Ongoing and amplified climate change in the Arctic is leading to glacier retreat and to the exposure of an ever-larger portion of non-glaciated permafrost-dominated landscapes. Warming will also cause more precipitation to fall as rain, further enhancing the thaw of previously frozen ground. Yet, the impact of those perturbations on the geochemistry of Arctic rivers remains a subject of debate. Here, we determined the geochemical composition of waters from various contrasting non-glacial permafrost catchments and investigated their impact on a glacially dominated river, the Zackenberg River (Northeast Greenland), during late summer (August 2019). We also studied the effect of rainfall on the geochemistry of the Zackenberg River, its non-glacial tributaries, and a nearby independent non-glacial headwater stream Gr ae nse. We analyzed water properties, quantified and characterized dissolved organic matter (DOM) using absorbance and fluorescence spectroscopy and radiocarbon isotopes, and set this alongside analyses of the major cations (Ca, Mg, Na, and K), dissolved silicon (Si), and germanium/silicon ratios (Ge/Si). The glacier-fed Zackenberg River contained low concentrations of major cations, dissolved Si and dissolved organic carbon (DOC), and a Ge/Si ratio typical of bulk rock. Glacial DOM was enriched in protein-like fluorescent DOM and displayed relatively depleted radiocarbon values (i.e., old DOM). Non-glacial streams (i.e., tributaries and Gr ae nse) had higher concentrations of major cations and DOC and DOM enriched in aromatic compounds. They showed a wide range of values for radiocarbon, Si and Ge/Si ratios associated with variable contributions of surface runoff relative to deep active layer leaching. Before the rain event, Zackenberg tributaries did not contribute notably to the solute export of the Zackenberg River, and supra-permafrost ground waters governed the supply of solutes in Zackenberg tributaries and Gr ae nse stream. After the rain event, surface runoff modified the composition of Gr ae nse stream, and non-glacial tributaries strongly increased their contribution to the Zackenberg River solute export. Our results show that summer rainfall events provide an additional source of DOM and Si-rich waters from permafrost-underlain catchments to the discharge of glacially dominated rivers. This suggests that the magnitude and composition of solute exports from Arctic rivers are modulated by permafrost thaw and summer rain events. This event-driven solute supply will likely impact the carbon cycle in rivers, estuaries, and oceans and should be included into future predictions of carbon balance in these vulnerable Arctic systems.

Long-term measurements of ecological effects of warming are often not statistically significant because of annual variability or signal noise. These are reduced in indicators that filter or reduce the noise around the signal and allow effects of climate warming to emerge. In this way, certain indicators act as medium pass filters integrating the signal over years-to-decades. In the Alaskan Arctic, the 25-year record of warming of air temperature revealed no significant trend, yet environmental and ecological changes prove that warming is affecting the ecosystem. The useful indicators are deep permafrost temperatures, vegetation and shrub biomass, satellite measures of canopy reflectance (NDVI), and chemical measures of soil weathering. In contrast, the 18-year record in the Greenland Arctic revealed an extremely high summer air-warming of 1.3 degrees C/decade; the cover of some plant species increased while the cover of others decreased. Useful indicators of change are NDVI and the active layer thickness.

A spatially distributed, physically based, hydrologic modeling system (MIKE SHE) was applied to quantify intra- and inter-annual discharge from the snow and glacierized Zackenberg River drainage basin (512 km 2; 20% glacier cover) in northeast Greenland. Evolution of snow accumulation, distribution by wind-blown snow, blowing-snow sublimation, and snow and ice surface melt were simulated by a spatially distributed, physically based, snow-evolution modelling system (SnowModel) and used as input to MIKE SHE. Discharge simulations were performed for three periods 1997-2001 (calibration period), 2001-2005 (validation period), and 2071-2100 (scenario period). The combination of SnowModel and MIKE SHE shows promising results; the timing and magnitude of simulated discharge were generally in accordance with observations (R-2 = 0.58); however, discrepancies between simulated and observed discharge hydrographs do occur (maximum daily difference up to 44.6 m(3) s(-1) and up to 9% difference between observed and simulated cumulative discharge). The model does not perform well when a sudden outburst of glacial dammed water occurs, like the 2005 extreme flood event. The modelling study showed that soil processes related to yearly change in active layer depth and glacial processes (such as changes in yearly glacier area, seasonal changes in the internal glacier drainage system, and the sudden release of glacial bulk water storage) need to be determined, for example, from field studies and incorporated in the models before basin runoff can be quantified more precisely. The SnowModel and MIKE SHE model only include first-order effects of climate change. For the period 2071-2100, future IPCC A2 and B2 climate scenarios based on the HIRHAM regional climate model and HadCM3 atmosphere-ocean general circulation model simulations indicated a mean annual Zackenberg runoff about 1.5 orders of magnitude greater (around 650 mmWE year(-1)) than from today 1997-2005 (around 430 mmWE year(-1)), mainly based on changes in negative glacier net mass balance. Copyright (c) 2007 John Wiley & Sons, Ltd.