Methyl iodide production in the ocean: Implications for climate change

Abstract

[1] Methyl iodide concentrations of up to 45 pmol L À1 , which flux into the marine boundary layer, have been found in low latitude waters of the Atlantic and Indian oceans. These high concentrations correlate well with the abundance of Prochlorococcus, and we have confirmed the release of methyl iodide by this species in laboratory culture experiments. Extrapolating, we estimate the global ocean flux of iodine to the marine boundary layer from this single source to be 5.3 Â 10 11 g I yr À1 , which is a large fraction of the previously estimated total global flux and the implications are far reaching. Climate prediction models suggest increases in sea surface temperature and changes in biogeographical provenances in response to global warming. Such changes are likely to increase the abundance of Prochlorococcus, and we estimate a concomitant $15% increase in the release of iodine species to the atmosphere. Potentially, this could help mitigate global warming.

Biogeochemical Considerations Related To The Remediation Of I-129 Plumes

“…Among the reasons for this is that the analytical chemistry at the extremely low concentrations necessary to study ambient 129 I (10 -7 to 10 -11 M) have not been readily available and the analytical procedures were (and still are) arduous (Denham et al, 2009 129 I concentration was 232 pCi L -1 immediately downstream of the seepage basins (source terms) and decreased with distance from the seepage basin. 127 I concentration decreased similarly to that of 129 I. Near the seepage basins, the majority (55 -86%) of iodine existed as iodide for both 129 I and 127 I.…”

“…Schmitz and Aumann (1995) analyzed soils collected from a reprocessing plant in Germany and reported that 39 to 49% of the 129 I was associated with the water soluble fraction, whereas only 4 to 15% was associated with the organic and 7 to 13% was associated with the residual fraction. However, a different distribution of stable iodine, 127 I, was observed where only <4% occurred in the water soluble fraction. This difference between the two isotopes may be attributed to the different sources of the two isotopes and underscores an important point that the fate of iodine in the environment is controlled by more than just geochemical behavior.…”

“…These natural processes account for trace levels of radioiodine in the environment but results in no human health risk. The ratio of stable 127 I to radioactive 129 I in the environment is more than 10,000,000 to 1. The global inventory of natural 129 I accumulated over the lifetime of the earth is estimated to be 10 Ci in the terrestrial environment and 30 Ci in oceans and the atmosphere (NCRP, 1983).…”

“…As stated in Section 1.1, 90% of the groundwater samples analyzed in this area are ≤ 3.5 pCi L -1 (≤ 1 x 10 -10 M). Furthermore, natural stable iodine, 127 I, also exists in the plume in much greater concentrations, in the order of 10 -8 M.…”

“…In order for most strong sorbents (or getters), such as those based on anion exchange, irreversible complexation, and precipitation, to work effectively to lower the 129 I concentrations, would also have to lower the natural iodine concentrations, 127 I, about two orders of magnitude. Upon lowering the 127 I concentrations, the Hanford sediment would release more 127 I as the subsurface system adjusts to the altered adsorption/desorption and solubility equilibrium.…”