TECO: Patterns and Controls of Temporal Variation in CO2 Sequestration and Loss in Arctic Ecosystems

这项研究将阐明北极冻土带生态系统对气候变化的短期和长期响应，以及与之相关的土壤含水量和活动层深度的变化。这些目标将通过实地观测、操作实验和建模相结合来实现。北纬温度记录和永久冻土温度剖面表明，在过去30年里，年平均气温上升了2-4摄氏度。与这种变暖相关的是生长季节长度的增加，表层土壤含水量的减少，以及冰雪覆盖范围和分布的减少。这些物理变化改变了北极生态系统的功能，这可能对全球大气二氧化碳浓度产生显著的正反馈或负反馈。大部分二氧化碳净通量数据来自生长季节对陆地表面的测量，然而，水生系统已知是二氧化碳的净来源，最近已证明冷季二氧化碳的大量损失。该项目将使用涡动相关方法测量年周期内的二氧化碳净交换，该方法可以直接测量二氧化碳、水蒸汽和能量的公顷尺度交换。这些测量将在年周期内进行，以确定温暖季节和寒冷季节对北极冻土带生态系统年二氧化碳净交换的贡献。此外，现场操作实验将允许确定整个生态系统净CO2交换的短期和长期响应，以及驱动净CO2通量对土壤温度和地下水位变化的生理成分。这些研究将有助于阐明植物和整个生态系统对气候变化的重要反应机制，以及潜在补偿反应的长期轨迹。迄今为止的观测表明，北极生态系统对气候变化的长期反应可能与最初的短期反应大不相同。

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.