9730004 Oechel This research will elucidate the short- and long-term responses of arctic tundra ecosystems to climate change and associated changes in soils water content and active layer depth. These objectives will be accomplished by a combination of field observations, manipulative experiments, and modeling. Northern latitude temperature records and permafrost temperature profiles indicate that average annual temperature has increased by 2-4 C over the last 30 years. Associated with this warming has been an increase in growing season length, a decrease in surface soil water content, and a decrease in the extent and distribution in snow and ice cover. These physical changes have altered arctic ecosystem function, which could result in a significant positive or negative feedback to global atmospheric CO2 concentrations. Much of the net CO2 flux data is from growing season measurements of terrestrial surfaces, however, aquatic systems are known to be net sources of CO2, and substantial cold season CO2 losses have recently been demonstrated. This project will measure net CO2 exchange over annual cycles using eddy covariance methodology, which allows direct measurement of hectare-scale exchanges in CO2, H2O vapor, and energy. These measurements will be conducted over the annual cycle to determine both the warm- and cold-season contribution to annual net CO2 exchange in arctic tundra ecosystems. In addition, in-situ manipulative experiments will allow determination of short- and long-term responses of whole ecosystem net CO2 exchange and the physiological components that drive net CO2 flux to alterations in soil temperature and water table depth. These studies will help elucidate important mechanisms involved with plant- and whole-ecosystem responses to alterations in climate, as well as long-term trajectories of potential compensatory responses. Observations to date indicate that the long-term response of arctic ecosystems to climate change may be quite different than initial short-term response s.
