Abrupt thaw and the permafrost carbon feedback

• Main Author: Rodenhizer, Heidi Greimel
• Format: Thesis
• Language: English
• Published: 2022
• Subjects: QK Botany; Arctic; Ice; permafrost; Thermokarst; Tundra
• Online Access: https://openknowledge.nau.edu/id/eprint/5925/; https://openknowledge.nau.edu/id/eprint/5925/1/Rodenhizer_2022_abrupt_thaw_permafrost_carbon_feedback.pdf

Air temperatures in the Arctic are rising more than two times faster than the global average, and this is causing permafrost to thaw both gradually, with incremental increases in ALT, and abruptly, with rapid collapse of ice-rich permafrost ground forming discrete thermokarst features. When permafrost carbon that has been frozen for years to thousands of years thaws, it becomes susceptible to microbial respiration and release to the atmosphere as greenhouse gases. This depends, in part, on how much of the permafrost region will undergo abrupt thaw and how susceptible abruptly thawed permafrost carbon is to respiration, as hydrology can shift rapidly with abrupt thaw and lead to conditions more or less suited to plant growth, ecosystem respiration, and methanogenesis. This dissertation investigated the rate of ground subsidence and the impact it has on thawed permafrost carbon stocks, the extent and morphology of abrupt thaw in a warming tundra ecosystem and the role it plays in CO2 and CH4 release to the atmosphere at the landscape scale, and the fine scale responses of hydrology to abrupt thaw and how this determines the spatial heterogeneity of CO2 fluxes. In a permafrost warming experiment, subsidence of up to ~1 m per decade masked the full rate of permafrost thaw and was responsible for doubling the rate of carbon thaw. On the landscape as a whole, abrupt thaw covered 7% of the landscape, with the largest extent being due to water tracks. On an annual scale, abrupt thaw resulted in higher CO2 and CH4 release, although CO2 uptake was higher during the growing season. This highlights the importance of winter emissions in determining tundra carbon balance, particularly when and where abrupt thaw occurs. Additionally, abrupt thaw caused diverging hydrologic regimes, with the most deeply subsided regions becoming consistently wet and adjacent areas of high relief becoming intermittently dry and wet. Both growing season GPP and Reco were higher in intermittently dry and wet areas, while they were suppressed in ...