Effects of environmental change on the activation of sediment sources in different cold-climate drainage basins in Norway 

It is widely stated that atmospheric warming, together with an increasing frequency of rainfall events, enhance the activation of sediment sources, erosion and sediment-transport processes in cold-climate environments, with these increases being mainly driven by cryosphere degradation. In this study we compare the effects of ongoing environmental changes on measured sediment yields in three different cold-climate environments in Norway: (i) partially-glacierized drainage basins (Bødalen and Erdalen, connected to the Jostedalsbreen ice cap, western Norway), (ii) one drainage-basin system with discontinuous permafrost (upper Driva, central Norway), and (iii) one boreal drainage-basin system free of permafrost (Selbusjøen, central Norway).  Our study includes the multi-year (>10 yr) monitoring of fluvial solute and sediment transport using a range of different advanced techniques. In the partially-glacierized drainage basins mechanical denudation dominates over chemical denudation. Most sediment transport occurs during pluvial events in fall, followed by thermally-determined glacier melt in summer, and thermally-determined snowmelt in spring.  An increasing frequency of extreme rainfall events leads to increased sediment yields whereas smaller amounts of wintry snow and the ongoing retreat of outlet glaciers are not causing a detectable increase of sediment yields. For the drainage-basin system with discontinuous permafrost it is found that global warming and the connected shifts in the ratio of snow and rain, the increased frequency of heavy rainfall events, and the continued thawing of permafrost have complex effects on denudation, with an increasing importance of pluvially-induced denudational events, a decreasing importance of snowmelt-induced denudation processes, and an increasing dominance of chemical denudation over mechanical denudation. Also in the boreal environment an increasing importance of pluvially-induced denudational events, a decreasing importance of snowmelt-induced denudation processes, and an increasing dominance of chemical over mechanical denudation can be observed. As a result, the different cold-climate environments respond differently to ongoing environmental changes. A significant increase of mechanical denudation due to cryosphere degradation cannot be detected in our study areas while an increased frequency of pluvial events causes an enhanced activation of sediment sources and rising mechanical denudation.