The project was divided into four work packages (WP).
WP1 focused on the circumpolar mineral element content in the permafrost. We have collected data to build an estimate of the permafrost’s mineral element reservoir which is susceptible to rapidly respond to enhanced thawing. We have included regions of ice-rich permafrost (Yedoma-alas) sensitive to thermokarst processes, which 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) (Monhonval et al, Frontiers, 2021a; Monhonval et al PANGAEA, 2021; Monhonval et al, Frontiers, 2021b; Monhonval et al, Permafrost Periglacial Processes, 2022; Monhonval, under review in Geoderma a; Thomas et al, under review in Geoderma).
WP2 aimed 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 processes controlling mineral element release from the permafrost (Opfergelt, 2020; Monhonval et al, Frontiers, 2021b; Monhonval et al, Permafrost Periglacial Processes, 2022; Monhonval, under review in Geoderma b; Hirst et al Global Biogeochem Cycles, 2022).
WP3 focused on determining controls on the soil-to-plant transfer of mineral elements. We led field campaigns in Alaska and in Abisko to collect soil, plant, soil pore waters and river water samples at contrasted seasons: ice break-up, maximum thaw depth, and late shoulder season. Mineral element distribution in plants and soils were 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 (Mauclet et al, Biogeosciences, 2022; Villani et al, 2022; Mauclet et al, ESSD, 2022; Mauclet et al, under revisions in Geoderma).
WP4 aimed 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 was 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 was 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 (Hirst et al, Frontiers, 2020; Hirst et al Global Biogeochem Cycles 2022; Hirst et al, under review in Communications Earth & Environment).
Overall, the project has led four field missions in the Arctic (three in Alaska, one in Northern Sweden), and involved samples from more than 30 different sites in the major circum-Arctic regions (Siberia, Alaska, Canada, Greenland, Svalbard, Sweden). A major synthesis effort is ongoing with the Permafrost Carbon Network.
