Efficiency of carbon removal per added iron in ocean iron fertilization

Efficiency of carbon removal per added iron in ocean iron fertilization

Efficiency of carbon removal per added iron in ocean iron fertilization


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272Mar Ecol Prog Ser 364: 269–282, 2008Table 2. The thus-far best estimate <strong>of</strong> (C:Fe) large-diatoms-optimal , ~23 000, as well as various other estimates from the literature forC:Fe <strong>of</strong> diatoms and whole plankton assemblages (Bruland et al. 1991, based on Mart<strong>in</strong> & Knauer 1973, Mart<strong>in</strong> et al. 1976, Collier& Edmond 1983) and their deep <strong>ocean</strong> debris and m<strong>in</strong>eralization ratios (Mart<strong>in</strong> et al. 1989). Literature values <strong>of</strong> diatoms forthe 84% (n = 21) lower <strong>per</strong>centile <strong>of</strong> all published values, after Sarthou et al. (2005). Us<strong>in</strong>g all sources (n = 25), <strong>in</strong>clud<strong>in</strong>g 4 moreoutlier ratio values, the average <strong>in</strong>creases to C:Fe = 68 863 ± 112 167 (mean ± SD). GFAAS: graphite furnace atomic absorptionspectrometry. See ‘Results’ for def<strong>in</strong>itions <strong>of</strong> study area acronymsDescription C:Fe ratio value Method Source(C:Fe) large-diatoms-optimal ~23 000 SOFeX IN patch; synchrotron X-ray Tw<strong>in</strong><strong>in</strong>g et al. (2004)(C:Fe) large-diatoms-Fe-limited ~100 000–160 000 SOFeX OUT patch Tw<strong>in</strong><strong>in</strong>g et al. (2004)(C:Fe) diatoms-literature 28 571 ± 24 440 84% <strong>per</strong>centile (n = 21) Sarthou et al. (2005)(C:Fe) diatoms-literature 68 863 ± 112 167 100% <strong>per</strong>centile (n = 25) Sarthou et al. (2005)(C:Fe) whole-plankton–tows ~21 000 GFAAS Bruland et al. (1991)(C:Fe) excess-deep-particles ~33 000 Debris by GFAAS Mart<strong>in</strong> et al. (1989)(C:Fe) Thalassiosira <strong>ocean</strong>ica ~30 000–100 000 Optimal growth rate Sunda et al. (1991)(C:Fe) Thalassiosira <strong>ocean</strong>ica ~500 000 Suboptimal 90% growth Sunda et al. (1991)(C:Fe) nitricl<strong>in</strong>e ~483 000 L<strong>in</strong>ear regression Mart<strong>in</strong> et al. (1989)(C:Fe) oxycl<strong>in</strong>e ~384 000 L<strong>in</strong>ear regression Mart<strong>in</strong> et al. (1989)(C:Fe) plankton-content 227000 ± 5000 (n = 10) KEOPS shipboard; Sarthou et al. (2008)175 000–333 000 range 55 Fe radiotracer, with oxalatewash<strong>in</strong>g <strong>of</strong>f the extracellular FeAnother approach to assess <strong>iron</strong> requirement is byassess<strong>in</strong>g growth rate as a function <strong>of</strong> the ambient concentration<strong>of</strong> dissolved trace-nutrient Fe. As there is nogood understand<strong>in</strong>g yet on the effect <strong>of</strong> Fe chemicalspeciation (notably Fe-organic complexes) on thegrowth rate <strong>of</strong> a given phytoplankton species, it is bestto simply take the dissolved Fe concentration as thegrowth-rate-controll<strong>in</strong>g parameter <strong>in</strong> otherwise natural,un<strong>per</strong>turbed, Antarctic seawater (Timmermans etal. 2004). Timmermans et al. (2004) demonstrated thatthe K m values for growth <strong>of</strong> large Antarctic <strong>ocean</strong>icdiatoms Fragilariopsis kerguelensis, Chaetocerosdichaeta, Thalassiosira sp., Corethron pennatum andAct<strong>in</strong>ocyclus sp. range from 0.19 nM to 1.14 nM, i.e.generally well above the average concentration <strong>of</strong> dissolvedFe <strong>in</strong> Antarctic surface waters. Moreover, theseK m values have been shown to be <strong>in</strong>versely related tothe surface:volume ratio <strong>of</strong> these diatoms (de Baar etal. 2005). These results are consistent with the observationthat large diatoms bloom only occasionally <strong>in</strong>the open Antarctic Ocean, presumably upon an event<strong>of</strong> Fe supply either from below (de Baar et al. 1995) orfrom above by wet deposition <strong>of</strong> Fe-rich dust. Notably<strong>in</strong> the Southern Ocean Iron Enrichment Ex<strong>per</strong>iment(SOIREE) <strong>fertilization</strong>, the (<strong>in</strong>side-patch) dissolved Fewas always above ~0.2 nM, allow<strong>in</strong>g Fragilariopsiskerguelensis to ma<strong>in</strong>ta<strong>in</strong> at least its half maximumgrowth rate (de Baar et al. 2005) and eventuallybecome the dom<strong>in</strong>ant species <strong>in</strong> response to the Fe <strong>fertilization</strong>.The above <strong>in</strong>dependent estimates <strong>of</strong> <strong>in</strong>tracellular Feconcentration (Tw<strong>in</strong><strong>in</strong>g et al. 2004) and large diatomsgrowth rates (Timmermans et al. 2004) were shown tobe <strong>in</strong> <strong>per</strong>fect agreement with the diffusion limitation <strong>of</strong>growth rate <strong>of</strong> these diatoms (de Baar et al. unpubl.data). At <strong>in</strong>creas<strong>in</strong>g size the less favorable surface:volume ratio prescribes a necessary higher ambient Feconcentration for growth cont<strong>in</strong>uation. Conversely,small cells with the same <strong>in</strong>tracellular Fe concentration,i.e. spheres with a typical diameter less than~8 µm, are never Fe-limited <strong>in</strong> an <strong>ocean</strong> where dissolvedFe always exceeds an 0.01 nM concentration(de Baar et al. unpubl. data). This is consistent with theobservation that small Chaetoceros brevis is neverFe-limited (Timmermans et al. 2001).While Fe enrichments thus far have shown a responsefrom the larger size class <strong>of</strong> diatoms, fromdecades <strong>of</strong> <strong>in</strong>dependent field observations we knowthat major blooms <strong>in</strong> the Antarctic Ocean are due toeither such large diatoms, or the colony-form<strong>in</strong>gPhaeocystis antarctica. For example, <strong>in</strong> the Ross Seathere are blooms <strong>of</strong> either diatoms or P. antarctica <strong>in</strong>dist<strong>in</strong>ct regions and seasons, and the cause for this dist<strong>in</strong>ctionis <strong>of</strong> great <strong>in</strong>terest (Arrigo et al. 2003, Tagliabue& Arrigo 2005). Recently, Sedwick et al. (2007)have shown from P. antarctica cultures <strong>in</strong> natural Antarcticseawater the K m value for growth <strong>of</strong> ~0.45 nMdissolved Fe. This is <strong>in</strong> the same range as for the abovelarge diatoms. Previous estimates for <strong>in</strong>cubations <strong>of</strong>Ross Sea Prymnesiophytes were about one order <strong>of</strong>magnitude lower (Coale et al. 2003), the latter presumablysolitary P. antarctica cells (diameter ~4 to 6 µm;Rousseau et al. 2007) with a more favorable surface:volumeratio for diffusive Fe assimilation.

de Baar et al.: <strong>Efficiency</strong> <strong>of</strong> <strong>ocean</strong> <strong>iron</strong> <strong>fertilization</strong>273Other literature estimates <strong>of</strong> <strong>iron</strong> requirement <strong>of</strong>diatomsIn context <strong>of</strong> the Iron Resources and Oceanic Nutrients:Advancement <strong>of</strong> Global Ecosystem Simulations(IRONAGES) project, reviews based on previous studieshave focused on the limitations by light, majornutrients and <strong>iron</strong>, <strong>of</strong> major bloom-form<strong>in</strong>g groups, thediatoms (Sarthou et al. 2005), Phaeocystis spp. (Schoemannet al. 2005), diazotrophs (La Roche & Breitbarth2005), and picoplankton (Timmermans et al. 2005),while f<strong>in</strong>e reviews already existed for the coccolithophorids(Iglesias-Rodríguez et al. 2002, Paasche2002). Briefly, the cell quota for diatoms have an average(mean ± SD) C:Fe = 28 571 ± 24 440 based on 21publications <strong>of</strong> laboratory <strong>in</strong>cubation studies (Sarthouet al. 2005).Several <strong>of</strong> the previous studies, while novel at thetime, may <strong>in</strong> retrospect require caveats for the follow<strong>in</strong>greasons. Firstly, the problem <strong>of</strong> measur<strong>in</strong>g true<strong>in</strong>tracellular Fe content as mentioned above rendersmany old C:Fe values questionable. Secondly, <strong>in</strong> thepioneer<strong>in</strong>g days <strong>of</strong> metal–phytoplankton <strong>in</strong>teractionex<strong>per</strong>iments, it was not yet possible to achieve theultraclean dissolved metal concentrations we know toexist <strong>in</strong> the real <strong>ocean</strong>. In order to overcome this, theculture media were overdosed with 10 –4 M EDTA,which b<strong>in</strong>ds all dissolved metal ions; by then overdos<strong>in</strong>gwith the metal <strong>of</strong> <strong>in</strong>terest, a ‘free metal’ concentrationsimilar to the total metal <strong>in</strong> the real <strong>ocean</strong> wasachieved (Provasoli et al. 1957). This method has ledto many breakthroughs (e.g. Sunda & Guillard 1976).For Fe limitation, the <strong>in</strong>herent paradigm has become(de Baar 1994) that the calculated free Fe’ is the controll<strong>in</strong>gagent for phytoplankton growth. However,these ex<strong>per</strong>iments were conducted <strong>in</strong> EDTA media.S<strong>in</strong>ce the 1994 discovery <strong>of</strong> >99% organic complexation<strong>of</strong> dissolved Fe <strong>in</strong> the real <strong>ocean</strong> (Gledhill & vanden Berg 1994), EDTA media now are known to be notrepresentative <strong>of</strong> the real <strong>ocean</strong> (Gerr<strong>in</strong>ga et al. 2000).Moreover, with the ultraclean methods <strong>of</strong> today, it isnot necessary anymore to add EDTA to circumvent<strong>in</strong>advertent contam<strong>in</strong>ation.From a comparison <strong>of</strong> the cellular Fe requirements <strong>of</strong>the coastal diatom Thalassiosira pseudonana and the<strong>ocean</strong>ic diatom T. <strong>ocean</strong>ica (Sunda et al. 1991), one candeterm<strong>in</strong>e from the reported growth curve that at theoptimum growth rate <strong>of</strong> ~1.2 d –1 <strong>of</strong> T. <strong>ocean</strong>ica, the correspond<strong>in</strong>gsuggested cell ratio is <strong>in</strong> the range <strong>of</strong> C:Fe= ~30 000 to 100 000. At suboptimal (~90% <strong>of</strong> maximum)rate <strong>of</strong> growth the correspond<strong>in</strong>g cell ratio presumablyis <strong>in</strong> the order <strong>of</strong> C:Fe = ~500 000. However,these ex<strong>per</strong>iments were <strong>in</strong> EDTA media and not relevantfor the real <strong>ocean</strong>. Otherwise, (Sunda et al. 1991)reported that it was not possible to drive T. <strong>ocean</strong>ica<strong>in</strong>to Fe limitation, at most a suppression to 90% <strong>of</strong>maximum growth was realized. This is consistent withthe fact that T. <strong>ocean</strong>ica is a very small diatom andtherefore will never be Fe diffusion limited <strong>in</strong> real<strong>ocean</strong> waters (de Baar et al. 2008), ak<strong>in</strong> to the similarlysmall <strong>ocean</strong>ic diatom Chaetoceros brevis which couldnot be driven <strong>in</strong>to Fe limitation <strong>in</strong> natural Antarcticseawater either (Timmermans et al. 2001), except afterthe addition <strong>of</strong> very strong siderophore DFOB (desferrioxam<strong>in</strong>e-B)mak<strong>in</strong>g Fe unavailable for uptake.Quite remarkably, addition <strong>of</strong> DFOB to natural Antarcticseawater cannot even drive T. <strong>ocean</strong>ica <strong>in</strong>to Fe limitation(K. R. Timmermans et al. unpubl. data). Somehow,DFOB-bound Fe appears to be available toT. <strong>ocean</strong>ica, but not at all available to C. brevis (Timmermanset al. 2001). Similarly, Hutch<strong>in</strong>s et al. (1999)reported that different phytoplankton species canaccess different Fe-organic species, i.e. someth<strong>in</strong>gmore than just <strong>in</strong>organic Fe’(III) is affect<strong>in</strong>g growth.Sedwick et al. (2007) also report that DFOB bound Fesomehow is partly available for Phaeocystis antarctica.Researchers are only beg<strong>in</strong>n<strong>in</strong>g to unravel the <strong>in</strong>trigu<strong>in</strong>g<strong>in</strong>teractions between several organic ligands andseveral different phytoplankton species (Rijkenberg etal. 2006, 2008), as natural <strong>iron</strong>–plankton <strong>in</strong>teractionscan only be assessed <strong>in</strong> natural seawater.Efforts to derive C:Fe ratio values from the deep<strong>ocean</strong>One <strong>of</strong> the first reliable vertical pr<strong>of</strong>iles <strong>of</strong> dissolvedFe <strong>in</strong> the deep <strong>ocean</strong> was <strong>in</strong> the north Pacific Ocean at50° N, 145° W (Ocean Station Papa) which appeared toexhibit similarity to the vertical distribution <strong>of</strong> nitrate(Mart<strong>in</strong> et al. 1989) but, l<strong>in</strong>ear correlation, ak<strong>in</strong> to e.g.phosphate versus nitrate (Redfield et al. 1963), betweenFe and nitrate was not successful. However, bycomb<strong>in</strong><strong>in</strong>g data only <strong>in</strong> the nitricl<strong>in</strong>e <strong>of</strong> 50° N, 145° W(Ocean Station Papa) and adjacent stations at 40° N,140° W (Vertex T-5) and 45° N, 143° W (Vertex T-6) al<strong>in</strong>ear relation was achieved (Mart<strong>in</strong> et al. 1989). Conversion<strong>of</strong> N to C by classical Redfield (C:N = 106:16 =~6.6) yielded C:Fe = ~483 000 (de Baar & de Jong 2001,p. 164). Similarly, versus the oxycl<strong>in</strong>e, C:Fe = ~384 000was obta<strong>in</strong>ed. On the other hand, excess Fe on deepparticles (excess over lithogenic Fe) presumably representsbiogenic Fe and led to a C:Fe = ~33 000 (Mart<strong>in</strong>et al. 1989). This is similar to the C:Fe = ~21 000 <strong>of</strong>whole plankton tows (Bruland et al. 1991).With some more recent vertical pr<strong>of</strong>iles <strong>of</strong> dissolved Fe<strong>in</strong> other <strong>ocean</strong> bas<strong>in</strong>s (de Baar & de Jong 2001, Parekh etal. 2005, Bergquist & Boyle 2006), it now appears thatdissolved Fe <strong>in</strong> the deep <strong>ocean</strong>s is with<strong>in</strong> a narrow band<strong>of</strong> concentrations and does not show the general <strong>in</strong>-

274Mar Ecol Prog Ser 364: 269–282, 2008crease from young deep Atlantic to old deep Pacificwaters as do the micronutrients N, P and Si. This is likelydue to net <strong>removal</strong> <strong>of</strong> dissolved Fe from deep waters byadsorptive scaveng<strong>in</strong>g, while there is no net <strong>removal</strong> <strong>of</strong>micronutrients (Parekh et al. 2005). Hence, it appearsthat each <strong>ocean</strong> bas<strong>in</strong> has its own Fe cycle and that thereis little exchange <strong>of</strong> Fe between bas<strong>in</strong>s (de Baar & deJong 2001). It seems there is no straightforward relationshipbetween deep Fe and deep micronutrients. Mostlikely the deep <strong>ocean</strong> ratio <strong>of</strong> dissolved Fe versus majornutrient (e.g. nitrate or phosphate) tends to decreasewith the age <strong>of</strong> deep water; hopefully, the ongo<strong>in</strong>g Geotracesglobal mapp<strong>in</strong>g project will provide new <strong>in</strong>sight<strong>in</strong>to this area <strong>in</strong> the near future.Values <strong>of</strong> C:Fe ratio derived from the 1993–2002 <strong>in</strong>situ <strong>fertilization</strong> ex<strong>per</strong>imentsBy comparison <strong>of</strong> the <strong>in</strong> situ <strong>fertilization</strong> ex<strong>per</strong>iments,a compilation <strong>of</strong> efficiency values (ΔDIC:Fe) NCPhas been reported before (de Baar et al. 2005, theirTable 3) and is given <strong>in</strong> Table 3. Moreover, we havecalculated the other efficiency ratio values for gas<strong>in</strong>flux dur<strong>in</strong>g the observation <strong>per</strong>iod <strong>of</strong> each ex<strong>per</strong>iment,as well as the export efficiency at the 100 mdepth horizon. Note that <strong>in</strong> most <strong>ocean</strong> regions, theexport efficiency at the 250 m depth horizon would beabout half that at 100 m, as observed and applied byBuesseler et al. (2004) <strong>in</strong> the context <strong>of</strong> the SOFeX-South ex<strong>per</strong>iment <strong>in</strong> the Antarctic Ocean.The (C:Fe) gas-flux-efficiency varies between 100 and1000 mol CO 2 gas <strong>in</strong>flux <strong>in</strong>to the <strong>ocean</strong> mol –1 Fe <strong>added</strong>.This estimate may, on the one hand, be considered alower limit, as gas <strong>in</strong>flux would presumably cont<strong>in</strong>uewhen the bloom cont<strong>in</strong>ued after the <strong>per</strong>iod <strong>of</strong> observation,i.e. after the ships had left. On the other hand, itmay just as well be considered an up<strong>per</strong> limit. Forexample, upon the collapse <strong>of</strong> a bloom (e.g. at end <strong>of</strong>SERIES), the ecosystem would most likely tend to shiftto net community respiration, eventually accompaniedby outgass<strong>in</strong>g <strong>of</strong> CO 2 <strong>in</strong> this post-bloom <strong>per</strong>iod. Such amajor shift has been reported for the f<strong>in</strong>al observation<strong>per</strong>iod at the natural Kerguelen Plateau study (Lefèvreet al. 2008).The estimates <strong>of</strong> export flux efficiency (C:Fe) exportefficiency-100mor (C:Fe) export-efficiency-250m are very modestcompared to those that have been suggested <strong>in</strong> geoeng<strong>in</strong>eer<strong>in</strong>gproposals (C:Fe > 100 000) for reduc<strong>in</strong>gthe greenhouse effect by remov<strong>in</strong>g CO 2 from the atmosphere(Buesseler et al. 2004). These efficiency valuesare <strong>in</strong> the range 650 < (C:Fe) export-efficiency < 6600; muchlower than <strong>in</strong>itial suggestions derived directly fromassumed cellular composition ratio <strong>of</strong> plankton <strong>of</strong> C:Fe= ~100 000 or more (Table 2). The low export efficienciesmay partly be ascribed to the fact that ~75% <strong>of</strong>the <strong>added</strong> fresh Fe(II) is removed rapidly <strong>in</strong>to f<strong>in</strong>ecolloids (Nishioka et al. 2005) with<strong>in</strong> 24 to 48 h aftereach <strong>fertilization</strong>:[Colloidal Fe] = 0.76 [Dissolved Fe] + 0.052(R 2 = 0.93) (4)This <strong>removal</strong> is likely the first step towards the nextstage <strong>of</strong> aggregation <strong>in</strong>to larger particles, which thenare lost due to settl<strong>in</strong>g <strong>in</strong>to dee<strong>per</strong> water layers. Thiswould appear consistent with ~63% <strong>of</strong> <strong>added</strong> Fe (1100out <strong>of</strong> 1740 kg Fe) that cannot be accounted for <strong>in</strong> anFe budget <strong>of</strong> SOIREE (Bowie et al. 2001). Such majorloss does not only require repeated <strong>fertilization</strong>s, butalso causes a ~4-fold decrease <strong>of</strong> efficiency. Dur<strong>in</strong>gTable 3. Calculated values <strong>of</strong> efficiency ratio <strong>of</strong> C versus total <strong>added</strong> Fe <strong>in</strong> each ex<strong>per</strong>iment for total estimates over complete <strong>per</strong>iod<strong>of</strong> each ex<strong>per</strong>iment for net community production, CO 2 gas <strong>in</strong>flux from the air, <strong>carbon</strong> export across 100 m depth horizon <strong>in</strong>todee<strong>per</strong> waters, and by extrapolation, export across 250 m depth horizon (Buesseler et al. 2004). Each value has large uncerta<strong>in</strong>ty.Compilation <strong>of</strong> best estimates follow<strong>in</strong>g de Baar et al. (2005) with many <strong>in</strong>compatibilities between ex<strong>per</strong>iments and <strong>in</strong>herent uncerta<strong>in</strong>ties(de Baar et al. 2005, their Fig. 22 & Table 3). For SOFeX-South the (ΔDIC:Fe) NCP estimate is <strong>in</strong>tegrated over a 225 km 2patch area, while the (ΔDIC:Fe) NCP Option 2 is <strong>in</strong>tegrated over a 1000 km 2 patch area, follow<strong>in</strong>g Buesseler et al. (2004). For someother ex<strong>per</strong>iments, other (ΔDIC:Fe) NCP options have also been published (de Baar et al. 2005, their Table 3, italics), but these wereconsidered not the best estimates. If noth<strong>in</strong>g else, the variations between presumed best estimates and other-option estimates forany one ex<strong>per</strong>iment underl<strong>in</strong>es the <strong>in</strong>tr<strong>in</strong>sic difficulty <strong>of</strong> quantification. Moreover, <strong>in</strong> some ex<strong>per</strong>iments it is not clear if the publishedchanges <strong>of</strong> terms <strong>in</strong> the <strong>carbon</strong> budget are truly by difference between the fertilized <strong>in</strong>-patch and the control site (as heredef<strong>in</strong>ed <strong>in</strong> Table 1, ‘Complete equation’), or only for the fertilized <strong>in</strong>-patch, i.e. without correct<strong>in</strong>g for simultaneous changes <strong>of</strong>terms <strong>in</strong> the the <strong>carbon</strong> budget at the unfertilized control site<strong>Efficiency</strong> ratio IronEx II SOIREE EisenEx SEEDS I SOFeX- SOFeX- SERIESSouth North(ΔDIC:Fe) NCP 9672 3701 2847 15 000 8028 4110 16 887(ΔDIC:Fe) NCP Option 2 – – – – 35 680 – –(C:Fe) gas-flux-efficiency 630.5 100.8 219.0 853.7 1003.5 548.0 –(C:Fe) export-efficiency-100m 3150 Negligible – 766 6648 – 650(C:Fe) export-efficiency-250m – – – – 3300 – –

de Baar et al.: <strong>Efficiency</strong> <strong>of</strong> <strong>ocean</strong> <strong>iron</strong> <strong>fertilization</strong>275the Subarctic Pacific Iron Ex<strong>per</strong>iment for EcosystemDynamics Study (SEEDS) I ex<strong>per</strong>iment, the over 75%colloid Fe fraction tended to rema<strong>in</strong> <strong>in</strong> the surfacewaters (Nishioka et al. 2003), at least dur<strong>in</strong>g the 13 d <strong>of</strong>observations, nevertheless be<strong>in</strong>g colloids this fractionwould rema<strong>in</strong> <strong>in</strong>accessible for direct uptake by phytoplankton.F<strong>in</strong>e colloidal Fe is itself deemed unavailable foruptake by phytoplankton, but reduction by daytimephotochemistry, or <strong>per</strong>haps also <strong>in</strong> the vic<strong>in</strong>ity <strong>of</strong> thecell wall due to membrane-bound reductases (Salmonet al. 2006), may br<strong>in</strong>g colloidal Fe back <strong>in</strong>to a solublestate suitable for plankton uptake. The diurnal physicalchemistry <strong>of</strong> Fe colloids (Nishioka et al. 2005, Crootet al. 2005) requires further <strong>in</strong>vestigation.Perhaps <strong>in</strong> future ex<strong>per</strong>iments, when add<strong>in</strong>g dissolvedFe <strong>in</strong> a dissolved organic-complexed form (e.g.bound with excess EDTA), this could be overcome and4-fold higher export efficiencies (rang<strong>in</strong>g from 2600

276Mar Ecol Prog Ser 364: 269–282, 2008Values <strong>of</strong> C:Fe ratio <strong>in</strong> natural <strong>fertilization</strong>The Fe supply <strong>in</strong> natural Fe <strong>fertilization</strong>s at both theKerguelen plateau and the Crozet Island plateaucomes from suboxic or anoxic sediments. These sedimentscan be just below the surface waters exhibit<strong>in</strong>genhanced phytoplankton, i.e. there may be an upwardtransport <strong>of</strong> dissolved Fe from the sediments to the surfacewaters, as suggested for the Kerguelen Plateau(Bla<strong>in</strong> et al. 2007). Alternatively, dissolved Fe from sedimentsat an adjacent island plateau might be transportedlaterally by horizontal currents and water massmix<strong>in</strong>g to a site with observed enhanced phytoplankton,as suggested for the Crozet Island region (Planquetteet al. 2007). Due to the >99% organic complexation(Gerr<strong>in</strong>ga et al. 2008), this Fe is ma<strong>in</strong>ta<strong>in</strong>ed <strong>in</strong>solution far better than the artificial fresh Fe(II) additions<strong>of</strong> the <strong>in</strong> situ <strong>fertilization</strong> ex<strong>per</strong>iments, wherewith<strong>in</strong> 12 to 48 h some 75% <strong>of</strong> the <strong>added</strong> Fe (II) islost very rapidly due to oxidation <strong>in</strong>to colloids (Eq. 4)which <strong>in</strong> turn may aggregate <strong>in</strong>to large particles.Hence, for natural <strong>fertilization</strong> the efficiency ratio valuesmay well be on the order <strong>of</strong> 4-fold higher (or more)than for the ex<strong>per</strong>imental <strong>fertilization</strong>s.Values <strong>of</strong> C:Fe <strong>in</strong> natural <strong>fertilization</strong> at the CrozetPlateauAt the Crozet Plateau, high <strong>carbon</strong> export rates havebeen reported from sediment trap collection. Normalizedto 100 m depth these export rates range from ~1 to~36 mmol C m –2 d –1 <strong>in</strong> the productive region north <strong>of</strong>the plateau and ~2 to 4 mmol C m –2 d –1 <strong>in</strong> the HNLCcontrol region south <strong>of</strong> the plateau (Salter et al. 2007).These values are <strong>in</strong> good agreement with <strong>in</strong>dependentestimates by the 234 Th deficiency method, rang<strong>in</strong>gfrom <strong>in</strong>itially 15 mmol C m –2 d –1 <strong>in</strong> the high-chlorophyllbloom region, compared with 5 mmol C m –2 d –1 <strong>in</strong> thelow-chlorophyll, non-bloom region (Morris et al. 2007).After a moderately small bloom and export event atthe southern control stations, the POC export becamemore uniform, result<strong>in</strong>g <strong>in</strong> equally high levels <strong>of</strong> POCexport (~20 mmol C m –2 d –1 ) throughout the studyregion.The magnitude <strong>of</strong> Fe <strong>in</strong>flux from various sources isvery difficult to quantify. For the bloom<strong>in</strong>g area <strong>of</strong> theCrozet Natural Iron Bloom and Export Ex<strong>per</strong>iment(CROZEX) the soluble Fe <strong>in</strong>flux from aerosols hasbeen assessed at 100 nmol m –2 d –1 , the vertical <strong>in</strong>fluxfrom below sediments at 61 nmol m –2 d –1 , and thehorizontal <strong>in</strong>flux from the nearby islands at 390 nmolm –2 d –1 (Planquette et al. 2007). Each <strong>of</strong> these values isbased on a suite <strong>of</strong> estimates and <strong>in</strong>herent assumptions(see Planquette et al. 2007); assum<strong>in</strong>g that the atmosphericand vertical fluxes are also present at theHNLC control site, and that the horizontal flux cont<strong>in</strong>uesfor 100 d <strong>of</strong> w<strong>in</strong>ter, then the estimated stock <strong>of</strong>Fe available at the start <strong>of</strong> spr<strong>in</strong>g is equivalent to0.039 mmol m –2 yr –1 (Pollard et al. unpubl. data).Next, by compar<strong>in</strong>g the 234 Th-deficiency-derived export(mmol m –2 d –1 ) <strong>of</strong> biogenic Si (i.e. diatoms) withthe seasonal deficit (mmol m –2 ) <strong>of</strong> dissolved silicate <strong>in</strong>the up<strong>per</strong> water layer, Pollard et al. (unpubl. data)arrive at an estimated bloom duration <strong>of</strong> 61 d. Thisyields an excess C export <strong>of</strong> the productive bloomregion compared to the low production control region<strong>of</strong> 670 mmol m –2 <strong>per</strong> grow<strong>in</strong>g season, which, dividedby the excess Fe supply <strong>of</strong> 0.039 mmol m –2 yr –1 yieldstheir reported best estimate efficiency (C:Fe) export-efficiency-100m= ~17 200 for export across the 100 m depthhorizon (Pollard et al. unpubl. data). Furthermore, byus<strong>in</strong>g up<strong>per</strong> and lower limits <strong>of</strong> C export and Fe supply,up<strong>per</strong> and lower limits <strong>of</strong> efficiency <strong>of</strong> (C:Fe) exportefficiency-100m= ~60 400 and ~5400, respectively, areachieved (Pollard et al. unpubl. data).The vertical POC flux collected <strong>in</strong> a deep sedimenttrap at 3000 m depth was found to have only 4% <strong>of</strong> theabove-mentioned downward-POC flux across the 100 mdepth horizon, i.e. 96% <strong>of</strong> the downward-settl<strong>in</strong>gPOC flux was lost <strong>in</strong> the 100 to 3000 m depth <strong>in</strong>terval.This is consistent with the expectations mentioned <strong>in</strong>the above subsection ‘Parameterization—Fate <strong>in</strong> deep<strong>ocean</strong> waters’ for the fate <strong>of</strong> POC <strong>in</strong> the deep <strong>ocean</strong>and yields an efficiency ratio at 3000 m <strong>of</strong> (C:Fe) exportefficiency-3000m= ~730. For <strong>in</strong>termediate depths <strong>in</strong> the 100to 3000 m range the efficiency ratio would be between~17 200 and ~730. When comb<strong>in</strong><strong>in</strong>g this with an <strong>ocean</strong>circulation model, the a priori expectation is that thedeepest regenerated CO 2 (with lowest C:Fe efficiency)will have the longest <strong>ocean</strong> storage time, while themajor regeneration <strong>in</strong> the 100 to 1000 m depth ‘<strong>ocean</strong>twilight zone’ (Buesseler et al. 2007), with its relativelyhigh C:Fe efficiency, will have shorter deep <strong>ocean</strong>storage time. Thus for a range <strong>of</strong> depth <strong>in</strong>tervals themore favorable C:Fe efficiency tends to be coupledwith less favorable storage time. However, regionalcirculation and mix<strong>in</strong>g — as well as rapid deep sedimentationevents with or without enhancement-byballasteffects <strong>of</strong> Si opal and CaCO 3 skeletons — willcause deviations from this simple a priori expectation.Natural <strong>fertilization</strong> at the Kerguelen plateauThe Kerguelen plateau consistently shows elevatedchlorophyll a (chl a) levels (as observed by satellite) andthis ‘<strong>ocean</strong> island effect’ has been <strong>in</strong>vestigated <strong>in</strong> KEOPS(Bla<strong>in</strong> et al. 2007). The diffusive upward flux <strong>of</strong> Fe fromsediments below was 31 nM m –2 d –1 (partly due to

de Baar et al.: <strong>Efficiency</strong> <strong>of</strong> <strong>ocean</strong> <strong>iron</strong> <strong>fertilization</strong>277Table 4. Ratio values <strong>of</strong> plankton uptake rate, plankton content, and various efficiency values derived for the KEOPS field study<strong>of</strong> natural <strong>fertilization</strong> processes (Bla<strong>in</strong> et al. 2007). The reported 200 000 ± 118 000 mol mol –1 value (Bla<strong>in</strong> et al. 2007) apparentlyslightly deviates from the actual value <strong>of</strong> 274 000 ± 142 000 mol mol –1 (range is 131 000 to 416 000) <strong>in</strong> the more recently publishedarticle <strong>of</strong> the shipboard ex<strong>per</strong>iments (Sarthou et al. 2008). Export efficiencies at 100 and 200 m reported by Bla<strong>in</strong> et al. (2007); alternativeexport efficiency values (Invoked 2) calculated <strong>in</strong> this study. Ratio values C:Fe <strong>of</strong> plankton uptake rate and planktoncontent after <strong>in</strong>version <strong>of</strong> ratio values Fe:C reported by Sarthou et al. (2008). Also shown is an Invoked 3 scenario for sake <strong>of</strong>comparison with diatom C:Fe composition under optimal Fe-replete conditions, see ‘Discussion—Concordia’Ratio values KEOPS KEOPS KEOPS KEOPSInvoked 1 Invoked 2 Invoked 3(Bla<strong>in</strong> et al. 2007) (present study) (present study)Plankton uptake rate(C:Fe) plankton-uptake-rate – 200 000 ± 118 000 a – –– 131 000 to 416 000 (n = 6) b – –Plankton content(C:Fe) plankton-content – 227 000 ± 5000 (n = 10) b – –175 000 to 333 000(C:Fe) large-diatoms-Fe-limited – – ~160 000 c –(C:Fe) large-diatoms-optimal – – – ~23000 c<strong>Efficiency</strong> ratiosExcess Fe supply rate 27 204 ± 77 ~289 ~2013(nM m –2 d –1 ) (Invoked 1) (Invoked 2) (Invoked 3)(ΔDIC:Fe) NCP 668 000 – – –Seasonal budget – – –(ΔDIC:Fe) NCP – 149 000 – –Seasonal budget <strong>in</strong>clud<strong>in</strong>glithogenic Fe supply(C:Fe) export-efficiency-100m 400 000 ± 180 000 21 000 to 123 600 16 800 to 98 880 2415 to 14 214(C:Fe) export-efficiency-200m 526 000 ± 290 000 70 000 ± 46 000 56 000 ± 37 000 8050 ± 529022 400 to 174 000 17 920 to 193 200 2576 to 20 010a Bla<strong>in</strong> et al. (2007); b Sarthou et al. (2008); c Tw<strong>in</strong><strong>in</strong>g et al. (2004)enhanced vertical diffusivity) as compared to 4 nM m –2d –1 at the <strong>of</strong>f-plateau control site. The mean excess <strong>of</strong>234 Th-derived export production on the plateau versus atthe control site was 10.8 ± 4.9 mmol C m –2 d –1 at 100 mdepth and 14.2 ± 7.9 mmol C m –2 d –1 at 200 m depth.Divid<strong>in</strong>g by the excess upward diffusive Fe flux <strong>of</strong> 27 nMm –2 d –1 leads to (C:Fe) export-efficiency-100m = 400 000 and(C:Fe) export-efficiency-200m = 526 000. Presumably theserecord high export efficiencies were deemed nonrealisticby the authors. Therefore, an additional FeTable 5. Export efficiency at 100 m depth dur<strong>in</strong>g SEEDS II, estimatedafter A. Tsuda et al. (unpubl. data), and the export efficiencyat 150 m dur<strong>in</strong>g EIFEX follow<strong>in</strong>g Smetacek (2005)and Jacquet et al. (2008) for the two 7 t <strong>iron</strong>-sulphate(FeSO 4 .7H 2 O) enrichments (<strong>in</strong> ~150 km 2 and ~400 km 2patches). One mol FeSO 4 .7H 2 O equals 278 g, 1 mol Fe equals55.847 g. Upon publication <strong>of</strong> f<strong>in</strong>d<strong>in</strong>gs for dissolved <strong>in</strong>organic<strong>carbon</strong> (DIC) and pCO 2 , differences between <strong>in</strong>-patch andout-patch stations the (ΔDIC:Fe) NCP and (C:Fe) gas-flux-efficiencymay also be assessed<strong>Efficiency</strong> ratio SEEDS II EIFEX(C:Fe) export-efficiency-100m ~1600–25000 –(C:Fe) export-efficiency-150m – ~2780supply term was <strong>in</strong>voked. Shipboard 55 Fe uptake andregeneration ex<strong>per</strong>iments would lead to a hypothesizedexcess Fe <strong>in</strong>put <strong>of</strong> 204 ± 77 nM m –2 d –1 over the plateau,but the source <strong>of</strong> this excess Fe is unaccounted for.With the same above <strong>carbon</strong> export at 200 m depth, wecalculate a range <strong>of</strong> 22 400 < (C:Fe) export-efficiency-200m

de Baar et al.: <strong>Efficiency</strong> <strong>of</strong> <strong>ocean</strong> <strong>iron</strong> <strong>fertilization</strong>279for quantification <strong>of</strong> the <strong>carbon</strong> C stocks and turnoverrates are the same or similar, hence the <strong>in</strong>herent uncerta<strong>in</strong>tieslikely are similar. On the other hand, the quantifications<strong>of</strong> the Fe supply, stocks and turnover ratesare vastly different. For the <strong>in</strong> situ ex<strong>per</strong>iments, thetotal amount <strong>of</strong> <strong>added</strong> Fe is accurately known, but thefate <strong>of</strong> this Fe is very poorly quantified due to some 60to 75% be<strong>in</strong>g lost, somehow, somewhere. Budget estimations<strong>of</strong> the fate <strong>of</strong> <strong>added</strong> Fe are difficult and onlyone budget assessment has been published (Bowie etal. 2001). For the natural <strong>fertilization</strong> ex<strong>per</strong>iments, thequantification <strong>of</strong> Fe supply from below sediments isdifficult and <strong>in</strong> KEOPS was shown to be far lower thandesirable.Ranges <strong>of</strong> estimatesThe <strong>ocean</strong>s are dynamic regions, with much variability<strong>in</strong> time and place, where day-to-day variability <strong>of</strong>the weather (w<strong>in</strong>d, <strong>in</strong>solation) is a major driver <strong>of</strong> variability<strong>of</strong> any one up<strong>per</strong> <strong>ocean</strong> plankton ecosystem. Inevery s<strong>in</strong>gle <strong>fertilization</strong> ex<strong>per</strong>iment or natural <strong>fertilization</strong>study, the complete 3D mapp<strong>in</strong>g every day <strong>of</strong>all key variables cannot be achieved with merely 1 (orat most 3) ships and their shipboard observers. Foreach ex<strong>per</strong>iment the ensu<strong>in</strong>g dataset, therefore, is verylimited <strong>in</strong> space, <strong>in</strong> time, and <strong>in</strong> a very restricted number<strong>of</strong> key variables. Thus, we are only scratch<strong>in</strong>g thesurface. Nevertheless, for each study, the overarch<strong>in</strong>gsynthesis article (e.g. Tsuda et al. 2003, 2007, Boyd etal. 2004, Coale et al. 2004, Bla<strong>in</strong> et al. 2007) very cleverlycomb<strong>in</strong>es these limited observations <strong>in</strong>to an overallcoherent <strong>in</strong>terpretation, based on the underly<strong>in</strong>gmore specific reports (e.g. Buesseler et al. 2004, Nishiokaet al. 2005, Gerr<strong>in</strong>ga et al. 2008) <strong>of</strong> that 1 study.Previously (de Baar et al. 2005, Boyd et al. 2007) and<strong>in</strong> this article, an effort has been made to comb<strong>in</strong>ethese <strong>in</strong>dividual field projects (IronEx II throughCROZEX, KEOPS) <strong>in</strong>to a synthesis, where <strong>in</strong>evitablyits conclusions carry the sum <strong>of</strong> all uncerta<strong>in</strong>ties <strong>of</strong> thes<strong>in</strong>gle studies. Moreover, the various estimates as citedhere from work by others, as well as <strong>in</strong> this article, areall based on many <strong>in</strong>evitable assumptions, as requireddue to lack <strong>of</strong> data or knowledge, where a large number<strong>of</strong> these assumptions are highly debatable, if notquestionable. In other words, due to the limiteddatasets, there is much room for alternative <strong>in</strong>terpretationsand conclusions.CONCLUSIONSThe most reliable estimate <strong>of</strong> (C:Fe) large-diatoms-optimalis to date ~23 000 for <strong>in</strong> situ large Antarctic diatomswith<strong>in</strong> the Fe-replete SOFeX-South patch. This is <strong>in</strong>good agreement with the diffusion limitation (de Baaret al. unpubl. data) <strong>of</strong> the rate <strong>of</strong> growth <strong>of</strong> largeAntarctic diatoms <strong>in</strong> shipboard and laboratory ex<strong>per</strong>iments<strong>of</strong> <strong>in</strong>cubations <strong>of</strong> s<strong>in</strong>gle species diatoms <strong>in</strong> filteredultraclean natural Antarctic seawater (Timmermanset al. 2004). In the Fe-limited, suboptimal growthconditions <strong>of</strong> the open Antarctic Ocean, large diatomssurvive at very low, but likely <strong>per</strong>sistent, rates <strong>of</strong>growth and may have lower suboptimal <strong>in</strong>tracellularC:Fe ratio values, from ~160 000 at out-patch stations<strong>of</strong> SOFeX-South to ~227 000 <strong>in</strong> the ambient 0.09 nM Fesurface waters <strong>of</strong> Kerguelen Plateau.In the artificial Fe <strong>fertilization</strong> ex<strong>per</strong>iments, the 4estimates thus far <strong>of</strong> (C:Fe) gas-flux-efficiency range from 100to 1000 (Table 3). In the <strong>per</strong>iod after observation shipshave left, this efficiency may either <strong>in</strong>crease ordecrease, due to either cont<strong>in</strong>ued net community productionor a shift to f<strong>in</strong>al net community respiration,respectively.The estimates <strong>of</strong> <strong>carbon</strong> export efficiency at 100 mdepth range from 650 (SERIES) to 6648 (SOFeX-South)with an extrapolated value at 250 m <strong>of</strong> ~3300 forSOFeX-South (Tables 3 & 5). For EIFEX the export efficiencyat 150 m depth is estimated at ~2780 (Table 5).For these artificial <strong>fertilization</strong>s the ~75% immediateloss <strong>of</strong> <strong>added</strong> Fe may be corrected for by a factor<strong>of</strong> ~4 when assum<strong>in</strong>g future or natural <strong>fertilization</strong> asa more stable Fe-organic complex. This would<strong>in</strong>crease the CO 2 drawdown efficiency <strong>in</strong> the 400 to4000 range and the various export efficiency estimatesto a range from ~2600 (SERIES) to ~26 600(SOFeX-South), or even ~100 000 when <strong>in</strong>clud<strong>in</strong>g thehigh estimate <strong>of</strong> SEEDS II based on an assumed verylarge 1000 km 2 patch size.For the artificial <strong>in</strong> situ Fe <strong>fertilization</strong> ex<strong>per</strong>iments,at least the amount <strong>of</strong> <strong>added</strong> Fe is accurately known,such that the uncerta<strong>in</strong>ty <strong>in</strong> the above estimations <strong>of</strong>C:Fe efficiency is due solely to uncerta<strong>in</strong>ty <strong>in</strong> theassessment <strong>of</strong> the C budgets. For natural Fe <strong>fertilization</strong>sthe supply <strong>of</strong> Fe also must be derived from fieldobservations, such that the derived supply <strong>of</strong> Fe has anuncerta<strong>in</strong>ty equal or larger than the uncerta<strong>in</strong>ty <strong>in</strong> theparallel estimation <strong>of</strong> the C budget. Therefore, the(C:Fe) export-efficiency <strong>of</strong> natural <strong>fertilization</strong>s has an <strong>in</strong>herentlylarger uncerta<strong>in</strong>ty than that <strong>of</strong> the artificial <strong>fertilization</strong>ex<strong>per</strong>iments.In the natural Fe <strong>fertilization</strong> at the Crozet Plateauthe (C:Fe) export-efficiency at 100 m depth was reported tobe ~17 200, with<strong>in</strong> reported up<strong>per</strong> and lower estimates<strong>of</strong> ~60 400 and ~5400, respectively (Pollard et al. 2008).In the natural Fe <strong>fertilization</strong> at the Kerguelen Plateau,the derived (C:Fe) export-efficiency at either 100 m or 200 mdepth ranged from ~8050 to ~526 000, largely depend<strong>in</strong>gon the assumed or <strong>in</strong>voked Fe supply term.

280Mar Ecol Prog Ser 364: 269–282, 2008RECOMMENDATIONSWhen deliver<strong>in</strong>g the <strong>iron</strong> fertilizer <strong>in</strong> a more stableorganic-complexed dissolved form, the efficiency <strong>of</strong><strong>carbon</strong> export <strong>in</strong>to dee<strong>per</strong> <strong>ocean</strong> waters may rangefrom ~2600 to ~26 600 <strong>per</strong> <strong>added</strong> amount <strong>of</strong> <strong>iron</strong>. Laboratoryresearch is needed to unravel which specificFe-organic complex<strong>in</strong>g chemical molecule would bothstabilize Fe <strong>in</strong> solution and leave it available for uptakeby the target group <strong>of</strong> phytoplankton, e.g. largediatoms. This will be <strong>in</strong>fluenced by photochemistry(notably Fe photoreduction) which should be part<strong>of</strong> such studies.The wide variability <strong>of</strong> export efficiency is due towide variations <strong>of</strong> <strong>in</strong>itial <strong>ocean</strong> conditions before <strong>iron</strong>addition and wide variation <strong>of</strong> weather conditions after<strong>iron</strong> addition. Initial conditions <strong>of</strong> major <strong>in</strong>fluence arethe <strong>in</strong>itial abundance <strong>of</strong> phytoplankton and its majortaxonomic groups and size classes, micro- and mesozooplankton,water column stratification, and tem<strong>per</strong>ature.For nutrient-rich HNLC regions, the <strong>in</strong>itial concentrations<strong>of</strong> major nutrients are deemed <strong>in</strong> amplesupply, yet the weather strongly controls the lightclimate for photosynthesis, not only by the variations<strong>of</strong> cloud cover controll<strong>in</strong>g <strong>in</strong>com<strong>in</strong>g solar irradiance atthe <strong>ocean</strong> surface, but <strong>per</strong>haps even more by w<strong>in</strong>dforc<strong>in</strong>g algae to be mixed dee<strong>per</strong> down, where lightconditions are unfavorable. This strong weatherdependencerenders the outcome <strong>of</strong> commercial-scaleOIF unpredictable, its statistics more ak<strong>in</strong> to gambl<strong>in</strong>gthan prudent f<strong>in</strong>ancial <strong>in</strong>vestment. Moreover, even thevery highest efficiency value <strong>of</strong> ~25 000 is far less thanthe first-hypothesized values <strong>in</strong> the ~500 000 range andOIF bus<strong>in</strong>ess plans should at least use a 20-fold higheramount <strong>of</strong> Fe than <strong>in</strong>itially hypothesized.The <strong>iron</strong> <strong>fertilization</strong> ex<strong>per</strong>iments done thus far wereby no means designed for assess<strong>in</strong>g commercial-scaleOIF. When pursu<strong>in</strong>g commercial-scale OIF, far moreextensive quantification <strong>of</strong> <strong>carbon</strong> export (e.g. by farmore <strong>in</strong>tensive 234 Th mapp<strong>in</strong>g, many more sedimenttrap deployments, or other methods yet to be designedand validated) is required for accurate accountability<strong>of</strong> the <strong>carbon</strong> storage, which <strong>in</strong> turn is required forappropriate accountability <strong>of</strong> <strong>in</strong>tended f<strong>in</strong>ancial <strong>carbon</strong>credits.Beyond the efficiency <strong>of</strong> CO 2 <strong>in</strong>flux from the atmosphere<strong>in</strong>to the <strong>ocean</strong> and efficiency <strong>of</strong> export below adef<strong>in</strong>ed 100 m or 250 m depth horizon, there are additionalfactors beyond the scope <strong>of</strong> this pa<strong>per</strong> (someeven beyond the scope <strong>of</strong> <strong>ocean</strong>ography). These havebeen considered elsewhere and <strong>in</strong> companion articles<strong>of</strong> this Theme Section and <strong>in</strong>clude (1) longevity <strong>of</strong> deep<strong>ocean</strong> storage <strong>in</strong> relation to the ventilation time <strong>of</strong>underly<strong>in</strong>g waters (after how many years, decades, or<strong>per</strong>haps centuries, will the temporarily stored deep<strong>ocean</strong> CO 2 surface aga<strong>in</strong> and ventilate back <strong>in</strong>to theatmosphere); (2) negative feedbacks (i.e. enhancedproduction <strong>of</strong> stronger greenhouse gases methane andnitrous oxide); (3) the f<strong>in</strong>ancial and energy expenditureand CO 2 emission (e.g. by ships) <strong>of</strong> OIF; (4) env<strong>iron</strong>mentalprotection; (5) <strong>in</strong>ternational treaties (theLondon ‘Dump<strong>in</strong>g’ Convention, Antarctic Treaty, etc.);and last, but not least, (6) the ethics <strong>of</strong> OIF <strong>in</strong>, for example,the precautionary pr<strong>in</strong>ciple and the transgenerationalpr<strong>in</strong>ciple. Briefly, even when ignor<strong>in</strong>gthe latter two factors (<strong>in</strong>ternational treaties and ethics)<strong>per</strong>haps the question to ask a proponent <strong>of</strong> OIF iswhether or not one would <strong>in</strong>vest his or her own <strong>per</strong>sonalsav<strong>in</strong>gs <strong>in</strong> an OIF enterprise, or advise his or herchildren to <strong>in</strong>vest their money as a means <strong>of</strong> secur<strong>in</strong>gtheir <strong>per</strong>sonal future f<strong>in</strong>ancial security.Acknowledgements. The authors are grateful to the editorsfor the <strong>in</strong>vitation and their patience until delivery <strong>of</strong> the manuscript.This article is merely a synthesis <strong>of</strong> the orig<strong>in</strong>alresearch and we are much <strong>in</strong>debted to authors and colleagues<strong>of</strong> these orig<strong>in</strong>al research articles. Given the prescribedmaximum length and rapid publication objective, it was notpossible to describe and give citations <strong>of</strong> all preced<strong>in</strong>gresearch <strong>of</strong> relevance, for which we <strong>of</strong>fer our apologies, yetsurely this manuscript is based on far more published workthan reflected <strong>in</strong> the citations. Special thanks go to Dr. A.Saito and Pr<strong>of</strong>essor A. Tsuda for provid<strong>in</strong>g <strong>in</strong>formation,<strong>in</strong>sights and prepr<strong>in</strong>ts and repr<strong>in</strong>ts on the SEEDS I and IIex<strong>per</strong>iments, and Pr<strong>of</strong>essor R. Pollard for <strong>in</strong>formation, <strong>in</strong>sightsand a prepr<strong>in</strong>t <strong>of</strong> his manuscript on the Crozet observations.LITERATURE CITEDArrigo KR, Worthen DL, Rob<strong>in</strong>son DH (2003) A coupled<strong>ocean</strong>-ecosystem model <strong>of</strong> the Ross Sea. 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