Subsurface release and transport of dissolved carbon in a discontinuous permafrost region

Warming and thawing of permafrost and deepening of the active layer related to climate change have been reported in arctic and subarctic environments. These changes alter subsurface hydrological flow pathways and advection rates through the landscape, and thereby also affect the quantity and timing of hydrological transport of dissolved carbon. This study investigates hydrological carbon transport through the subsurface to streams and how it is affected by the distribution of subsurface hydrological pathways and travel times through the landscape. We develop a consistent mechanistic, pathway- and travel time-based modeling approach for release and transport of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC). The model implications are tested against observations in the subarctic Abiskojokken catchment (68°21' N, 18°49' E) as a field case example of a discontinuous permafrost region. The results show: (a) Essentially flow-independent concentration and load of the annually renewed and depleted DOC, due to the small characteristic respiration-dissolution time scale relative to the average travel time of water through the subsurface to the stream. (b) High flow-dependence of DIC load, due to its large characteristic weathering-dissolution time relative to the average subsurface water travel time to the stream, which also keeps the DIC concentration essentially flow-independent and less fluctuating in time than the DIC load.