The role of non-growing season processes in the methane and nitrous oxide budgets in pristine northern ecosystems

ended

The response of the terrestrial biosphere to climate change is still largely unknown and represents a key uncertainty in climate change predictions. High latitude regions, including Arctic and boreal ecosystems, constitute a key component of the earth system due to significant soil carbon stocks. High latitude regions are net sources of greenhouse gases, such as methane (CH4) and nitrous oxide (N2O), but there is significant disagreement among flux estimates with further uncertainty due to a rapidly changing environment. Climate change effects are particularly strong during the non-growing season, altering the timing of spring snowmelt, fall freeze-up, and increasing winter temperatures. The changes have significant implications for biogeochemical cycles and ecosystem function across high latitude regions. Despite growing evidence of the importance of non-growing season greenhouse gas emissions, few measurements have been made in pristine Arctic and boreal ecosystems. Non-growing season CH4 emissions can account for 10-100% of annual CH4 flux, while next to nothing is known about emissions of N2O during this period. Process-based models miss non-growing season emissions of CH4, underestimating them by 67% and annual emissions by 25%. I will use complementary observations (WP1), modelling (WP2), and experiments (WP3) to quantify the annual magnitude of CH4 and N2O flux, identify controls on non-growing season flux, and assess why existing models of CH4 flux fail outside of the growing season. Are environmental conditions so different that existing model parameters fail, or is non-growing season biogeochemistry fundamentally different? The overall impact is to shift the paradigm from “nothing happens outside of the growing season” to “capturing non-growing season processes is key to understanding ecosystem dynamics.” Ultimately, results will provide novel insights into greenhouse gas budgets and transform our understanding of fundamental earth system dynamics.