Ninth International Conference on Permafrost ... - IARC Research

Variable Peat Accumulation Rates in Stable Subarctic Peat Plateaus,West-Central CanadaA.B.K. SannelDepartment of Physical Geography and Quaternary Geology, Stockholm University, SwedenP. KuhryDepartment of Physical Geography and Quaternary Geology, Stockholm University, SwedenIntroductionPeatland ecosystems located in the boreal forest andtundra biomes contain a large and significant pool of soilorganic carbon. The carbon storage in boreal and subarcticpeat deposits is approximately 455 Pg C, representing onethirdof the total world pool of soil carbon (Gorham 1991).As a result of global warming, the highest increases intemperature are predicted to take place at high northernlatitudes. For most permafrost regions a reductionin permafrost area and an increase in thaw depth areexpected (ACIA 2004, IPCC 2007). Permafrost peatlandsare sensitive ecosystems expected to respond rapidly tochanges in climate. Since perennially frozen peatlands inthe sporadic and discontinuous permafrost zones are alreadynear thawing, they are most sensitive to climate changes(Tarnocai 2006). Climate warming may affect permafrostpeatlands in many ways: permafrost degradation, formationof thaw lakes, increased thaw depth, drier peat surfaces,changes in carbon accumulation, methane emissions, plantcommunities, hydrology, and fire frequency (e.g., Gorham1991, Zoltai 1995, ACIA 2004).An increased knowledge of permafrost conditions andcarbon accumulation rates in subarctic permafrost peatlandsthroughout the Holocene is important for understanding howthese ecosystems might respond to the predicted future climatechanges.Figure 1. Location of Selwyn Lake and Ennadai Lake, permafrostzonation, and ecoclimatic regions in west-central Canada. CPZ =continuous permafrost zone, DPZ = discontinuous permafrost zoneand SPZ = sporadic permafrost zone (after Zoltai 1995). LA = lowarctic, HS = high subarctic, LS = low subarctic, HBs = subhumidhigh boreal and MBs = subhumid mid-boreal ecoclimatic region(after Ecoregions Working Group 1989).Aim, Study Area, and MethodsThe aim of this study is to better understand the long-termcarbon dynamics in subarctic peat plateaus in relation tovegetation and permafrost conditions.Selwyn Lake and Ennadai Lake are located within the lowsubarctic ecoclimatic region in west-central Canada, wherethe climate is characterized by very cold winters and short,warm summers (Fig. 1).The peat profile SL1 (59º53′N, 104º12′W) was collected inthe discontinuous permafrost zone from a treed peat plateaubog calving into Selwyn Lake (Fig. 2). The peat profile EL1(60º50′N, 101º33′W) was collected in the continuous permafrostzone from a polygonal peat plateau on the western shoreof a small lake located 1 km west of Ennadai Lake (Fig. 3).In both peat profiles (SL1 and EL1), vegetation successionand high-resolution peat and carbon accumulation rateshave been studied through plant macrofossil analyses andextensive AMS radiocarbon dating. Bulk densities weremeasured throughout the profiles as well as carbon (C) andnitrogen (N) content.Figure 2. The collection site of peat profile SL1 at a forested peatplateau calving into Selwyn Lake (Photo: © P. Kuhry).Results and DiscussionPeat formation at the two sites began around 6600–5900cal yr BP, and permafrost conditions have prevailed inthe peat plateaus since permafrost aggradation occurredbetween 5600–4500 cal yr BP (Sannel & Kuhry in press).An important characteristic of these peat plateaus are thealternating layers of Sphagnum fuscum and rootlet peatlayers. Sphagnum stages represent slightly more moistsurface conditions than rootlet stages, which mainly containroots, Picea needles, and leaves from ericaceous shrubs. Thelong-term peat and carbon accumulation rates for both thestudied peat profiles are 0.30–0.31 mm/yr and 12.5–12.7267