ABSTRACT: Modern and Late-Holocene carbon dynamics in a permafrost peatland near Kuujjuarapik, Hudson Bay, Subarctic Québec.

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Abstract

In Canada, peatlands cover more than 1 million km2 and most of them are located in the boreal and subarctic regions. Important greenhouse gas exchanges take place in these ecosystems as they store 1/3 of the world soil carbon. Overall, carbon dioxide (CO2) is absorbed by the surface vegetation through photosynthesis and methane (CH4) is released through decomposition of organic matter under depleted oxygen conditions. In permafrosted peatlands, CO2 and CH4 exchanges are of smaller magnitude compared to boreal peatlands because the colder peat temperatures slow the bacteria activity. Therefore, peat accumulation- CO2 absorption and CH4 release are less important than in non-permafrosted environments. Recent climate scenarios predict that sub-arctic regions of Canada will face an important increase in mean annual temperature over the next century. In the Kuujjuarapik region, the expected warming rates range from 0.03 to 0.01oC/year. On the eastern side of James Bay some frozen peatlands havealready lost 25% over their permafrost coverage over the last 50 years (Vallée and Payette, 2007). Carbon (C) dynamics of these peatlands in the subarctic area will be greatly affected by the melting of this permafrost, as the created surface water table will affect the decomposition of the unfrozen organic components. In order to study the impacts of melting of the permafrost peatland on C dynamics, surface greenhouse gas exchanges were measured using static chambers (CO2 and CH4) and an Eddy covariance tower (CO2) in a degradating palsa field located 8 km south of Kuujjuarapik (55o13’36”N, 77o41’18”W). Peat/ice cores were collected to study Late-Holocene C dynamics using C/N ratios and 14C dating. Multi proxy data (isotopic O18 ofcellulose, macrofossils and Testate Amoebae) will be used to reconstruct past temperatures and related water table depth variations. This study will provide a better understanding of the present and past C dynamics of peatlands in order to predict the effect of climate change and rising temperature on future C dynamics from subarctic region.

Bibliography of Canadian Geomorphology