Collaborative Research: The role of Ice in the response of Large Lakes to a Changing Climate

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The long-term response of large lakes to climate change is not well understood. Recent observational results have shown that winter ice cover plays a vital and previously underappreciated role in determining thermal conditions the following summer; the concentration of high albedo ice determines the timing of the spring overturn, which in turn affects summer temperatures. A long-term trend towards lesser ice cover in Lake Superior is causing a sustained and more effective warming season that is contributing to a rise in summer lake temperatures in significant excess of the rise in air temperature. However, the role that ice plays in this phenomenon and the ability to predict the thermal response of the lake to climate change is poorly understood. In addition, the thermal response of the lake to winter ice cover is critical to its carbon cycle, because temperature is perhaps the single most important determinant of biogeochemical reaction rates. Rates such as nutrient uptake rates by phytoplankton and bacterial respiration rates work in synchrony to regulate the lake carbon cycle. Nevertheless, little is known about what effect steadily rising lake temperatures may have on the long-term stability of biochemical cycles within large lakes. This project will fill in these gaps in knowledge and to gain a fundamental understanding of the role of ice in determining the full annual and interannual cycles of temperature and carbon in large lakes. The following questions that pertain to Lake Superior?s physics and biogeochemistry will be addressed: 1) What is primarily responsible for setting the amount of ice formation? 2) What role does the spatial and temporal variability of ice formation play in determining lake-wide summer conditions? 3) What are the trends in mixed layer depth? 4) Are increased temperatures and reduced ice cover playing a role in the long-term mass balance of the lake, and contributing to the general trend of lower water over the last few decades? 5) How much ?information? regarding heat and carbon, if any, is passed from one year to the next? 6) What is the impact of a progressively earlier ice melt, higher summer temperatures, and stronger thermal stratification on biological production and carbon cycle? The project will improve our understanding of lake levels, a significant factor to the shipping industry. The unprecedented dataset will be available to a variety of lake modelers. Expertise in ice and biogeochemical modeling will also be broadened.