Peter Thornton | Oak Ridge National Laboratory (original) (raw)

Papers by Peter Thornton

Journal of neurochemistry, 2006

Interleukin (IL)-1 expression is induced rapidly in response to diverse CNS insults and is a key ... more Interleukin (IL)-1 expression is induced rapidly in response to diverse CNS insults and is a key mediator of experimentally induced neuronal injury. However, the mechanisms of IL-1-induced neurotoxicity are unknown. The aim of the present study was to examine the toxic effects of IL-1 on rat cortical cell cultures. Treatment with IL-1beta did not affect the viability of pure cortical neurones. However, IL-1 treatment of cocultures of neurones with glia or purified astrocytes induced caspase activation resulting in neuronal death. Neuronal cell death induced by IL-1 was prevented by pre-treatment with the IL-1 receptor antagonist, the broad spectrum caspase inhibitor Boc-Asp-(OMe)-CH(2)F or the antioxidant alpha-tocopherol. The NMDA receptor antagonist dizolcipine (MK-801) attenuated cell death induced by low doses of IL-1beta but the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX) had no effect...

Global biogeochemical research must increasingly address the problems of "detection" or... more Global biogeochemical research must increasingly address the problems of "detection" or quantification of changing fluxes to the atmosphere, and "attribution" or explanation of those fluxes in terms of specific mechanisms. Today, neither our measurement nor analysis capabilities are sufficient to meet the twin challenges of biogeochemical detection and attribution with sufficient accuracy and resolution. We propose a summer school to

Ecosystems, 2002

We used a 10-year record (1990–99) of composited and cloud-screened reflectances from the Advance... more We used a 10-year record (1990–99) of composited and cloud-screened reflectances from the Advanced Very High Resolution Radiometer (AVHRR) to test for phenological differences between urban and rural areas in the eastern United States deciduous broadleaf forest (DBF). We hypothesized that well-documented urban heat island effects would be associated with alterations in temperature-sensitive vegetation phenology. Our objectives were thus (a)

The assimilation of terrestrial carbon, water and nutrient cycle measurements into land surface m... more The assimilation of terrestrial carbon, water and nutrient cycle measurements into land surface models of these processes is fundamental to improving our ability to predict how these ecosystems may respond to climate change. A combination of measurements and models, each with their own systematic biases, must be considered when constraining the nonlinear behavior of these coupled dynamics. As such, we

Summary A process-based, general ecosystem model (BI- OME--BGC) was used to simulate daily gross ... more Summary A process-based, general ecosystem model (BI- OME--BGC) was used to simulate daily gross primary produc- tion, maintenance and heterotrophic respiration, net primary production and net ecosystem carbon exchange of boreal as- pen, jack pine and black spruce stands. Model simulations of daily net carbon exchange of the ecosystem (NEE) explained 51.7% (SE = 1.32 g C m -2 day

Disturbance and management regimes in forested ecosystems have been recently highlighted as impor... more Disturbance and management regimes in forested ecosystems have been recently highlighted as important factors contributing to quantification of carbon stocks and fluxes. Disturbance events, such as stand-replacing fires and current management regimes that emphasize understory and tree thinning are primary suspects influencing ecosystem processes, including net ecosystem productivity (NEP) in forests of the Pacific Northwest. Several recent analyses have compared simulated to measured component stocks and fluxes of carbon in Ponderosa Pine (Pinus ponderosa var. Laws) at 12 sites ranging from 9 to 300 years in central Oregon (Law et al. 2001, Law et al. 2003) using the BIOME-BGC model. Major emphases on ecosystem model developments include improving allocation logic, integrating ecosystem processes with disturbance such as fire and including nitrogen in biogeochemical cycling. In Law et al. (2001, 2003), field observations prompted BIOME-BGC improvements including dynamic allocation o...

Journal of Physics: Conference Series, 2007

This paper describes the Carbon-Land Model Intercomparison Project (C-LAMP) being carried out thr... more This paper describes the Carbon-Land Model Intercomparison Project (C-LAMP) being carried out through a collaboration between the Community Climate System Model (CCSM) Biogeochemistry Working Group, a DOE SciDAC-2 project, and the DOE Program for Climate Model Diagnosis and Intercomparison (PCMDI). The goal of the project is to intercompare terrestrial biogeochemistry models running within the CCSM framework to determine the best set of processes to include in future versions of CCSM. As a part of the project, observational datasets are being collected and used to score the scientific performance of these models following a well-defined set of metrics. In addition, metadata standards for terrestrial biosphere models are being developed to support archival and distribution of the C-LAMP model output via the Earth System Grid (ESG). Progress toward completion of this project and preliminary results from the first set of experiments are reported.

Journal of Hydrometeorology, 2007

Although the global partitioning of evapotranspiration (ET) into transpiration, soil evaporation,... more Although the global partitioning of evapotranspiration (ET) into transpiration, soil evaporation, and canopy evaporation is not well known, most current land surface schemes and the few available observations indicate that transpiration is the dominant component on the global scale, followed by soil evaporation and canopy evaporation. The Community Land Model version 3 (CLM3), however, does not reflect this global view of ET partitioning, with soil evaporation and canopy evaporation far outweighing transpiration. One consequence of this unrealistic ET partitioning in CLM3 is that photosynthesis, which is linked to transpiration through stomatal conductance, is significantly underestimated on a global basis. A number of modifications to CLM3 vegetation and soil hydrology parameterizations are described that improve ET partitioning and reduce an apparent dry soil bias in CLM3. The modifications reduce canopy interception and evaporation, reduce soil moisture stress on transpiration, increase transpiration through a more realistic canopy integration scheme, reduce within-canopy soil evaporation, eliminate lateral drainage of soil water, increase infiltration of water into the soil, and increase the vertical redistribution of soil water. The partitioning of ET is improved, with notable increases seen in transpiration (13%-41% of global ET) and photosynthesis (65-148 Pg C yr Ϫ1 ). Soils are wetter and exhibit a far more distinct soil moisture annual cycle and greater interseasonal soil water storage, which permits plants to sustain transpiration through the dry season.

Journal of Hydrology, 1997

A method for generating daily surfaces of temperature, precipitation, humidity, and radiation ove... more A method for generating daily surfaces of temperature, precipitation, humidity, and radiation over large regions of complex terrain is presented. Required inputs include digital elevation data and observations of maximum temperature, minimum temperature and precipitation from ground-based meteorological stations. Our method is based on the spatial convolution of a truncated Gaussian weighting filter with the set of station locations. Sensitivity to the typical heterogeneous distribution of stations in complex terrain is accomplished with an iterative station density algorithm. Spatially and temporally explicit empirical analyses of the relationships of temperature and precipitation to elevation were performed, and the characteristic spatial and temporal scales of these relationships were explored. A daily precipitation occurrence algorithm is introduced, as a precursor to the prediction of daily precipitation amount. Surfaces of humidity (vapor pressure deficit) are generated as a function of the predicted daily minimum temperature and the predicted daily average daylight temperature. Daily surfaces of incident solar radiation are generated as a function of Sun-slope geometry and interpolated diurnal temperature range. The application of these methods is demonstrated over an area of approximately 400000 km 2 in the northwestern USA, for I year, including a detailed illustration of the parameterization process. A cross-validation analysis was performed, comparing predicted and observed daily and annual average values. Mean absolute errors (MAE) for predicted annual average maximum and minimum temperature were 0.7°C and 1.2°C, with biases of +0. loC and -0. loC, respectively. MAE for predicted annual total precipitation was 13.4 cm, or, expressed as a percentage of the observed annual totals, 19.3%. The success rate for predictions of daily precipitation occurrence was 83.3%. Particular attention was given to the predicted and observed relationships between precipitation frequency and intensity, and they were shown to be similar. We tested the sensitivity of these methods to prediction grid-point spacing, and found that areal averages were unchanged for grids ranging in spacing from 500 m to 32 km. We tested the dependence of the results on timestep, and found that the temperature prediction algorithms scale perfectly in this respect. Temporal scaling of precipitation predictions was complicated by the daily * Corresponding author. 0022-1694/97/$17.00 @ 1997-Elsevier Science B.V. All rights reserved PIl SOO22-1694(96)03128-9

Journal of Geophysical Research, 2008

1] The Community Land Model version 3 (CLM3) is the land component of the Community Climate Syste... more 1] The Community Land Model version 3 (CLM3) is the land component of the Community Climate System Model (CCSM). CLM3 has energy and water biases resulting from deficiencies in some of its canopy and soil parameterizations related to hydrological processes. Recent research by the community that utilizes CLM3 and the family of CCSM models has indicated several promising approaches to alleviating these biases. This paper describes the implementation of a selected set of these parameterizations and their effects on the simulated hydrological cycle. The modifications consist of surface data sets based on Moderate Resolution Imaging Spectroradiometer products, new parameterizations for canopy integration, canopy interception, frozen soil, soil water availability, and soil evaporation, a TOPMODEL-based model for surface and subsurface runoff, a groundwater model for determining water table depth, and the introduction of a factor to simulate nitrogen limitation on plant productivity. The results from a set of offline simulations were compared with observed data for runoff, river discharge, soil moisture, and total water storage to assess the performance of the new model (referred to as CLM3.5). CLM3.5 exhibits significant improvements in its partitioning of global evapotranspiration (ET) which result in wetter soils, less plant water stress, increased transpiration and photosynthesis, and an improved annual cycle of total water storage. Phase and amplitude of the runoff annual cycle is generally improved. Dramatic improvements in vegetation biogeography result when CLM3.5 is coupled to a dynamic global vegetation model. Lower than observed soil moisture variability in the rooting zone is noted as a remaining deficiency.

Journal of Geophysical Research, 2008

1] Predicting the global carbon and water cycle requires a realistic representation of vegetation... more 1] Predicting the global carbon and water cycle requires a realistic representation of vegetation phenology in climate models. However most prognostic phenology models are not yet suited for global applications, and diagnostic satellite data can be uncertain and lack predictive power. We present a framework for data assimilation of Fraction of Photosynthetically Active Radiation absorbed by vegetation (FPAR) and Leaf Area Index (LAI) from the MODerate Resolution Imaging Spectroradiometer (MODIS) to constrain empirical temperature, light, moisture and structural vegetation parameters of a prognostic phenology model. We find that data assimilation better constrains structural vegetation parameters than climate control parameters. Improvements are largest for drought-deciduous ecosystems where correlation of predicted versus satellite-observed FPAR and LAI increases from negative to 0.7-0.8. Data assimilation effectively overcomes the cloud-and aerosol-related deficiencies of satellite data sets in tropical areas. Validation with a 49-year-long phenology data set reveals that the temperature-driven start of season (SOS) is light limited in warm years. The model has substantial skill (R = 0.73) to reproduce SOS inter-annual and decadal variability. Predicted SOS shows a higher inter-annual variability with a negative bias of 5-20 days compared to species-level SOS. It is however accurate to within 1-2 days compared to SOS derived from net ecosystem exchange (NEE) measurements at a FLUXNET tower. The model only has weak skill to predict end of season (EOS). Use of remote sensing data assimilation for phenology model development is encouraged but validation should be extended with phenology data sets covering mediterranean, tropical and arctic ecosystems.

Journal of Climate, 2006

System Model (CCSM). This paper reports an analysis of the land component of these simulations. G... more System Model (CCSM). This paper reports an analysis of the land component of these simulations. Global annual averages over land appear to be within the uncertainty of observational datasets, but the seasonal cycle over land of temperature and precipitation appears to be too weak. These departures from observations appear to be primarily a consequence of deficiencies in the simulation of the atmospheric model rather than of the land processes. High latitudes of northern winter are biased sufficiently warm to have a significant impact on the simulated value of global land temperature. The precipitation is approximately doubled from what it should be at some locations, and the snowpack and spring runoff are also excessive. The winter precipitation over Tibet is larger than observed. About two-thirds of this precipitation is sublimated during the winter, but what remains still produces a snowpack that is very large compared to that observed with correspondingly excessive spring runoff. A large cold anomaly over the Sahara Desert and Sahel also appears to be a consequence of a large anomaly in downward longwave radiation; low column water vapor appears to be most responsible. The modeled precipitation over the Amazon basin is low compared to that observed, the soil becomes too dry, and the temperature is too warm during the dry season.

Global Change Biology, 2001

We compared carbon storage and¯uxes in young and old ponderosa pine stands in Oregon, including p... more We compared carbon storage and¯uxes in young and old ponderosa pine stands in Oregon, including plant and soil storage, net primary productivity, respiration uxes, eddy¯ux estimates of net ecosystem exchange (NEE), and Biome-BGC simulations of¯uxes. The young forest (Y site) was previously an old-growth ponderosa pine forest that had been clearcut in 1978, and the old forest (O site), which has never been logged, consists of two primary age classes (50 and 250 years old). Total ecosystem carbon content (vegetation, detritus and soil) of the O forest was about twice that of the Y site (21 vs. 10 kg C m ±2 ground), and signi®cantly more of the total is stored in living vegetation at the O site (61% vs. 15%). Ecosystem respiration (R e ) was higher at the O site (1014 vs. 835 g C m ±2 year ±1 ), and it was largely from soils at both sites (77% of R e ). The biological data show that above-ground net primary productivity (ANPP), NPP and net ecosystem production (NEP) were greater at the O site than the Y site. Monte Carlo estimates of NEP show that the young site is a source of CO 2 to the atmosphere, and is signi®cantly lower than NEP(O) by c. 100 g C m ±2 year ±1 . Eddy covariance measurements also show that the O site was a stronger sink for CO 2 than the Y site. Across a 15-km swath in the region, ANPP ranged from 76 g C m ±2 year ±1 at the Y site to 236 g C m ±2 year ±1 (overall mean 158 T 14 g C m ±2 year ±1 ). The lowest ANPP values were for the youngest and oldest stands, but there was a large range of ANPP for mature stands. Carbon, water and nitrogen cycle simulations with the Biome-BGC model suggest that disturbance type and frequency, time since disturbance, age-dependent changes in below-ground allocation, and increasing atmospheric concentration of CO 2 all exert signi®cant control on the net ecosystem exchange of carbon at the two sites. Model estimates of major carbon¯ux components agree with budget-based observations to within T 20%, with larger differences for NEP and for several storage terms. Simulations showed the period of regrowth required to replace carbon lost during and after a stand-replacing ®re (O) or a clearcut (Y) to be between 50 and 100 years. In both cases, simulations showed a shift from net carbon source to net sink (on an annual basis) 10±20 years after disturbance. These results suggest that the net ecosystem production of young stands may be low because heterotrophic respiration, particularly from soils, is higher than the NPP of the regrowth. The amount of carbon stored in long-term pools (biomass and soils) in addition to short-term¯uxes has important implications for management of forests in the Paci®c North-west for carbon sequestration.

Global Change Biology, 2009

Global Biogeochemical Cycles, 2007

1] Nutrient cycling affects carbon uptake by the terrestrial biosphere and imposes controls on ca... more 1] Nutrient cycling affects carbon uptake by the terrestrial biosphere and imposes controls on carbon cycle response to variation in temperature and precipitation, but nutrient cycling is ignored in most global coupled models of the carbon cycle and climate system. We demonstrate here that the inclusion of nutrient cycle dynamics, specifically the close coupling between carbon and nitrogen cycles, in a terrestrial biogeochemistry component of a global coupled climate system model leads to fundamentally altered behavior for several of the most critical feedback mechanisms operating between the land biosphere and the global climate system. Carbon-nitrogen cycle coupling reduces the simulated global terrestrial carbon uptake response to increasing atmospheric CO 2 concentration by 74%, relative to a carbon-only counterpart model. Global integrated responses of net land carbon exchange to variation in temperature and precipitation are significantly damped by carbon-nitrogen cycle coupling. The carbon cycle responses to temperature and precipitation variation are reduced in magnitude as atmospheric CO 2 concentration rises for the coupled carbon-nitrogen model, but increase in magnitude for the carbon-only counterpart. Our results suggest that previous carbon-only treatments of climate-carbon cycle coupling likely overestimate the terrestrial biosphere's capacity to ameliorate atmospheric CO 2 increases through direct fertilization. The next generation of coupled climate-biogeochemistry model projections for future atmospheric CO 2 concentration and climate change should include explicit, prognostic treatment of terrestrial carbon-nitrogen cycle coupling. Citation: Thornton, P. E., J.-F. Lamarque, N. A. Rosenbloom, and N. M. Mahowald (2007), Influence of carbon-nitrogen cycle coupling on land model response to CO 2 fertilization and climate variability, Global Biogeochem. Cycles, 21, GB4018,

Global Biogeochemical Cycles, 1997

Regional phenology is important in ecosystem simulation models and coupled biosphere/atmosphere m... more Regional phenology is important in ecosystem simulation models and coupled biosphere/atmosphere models. In the continental United States, the timing of the onset of greenness in the spring (leaf expansion, grass green-up) and offset of greenness in the fall (leaf abscission, cessation of height growth, grass brown-off) are strongly influenced by meteorological and climatological conditions. We developed predictive phenology models based on traditional phenology research using commonly available meteorological and climatological data. Predictions were compared with satellite phenology observations at numerous 20 km x 20 km contiguous landcover sites. Onset mean absolute error was 7.2 days in the deciduous broadleaf forest (DBF) biome and 6.1 days in the grassland biome. Offset mean absolute error was 5.3 days in the DBF biorne and 6.3 days in the grassland biome. Maximum expected errors at a 95% probability level ranged from 10 to 14 days. Onset was strongly associated with temperature summations in both grassland and DBF biomes; DBF offset was best predicted with a photoperiod function, while grassland offset required a combination of precipitation and temperature controls. A long-term regional test of the DBF onset model captured field-measured interannual variability trends in lilac phenology. Continental application of the phenology models for 1990-1992 revealed extensive interannual variability in onset and offset. Median continental growing season length ranged from a low of 129 days in 1991 to a high of 146 days in 1992. Potential uses of the models include regulation of the timing and length of the growing season in large-scale biogeochemical models and monitoring vegetation response to interannual climatic variability.

Global and Planetary Change, 1996

Results from the 14 land surface parameterization schemes involved in the PILPS-RICE Workshop are... more Results from the 14 land surface parameterization schemes involved in the PILPS-RICE Workshop are compared for a soya crop growing season (from June to September). During this period, the transpiration flux dominates the total surface evapotranspiration and observed data from HAPEX-MOBILHY are available for comparison. Results indicate that during the month of June half of the models fall within the uncertainty range of the observations.

Geophysical Research Letters, 2002

... In this context, results from this study show that recent changes in the hydrologic cycle int... more ... In this context, results from this study show that recent changes in the hydrologic cycle interacted positively with CO2 fertilization, con ... Barber, VA, GP Juday, and BP Finney, Reduced growth of Alaska white spruce in the twentieth century from temperature-induced drought stress ...

Ecosystems, 2003

This paper provides the first steps toward a regional-scale analysis of carbon (C) budgets. We ex... more This paper provides the first steps toward a regional-scale analysis of carbon (C) budgets. We explore the ability of the ecosystem model BIOME-BGC to estimate the daily and annual C dynamics of four European coniferous forests and shifts in these dynamics in response to changing environmental conditions. We estimate uncertainties in the model results that arise from incomplete knowledge of site management history (for example, successional stage of forest). These uncertainties are especially relevant in regional-scale simulations, because this type of information is difficult to obtain. Although the model predicted daily C and water fluxes reasonably well at all sites, it seemed to have a better predictive capacity for the photosynthesis-related processes than for respiration. Leaf area index (LAI) was modeled accurately at two sites but overestimated at two others (as a result of poor long-term climate drivers and uncertainties in model parameterization). The overestimation of LAI (and consequently gross photosynthetic production (GPP)), in combination with reasonable estimates of the daily net ecosystem productivity (NEP) of those forests, also illustrates the problem with modeled respiration. The model results suggest that all four European forests have been net sinks of C at the rate of 100 -300 gC/m 2 /y and that this C sequestration capacity would be 30%-70% lower without increasing nitrogen (N) deposition and carbon dioxide (CO 2 ) concentrations. The magnitude of the forest responses was dependent not only on the rate of changes in environmental factors, but also on sitespecific conditions such as climate and soil depth. We estimated that the modeled C exchange at the study sites was reduced by 50%-100% when model simulations were performed for climax forests rather than regrowing forests. The estimates of water fluxes were less sensitive to different initializations of state variables or environmental change scenarios than C fluxes.

Journal of neurochemistry, 2006

Ecosystems, 2002

Journal of Physics: Conference Series, 2007

Journal of Hydrometeorology, 2007

Journal of Hydrology, 1997

Journal of Geophysical Research, 2008

Journal of Climate, 2006

Global Change Biology, 2001

Global Change Biology, 2009

Global Biogeochemical Cycles, 2007

Global Biogeochemical Cycles, 1997

Global and Planetary Change, 1996

Geophysical Research Letters, 2002

Ecosystems, 2003