Atmospheric Chemistry and Physics
www.atmos-chem-phys.net
1680-7316
1680-7324
6
11
2006
10.5194/acp-6-3423-2006
http://www.atmos-chem-phys.net/6/3423/2006/
http://www.atmos-chem-phys.net/6/3423/2006/acp-6-3423-2006.html
http://www.atmos-chem-phys.net/6/3423/2006/acp-6-3423-2006.pdf
3423
3441
2006-08-21
Interannual variability in global biomass burning emissions from 1997 to 2004
G. R. van der Werf
guido.van.der.werf@falw.vu.nl
J. T. Randerson
L. Giglio
G. J. Collatz
P. S. Kasibhatla
A. F. Arellano Jr.
Department of Hydrology and Geo-Environmental Sciences, Faculty of Earth and Life Sciences, Vrije Universiteit, Amsterdam, Netherlands
Department of Earth System Science, University of California, Irvine, California, USA
Science Systems and Applications, Inc., NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Nicholas School of the Environment and Earth Sciences, Duke University, Durham, North Carolina, USA
now at: National Center for Atmospheric Research, Boulder, Colorado, USA
Biomass burning represents an important source of atmospheric aerosols and
greenhouse gases, yet little is known about its interannual variability or
the underlying mechanisms regulating this variability at continental to
global scales. Here we investigated fire emissions during the 8 year period
from 1997 to 2004 using satellite data and the CASA biogeochemical model.
Burned area from 2001–2004 was derived using newly available active fire and
500 m. burned area datasets from MODIS following the approach described by
Giglio et al. (2006). ATSR and VIRS satellite data were used to extend the
burned area time series back in time through 1997. In our analysis we
estimated fuel loads, including organic soil layer and peatland fuels, and
the net flux from terrestrial ecosystems as the balance between net primary
production (NPP), heterotrophic respiration (<i>R<sub>h</sub></i>), and biomass burning,
using time varying inputs of precipitation (PPT), temperature, solar
radiation, and satellite-derived fractional absorbed photosynthetically
active radiation (fAPAR). For the 1997–2004 period, we found that on
average approximately 58 Pg C year<sup>−1</sup> was fixed by plants as NPP, and
approximately 95% of this was returned back to the atmosphere via
<i>R<sub>h</sub></i>. Another 4%, or 2.5 Pg C year<sup>−1</sup> was emitted by biomass
burning; the remainder consisted of losses from fuel wood collection and
subsequent burning. At a global scale, burned area and total fire emissions
were largely decoupled from year to year. Total carbon emissions tracked
burning in forested areas (including deforestation fires in the tropics),
whereas burned area was largely controlled by savanna fires that responded
to different environmental and human factors. Biomass burning emissions
showed large interannual variability with a range of more than 1 Pg C year<sup>−1</sup>,
with a maximum in 1998 (3.2 Pg C year<sup>−1</sup>) and a minimum in
2000 (2.0 Pg C year<sup>−1</sup>).
Adler, R. F., Huffman, G. J., Chang, A., Ferraro, R., Xie, P. P., Janowiak, J., Rudolf, B., Schneider, U., Curtis, S., Bolvin, D., Gruber, A., Susskind, J., Arkin, P., and Nelkin, E.: The version-2 global precipitation climatology project (GPCP) monthly precipitation analysis (1979–present), J. Hydrometeorol., 4, 1147–1167, 2003.
Amiro, B. D., Todd, J. B., Wotton, B. M., Logan, K. A., Flannigan, M. D., Stocks, B. J., Mason, J. A., Martell, D. L., and Hirsch, K. G.: Direct carbon emissions from Canadian forest fires, 1959–1999, Canadian J. Forest Res., 31, 512–525, 2001.
Andreae, M. O. and Merlet, P.: Emission of trace gases and aerosols from biomass burning, Global Biogeochem. Cycles, 15, 955–966, 2001.
Arellano, A. F., Kasibhatla, P. S., Giglio, L., van der Werf, G. R., and Randerson, J. T.: Topdown estimates of global CO sources using MOPITT measurements, Geophys. Res. Lett., 31, L01104, doi:10.1029/2003GL018609, 2004.
Arellano, A. F., Kasibhatla, P. S., Giglio, L., van der Werf, G. R., Randerson, J. T., and Collatz, G. J.:, Time-dependent inversion estimates of global biomass-burning CO emissions using Measurement of Pollution in the Troposphere (MOPITT) measurements, J. Geophys. Res., 111, D09303, doi:10.1029/2005JD006613, 2006.
Arino, O., Rosaz, J.-M., and Goloub, P.: The ATSR World Fire Atlas. A synergy with "Polder" aerosol products, Earth Obs. Quarterly, 1–6, 1999.
Bacastow, R. B.: Modulation of atmospheric carbon-dioxide by Southern Oscillation, Nature, 15 261, 116–118, 1976.
Balzter, H., Gerard, F. F., George, C. T., Rowland, C. S., Jupp, T. E., McCallum, I., Shvidenko, A., Nilsson, S., Sukhinin, A., Onuchin, A., and Schmullius, C.: Impact of the Arctic Oscillation pattern on interannual forest fire variability in Central Siberia, Geophys. Res. Lett., 32, L14709, doi:10.1029/2005GL022526, 2005.
Barbosa, P. M., Stroppiana, D., Grégoire, J. M., and Pereira, J. M. C.: An assessment of vegetation fire in Africa (1981–1991): Burned areas, burned biomass, and atmospheric emissions, Global Biogeochem. Cycles , 13, 933–950, 1999.
Batjes, N. H.: Total carbon and nitrogen in the soils of the world, Eur. J. Soil Sci., 47, 151–163, 1996.
Battle, M., Bender, M. L., Tans, P. P., White, J. W. C., Ellis, J. T., Conway, T., and Francey, R. J.: Global carbon sinks and their variability inferred from atmospheric O-2 and delta C-13, Science, 287, 2467–2470, 2000.
Bishop, J. K. B. and Rossow, W. B.: Spatial and temporal variability of global surface solar irradiance, J. Geophys. Res.-Oceans, 96, 839–858, 1991.
Bousquet, P., Peylin, P., Ciais, P., Le Quere, C., Friedlingstein, P., and Tans, P. P.: Regional changes in carbon dioxide fluxes of land and oceans since 1980, Science, 290, 1342–1346, 2000.
Carrasco, J. J., Neff, J. C., and Harden, J. W.: Modeling physical and biogeochemical controls over carbon accumulation in a boreal forest soil, J. Geophys. Res. – Biogeosci., 111, G02004, doi:10.1029/2005JG000087, 2006.
Carvalho, J. A., Santos, J. M., Santos, J. C., and Leitao, M. M.: A tropical rain-forest clearing experiment by biomass burning in the Manaus region, Atmos. Environ., 29, 2301–2309, 1995.
Ciais, P., Reichstein, M., Viovy, N., Granier, A., Ogee, J., Allard, V., Aubinet, M., Buchmann, N., Bernhofer, C., Carrara, A., Chevalier, F., De Noblet, N., Friend, A. D., Friedlingstein, P., Grunwald, T., Heinesch, B., Keronen, P., Knohl, A., Krinner, G., Loustau, D., Manca, G., Matteucci, G., Miglietta, F., Ourcival, J. M., Papale, D., Pilegaard, K., Rambal, S., Seufert, G., Soussana, J. F., Sanz, M. J., Schulze, E. D., Vesala, T., and Valentini, R.: Europe-wide reduction in primary productivity caused by the heat and drought in 2003, Nature, 437, 529–533, 2005.
Duncan, B. N., Martin, R. V., Staudt, A. C., Yevich, R., and Logan, J. A.: Interannual and seasonal variability of biomass burning emissions constrained by satellite observations, J. Geophys. Res.-Atmos., 108, 4100, doi:10.1029/2002JD002378, 2003.
Edwards, D. P., Emmons, L. K., Hauglustaine, D. A., Chu, D. A., Gille, J. C., Kaufman, Y. J., Pétron, G., Yurganov, L. N., Giglio, L., Deeter, M. N., Yudin, V., Ziskin, D. C., Warner, J., Lamarque, J. F., Francis, G. L., Ho, S. P., Mao, D., Chen, J., Grechko, E. I., and Drummond, J. R.: Observations of carbon monoxide and aerosols from the Terra satellite: Northern Hemisphere variability, J. Geophys. Res.-Atmos., 109, D24202, doi:10.1029/2004JD004727, 2004.
Fearnside, P. M.: Fire in the tropical rain forest of the Amazon basin, in: Fire in the tropical biota: ecosystem processes and global challenges, edited by: Goldammer, J. G., 106–116, Ecological Studies, 84, Springer-Verlag, Berlin, Germany, 1990.
Field, C. B., Randerson, J. T., and Malmstrom, C. M.: Global net primary production – Combining ecology and remote-sensing, Remote Sens. Environ., 51, 74–88, 1995.
Flannigan, M. D., Logan, K. A., Amiro, B. D., Skinner, W. R., and Stocks, B. J.: Future area burned in Canada, Climatic Change, 72, 1–16, 2005.
French, N. H. F., Goovaerts, P., and Kasischke, E. S.: Uncertainty in estimating carbon emissions from boreal forest fires, J. Geophys. Res., 109, D14S08, doi:10.1029/2003JD003635, 2004.
Giglio, L., Descloitres., J., Justice, C. O., and Kaufman, Y. J.: An enhanced contextual fire detection algorithm for MODIS, Remote Sens. Environ, 87(2–3), 273–282, 15 October, 2003a
Giglio, L., Kendall, J. D., and Mack, R.: A multi-year active fire dataset for the tropics derived from the TRMM VIRS, Int. J. Remote Sens., 24, 4505–4525, 2003b.
Giglio, L., van der Werf, G. R., Randerson, J. T., Collatz, G. J., and Kasibhatla, P. S.: Global estimation of burned area using MODIS active fire observations, Atmos. Chem. Phys., 6, 957–974, 2006.
Gill, A. M.: Fire adaptive traits of vascular plants, in: Fire Regimes and Ecosystem Properties, edited by: Mooney, H. A., Bonnickson, J. M., Christensen, N. L., Lotan, J. E., and Reiners, W. A., 208–230, U.S Dep Agric Forest Sci. General Technical Report, Washington, D.C., 1981.
Goulden, M. L., Munger, J. W., Fan, S. M., Daube, B. C., and Wofsy, S. C.: Exchange of carbon dioxide by a deciduous forest: Response to interannual climate variability, Science, 271, 1576–1578, 1996.
Goulden, M. L., Wofsy, S. C., Harden, J. W., Trumbore, S. E., Crill, P. M., Gower, S. T., Fries, T., Daube, B. C., Fan, S. M., Sutton, D. J., Bazzaz, A., and Munger, J. W.: Sensitivity of boreal forest carbon balance to soil thaw, Science, 279, 214–217, 1998.
Grégoire, J.-M., Tansey, K., and Silva, J. M. N.: The GBA2000 initiative: Developing a global burned area database from SPOT-VEGETATION imagery, Int. J. Remote Sens., 24, 1369–1376, 2002.
Hansen, J., Ruedy, R., Glascoe, J., and Sato, M.: GISS analysis of surface temperature change, J. Geophys. Res.-Atmos., 104, 30 997–31 022, 1999.
Hansen, M. C., DeFries, R. S., Townshend, J. R. G., Carroll, M., Dimiceli, C., and Sohlberg, R.: Global percent tree cover at a spatial resolution of 500 meters: First results of the MODIS vegetation continuous fields algorithm, Earth Interactions, 7, 1–15, 2003.
Hély, C., Dowty, P. R., Alleaume, S., Caylor, K. K., Korontzi, S., Swap, R. J., Shugart, H. H., and Justice, C. O.: Regional fuel load for two climatically contrasting years in southern Africa, J. Geophys. Res.-Atmos., 108, 8475, doi:10.1029/2002JD002341, 2003.
Hess, J. C., Scott, C. A., Hufford, G. L., and Fleming, M. D.: El Niño and its impact on fire weather conditions in Alaska, Int. J. Wildland Fire, 10, 1–13, 2001.
Hoelzemann, J. J., Schultz, M. G., Brasseur, G. P., Granier, C., and Simon, M.: Global Wildland Fire Emission Model (GWEM): Evaluating the use of global area burnt satellite data, J. Geophys. Res.-Atmos., 109, D14S04 doi:10.1029/2003JD003666, 2004.
Hoffa, E. A., Ward, D. E., Hao, W. M., Susott, R. A., and Wakimoto, R. H.: Seasonality of carbon emissions from biomass burning in a Zambian savanna, J. Geophys. Res.-Atmos., 104, 13 841–13 853, 1999.
Houghton, R. A., Lawrence, K. T., Hackler, J. L., and Brown, S.: The spatial distribution of forest biomass in the Brazilian Amazon: a comparison of estimates, Global Change Biol., 7, 731–746, 2001.
Ichoku, C. and Kaufman, Y. J.: A method to derive smoke emission rates from MODIS fire radiative energy measurements, IEEE Transact. Geosci. Remote Sensing, 43, 2636–2649, 2005.
Ito, A. and Penner, J. E.: Global estimates of biomass burning emissions based on satellite imagery for the year 2000, J. Geophys. Res. Atmos., 109, D14S05, doi:10.1029/2003JD004423, 2004.
Kanamitsu, M., Ebisuzaki, W., Woollen, J., Yang, S. K., Hnilo, J. J., Fiorino, M., and Potter, G. L.: NCEP-DOE AMIP-II reanalysis (R-2), Bull. Am. Meteorol. Soc., 83, 1631–1643, 2002.
Kasischke, E. S., Hyer, E. J., Novelli, P. C., Bruhwiler, L. P., French, N. H. F., Sukhinin, A. I., Hewson, J. H., and Stocks, B. J.: Influences of boreal fire emissions on Northern Hemisphere atmospheric carbon and carbon monoxide, Global Biogeochem. Cycles, 19, GB1012, doi:10.1029/2004GB002300, 2005.
Kasischke, E. S. and Penner, J. E.: Improving global estimates of atmospheric emissions from biomass burning, J. Geophys. Res.-Atmos., 109, D14S01, doi:10.1029/2004JD004972, 2004.
Keeling, C. D., Whorf, T. P., Wahlen, M., and Vanderplicht, J.: Interannual extremes in the rate of rise of atmospheric carbon-dioxide since 1980, Nature, 375, 666–670, 1995.
Korontzi, S., Justice, C. O., and Scholes, R. J.: Influence of timing and spatial extent of savanna fires in southern Africa on atmospheric emissions, J. Arid Env., 54, 395–404, 2003.
Langenfelds, R. L., Francey, R. J., Pak, B. C., Steele, L. P., Lloyd, J., Trudinger, C. M., and Allison, C. E.: Interannual growth rate variations of atmospheric CO<sub>2</sub> and its delta C-13, H<sub>2</sub>, CH<sub>4</sub>, and CO between 1992 and 1999 linked to biomass burning, Global Biogeochem. Cycles, 16, 1048, doi:10.1029/2001GB001466, 2002.
Le Toan, T., Quegan, S., Woodward, I., Lomas, M., Delbart, N., and Picard, G.: Relating radar remote sensing of biomass to modelling of forest carbon budgets, Climatic Change, 67, 379–402, 2004.
Lee, K., Wanninkhof, R., Takahashi, T., Doney, S. C., and Feely, R. A.: Low interannual variability in recent oceanic uptake of atmospheric carbon dioxide, Nature, 396, 155–159, 1998.
Leemans, R. and Cramer, W.: The IIASA database for mean monthly values of temperature, precipitation and cloudiness of a global terrestrial grid. International Institute for Applied Systems Analysis (IIASA), RR-91-18., 1991.
Los, S. O., Collatz, G. J., Sellers, P. J., Malmstrom, C. M., Pollack, N. H., DeFries, R. S., Bounoua, L., Parris, M. T., Tucker, C. J., and Dazlich, D. A.: A global 9-yr biophysical land surface dataset from NOAA AVHRR data, J. Hydrometeorol., 1, 183–199, 2000.
Matthews, E. and Fung, I.: Methane emission from natural wetlands: Global area, distribution and environmental characteristics of sources, Global Biogeochem. Cycles, 1, 61–86, 1987.
Novelli, P. C., Masarie, K. A., Lang, P. M., Hall, B. D., Myers, R. C., and Elkins, J.W.: Re-analysis of tropospheric CO trends: Effects of the 1997–1998 wild fires, J. Geophys. Res. Atmos., 108, 4464, doi:10.1029/2002JD003031, 2003.
Oechel, W. C., Hastings, S. J., Vourlitis, G., Jenkins, M., Riechers, G., and Grulke, N.: Recent change of Arctic tundra ecosystems from a net carbon-dioxide sink to a source, Nature, 30 361, 520–523, 1993.
Olson, R., Scurlock, J., Prince, S., Zheng, D., and Johnson, K. (Eds.): NPP multi-biome: NPP and driver data for ecosystem model-data intercomparison. Available on-line (http://www.daac.ornl.gov) from the Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, USA, 2001.
Page, S. E., Siegert, F., Rieley, J. O., Boehm, H. D. V., Jaya, A., and Limin, S.: The amount of carbon released from peat and forest fires in Indonesia during 1997, Nature, 420, 61–65, 2002.
Pétron, G., Granier, C., Khattatov, B., Yudin, V., Lamarque, J. F., Emmons, L., Gille, J., and Edwards, D. P.: Monthly CO surface sources inventory based on the 2000–2001 MOPITT satellite data, Geophys. Res. Lett., 31, L21107, doi:10.1029/2004GL020560, 2004.
Pinzón, J. E., Brown, M. E., and Tucker, C. J.: EMD correction of orbital drift artifacts in satellite data stream, Chapter 8, Part II. Applications, in: Hilbert-Huang transform and its applications, edited by: Huang, N. E. and Shen, S. S., World Scientific, Singapore, 167–186, 2005.
Plummer, S., Arino, O., Simon, M., and Steffen, W.: Establishing an earth observation product service for the terrestrial carbon community: the GLOBCARBON initiative, Mitigation and adaptation strategies for global change, 11, 97–111, 2006.
Potter, C. S., Randerson, J. T., Field, C. B., Matson, P. A., Vitousek, P. M., Mooney, H. A., and Klooster, S. A.: Terrestrial ecosystem production – A process model based on global satellite and surface data, Global Biogeochem. Cycles, 7, 811–841, 1993.
Randerson, J. T., Thompson, M. V., Malmstrom, C. M., Field, C. B., and Fung, I. Y.: Substrate limitations for heterotrophs: Implications for models that estimate the seasonal cycle of atmospheric CO<sub>2</sub>, Global Biogeochem. Cycles, 10, 585–602, 1996.
Randerson, J. T., van der Werf, G. R., Collatz, G. J., Giglio, L., Still, C. J., Kasibhatla, P., Miller, J. B., White, J. W. C., DeFries, R. S., and Kasischke, E. S.: Fire emissions from C-3 and C-4 vegetation and their influence on interannual variability of atmospheric CO<sub>2</sub> and delta(CO<sub>2</sub>)-C-13, Global Biogeochem. Cycles, 19, GB2019, doi:10.1029/2004GB002366, 2005.
Roberts, G., Wooster, M. J., Perry, G. L. W., Drake, N., Rebelo, L. M., and Dipotso, F.: Retrieval of biomass combustion rates and totals from fire radiative power observations: Application to southern Africa using geostationary SEVIRI imagery, J. Geophys. Res.-Atmos., 110, D21111, doi:10.1029/2005JD006018, 2005.
Saatchi, S., Agosti, D., Alger, K., Delabie, J., and Musinsky, J.: Examining fragmentation and loss of primary forest in the southern Bahian Atlantic forest of Brazil with radar imagery, Conservation Biol., 15, 867–875, 2001.
Saleska, S. R., Miller, S. D., Matross, D. M., Goulden, M. L., Wofsy, S. C., da Rocha, H. R., de Camargo, P. B., Crill, P., Daube, B. C., de Freitas, H. C., Hutyra, L., Keller, M., Kirchhoff, V., Menton, M., Munger, J. W., Pyle, E. H., Rice, A. H., and Silva, H.: Carbon in amazon forests: Unexpected seasonal fluxes and disturbance-induced losses, Science, 302, 1554–1557, 2003.
Schimel, D. and Baker, D.: Carbon cycle: The wildfire factor, Nature, 420, 29–30, 2002.
Scholes, R. J., Kendall, J., and Justice, C. O.: The quantity of biomass burned in southern Africa, J. Geophys. Res. Atmos, 101, 23 667–23 676, 1996.
Schuur, E. A. G.: Productivity and global climate revisited: The sensitivity of tropical forest growth to precipitation, Ecology, 84, 1165–1170, 2003.
Shea, R. W., Shea, B. W., Kauffman, J. B., Ward, D. E., Haskins, C. I., and Scholes, M. C.: Fuel biomass and combustion factors associated with fires in savanna ecosystems of South Africa and Zambia, J. Geophys. Res. Atmos., 101, 23 551–23 568, 1996.
Silva, J. M. N., Sa, A. C. L., and Pereira, J. M. C.: Comparison of burned area estimates derived from SPOT-VEGETATION and Landsat ETM plus data in Africa: Influence of spatial pattern and vegetation type, Remote Sens. Environ., 96, 188–201, 2005.
Simon, M., Plummer, S., Fierens, F., Hoelzemann, J. J., and Arino, O.: Burnt area detection at global scale using ATSR-2: The GLOBSCAR products and their qualification, J. Geophys. Res.-Atmos., 109, D14S02, doi:10.1029/2003JD003622, 2004.
Stocks, B. J., Mason, J. A., Todd, J. B., Bosch, E. M., Wotton, B. M., Amiro, B. D., Flannigan, M. D., Hirsch, K. G., Logan, K. A., Martell, D. L., and Skinner, W. R.: Large forest fires in Canada, 1959–1997, J. Geophy. Res., 108, 8149, doi:10.1029/2001JD000484, 2002.
Sukhinin, A. I., French, N. H. F., Kasischke, E. S., Hewson, J. H., Soja, A. J., Csiszar, I. A., Hyer, E. J., Loboda, T., Conrad, S. G., Romasko, V. I., Pavlichenko, E. A., Miskiv, S. I., and Slinkina, O. A.: AVHRR-based mapping of fires in Russia: New products for fire management and carbon cycle studies, Remote Sens. Environ., 93, 546–564, 2004.
Thonicke, K., Prentice, I., and Hewitt, C.: Modeling glacial-interglacial changes in global fire regimes and trace gas emissions, Global Biogeochem. Cycles, 19, GB3008, doi:10.1029/2004GB002278, 2005.
Tucker, C. J., Pinzón, J. E., Brown, M. E., Slayback, D. A., Pack, E. W., Mahoney, R., Vermote, E. F., and El Saleous, N.: An extended AVHRR 8-km NDVI dataset compatible with MODIS and SPOT vegetation NDVI data, Int. J. of Remote Sens., 26(20), 4485–4498, 2005.
van der Werf, G. R., Randerson, J. T., Collatz, G. J., and Giglio, L.: Carbon emissions from fires in tropical and subtropical ecosystems, Global Change Biol., 9, 547–562, 2003.
van der Werf, G. R., Randerson, J. T., Collatz, G. J., Giglio, L., Kasibhatla, P. S., Arellano, A. F., Olsen, S. C., and Kasischke, E. S.: Continental-scale partitioning of fire emissions during the 1997 to 2001 El Niño/La Niña period, Science, 303, 73–76, 2004.
van Wilgen, B. W. and Scholes, R. J.: The vegetation and fire regimes of southern hemisphere Africa, in: Fire in Southern African Savannas: Ecological and Atmospheric Perspectives, edited by: van Wilgen, B. W., Andreae, M. O., Goldammer, J. G., Lindesay, J., et al., 27–46, Witswatersrand Univ. Press, Johannesburg, South Africa, 1997.
Wooster, M. J.: Small-scale experimental testing of fire radiative energy for quantifying mass combusted in natural vegetation fires, Geophys. Res. Lett., 29, 2027, doi:10.1029/2002GL015487, 2002.
Yurganov, L. N., Duchatelet, P., Dzhola, A. V., Edwards, D. P., Hase, F., Kramer, I., Mahieu, E., Mellqvist, J., Notholt, J., Novelli, P. C., Rockmann, A., Scheel, H. E., Schneider, M., Schulz, A., Strandberg, A., Sussmann, R., Tanimoto, H., Velazco, V., Drummond, J. R., and Gille, J. C.: Increased Northern Hemispheric carbon monoxide burden in the troposphere in 2002 and 2003 detected from the ground and from space, Atmos. Chem. Phys., 5, 563–573, 2005.
Zheng, D. L., Prince, S., and Wright, R.: Terrestrial net primary production estimates for 0.5 degrees grid cells from field observations – a contribution to global biogeochemical modeling, Global Change Biol., 9, 46–64, 2003.