The water balance of an arctic lake and its dependence on climate change: Tvillingvatnet in Ny-Ålesund, Svalbard

Lake Tvillingvatnet is the water supply to the arctic research settlement Ny-Ålesund in Svalbard. In the period 1920-1930 it was observed that the lake received groundwater from a sandstone-aquifer underlying the lake. Recent water balance studies indicate that there is no longer any groundwater flow of that type into the lake. This change can be explained by a warmer climate resulting in a fast retreat of the glaciers after the Little Ice Age. Large amounts of melt water combined with a steep hydraulic gradient may have caused partial melting of permafrost along the front of the Brøggerbreen Glacier, which was situated c . 0.5 km west of Lake Tvillingvatnet at that time. Today, the glacier front is more than a kilometre SW of the lake. The formation of new permafrost has resulted in freezing of the previously active groundwater outflow channels. The present flow of water into Tvillingvatnet during the autumn is probably due to shallow groundwater in the active layer along the talus of the Zeppelinfjellet Mountain.