FILE NAME: TEM00-snowpack.doc YEARS: NA PI: A. Dave McGuire OTHERS: J. Clein, M. Heimann, D. Kicklighter, R. Meier, J. Melillo, W. Parton, J. Randerson, W. Sauf MANUSCRIPT TITLE: Modeling the effects of snowpack on heterotrophic respiration across northern temperate and high latitude regions: Comparison with measurements of atmospheric carbon dioxide in high latitudes (see full citation below). BRIEF DESCRIPTION: This data set contains the model output data of TEM, Century, and Carnegie-Ames-Stanford Approach (CASA) simulations for the terrestrial biosphere of the globe. RESEARCH LOCATION: The terrestrial biosphere of the globe. METHODS: In this study we conducted two simulations each of three terrestrial biogeochemical models (TBMs) to evaluate how a representation of the insulative effects of snowpack influences the seasonal cycle of atmospheric CO2 at high latitude monitoring stations in comparison to the baseline version of each model. For the snowpack version of each model, we modified the RH formulation in the baseline version so that temperature is maintained at 0o C when modeled snowpack is present. For each simulation in this study, monthly NPP, RH, and NEP is estimated for each 0.5o grid cell of the terrestrial biosphere. The spatially explicit monthly NEP estimates are combined with equivalent CO2 flux fields generated by an ocean biogeochemical model, and fossil fuel source fields; monthly CO2 emission fields from fossil fuel burning and cement manufacture are computed based on a global 1o X 1o map compiled by Marland et al. (1989) assuming constant emissions throughout the year. The terrestrial, oceanic, and fossil fuel fields of CO2 fluxes provide the lower boundary condition for a three-dimensional atmospheric transport model forced by observed winds. To evaluate the simulation of atmospheric CO2 concentrations, we extracted the monthly estimates of atmospheric CO2 from locations corresponding to monitoring stations and compared the estimates with the detrended observations at each station. MODEL NAME(S): CASA as described in Randerson et al. (1996); Century, version 4.0, as described in Parton et al. (1993); TEM, version 4.1, in which the formulations for autotrophic and heterotrophic respiration have been modified from earlier versions as described in McGuire et al. (1997) and Tian et al. (1999). MODEL INPUT: The data sets used as driving variables for each model are the same as used in the "Potsdam 95" comparison of NPP among global TBMs (Cramer et al. 1999). CASA: The CASA model calculates NPP from satellite-derived photosynthetically active radiation using a light use efficiency model (Field et al., 1995, 1998). For each monthly time step, a globally uniform maximum light use efficiency (?*) is reduced by temperature and soil moisture stress scalars that reflect local environmental conditions. The calibration process involves adjusting ?* to minimize the difference between observed and modeled NPP estimates across a number of sites worldwide. Simulated NPP in CASA is allocated to three living biomass pools, which include leaves, fine roots, and wood (Thompson et al., 1996). Biomass is delivered to the soil as leaf litterfall, coarse woody debris, and fine root turnover (Randerson et al., 1996). Transformations of soil organic matter are represented following the structure of the Century model, with a suite of active and slow organic matter fractions (Parton et al., 1993). In the version of CASA used in this study, the ratio of carbon to nitrogen in leaf litterfall is held constant for each biome type (Randerson et al., 1996). A Q10 of 1.5 is used to describe the response of microbial activity to surface air temperature (Raich and Potter, 1995). CENTURY: The Century model uses information on climate, atmospheric CO2, and nitrogen inputs to estimate the monthly fluxes and pools of carbon and nitrogen in terrestrial ecosystems (Parton et al., 1987, 1993). In this study, we applied version 4.0 of Century, which is described by Parton et al. (1993). In Century, maximum plant production is controlled by soil temperature, available water, and leaf area. A temperature-production function is specified according to plant functional types, such as C3 cool season plants or C4 warm season plants. Production is further modified by the current amount of aboveground plant material (i.e., self-shading), atmospheric CO2 concentrations, and available soil nitrogen. To simulate savanna and shrubland ecosystems, grass and forest components compete for water, light, and nutrients in a prescribed manner. Simulated NPP in Century is allocated to eight vegetation pools. Tissues that senescence from the vegetation pools of Century enter the soil as plant residues. The Century model simulates the decomposition of plant residues with a detailed submodel (13 pools) that divides soil organic carbon into three fractions: an active soil fraction (< 10-year turnover time) consisting of live microbes and microbial products; a protected fraction (decadal turnover time) that is more resistant to decomposition as a result of physical or chemical protection; and a fraction that has a very long turnover time (millenial turnover time). The decomposition of each soil organic fraction is calculated at a monthly time step as a function of the soil organic carbon in the fraction, air temperature, and soil moisture. A Q10 of approximately 1.6 is used to describe the response of microbial activity to surface air temperature. TEM: The TEM is a highly aggregated TBM that uses spatially referenced information on climate, elevation, soils, and vegetation to make monthly estimates of important carbon and nitrogen fluxes and pool sizes in the global terrestrial biosphere. In this study we applied version 4.1 of TEM, in which the formulations for autotrophic and heterotrophic respiration have been modified from earlier versions as described in McGuire et al. (1997) and Tian et al. (1999). In TEM, NPP is the difference between carbon captured from the atmosphere as gross primary production (GPP) and carbon respired to the atmosphere by the vegetation. Monthly GPP is initially calculated in TEM as a function of photosynthetically active radiation, air temperature, atmospheric carbon dioxide concentration, and moisture availability. If nitrogen supply, which is the sum of nitrogen uptake and labile nitrogen in the vegetation, cannot meet the stoichiometric carbon to nitrogen ratio of biomass production, then GPP is reduced to meet the constraint. In the case where nitrogen supply does not limit biomass production, nitrogen uptake is reduced so that nitrogen supply meets the constraint of biomass production. In this way, the carbon-nitrogen status of the vegetation causes the model to allocate more effort toward either carbon or nitrogen uptake (McGuire et al., 1992). Plant respiration, which includes growth and maintenance respiration, is a function of GPP, vegetation carbon, and surface air temperature. Biomass is delivered to the soil as litter production, which is calculated as a linear function of vegetation carbon (Raich et al., 1991). In TEM, the flux RH represents decomposition of all organic matter in an ecosystem and is calculated at a monthly time step as a function of one soil organic carbon compartment, air temperature, and soil moisture. Although the model does not track separate pools of soil organic matter, the formulations in the model implicitly consider issues of organic matter quality and turnover (McGuire et al., 1995, 1997). A Q10 of 2.0 is used to describe the response of microbial activity to surface air temperature (Raich et al., 1991). CONDITIONS FOR USE: Acceptance and utilization of this data requires that: The Principal Investigator is sent a notice stating reasons for acquiring any data and a description of the publication intentions. The Principal Investigator of the data set be sent a copy of the report or manuscript prior to submission and be adequately cited in any resultant publications. A copy of any resultant publications should be sent to: A Dave McGuire 216 Irving I Building University of Alaska Fairbanks Fairbanks, AK 99775 VARIABLE DESCRIPTION: Variable name Variable description Units -------------------------------------------------------------------------------- --------------------------------------------------------------------- NPP Net Primary Production g C m-2 yr-1 RH Heterotrophic Respiration g C m-2 yr-1 FOR MORE INFORMATION, CONTACT: A Dave McGuire 216 Irving I Building, University of Alaska Fairbanks Fairbanks, AK 99775 Email: ffadm@uaf.edu FILES: File Name: CASABASE00-NPP.dat File Type: Comma-delimited ASCII File Name: CASABASE00-RH.dat File Type: Comma-delimited ASCII File Name: CASASNOW00-NPP.dat File Type: Comma-delimited ASCII File Name: CASASNOW00-RH.dat File Type: Comma-delimited ASCII File Name: CENBASE00-NPP.dat File Type: Comma-delimited ASCII File Name: CENBASE00-RH.dat File Type: Comma-delimited ASCII File Name: CENSNOW00-NPP.dat File Type: Comma-delimited ASCII File Name: CENSNOW00-RH.dat File Type: Comma-delimited ASCII File Name: TEMBASE00-NPP.dat File Type: Comma-delimited ASCII File Name: TEMBASE00-RH.dat File Type: Comma-delimited ASCII File Name: TEMSNOW00-NPP.dat File Type: Comma-delimited ASCII File Name: TEMSNOW00-RH.dat File Type: Comma-delimited ASCII FILE FORMAT: CASA: longitude, latitude, variable, veg type, NA*, NA*, NA*, cell area, NA*, sum, max, mean, min, jan, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec, continent/country CENTURY: longitude, latitude, variable, veg type, NA*, NA*, NA*, cell area, NA*, sum, max, mean, min, jan, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec, continent/country TEM: longitude, latitude, variable, veg type, NA*, NA*, NA*, cell area, NA*, sum, max, mean, min, jan, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec, continent/country NA* = not used All monthly values: CASA, TEM and Century - 1 decimal place, excluding the mean, which has 2 decimal places NUMBER OF RECORDS: CASABASE and CASASNOW: 58,224; CenturyBASE: 53,455, CenturySNOW: 53,406; TEMBASE and TEMSNOW: 62,483. (per file) REFERENCE CITATIONS: Cramer W, Kicklighter DW, Bondeau A, Moore B III, Churkina G, Nemry B, Ruimy A, Schloss A, participants of "Potsdam 95" (1999) Comparing global models of terrestrial net primary production (NPP): Overview and key results. Global Change Biology. In press. Field CB, Randerson JT & Malmstrom CM (1995) Ecosystem net primary production: Combining ecology and remote sensing. Remote sensing of Environment 51:74-88. Field CB, Berenfeld MJ, Randerson JT & Falkowski P (1998) Primary production of the biosphere: Integrating terrestrial and oceanic components. Science 281:237-240. Marland G., Boden TA, Griffin RC, Huang SF, Kanciruk P, Nelson TR (1989) Estimates of CO2 Emissions from Fossil Fuel Burning and Cement Manufacturing, Based on the U.S. Bureau of Mines Cement Manufacturing Data. ORNL/CDIAC-25, NDP-030, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, USA. 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Randerson JT, Thompson MV, Malmstrom MV, Field CB & Fung IY (1996) Substrate limitation for heterotrophs: Implications for models that estimate the seasonal cycle of atmospheric CO2. Global Biogeochemical Cycles 10:585-602. Thompson MV, Randerson JT, Malmstrom CM & Field CB (1996) Change in net primary production and heterotrophic respiration: How much is necessary to sustain the terrestrial carbon sink? Global Biogeochemical Cycles 10:711-726. Tian, H, Melillo JM, Kicklighter DW, McGuire AD (1999) The sensitivity of terrestrial carbon storage to historical atmospheric CO2 and climate variability in the United States. Tellus. In press. ACKNOWLEDGEMENTS: This research was supported by funds from the ARCSS Program of NSF as a Synthesis, Integration, and Modeling Study (SIMS: OPP-9614253).