The CICS Science group is working with GFDL through CICS to maintain a group of scientists able to analyze mitigation options as they arise. While iron fertilization and deep-sea injection do not appear to be gaining traction as viable options, there does continue to be strong interest in them, including amongst private commercial ventures. There are many unresolved questions that are of considerable interest scientifically, and the outcomes will have significant impact on our evaluations of the viability of these options.
Simulations of iron fertilization
During the last year, Sarmiento’s group carried out a set of iron fertilization simulations making use of the new generation of ecosystem and iron chemistry models that have been developed over the past decade at Princeton and GFDL. These fertilization model results differ significantly from the major conclusions of our previous research in showing greater sequestration efficiency. The main reason for this discrepancy is that the added iron is retained for a long period of time in the new models, and thus continues to draw down carbon each time it returns to the surface. In previous research, it had been assumed that the added iron would be scavenged very rapidly.
Additional tests that were performed included the addition of a simple global atmosphere for carbon, which reduced the efficiency by about 40% due to decreased uptake elsewhere, and a simulation where the added iron is only allowed to be used once before it is then removed from the system, which reduced the efficiency by up to a factor of 10. Other simulations were performed to help us better understand the mechanisms which differentiate the new generation of models from past and to compare our results more directly with some of the oceanic iron fertilization experiments (IRONEX).
As a complement to the iron fertilization study, Keith Rodgers conducted a modeling study of natural decadal variability in iron concentrations in the Equatorial Pacific. This study indicates that the supply of iron to the upwelling region along the equator may exhibit large decadal variability. Understanding such variability in iron cycling will be valuable when interpreting the representativeness of the background state at the time of particular in situ fertilization experiments, and in assessing the potential of fertilization to reduce atmospheric CO2 concentrations.