The importance of freeze–thaw cycles for lateral tracer transport in ice-wedge polygons

Elchin E Jafarov,Dylan Harp,Daniil Svyatsky,Brent Newman,Cathy Wilson,David Moulton

doi:10.5194/tc-16-851-2022

Elchin E Jafarov, Dylan Harp + Show 4 more

Open Access

https://doi.org/10.5194/tc-16-851-2022

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Abstract

Abstract. A significant portion of the Arctic coastal plain is classified as polygonal tundra and plays a vital role in soil carbon cycling. Recent research suggests that lateral transport of dissolved carbon could exceed vertical carbon releases to the atmosphere. However, the details of lateral subsurface flow in polygonal tundra have not been well studied. We incorporated a subsurface transport process into an existing state-of-the-art hydrothermal model. The model captures the physical effects of freeze–thaw cycles on lateral flow in polygonal tundra. The new modeling capability enables non-reactive tracer movement within subsurface. We utilized this new capability to investigate the impact of freeze–thaw cycles on lateral flow in the polygonal tundra. Our study indicates the important role of freeze–thaw cycles and the freeze-up effect in lateral tracer transport, suggesting that dissolved species could be transported from the middle of the polygon to the sides within a couple of thaw seasons. Introducing lateral carbon transport into the climate models could substantially reduce the uncertainty associated with the impact of thawing permafrost.

Highlights

Permafrost stores a vast amount of frozen carbon, which, once thawed, can be released into the atmosphere, amplifying current rates of global warming (McGuire et al, 2018)
Is the rate of carbon transport important for understanding fluxes to lakes and rivers, for example, but lateral transport conditions will affect how carbon is cycled along a flow path and what form that carbon might take
We developed a new subsurface transport capability in an existing thermal hydrology permafrost model to investigate the effect of freeze–thaw dynamics on the lateral transport of a non-reactive tracer in the polygonal tundra

Summary

Introduction

Permafrost stores a vast amount of frozen carbon, which, once thawed, can be released into the atmosphere, amplifying current rates of global warming (McGuire et al, 2018). A recent study by Plaza et al (2019) indicates that lateral subsurface flow can be responsible for more than half of the permafrost carbon loss, but many models only consider vertical transport. Is the rate of carbon transport important for understanding fluxes to lakes and rivers, for example, but lateral transport conditions will affect how carbon is cycled along a flow path and what form that carbon might take (e.g., carbon dioxide, methane, or dissolved organic carbon). A review by O’Donnell et al (2021) highlights several studies that demonstrate a variety of Arctic flow and transport conditions that affect dissolved organic carbon (DOC) and nutrients such as nitrogen and phosphorous. DOC compositions shift as lateral flow through mineral soils increases or mixing with deeper groundwater sources becomes more important.

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