Spatial and Temporal Groundwater Oxygen-18 and Deuterium Values Measured in a Discontinuous Permafrost Aquifer Located in Interior Alaska

Groundwater samples were collected from an extensive monitoring well network in a discontinuous permafrost aquifer. The sampled groundwater was analyzed for the stable isotopes oxygen-18 (18O) and deuterium (2H). Sampling was approximately aligned with season; spring (March 1 – April 2), summer (July 12 – Sept. 11), fall (Oct. 2 – Dec. 10), and winter (Jan. 9 – March 26). Wells were purged until geochemical parameters (water temperature, dissolved oxygen, conductivity, pH, and oxidation-reduction potential) stabilized or three well volumes of groundwater were pumped from the monitoring well. Samples were analyzed for 18O and 2H concentrations at the Alaska Stable Isotope Facility at the University of Alaska Fairbanks using continuous-flow isotope ratio mass spectrometry (CF-IRMS). δ2H and δ18O values were measured using pyrolysis-EA-IRMS. This method utilizes a ThermoScientific high temperature elemental analyzer (TC/EA) and Conflo IV interface with a DeltaVPlus mass spectrometer. Stable isotope ratios are reported in ‰ notation as parts per thousand (‰) deviation from the international standards, V-SMOW (Vienna Standard Mean Ocean Water). Instrument precision is <3.0 ‰ for hydrogen and < 0.5 ‰ for oxygen. The aquifer is located in the flood plain of the Tanana River in interior Alaska near the city of North Pole, Alaska. Stable isotope results were used to evaluate the movement of groundwater in the discontinuous permafrost aquifer and isolate areas where suprapermafrost groundwater mixes with subpermafrost groundwater through open taliks in the permafrost.