Hydrological and geochemical approach to understand the glacier-permafrost subglacial-system interactions in a glaciated catchment of Western Spitsbergen
Résumé
The freshwater fluxes flowing from High Arctic glaciers mainly depend on climatic indicators (T, P) but also on other parameters like the thermal state of glacier, the water routing within and below the glacier, the permafrost distribution and the hydrodynamic characteristics of the moraines and rock structures forming the catchment. Using hydrological and geochemical methods, t he objective of the presentation is to show the relationships existing between the hydrological response of a small glacier of the Brogger peninsula (Austrelovenbre glacier), th e climatic conditions and these other parameters. I n the framework o f the Hydrosensor Flows program (IPEV 304, ANR hydrosensor flows), we have studied since 2007 the Austrelovenbr e glacier basin. Downstream, this basin has two well - defined outlets that con centrate all water fluxes: one connected to the glacier and the other influenced by the groundwater discharge in the proglacial moraine. The hydrological response of the river system has been studied by continuous monitoring of climate (T, P) and hydrologi cal parameters (Q, T, E lectrical conductivity ) at hourly intervals . In addition, geochemical measurements have performed on water samples ( major chemical elements, Sr, 18 O, 2 H, 3 H, 34 S) in order to discuss the water origin, the water routing in the catchme nt and the water - rock interaction processes. The main outlet of the glacier (Goule River) shows hydrographs (Q vs time curve) with two dynamics: a daily cyclicity and several isolated flood events. The daily fluctuations are induced by air - temperature va riations. Most main flood events mainly result from rainfall events. W hen rainy events occur during warm periods or at the beginning of the freezing period, the floods may be highly amplified. The inertia of the basin has been approached using the correlat ion methods : t he Q autocorrelation data indicate the runoff has a quite high " memory effect " (32 days). This may reveal that meltwater infiltrated into shallow aquifers and is gradually restored as a base flow to streams . As expected, the mineralization of stream water is rather low during the summer due to glacier and snow melting. However, h igh mineralized waters ( ca. 700 - 800 μS/cm) flow out before and after the summer. The composition in major elements and in stable isotopes indicates that t he streams water actually comes from the water mixture of three reservoirs : snow/ice mainly during July and August, subglacial system (all year round) and supra - permafro s t aquifer (July to September). The progressive discharge of subglacial water and supra - permafrost groundwater is therefore responsible of high concentrations in dissolved elements. The dominant major elements are Ca ( abundant element in the geological formations ) and S ( due to pyrite oxidation and jarosite dissolution ) . The second outlet displays sm oothed hydrographs almost with no variations . The Q - curve therefore results from (1) the discharge of the supra - permafrost aquifer within the proglacial moraine, (2) the snow melting and (3) the permafrost thawing. The geochemical results confirm these ori gins of the stream water.