DOI: 10.1126/science.281.5374.237 237 (1998) 281, Science et al. Christopher B. Field, Terrestrial and Oceanic Components Primary Production of the Biosphere: Integrating www.sciencemag.org (this information is current as of April 16, 2009 ): The following resources related to this article are available online at http://www.sciencemag.org/cgi/content/full/281/5374/237 version of this article at: including high-resolution figures, can be found in the online Updated information and services, http://www.sciencemag.org/cgi/content/full/281/5374/237#otherarticles 6 of which can be accessed for free: cites 25 articles, This article 359 article(s) on the ISI Web of Science. cited by This article has been http://www.sciencemag.org/cgi/content/full/281/5374/237#otherarticles 44 articles hosted by HighWire Press see: cited by This article has been http://www.sciencemag.org/cgi/collection/atmos Atmospheric Science subject collections: This article appears in the following http://www.sciencemag.org/about/permissions.dtl in whole or in part can be found at: this article permission to reproduce of this article or about obtaining reprints Information about obtaining registered trademark of AAAS. is a Science 1998 by the American Association for the Advancement of Science all rights reserved. The title Copyright American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075 online ISSN 1095-9203) is published weekly, except the last week in December, by the Science on April 16, 2009 www.sciencemag.org Downloaded from

to support positive NPP, f(PAR) describes the fraction of the water column from the surface to Zeu in which photosynthesis is light saturated, and Popt b (T) is the maximum, chlo- rophyll-specific carbon fixation rate (in mil- ligrams of C per milligram of chlorophyll per day), estimated as a function of sea-surface temperature (11, 16). For the VGPM, varia- tion in the fraction of absorbed PAR is a function of depth-integrated phytoplankton biomass (that is, Csat 3 Zeu). The product of P opt b and f(PAR) yields an average water column light utilization efficiency, making it the corollary of �� in Eq. 1. The VGPM op- erates with a daily time step, whereas CASA has a monthly time step. Biospheric NPP was calculated from Eqs. 2 and 3, on the basis of observations averaged over several years. Because the satellite data necessary for estimating APAR cover differ- ent time periods for the oceans and land, the averaging periods are different: 1978 to 1983 for the oceans and 1982 to 1990 for land. The input data include Csat from the Coastal Zone Color Scanner (CZCS) (28), NDVI from the Advanced Very High-Resolution Radiometer (AVHRR) (29���31), cloud-corrected surface solar radiation (32), sea-surface temperature (33), terrestrial surface temperature (34), pre- cipitation (35), soils (36), and vegetation (37), plus field-based parameterizations of �� (16, 21, 26). Our results based on time-aver- aged data are likely to characterize typical NPP from this time period but certainly miss key anomalies such as El Nin ��o���Southern Os- cillation, as well as progressive global chang- es. The contribution of models like the one used here to quantifying these changes will depend on continuous, high-quality data, over extended periods. Using the integrated CASA-VGPM bio- sphere model, we obtained an annual global NPP of 104.9 Pg of C (Table 1), with similar contributions from the terrestrial [56.4 Pg of C (53.8%)] and oceanic [48.5 Pg of C (46.2%)] components (38). This estimate for ocean productivity is nearly two times greater than estimates made before satellite data (39, 40). Average NPP on land without permanent ice cover is 426 g of C m22 year21, whereas that for oceans is 140 g of C m22 year21. The lower NPP per unit area of the ocean largely results from competition for light between phytoplankton and their strongly absorbing medium. For the average ocean Csat of 0.19 mg m23 (16, 41), only 7% of the PAR inci- dent on the ocean surface is absorbed by the phytoplankton (14), with the remainder ab- sorbed by water and dissolved organics. In contrast, leaves of terrestrial plants absorb about 31% of the PAR incident on land with- out permanent ice cover. Although primary producers in the ocean are responsible for nearly half of the biospheric NPP, they rep- resent only 0.2% of global primary producer biomass (3, 16, 21). This uncoupling between NPP and biomass is a consequence of the more than three orders of magnitude faster turnover time of plant organic matter in the oceans (average 2 to 6 days) (1) than on land (average 19 years) (42). On land and in the oceans, spatial hetero- geneity in NPP is comparable, with both systems exhibiting large regions of low pro- duction and smaller areas of high production. In general, the extreme deserts are even less productive than the vast mid-ocean gyres (Fig. 1). Maximal NPP is similar in both systems (1000 to 1500 g of C m22 year21), but regions of high NPP are spatially more restricted in the oceans (essentially limited to estuarine and upwelling regions) than in ter- restrial systems (for example, humid tropics) (Fig. 1). On land, 25.0% of the surface area without permanent ice (3.3 3 107 km2) sup- ports an NPP greater than 500 g of C m22 year21, whereas in the oceans, that figure is only 1.7% (5.0 3 106 km2). Highly produc- tive (that is, eutrophic) regions in the oceans contribute less than 18% to total ocean NPP (Table 1). Globally, NPP reaches maxima in three distinct latitudinal bands (Fig. 2). The largest peak ( 1.6 Pg of C per degree of latitude) near the equator and the secondary peak at midtemperate latitudes of the Northern Hemi- sphere are driven primarily by regional max- ima in terrestrial NPP. The smaller peak at midtemperate latitudes in the Southern Hemi- sphere (Fig. 2) results from a belt of enhanced oceanic productivity corresponding to en- hanced nutrient availability in the Southern Subtropical Convergence (43). At mid and low latitudes, ocean NPP is remarkably uni- form, consistent with the predominant influ- ence of large-scale ocean circulation patterns. Seasonal fluctuations in ocean NPP are modest globally, even though regional season- ality can be very important (44). Ocean NPP ranges from 10.9 Pg of C in the Northern Hemisphere spring (April to June) to 13.0 Pg of C in the Northern Hemisphere summer (July to September) (Table 1). The July to September maximum in ocean NPP is largely a result of SP -60 -30 EQ 30 60 NP 180 120 W 60 W 0 60 E 120 E 180 0 100 200 300 400 500 600 700 800 Fig. 1. Global annual NPP (in grams of C per square meter per year) for the biosphere, cal- culated from the inte- grated CASA-VGPM model. The spatial res- olution of the calcula- tions is 1�� 3 1�� for land and 1/6�� 3 1/6�� for the oceans. Input data for ocean color from the CZCS sensor are averages from 1978 to 1983. The land vegetation index from the AVHRR sen- sors is the average from 1982 to 1990. Global NPP is 104.9 Pg of C year21 (104.9 3 1015 g of C year21), with 46.2% contributed by the oceans and 53.8% contributed by the land. Seasonal ver- sions of this map are available at www. sciencemag.org/feature/data/982246.shl. NP, North Pole EQ, equator Sp, South Pole. R E P O R T S 10 JULY 1998 VOL 281 SCIENCE www.sciencemag.org 238 on April 16, 2009 www.sciencemag.org Downloaded from