APh/BE161: Physical Biology of the Cell Winter 2009 “Lecture # 1” – will take several days Rob Phillips to support positive NPP, f(PAR) describesthe fraction of the water column from thesurface to Zeuin which photosynthesis is lightsaturated, and Poptb(T ) is the maximum, chlo-rophyll-specific carbon fixation rate (in mil-ligrams of C per milligram of chlorophyll perday), estimated as a function of sea-surfacetemperature (11, 16). For the VGPM, varia-tion in the fraction of absorbed PAR is afunction of depth-integrated phytoplanktonbiomass (that is, Csat! Zeu). The product ofPoptband f(PAR) yields an average watercolumn light utilization efficiency, making itthe corollary of " in Eq. 1. The VGPM op-erates with a daily time step, whereas CASAhas a monthly time step.Biospheric NPP was calculated from Eqs.2 and 3, on the basis of observations averagedover several years. Because the satellite datanecessary for estimating APAR cover differ-ent time periods for the oceans and land, theaveraging periods are different: 1978 to 1983for the oceans and 1982 to 1990 for land. Theinput data include Csatfrom the Coastal ZoneColor Scanner (CZCS) (28), NDVI from theAdvanced Very High-Resolution Radiometer(AVHRR) (29–31), cloud-corrected surfacesolar 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 typicalNPP from this time period but certainly misskey anomalies such as El Nin˜o–Southern Os-cillation, as well as progressive global chang-es. The contribution of models like the oneused here to quantifying these changes willdepend on continuous, high-quality data, overextended periods.Using the integrated CASA-VGPM bio-sphere model, we obtained an annual globalNPP of 104.9 Pg of C (Table 1), with similarcontributions from the terrestrial [56.4 Pg ofC (53.8%)] and oceanic [48.5 Pg of C(46.2%)] components (38). This estimate forocean productivity is nearly two times greaterthan estimates made before satellite data (39,40). Average NPP on land without permanentice cover is 426 g of C m#2year#1, whereasthat for oceans is 140 g of C m#2year#1. Thelower NPP per unit area of the ocean largelyresults from competition for light betweenphytoplankton and their strongly absorbingmedium. For the average ocean Csatof 0.19mg m#3(16, 41), only 7% of the PAR inci-dent on the ocean surface is absorbed by thephytoplankton (14), with the remainder ab-sorbed by water and dissolved organics. Incontrast, leaves of terrestrial plants absorbabout 31% of the PAR incident on land with-out permanent ice cover. Although primaryproducers in the ocean are responsible fornearly half of the biospheric NPP, they rep-resent only 0.2% of global primary producerbiomass (3, 16, 21). This uncoupling betweenNPP and biomass is a consequence of themore than three orders of magnitude fasterturnover time of plant organic matter in theoceans (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 bothsystems exhibiting large regions of low pro-duction and smaller areas of high production.In general, the extreme deserts are even lessproductive than the vast mid-ocean gyres(Fig. 1). Maximal NPP is similar in bothsystems (1000 to 1500 g of C m#2year#1),but regions of high NPP are spatially morerestricted in the oceans (essentially limited toestuarine and upwelling regions) than in ter-restrial systems (for example, humid tropics)(Fig. 1). On land, 25.0% of the surface areawithout permanent ice (3.3 ! 107km2) sup-ports an NPP greater than 500 g of C m#2year#1, whereas in the oceans, that figure isonly 1.7% (5.0 ! 106km2). Highly produc-tive (that is, eutrophic) regions in the oceanscontribute less than 18% to total ocean NPP(Table 1).Globally, NPP reaches maxima in threedistinct latitudinal bands (Fig. 2). The largestpeak ($1.6 Pg of C per degree of latitude)near the equator and the secondary peak atmidtemperate latitudes of the Northern Hemi-sphere are driven primarily by regional max-ima in terrestrial NPP. The smaller peak atmidtemperate latitudes in the Southern Hemi-sphere (Fig. 2) results from a belt of enhancedoceanic productivity corresponding to en-hanced nutrient availability in the SouthernSubtropical Convergence (43). At mid andlow latitudes, ocean NPP is remarkably uni-form, consistent with the predominant influ-ence of large-scale ocean circulation patterns.Seasonal fluctuations in ocean NPP aremodest globally, even though regional season-ality can be very important (44). Ocean NPPranges from 10.9 Pg of C in the NorthernHemisphere spring (April to June) to 13.0 Pg ofC in the Northern Hemisphere summer (July toSeptember) (Table 1). The July to Septembermaximum in ocean NPP is largely a result ofSP -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 800Fig. 1. Global annualNPP (in grams of C persquare meter per year)for the biosphere, cal-culated from the inte-grated CASA-VGPMmodel. The spatial res-olution of the calcula-tions is 1° ! 1° forland and 1/6° ! 1/6°for the oceans. Inputdata for ocean colorfrom the CZCS sensorare averages from1978 to 1983. Theland vegetation indexfrom the AVHRR sen-sors is the averagefrom 1982 to 1990.Global NPP is 104.9Pg of C year#1(104.9 ! 1015g of Cyear#1), with 46.2%contributed by theoceans and 53.8%contributed by theland. Seasonal ver-sions of this map areavailable at www.sciencemag.org/feature/data/982246.shl. NP, North Pole; EQ, equator; Sp, South Pole.R E P O R T S10 JULY 1998 VOL 281 SCIENCE www.sciencemag.org238(Behrenfeld, Falkowski et al., Science, 1998)! “Who am I? Why am I here?” ! Who are you? Why are you here? - the diversity question. ! A few words on what this course is? Style and approach (graduate course in spirit and all that implies – “I don’t know”, all learning together, open-ended homeworks, trying to find the right questions to ask) – thinking, estimating and calculating biological phenomena. Often start with a) data from some experiment to change your life for and b) show and tell. This is followed by model building and analysis. ! Photosynthesis: show and tell - drinking from a powerpoint firehose. ! Course logistics: when, grades, TAs, expectations, website, etc. !
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