project brings together an interdisciplinary team to improve understanding of the "complex relationships between and within the global water and carbon cycles". By jointly considering coastal carbon processing and terrestrial carbon budgets, this project addresses research priorities of both the Ocean and Earth Sciences divisions. Broader Impacts This project will address fundamental questions about the upper Midwest carbon budget, improve knowledge of coastal carbon cycling, and generate a set of research priorities for future study of Great Lakes. Two students and one postdoc will learn about Lake Superior carbon cycling using data and models, and the project will increase regional collaborations for Great Lakes carbon science. Undergraduates from under-represented groups will actively participate in the project through MTUs REU program. The team will also work to communicate their findings to the general public.

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