Opti­ons to Enhan­ce, Main­tain, and Mana­ge Bio­lo­gi­cal Car­bon Reser­voirs and Geo-engi­nee­ring                                                                                                         S.   333

This might invol­ve pro­vi­ding nitro­gen or phos­pho­rus in lar­ge quan­ti­ties, but the quan­ti­ties to be sup­pli­ed would be much smal­ler if growth were limi­t­ed by a micro­nu­tri­ent. In par­ti­cu­lar, the­re is evi­dence that in lar­ge are­as of the Sou­thern Oce­an pro­duc­ti­vi­ty is limi­t­ed by avai­la­bi­li­ty of the micro­nu­tri­ent iron. Mar­tin (1990, 1991) sug­gested that the oce­an could be sti­mu­la­ted to take up addi­tio­nal CO2 from the atmo­sphe­re by pro­vi­ding addi­tio­nal iron, and that 300,000 ton­nes of iron could result in the rem­oval of 0.8GtC from the atmo­sphe­re.  Other ana­ly­ses have sug­gested that the effect may be more limi­t­ed.  Peng and Broe­cker (1991) exami­ned the dyna­mic aspects of this pro­po­sal and con­cluded that, even if the iron hypo­the­sis was com­ple­te­ly cor­rect, the dyna­mic issues of mixing the excess car­bon into the deep oce­an would limit the magni­tu­de of the impact on the atmo­sphe­re. Joos et al. (1991) repor­ted on a simi­lar model expe­ri­ment and found the oce­an dyna­mics to be less important, the time path of anthro­po­ge­nic CO2 emis­si­ons to be very important, and the maxi­mum poten­ti­al effect of iron fer­ti­liza­ti­on to be some­what grea­ter than repor­ted by Peng and Broe­cker (1991).

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