Pingo drilling reveals sodium-chloride dominated massive ice in Grøndalen, Spitsbergen

Drilling of a 21.8-m-deep borehole on top of the 10.5-m-high Nori pingo that stands at 32 m asl in Grøndalen Valley (Spitsbergen) revealed a 16.1-m-thick massive ice enclosed by frozen sediments. The hydrochemical compositions of both the massive ice and the sediment extract show a prevalence of Na+ and Cl� ions throughout the core. The upper part of the massive ice (stage A) has low mineralization and shows an isotopically closed-system trend in δ18O and δD isotopes decreasing down-core. Stage B exhibits high mineralization and an isotopically semi-open system. The crystallographic structure of Nori pingo’s massive ice provides evidence of several large groundwater intrusions that support the defined formation stages. Analysis of local aquifers leads to suggest that the pingo was hydraulically sourced through a local fault zone by low mineralized sodium–bicarbonate groundwater of a Paleogene strata aquifer. This groundwater was enriched by sodium and chloride ions while filtering through marine valley sediments with residual salinity. The comparison between the sodium–chloride-dominated massive ice of the Nori pingo and the sodium–bicarbonate-dominated ice of the adjacent Fili pingo that stands higher up the valley may serve as an indicator for groundwater source patterns of other Nordenskiöld Land pingos.