Modelling Holocene carbon accumulation and methane emissions of boreal wetlands – an Earth system model approach

R J Schuldt,J Winderlich,V Brovkin,T Kleinen

doi:10.5194/bg-10-1659-2013

R J Schuldt, J Winderlich + Show 2 more

Open Access

https://doi.org/10.5194/bg-10-1659-2013

Copy DOI

Abstract

Abstract. Since the Last Glacial Maximum, boreal wetlands have accumulated substantial amounts of peat, estimated at 180–621 Pg of carbon. Wetlands have significantly affected the atmospheric greenhouse gas composition in the past and will play a significant role in future changes of atmospheric CO2 and CH4 concentrations. In order to investigate those changes with an Earth system model, biogeochemical processes in boreal wetlands need to be accounted for. Thus, a model of peat accumulation and decay was developed and included in the land surface model JSBACH of the Max Planck Institute Earth System Model (MPI-ESM). Here we present the evaluation of model results from 6000 yr BP to the pre-industrial period. Over this period of time, 240 Pg of peat carbon accumulated in the model in the areas north of 40° N. Simulated peat accumulation rates agree well with those reported for boreal wetlands. The model simulates CH4 emissions of 49.3 Tg CH4 yr−1 for 6000 yr BP and 51.5 Tg CH4 yr−1 for pre-industrial times. This is within the range of estimates in the literature, which range from 32 to 112 Tg CH4 yr−1 for boreal wetlands. The modelled methane emission for the West Siberian Lowlands and Hudson Bay Lowlands agree well with observations. The rising trend of methane emissions over the last 6000 yr is in agreement with measurements of Antarctic and Greenland ice cores.

Highlights

Several hotspots of CH4 emissions can be detected at 6000 yr BP, 3000 yr BP and pre-industrial (Fig. 7): the Hudson Bay Lowlands and Newfoundland, Eastern Europe and Finland, the West Siberian Lowlands and the Far East (Manchuria)
We analyzed the development of CH4 emissions in three sub-boreal regions to get a detailed picture of where the carbon emissions originate: (i) North America, (ii) Europe, and (iii) Asia, (Fig. 10, left; Table 3). (i) In the North American domain we find a small increase of the emissions around 3000 yr BP, which decline to the initial values in preindustrial times. (ii) In the Asian domain we find an increase of CH4 emissions from 6000 yr BP (10 Tg CH4 yr−1) to preindustrial times (11 Tg CH4 yr−1). (iii) In Europe there is an increase in CH4 emissions between 6000 and 4000 yr BP, followed by a stable phase until pre-industrial times
In a transient Holocene experiment, the model was driven by soil temperature, leaf area index (LAI), soil moisture, and net primary production (NPP) from Max Planck Institute Earth System Model (MPI-ESM) simulations by Fischer and Jungclaus (2011) and pre-industrial wetland fraction and water table levels from CLIMBER-LPJ simulations by Kleinen et al (2012)

Summary

Objectives

This study aims at the evaluation of the effect of boreal wetlands on climate through fluxes of CO2 and CH4 on millennial timescales, based on plausible peat accumulation patterns (Sect. 1)

Methods

Results

Discussion

Conclusion