EGU2020-8790
https://doi.org/10.5194/egusphere-egu2020-8790
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Ground thermal variability and landscape dynamics in a northern Swedish permafrost peatland

A. Britta K. Sannel1,2
A. Britta K. Sannel
  • 1Department of Physical Geography, Stockholm University, Stockholm, Sweden (britta.sannel@natgeo.su.se)
  • 2Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden

Permafrost peatlands cover extensive areas in subarctic regions, and store large amounts of soil organic carbon that can be remobilized as active layer deepening and thermokarst formation is expected to increase in a future warmer climate. In northern Fennoscandia peatland initiation started soon after the last deglaciation, and throughout most of the Holocene the peatlands were permafrost-free fens. Colder conditions during the Little Ice Age resulted in epigenetic permafrost aggradation (Kjellman et al., 2018; Sannel et al., 2018). Today, these ecosystems are characterized by a complex mosaic of different landscape units including elevated peat plateaus and palsas uplifted above the surrounding wetlands by frost heave, and collapse features such as fens and thermokarst lakes formed as a result of ground-ice melt. This small-scale topographic variability makes the local hydrology, and possibly also the ground thermal regime very variable. In a peat plateau complex in Tavvavuoma, northern Sweden, ground temperatures and snow depth have been monitored within six different landscape units; on a peat plateau, in a depression within a peat plateau, along a peat plateau edge (close to a thermokarst lake), at a thermokarst lake shoreline, in lake sediments and in a fen. A thermal snapshot from 2007/08 shows that permafrost is present in all three peat plateau landscape units, and the mean annual ground temperature (MAGT) at 2 m depth is around -0.3 °C. In the three low-lying and saturated landscape units taliks are present and the MAGT at 1 m depth is 1.0-2.7 °C. Small-scale topographic variability is a key parameter for ground thermal patterns in this landscape affecting both local snow depth and soil moisture. Wind redistribution of snow creates a distinctive pattern with thin snow cover on elevated landforms and thicker cover in low-lying landscape units. Permafrost is present in peat plateaus where the mean December-April snow cover is shallow (<20 cm). In a small depression on the peat plateau permafrost exists despite a 60-80 cm mean December-April snow cover, but here the maximum annual ground temperature at 0.5 m depth is 8-9 °C warmer than in the surrounding peat plateau and the active layer is deeper (100-150 cm compared to 50-55 cm). In recent years, 2006-2019, the depression has experienced continued ground subsidence as a result of permafrost thaw, and the dominant vegetation has shifted from Sphagnum sp. to Cyperaceae. This transition could be the initial stage in collapse fen or thermokarst pond formation. In the same time period extensive block erosion and shoreline retreat has occurred along sections of the peat plateau edge where the mean December-April snow cover is deep (>80 cm). In a future warmer climate, permafrost thaw will have a continued impact on landscape changes, shifts in hydrology, vegetation and carbon exchange in this dynamic and climate-sensitive environment.

 

References

Kjellman, S.E. et al., 2018: Holocene development of subarctic permafrost peatlands in Finnmark, northern Norway. The Holocene 28, 1855–1869, doi:10.1177/0959683618798126.

Sannel, A.B.K. et al., 2018: Holocene development and permafrost history in sub-arctic peatlands in Tavvavuoma, northern Sweden. Boreas 47, 454–468, doi:10.1111/bor.12276.

How to cite: Sannel, A. B. K.: Ground thermal variability and landscape dynamics in a northern Swedish permafrost peatland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8790, https://doi.org/10.5194/egusphere-egu2020-8790, 2020

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Display material version 1 – uploaded on 24 Apr 2020
  • CC1: Comment on EGU2020-8790, Svetlana Selyanina, 04 May 2020

    What is the depth of the peat deposit in the study area?

    How was the depth of the active layer determined?

    Are there any visible differences in the degree of decomposition of peat? Were higher decomposition rates observed in the upper layers?

     

    • AC1: Reply to CC1, Britta Sannel, 04 May 2020

      In the peat plateau in Tavvavuoma the peat depth varies from around 0.5 to >2 m.

      The active layer (or rather the late-season thaw depth) was measured in late August or early September at three locations within 25 cm radius from each thermistor cable by probing a 1 m long steel rod into the ground until it reached the permafrost table. For more details, please see the open access paper published in Permafrost and Periglacial Processes (Sannel, 2020) - https://onlinelibrary.wiley.com/doi/10.1002/ppp.2045.

      The degree of decomposition in the peat is generally relative high in the top layers (0-20 cm) where there is a transition from fen peat below to rootlet peat close to the surface, representing a shift from non-permafrost to permafrost conditions at the site. For more information, please see Sannel et al. (2018) in Boreas.