Permafrost Formation in a Meandering River Floodplain

• Published in: AGU Advances
• Main Authors: Madison M. Douglas, Gen K. Li, A. Joshua West, Yutian Ke, Joel C. Rowland, Nathan Brown, Jon Schwenk, Preston C. Kemeny, Anastasia Piliouras, Woodward W. Fischer, Michael P. Lamb
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2024
• Subjects: alluvial deposits; radiocarbon dating; optically stimulated luminescence (OSL); vegetation; river migration; permafrost; Geology; QE1-996.5; Geophysics. Cosmic physics; QC801-809; Alaska
• Online Access: https://doi.org/10.1029/2024AV001175; https://doaj.org/article/3756bf5983b54c76a6542745cf03e507

Abstract Permafrost influences 25% of land in the Northern Hemisphere, where it stabilizes the ground beneath communities and infrastructure and sequesters carbon. However, the coevolution of permafrost, river dynamics, and vegetation in Arctic environments remains poorly understood. As rivers meander, they erode the floodplain at cutbanks and build new land through bar deposition, creating sequences of landforms with distinct formation ages. Here we mapped these sequences along the Koyukuk River floodplain, Alaska, analyzing permafrost occurrence, and landform and vegetation types. We used radiocarbon and optically stimulated luminescence (OSL) dating to develop a floodplain age map. Deposit ages ranged from modern to 10 ka, with more younger deposits near the modern channel. Permafrost rapidly reached 50% areal extent in all deposits older than 200 years then gradually increased up to ∼85% extent for deposits greater than 4 Kyr old. Permafrost extent correlated with increases in black spruce and wetland abundance, as well as increases in permafrost extent within wetland, and shrub and scrub vegetation classes. We developed an inverse model to constrain permafrost formation rate as a function of air temperature. Permafrost extent initially increased by ∼25% per century, in pace with vegetation succession, before decelerating to <10% per millennia as insulating overbank mud and moss slowly accumulated. Modern permafrost extent on the Koyukuk floodplain therefore reflects a dynamic balance between widespread, time‐varying permafrost formation and rapid, localized degradation due to cutbank erosion that might trigger a rapid loss of permafrost with climatic warming.