Climate Change Impacts on Active Zone Groundwater Dynamics in the High Arctic, Canada

With Arctic amplification, the rate of Arctic warming is estimated to be between two to four times greater than at lower latitudes. Northern warming is leading to environmental change, including permafrost thaw and changes in groundwater flow due to alterations in the timing and the depth of the active zone. Research suggests that, due to permafrost degradation and concomitant increased groundwater mobility, exfiltration to northern groundwater-fed lakes may increase with continued warming. Many parts of the terrestrial Arctic are experiencing warming and increased precipitation, both of which affect both the annual timing of formation and depth of the active zone, thereby controlling the amount of water that may be transmitted through the shallow subsurface. The objective of our research is to use a numerical modeling approach to disentangle the effects of changes in precipitation and warming for a site in the Canadian High Arctic (63°30′N).Through an archetypal modeling approach for a site with limited field data, we use SUTRA 4.0 to simulate groundwater flow and energy transport with dynamic freeze-thaw processes. To assess active layer zone changes, we simulate a two-dimensional 280 m long hill underlain by continuous permafrost that terminates in a lake. The site has thin unconsolidated overburden on bedrock, with current depth to permafrost between 1.3 m and 2.2 m. We simulate four cases using downscaled CMIP5 projections: modern conditions, near climate (2020s), mid-climate (2050s), and far-climate projection (2080s). The climate projects show increasing annual mean temperatures, decreasing annual temperature amplitude, and increasing precipitation. The groundwater model results primarily focus on the groundwater flux to the lake, as it integrates the flows across the entire system. The results show that there will be increasing flows of groundwater to the lake due to climate change. Further, the increase in mean annual temperature (as opposed to increased precipitation) and associated annual development of the active zone is the primary control on groundwater flow through the system. With warming, the active zone deepens and opens for a longer period each year, allowing for more groundwater flow, particularly during snowmelt.Understanding active zone changes and groundwater in the Arctic allows us to better assess potential future hydrologic changes and discharge into northern lakes. The results from this study have implications for the potential transport and fate of anthropogenic and geogenic contaminants in Northern environments.

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