PARENT SESSION
Oral Session #40: Carbon sequestration and flux.
Presiding: G. Koch
Tuesday, August 6. 1:00 PM to 4:45 PM. Gila Meeting Room, TCC.

Modeling the effects of soil thermal dynamics on the seasonality of carbon fluxes across northern temperate and high latitude regions.

Zhuang, Qianlai^*,1,2, Clein, Joy², McGuire, David³, Dargaville, Roger⁴, Romanovsky, Vladimir⁵, Harden, Jeniffer⁶, Kicklighter, David¹, Melillo, Jerry¹, ¹ The Ecosystems Center, Woods Hole, MA² The Institute of Arctic Biology, Fairbanks, AK³ U.S. Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, Fairbanks, AK⁴ Ecosystem Dynamics and the Atmosphere, Boulder, CO⁵ Geophysical Institute, Fairbanks, AK⁶ U.S. Geological Survey, Menlo park, CA

ABSTRACT- It is important to understand how soil thermal dynamics influences the seasonality of carbon fluxes of ecosystems in order to clarify the potential for ecosystems to act as a net source or sink of carbon in response to climate warming. To provide a tool for addressing this issue, the Terrestrial Ecosystem Model (TEM) was coupled to a soil thermal model (STM) and parameterized with observed soil thermal data for sites of the Long Term Ecological Research network in the United States. In addition to the influences of the soil thermal regime on below-ground ecosystem processes, the physical process of freeze/thaw simulated by the STM-TEM also influences the length of growing season. In this study, the STM-TEM was applied to simulate terrestrial carbon dynamics at the global scale from 1859 to 1995. The seasonal dynamics of net primary production (NPP), heterotrophic respiration (RH), and net ecosystem production (NEP) for the temperate region between latitudes 30^o to 60^o and for high latitudes between 60^o to 90^o N were compared with NPP, RH, and NEP simulated by previous versions of TEM. For the temperate region, NEP simulated by STM-TEM is similar from October to March, lower in April and May, and higher from June to September in comparison with previous simulations of TEM. For the high latitude region, simulated NEP by STM-TEM was similar to TEM from November to April, lower in May and June, higher in July and August, and lower in September and October. The seasonal patterns of NEP simulated by the STM-TEM in temperate and high latitude regions are similar to the seasonal patterns of net ecosystem exchange estimated from eddy covariance studies conducted in these regions. The seasonal carbon fluxes simulated by the STM-TEM and TEM were coupled with the Model of Atmospheric Transport and Chemistry (MATCH) to estimate atmospheric CO₂ concentrations at atmospheric chemistry monitoring stations. The comparison between the dynamics of simulated and observed CO₂ concentrations at the monitoring stations indicates that incorporation of the the effects of soil thermal dynamics on terrestrial ecosystem processes in STM-TEM substantially improves the ability of the model to simulate the seasonal dynamics of atmospheric CO₂.

KEY WORDS: Permafrost, carbon dynamics, CO2 concentration, seasonality of carbon dynamics