This work package deals with Arctic marine, limnic, terrestrial and glaciological ecosystems. The work package is divided into two sub-work packages, one focusing on terrestrial environments, and one focusing on aquatic environments. In both sub-work packages, the focus is to understand the function and structure of Arctic ecosystem and how their biodiversity and associated biogeochemical processes are impacted by various climatic drivers. This will include investigations along existing environmental gradients and different scales, time series from the long-term monitoring programs such as the Greenland Ecosystem Monitoring program and experimental approaches. The focus is to understand how climate variability affects Arctic ecosystems today and how they may change in the future due to climate change with respect to their function and how new incoming species will affect the system.