The coupling between hydrology, the development of the active layer and the chemical signature of surface water in a periglacial catchment in West Greenland

Abstract. An important factor for controlling the chemical signature of surface water is the interactions with soil particles and groundwater. In permafrost landscapes, ground ice restricts groundwater flow, which implies a limited influence of processes such as weathering on the chemical signature of the runoff. The aim of this study was to examine how freeze-thaw processes, hydrology and water age interact to shape the chemical and stable hydrogen and oxygen isotopic signature of surface water in a catchment in West Greenland. Measuring runoff in remote catchments is challenging, and therefore we used a validated hydrological model to estimate daily runoff over multiple years. We also applied a particle tracking simulation to determine groundwater ages and used data on stable isotopic and chemical composition from various water types – including surface water, groundwater, lake water and precipitation – spanning from early snowmelt to the end of the thawed season. Our results show that groundwater age generally is less than one year and rarely exceeds four years, total runoff is dominated by groundwater, and overland flow is restricted to the snowmelt period and after heavy rain events. Monitoring of thaw rates in the active layer indicates a rapid thawing in connection with running water, and meltwater from ground ice quickly becomes an important fraction of the runoff. Taken together, our data suggest that even in continuous permafrost landscapes with thin active layers and an absence of truly old and mobile groundwater, soil processes exert a strong influence on the chemical and stable isotopic signature of runoff, i.e., similar to what has been observed in other climatic settings.