Auxiliary material for Paper 2010GB003813

Is the northern high latitude land-based CO2 sink weakening?


D. J. Hayes
Institute of Arctic Biology, University of Alaska Fairbanks, 
Fairbanks, Alaska, USA

A. D. McGuire 
U.S. Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, 
University of Alaska Fairbanks, Fairbanks, Alaska, USA

D. W. Kicklighter
The Ecosystems Center, Marine Biological Laboratory, 
Woods Hole, Massachusetts, USA

K. R. Gurney 
Department of Earth and Atmospheric Sciences, Purdue University, 
West Lafayette, Indiana, USA
 
T. J. Burnside
Institute of Arctic Biology, University of Alaska Fairbanks, 
Fairbanks, Alaska, USA

J. M. Melillo
The Ecosystems Center, Marine Biological Laboratory, 
Woods Hole, Massachusetts, USA
 
 
Hayes, D. J., A. D. McGuire, D. W. Kicklighter, K. R. Gurney, T. J. Burnside, and J. M. Melillo (2011), Is the northern high-latitude land-based CO2 sink weakening?, 
Global Biogeochem. Cycles, 25, GB3018, doi:10.1029/2010GB003813.

Introduction
In this supplementary section, we provide detail on the updates to model components and process representations related to the simulated fluxes analyzed in this study. 
To improve the simulation of terrestrial carbon dynamics including the influence of permafrost on these dynamics in high latitude ecosystems, several modifications have 
been implemented in version 6.0 of the Terrestrial Ecosystem Model (TEM). These modifications include: 1) changes in the representation of carbon stored in soil organic 
matter; 2) changes in the potential availability of soil organic matter to decomposition; 3) consideration of dissolved organic carbon (DOC) leaching losses; 4) changes 
in the simulated influence of temperature on plant maintenance respiration and decomposition; 5) changes in the estimation of gross primary production (GPP), which 
represents the uptake of atmospheric carbon dioxide associated with photosynthesis; and 6) the implementation of a dynamic cohort approach to incorporate the influence 
of disturbances and land use change on the landscape. We conclude with a discussion on model evaluation, where we summarize evidence from other studies on the performance 
of the model in representing ecosystem processes as site to regional scales.

2010gb003813-txts01.doc
Table S1. Parameters used in simulating soil organic carbon dynamics and nonsymbiotic nitrogen fixation.
Table S2. Parameters used to describe the influence of vegetation type and soil texture on rooting depth (m).
Table S3. Parameters used to describe the influence of temperature on respiration processes.
Figure S1.  Representation of carbon pools and fluxes in terrestrial ecosystems across various versions of TEM.  Carbon pools include vegetation carbon (CV), total soil 
organic carbon (CS), reactive soil organic carbon (CRS), nonreactive soil organic carbon (CNS) and dissoloved organic carbon (DOC).  Carbon fluxes include gross primary 
productivity (GPP), autotrophic respiration (RA), heterotrophic respiration (RH), production of DOC (DOCPROD) and leaching of DOC from the ecosystem (LCHDOC).  
Dashed boxes represent carbon pools not explicitly simulated by that version of TEM.
Figure S2. Idealized representation of the distribution of total soil organic carbon (dotted line) and reactive soil organic carbon (solid line) over a soil profile and 
its relationship to permafrost dynamics when the lability of soil organic matter decreases with depth .  Note that as the active layer increases (top layer of permafrost 
changes from dashed line to dash-dot-dot line), more soil organic carbon becomes exposed to decomposition and that a larger proportion of reactive soil organic carbon 
in the soil profile may be exposed earlier than indicated by the distribution of total soil organic carbon.  In this study, the distribution of reactive soil organic 
carbon is assumed to be the same as the distribution of total soil organic carbon across the soil profile. 
Figure S3.  Assumed relationship of maximum rooting depth to soil texture, as represented by proportion silt plus clay, for different vegetation types by TEM.