Ninth International Conference on Permafrost ... - IARC Research

Permafrost Dynamics and Landscape Changes in a Subarctic Peat Plateau,Northern SwedenA.B.K. SannelDepartment of Physical Geography and Quaternary Geology, Stockholm University, SwedenP. KuhryDepartment of Physical Geography and Quaternary Geology, Stockholm University, SwedenIntroductionPerennially frozen peatlands in subarctic regions aresensitive to a warming climate, since permafrost temperaturesare close to the 0°C mean annual isotherm. Few monitoringstudies have been performed of permafrost dynamics insubarctic peatlands because of their often remote location,the expensive logistics, and the harsh field conditions.Rapid and extensive permafrost thawing in bogs andmixed mires underlain by permafrost in northern Sweden hasbeen recorded by Christensen et al. (2004). Zuidhoff (2002)conclude that in palsas block erosion, thermokarst and winderosion are the most important degradational processesinvolved in the decay. Sollid & Sørbel (1974) found thatwhere frozen palsa plateaus are in direct contact with water,the permafrost core is undermined, causing cracks in thepeat. The peat then slips sideways, creating a steep erosionedge. This edge gradually works its way in towards thecentral part of the palsa.In a modeling study from Russia, Mazhitova et al. (2004)suggest a 20–30 cm deepening of the active layer in peatplateaus until 2080 as a result of future global warming. Itis not only the air temperature that affects the thaw depth;precipitation, snow depth, the ice content in the ground, andother hydrogeological conditions are also important factorsfor the active layer distribution (Oberman & Mazhitova2001). Long-term ecosystem monitoring is important forpredicting the behaviour of subarctic peatlands under theexpected future warmer and wetter climate conditions.Aim, Methods, and Study AreaThe main objective of this project is to study local climateand ground dynamics in a subarctic peat plateau/thermokarstlake complex in order to get a better understanding of howthese permafrost peatlands will respond to climate change.Which factors and mechanisms cause the collapse of peatplateaus into thermokarst lakes? Why does the erosion occuronly in certain parts of the peat plateau and along certainparts of the thermokarst lake shoreline? How sensitive arethese ecosystems to global warming? At the peat plateau/thermokarst lake complex in Tavvavuoma (68°28′N,20°54′E), northern Sweden, permafrost temperature andlandscape dynamics are studied through monitoring ofground temperatures, meteorological data, and snow depth(since 2005), and a time series analysis of aerial photographsand satellite images (from 1963 to 2003). On the peat plateau,snow depth and ground temperatures down to 2 m depth arerecorded at 9 different microsites; on the peat plateau, at theFigure 1. Map showing the location of thermistor cables and snowdepth stakes at the monitoring site in Tavvavuoma.eroding edge of the peat plateau, in the thermokarst lake, andin a nearby non-permafrost fen (Fig. 1, 2, 3). A 20 m deepborehole for ground temperature measurements is planned.Air temperature, precipitation, and wind data are recordedon top of the plateau. Snow depth is monitored by using astationary digital camera that records one image per day.Preliminary Results and DiscussionA comparison of panchromatic aerial photographs with arecent IKONOS image shows that, on a landscape level,major thermokarst drainage has occurred between 1963 and2003. Along the present thermokarst lake shorelines, fieldobservations show that erosion is active. Ground subsidenceof up to 11 cm in 2 years has been observed along theshoreline, whereas the central parts of the monitored peatplateau surface appear to remain stable. The monitoringdata are indicating that the permafrost in the peat plateau isthawing out, probably due to recent warming. On the central,dry peat plateau sites, the ground temperatures below 1 mdepth are just below 0°C, implying that the peat plateauwill be very sensitive to any further increase in temperature.Winter observations indicate very thin snow cover at thetop of the peat plateau compared to the edges and in thethermokarst depressions, showing the importance of snowdistribution for the permafrost (Fig. 4).265