ALBERT

Beschreibung: Permafrost regions have been identified to host a soil organic carbon (C) pool of global importance, storing more than 1500 PgC. A large portion of this C pool is currently frozen in deep soils and permafrost deposits. Permafrost thaw hence may result in mobilization of large amounts of C as greenhouse gases, dissolved organic C, or particulate organic matter, with substantial impacts on C cycling and C pool distribution. Understanding potential consequences and feedbacks of permafrost degradation therefore requires better quantification of processes and landforms related to thaw. While many predictive land surface models so far consider a gradual increase in the average active layer thickness across the permafrost domain, rapid shifts in landscape topography and surface hydrology caused by thaw of ice-rich permafrost are much more difficult to project. Field studies of thermokarst and thermo-erosion indicate highly complex and rapid landscape-ecosystem feedbacks. Contrary to top-down permafrost thaw that may affect any permafrost type at the surface, both thermokarst and thermo-erosion are considered pulse disturbances that are closely linked to presence of near-surface ice-rich permafrost, are active on short sub-annual to decadal time scales, and may affect C stores tens of meters deep. Here we present a comprehensive review synthesizing measured and modeled rates of thermokarst and thermo-erosion processes from the scientific literature and own observations across the northern Hemisphere permafrost regions. The goal of our synthesis is (1) to provide an overview on the range of thermokarst and thermo-erosion rates that may be used for parameterization of thermokarst and thermo-erosion in ecosystem and landscape models; and (2) to assess simple back-of-the-envelope scenarios of the magnitude of C thaw due to thermokarst and thermo-erosion versus projected active layer thickening. Example scenarios considering thermokarst lake expansion and talik growth indicate that rapid thaw processes have a high possibility to contribute substantially to permafrost C mobilization over the coming century.

Beschreibung: Terrestrial ecosystems across the circumpolar Arctic region are undergoing unprecedented changes in structure and function as a result of rapid climate warming. Such changes have substantially altered energy, water and biogeochemical cycling in these regions, which has important global-scale consequences for climate and society. Recognizing the vulnerability of these ecosystems to change, scientists and decision-makers have identified a critical need for research that employs existing and new remote sensing technologies and methodologies to observe, monitor and understand changes in Arctic ecosystems. The unique capabilities provided by remote sensing imagery and data products have allowed us novel views of ecosystems and their dynamics over multiple scales in time and space across all regions of the globe. Here we offer a synthetic discussion of the recent and emerging science focused on understanding the dynamic landscape processes in Arctic terrestrial ecosystems using a variety of remotely-sensed information collected from passive and active sensors on ground-, aircraft- and satellite- based platforms. To consider the evolution of these technologies, methods and applications over recent decades, we look at key examples from the scientific literature that range from the use of radar sensors for local-scale characterization of active layer dynamics to the circumpolar-scale assessment of changes in vegetation productivity using long-term records of optical satellite imagery. This discussion has a particular focus on the use of remotely sensed data and products to parameterize, drive, evaluate and benchmark the modeling of Arctic ecosystem processes. We use these examples to demonstrate the opportunities for model-data integration, as well as to highlight the challenges of remote sensing studies in northern high latitude regions.