Skip to main content

Mineral Weathering in Thawing Permafrost: Causes and Consequences

Periodic Reporting for period 2 - WeThaw (Mineral Weathering in Thawing Permafrost: Causes and Consequences)

Reporting period: 2019-03-01 to 2020-08-31

Enhanced thawing of the permafrost in response to warming of the Earth’s high latitude regions exposes previously frozen soil organic carbon (SOC) to microbial decomposition, liberating carbon to the atmosphere and creating a dangerous positive feedback on climate warming. Thawing the permafrost may also unlock a cascade of mineral weathering reactions. These will be accompanied by mineral nutrient release and generation of reactive surfaces which will influence plant growth, microbial SOC degradation and SOC stabilization. Arguably, weathering is an important but hitherto neglected component for correctly assessing and predicting the permafrost carbon feedback. The goal of WeThaw is to provide the first comprehensive assessment of the mineral weathering response in permafrost regions subject to thawing. By addressing this crucial knowledge gap, WeThaw will significantly augment our capacity to develop models that can accurately predict the permafrost carbon feedback.

Specifically, the objectives are to provide the first estimate of the permafrost’s mineral element reservoir which is susceptible to rapidly respond to enhanced thawing, and to assess the impact of thawing on the soil nutrient storage capacity. To determine the impact of increased mineral weathering on mineral nutrient availability in terrestrial and aquatic ecosystems in permafrost regions, the abiotic and biotic sources and processes controlling their uptake and release are unraveled by combining isotope geochemistry with soil mineral and physico-chemical characterizations. This frontier research which crosses disciplinary boundaries between cryospheric science, soil science and isotope geochemistry is a mandatory step for being able to robustly explain the role of mineral weathering in modulating the permafrost carbon feedback.
The project is divided into four work packages (WP).
WP1 focuses on the circumpolar mineral element content in the permafrost. We collect data to build an estimate of the permafrost’s mineral element reservoir which is susceptible to rapidly respond to enhanced thawing. We include regions of ice-rich permafrost (Yedoma-alas) sensitive to thermokarst processed, a process that may affect one third of the Arctic by the end of the century. Our database contains data for permafrost soil samples from major circum-Arctic regions (Siberia, Alaska, Canada, Greenland, Svalbard).
WP2 aims at determining controls on mineral element release from the permafrost. We collected permafrost characteristics in areas characterized by abrupt thaw and gradual thaw in order to develop a better understanding of the controls on mineral element release upon thawing. We combine information from lab thaw experiments in controlled conditions and field thaw experiment to determine the parameters controlling the soil pore water chemistry. We use isotope geochemistry on sediments, soils, plants, river waters, and soil pore waters from permafrost regions to trace sources and processed controlling mineral element release from the permafrost.
WP3 focuses on determining controls on the soil-to-plant transfer of mineral elements. We led two field campaigns in Alaska to collect soil, plant and river water samples at two contrasted seasons: ice break-up and maximum thaw depth. Mineral element distribution in plants and soils are measured. The main vegetation types (sedge, forb, shrub deciduous and evergreen, moss, lichen) have been included in order to evaluate the influence of vegetation shift onto mineral nutrient cycling.
WP4 aims at determining seasonal controls on the mineral element transfer to rivers in polar regions. In the Arctic, the seasonal variation of water chemistry and isotope compositions of a headwater stream from Alaska is analyzed and related with soil processes upon thawing. And the variation of a larger river chemistry associated with a rain event in a thermokarst area is investigated in Greenland. In Antarctica, seasonal Si isotope variations in rivers from McMurdo Dry valleys have been shown to depend on the influence of mineral weathering.
The project is building knowledge beyond the state of the art regarding:
- Database of the mineral element content in the permafrost
- Understanding the seasonal response of mineral element transfer in permafrost environment upon thawing
- Integrated landscape scale understanding of the mineral element transfer along the soil-vegetation-river continuum in permafrost regions
- Advanced isotope techniques to trace environmental processes in polar regions