Interesting study - but of course the enormous amount of additional reactive nitrogen available today means that the past only offers limited insight into the present. Phosphate run off is also likely to be significant in making iron limitation more significant globally.
I suggest this paper will be useful to those setting up model runs, but extreme caution should be used when extrapolating to the present day without a proper model. A On 28 Jan 2016 20:47, "CE News Site" <[email protected]> wrote: > Scientific American and others cover the study you find below. > First the Scientific American article: > http://www.scientificamerican.com/article/geoengineering-would-not-work-in-all-oceans/?wt.mc=SA_Twitter-Share > > > http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html > No iron fertilization in the equatorial Pacific Ocean during the last ice > age > > - K. M. Costa > > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#auth-1> > , > - J. F. McManus > > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#auth-2> > , > - R. F. Anderson > > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#auth-3> > , > - H. Ren > > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#auth-4> > , > - D. M. Sigman > > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#auth-5> > , > - G. Winckler > > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#auth-6> > , > - M. Q. Fleisher > > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#auth-7> > , > - F. Marcantonio > > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#auth-8> > - & A. C. Ravelo > > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#auth-9> > > > - Affiliations > > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#affil-auth> > - Contributions > > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#contrib-auth> > - Corresponding author > > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#corres-auth> > > Nature 529, 519–522 (28 January 2016) doi:10.1038/nature16453 > > The equatorial Pacific Ocean is one of the major high-nutrient, > low-chlorophyll regions in the global ocean. In such regions, the > consumption of the available macro-nutrients such as nitrate and phosphate > is thought to be limited in part by the low abundance of the critical > micro-nutrient iron1 > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#ref1>. > Greater atmospheric dust deposition2 > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#ref2> > could have fertilized the equatorial Pacific with iron during the last ice > age—the Last Glacial Period (LGP)—but the effect of increased ice-age dust > fluxes on primary productivity in the equatorial Pacific remains uncertain > 3 > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#ref3>, > 4 > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#ref4>, > 5 > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#ref5>, > 6 > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#ref6>. > Here we present meridional transects of dust (derived from the 232Th > proxy), phytoplankton productivity (using opal, 231Pa/230Th and excess > Ba), and the degree of nitrate consumption (using foraminifera-bound δ15N) > from six cores in the central equatorial Pacific for the Holocene (0–10,000 > years ago) and the LGP (17,000–27,000 years ago). We find that, although > dust deposition in the central equatorial Pacific was two to three times > greater in the LGP than in the Holocene, productivity was the same or > lower, and the degree of nitrate consumption was the same. These > biogeochemical findings suggest that the relatively greater ice-age dust > fluxes were not large enough to provide substantial iron fertilization to > the central equatorial Pacific. This may have been because the absolute > rate of dust deposition in the LGP (although greater than the Holocene > rate) was very low. The lower productivity coupled with unchanged nitrate > consumption suggests that the subsurface major nutrient concentrations were > lower in the central equatorial Pacific during the LGP. As these nutrients > are today dominantly sourced from the Subantarctic Zone of the Southern > Ocean, we propose that the central equatorial Pacific data are consistent > with more nutrient consumption in the Subantarctic Zone, possibly owing to > iron fertilization as a result of higher absolute dust fluxes in this region > 7 > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#ref7>, > 8 > <http://www.nature.com/nature/journal/v529/n7587/full/nature16453.html#ref8>. > Thus, ice-age iron fertilization in the Subantarctic Zone would have > ultimately worked to lower, not raise, equatorial Pacific productivity. > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/geoengineering. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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