Saltwater Intrusion Intensifies Coastal Permafrost Thaw. Issue 19 (4th October 2021)

• Record Type: Journal Article
• Authors: Guimond, Julia A.; Mohammed, Aaron A.; Walvoord, Michelle A.; Bense, Victor F.; Kurylyk, Barret L.
• Is Part Of: Geophysical research letters. Volume 48:Issue 19(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-10-04
• Subjects: saltwater intrusion -- permafrost -- cryohydrogeology -- numerical model -- climate change; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL094776
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Surface effects of sea‐level rise (SLR) in permafrost regions are obvious where increasingly iceless seas erode and inundate coastlines. SLR also drives saltwater intrusion, but subsurface impacts on permafrost‐bound coastlines are unseen and unclear due to limited field data and the absence of models that include salinity‐dependent groundwater flow with solute exclusion and freeze‐thaw dynamics. Here, we develop a numerical model with the aforementioned processes to investigate climate change impacts on coastal permafrost. We find that SLR drives lateral permafrost thaw due to depressed freezing temperatures from saltwater intrusion, whereas warming drives top‐down thaw. Under high SLR and low warming scenarios, thaw driven by SLR exceeds warming‐driven thaw when normalized to the influenced surface area. Results highlight an overlooked feedback mechanism between SLR and permafrost thaw with potential implications for coastal infrastructure, ocean‐aquifer interactions, and carbon mobilization. Plain Language Summary: Along coastlines globally, sea‐level rise is causing saltwater to intrude into terrestrial environments and freshwater reservoirs (i.e., saltwater intrusion). The impact of saltwater intrusion on temperate and tropical environments has been extensively studied, but assessment of saltwater intrusion impacts on high‐latitude permafrost environments is lacking due to limited field data and appropriate models. This knowledge gap limits projections of climate change impacts to coastal Arctic ecosystems and communities. In this study, we develop and use a mathematical model that incorporates multiple, interrelated processes, including how salt content affects the freezing temperature of water, to evaluate the impacts of sea‐level rise and associated saltwater intrusion on coastal permafrost. Results show that sea‐level rise causes saltwater to intrude into the unfrozen pore space of permafrost. With a lower freezing temperature than freshwater, saltwater intrusion triggers permafrost thaw and lateral retreat. The combination of atmospheric and oceanic warming and sea‐level rise has the potential to drive extensive permafrost loss along Arctic coastlines. Key Points: Newly developed cryohydrogeological model incorporates salinity‐dependent freeze‐thaw processes and solute exclusion Subsurface saltwater intrusion drives lateral thaw of coastal ice‐saturated permafrost Combination of sea‐level rise and land surface warming results in extensive ice‐saturated permafrost loss