Elevated CO2 Boosts Iron's Positive Impact on Phytoplanktonic Productivity
Breitbarth, E., Bellerby, R.J., Neill, C.C., Ardelan, M.V., Meyerhofer, M., Zollner, E., Croot, P.L. and Riebesell, U. 2010. Ocean acidification affects iron speciation during a coastal seawater mesocosm experiment. Biogeosciences 7: 1065-1073.
Following the development of natural phytoplanktonic blooms in the Pelagic Ecosystem CO2 Enrichment (PeECE III) study -- where the blooms were monitored in mesocosms consisting of two-meter-diameter polyethylene bags submerged to a depth of ten meters in an adjacent fjord, where they were maintained in equilibrium with air possessing CO2 concentrations of either 350, 700 or 1050 ppm via aeration of the water column and the overlying atmosphere with air of the three CO2 concentrations (Schulz et al., 2008), Breitbarth et al. measured dissolved iron (dFe) concentrations as well as levels and oxidation rates of Fe(II) -- a necessary trace element (the ferrous species of iron) used by almost all living organisms -- over the course of the study to determine if ocean acidification may affect iron speciation in seawater.
Based upon their analysis, the eight researchers report that CO2 perturbation and phytoplanktonic bloom development resulted in pH value ranges of 7.67-7.97, 7.82-8.06 and 8.13-8.26 at 1050, 700 and 350 ppm CO2, respectively; and they say their measurements revealed that under these conditions there were significantly higher dFe concentrations in the high CO2 treatment compared to the mid and low CO2 treatments, and that the high-CO2 mesocosms showed higher values of FE(II) compared to the lower CO2 treatments.
Breitbarth et al. thus conclude that "ocean acidification may lead to enhanced Fe-bioavailability due to an increased fraction of dFe and elevated Fe(II) concentrations in coastal systems ... due to pH induced changes in organic iron complexation and Fe(II) oxidation rates," noting that these phenomena "will result in increased turnover of Fe in surface seawater, potentially maintaining iron bioavailability given a sufficient supply of total Fe, since equilibrium partitioning eventually restores the biolabile Fe pools that have been depleted by biological uptake." Hence, they opine that "these processes may further fuel increased phytoplankton carbon acquisition and export at future atmospheric CO2 levels," citing the work of Riebesell et al. (2007); and they thereby reach their final conclusion that "changes in iron speciation and the resulting potential negative feedback mechanism of phytoplankton productivity on atmospheric CO2" -- i.e., the drawdown of atmospheric CO2 due to enhanced phytoplanktonic growth and transferal of the carbon thus removed from the atmosphere to the ocean depths -- "need to be considered when assessing the ecological effects of ocean acidification," which is something climate alarmists are generally loath to do when the effects are beneficial.
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