ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-3773-2011 Magnitude and seasonality of wetland methane emissions from the Hudson Bay Lowlands (Canada) Pickett-Heaps C. A. 1 7 Jacob D. J. 1 Wecht K. J. 1 Kort E. A. 1 Wofsy S. C. 1 Diskin G. S. 2 Worthy D. E. J. 3 Kaplan J. O. 4 Bey I. 5 Drevet J. 6 School of Engineering and Applied Sciences & Department of Earth and Planetary Sciences, Harvard University, Cambridge MA 02138, USA NASA Langley Research Center, Hampton, Virginia, USA Environment Canada, Toronto, Ontario, Canada Environmental Engineering Institute, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland Center for Climate Systems Modeling (C2SM), ETH Zürich, Universitätstrasse 16, Zürich, Switzerland Laboratoire de Modélisation de Chimie Atmosphérique, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland current address: CSIRO – Marine and Atmospheric Research, GPO Box 3023, Canberra, ACT, 2601, Australia 27 04 2011 11 8 3773 3779 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/3773/2011/acp-11-3773-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/3773/2011/acp-11-3773-2011.pdf

The Hudson Bay Lowlands (HBL) is the second largest boreal wetland ecosystem in the world and an important natural source of global atmospheric methane. We quantify the HBL methane emissions by using the GEOS-Chem chemical transport model to simulate aircraft measurements over the HBL from the ARCTAS and pre-HIPPO campaigns in May–July 2008, together with continuous 2004–2008 surface observations at Fraserdale (southern edge of HBL) and Alert (Arctic background). The difference in methane concentrations between Fraserdale and Alert is shown to be a good indicator of HBL emissions, and implies a sharp seasonal onset of emissions in late May (consistent with the aircraft data), a peak in July–August, and a seasonal shut-off in September. The model, in which seasonal variation of emission is mainly driven by surface temperature, reproduces well the observations in summer but its seasonal shoulders are too broad. We suggest that this reflects the suppression of emissions by snow cover and greatly improve the model simulation by accounting for this effect. Our resulting best estimate for HBL methane emissions is 2.3 Tg a<sup>−1</sup>, several-fold higher than previous estimates (Roulet et al., 1994; Worthy et al., 2000).

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