Coupling iodine speciation to primary, regenerated or "new" production: a re-evaluation

In two recent studies (Tian et al., Deep-Sea Res. I 43 (1996) 723-738; Camp os et al., Deep-Sea Res. II 43 (1996) 455-466), in order to explain the obs erved temporal variations in the distributions of the dissolved iodine spec ies at the time-series stations in the Mediterranean Sea, the North Atlanti c and the North Pacific, diverse assumptions were invoked on the relationsh ips between changes in the speciation of dissolved iodine in the surface oc eans and biological production such that the surface enrichment of I- was l inked to both regenerated production and primary production while the surfa ce depletion of [IO3- + I-] was linked to "new" production. However, while some of the major conclusions in these studies are critically dependent on these assumptions, the validity of the assumptions has yet to be verified w ith experimental evidence. On the other hand, while there are still signifi cant unknowns in the understanding of the cycling among dissolved iodine sp ecies in the surface oceans, presently available data from laboratory cultu res and field observations are consistent with an alternative conceptual mo del in which IO3- and NO3- are taken up at some ratio to each other during NO3- uptake and almost all of the IO3- taken up is exuded as I-. Thus, the depletion of IO3- and the enrichment of I- in the surface water are linked to NO3- uptake. This alternative model is also consistent with the data set s presented by Tian et al. (1996) and Campos et al. (1996). By linking the surface depletion of IO3- to NO3- uptake, significantly different biogeoche mical behavior of the marine dissolved iodine system may be inferred. The e xtent to which I- may be oxidized to IO3- within the euphotic zone during t he residence time of the water in the surface ocean is still an open questi on. (C) 2001 Elsevier Science Ltd. All rights reserved.