Pingo development in Grøndalen, West Spitsbergen

Abstract. Pingos are common features in permafrost regions that form by subsurface massive-ice aggradation and create hill-like landforms. Pingos on Spitsbergen have been previously studied to explore their structure, formation timing, connection to springs as well as their role in post-glacial landform evolution. However, detailed hydrochemical and stable-isotope studies of massive ice samples recovered by drilling has yet to be used to study the origin and freezing conditions in pingos. Our core record of 20.7 m thick massive pingo ice from Grondalen differentiates into four units: two characterised by decreasing δ 18 O and δD and increasing d (units I and III), and two others show the opposite trend (units II and IV). These delineate changes between episodes of closed-system freezing with only slight recharge inversions of the water reservoir, and more complicated episodes of groundwater freezing under semi-closed conditions when the reservoir got recharged. The water source for pingo formation shows similarity to spring water data from the valley with prevalent Na + and HCO 3 - ions. The sub-permafrost groundwater originates from subglacial meltwater that most probably followed the fault structures of Grondalen and Bohmdalen. Today the pingo of Grondalen is relict and degrading due to warming surface temperatures. The state of pingos on Spitsbergen depends on complex interaction of climate, permafrost and groundwater hydrology conditions, and is thus highly sensitive to climate warming.