Impact of an abrupt cooling event on interglacial methane emissions in northern peatlands

Abstract

Rapid changes in atmospheric methane (CH₄), temperature and precipitation are documented by Greenland ice core data both for glacial times (the so called Dansgaard-Oeschger (D-O) events) as well as for a cooling event in the early Holocene (the 8.2 kyr event). The onsets of D-O warm events are paralleled by abrupt increases in CH₄ by up to 250 ppb in a few decades. Vice versa, the 8.2 kyr event is accompanied by an intermittent decrease in CH₄ of about 80 ppb over 150 yr. The abrupt CH₄ changes are thought to mainly originate from source emission variations in tropical and boreal wet ecosystems, but complex process oriented bottom-up model estimates of the changes in these ecosystems during rapid climate changes are still missing. Here we present simulations of CH₄ emissions from northern peatlands with the LPJ-Bern dynamic global vegetation model. The model represents CH₄ production and oxidation in soils and transport by ebullition, through plant aerenchyma, and by diffusion. Parameters are tuned to represent site emission data as well as inversion-based estimates of northern wetland emissions. The model is forced with climate input data from freshwater hosing experiments using the NCAR CSM1.4 climate model to simulate an abrupt cooling event. A concentration reduction of ~10 ppb is simulated per degree K change of mean northern hemispheric surface temperature in peatlands. Peatland emissions are equally sensitive to both changes in temperature and in precipitation. If simulated changes are taken as an analogy to the 8.2 kyr event, boreal peatland emissions alone could only explain 23% of the 80 ppb decline in atmospheric methane concentration. This points to a significant contribution to source changes from low latitude and tropical wetlands to this event

Present state of global wetland extent and wetland methane modelling: methodology of a model inter-comparison project (WETCHIMP)

“…LPJ-Bern is a subsequent development of the Lund-PotsdamJena dynamic global vegetation model Joos et al, 2004;Gerber et al, 2003) that combines processbased, large-scale representations of terrestrial vegetation dynamics, soil hydrology (Gerten et al, 2004;Wania et al, 2009a), human induced land use changes (Strassmann et al, 2008;Stocker et al, 2011), permafrost and peatland establishment (Wania et al, 2009a,b) and simulation of biogeochemical trace gas emissions, such as CH 4 (Wania et al, 2010;Spahni et al, 2011;Zürcher et al, 2013). LPJ-Bern uses a different ebullition mechanism for CH 4 emissions from peatlands, which includes variations in partial pressure of CO 2 .…”

Transient simulations of the carbon and nitrogen dynamics in northern peatlands: from the Last Glacial Maximum to the 21st century

“…This dynamic global vegetation model also predicts the release and uptake of the trace gases CO 2 , nitrous oxide (N 2 O; Xu-Ri and Prentice, 2008;Xu-Ri et al, 2012;Stocker et al, 2013) and methane (CH 4 ; Wania et al, 2010;Spahni et al, 2011;Zürcher et al, 2013). The model version applied here uses a vertically resolved soil hydrology, heat diffusion and an interactive thawing-freezing scheme (Gerten et al, 2004;Wania et al, 2009a).…”

Methane emissions from floodplains in the Amazon Basin: challenges in developing a process-based model for global applications

“…In LPX, natural wetland CH 4 emissions are computed for different classes of wetlands: boreal peatland, inundated wetland and wet mineral soils. Originally, for peatland CH 4 emissions, an additional scaling factor was used to account for the peatland microtopography (see Wania et al, 2010;Zürcher et al, 2013). In the present study, such a scaling procedure is not used for tropical floodplains (see Sect.…”