Abstract: Recent mesoscale iron fertilization studies in the Southern Ocean (e.g. SOIREE, EisenEx, SOFeX) have demonstrated the importance of iron as a limiting factor for phytoplankton growth in these high nutrient, low-chlorophyll (HNLC) waters. In addition to the generation of extensive phytoplankton blooms, some of the most striking results from these experiments concern the chemistry of iron in the Southern Ocean. In particular, the unexpected longevity of soluble reduced iron, Fe(II), within iron-enriched waters during these experiments has important implications for the future development of iron fertilization protocols to enhance carbon sequestration in high-latitude oceans. Creation of effective fertilization schemes will require more information about extended lifetimes of Fe(II) in Southern Ocean waters as a means to retain new iron within the euphotic zone. To contribute to our knowledge base, I propose to study the production and retention of dissolved Fe as Fe(II) across a significant natural gradient in chlorophyll concentrations in the Southern Drake Passage. This area will be the focus of a multidisciplinary NSF/OPP-funded investigation in February 2004 to determine the influence of mesoscale circulation and iron transport with regard to the observed patterns in sea surface chlorophyll in the region near the Shackleton Fracture Zone. A number of parameters will be assessed across this gradient in order to reveal interactions between plankton community structure and iron distributions. As a co-PI in the NSF/OPP-funded project, my role will be to conduct iron addition incubation and radiotracer experiments, and carry out shipboard analysis of iron chemistry, including iron-organic speciation. Herein I propose to analyse reduced iron species using an FeLume flow injection analysis chemiluminescence system as an extension of my planned work on the NSF/OPP project. Spatial and temporal gradients in Fe(II) will be determined, and on-board incubations will be conducted to study Fe(II) lifetime and production under different conditions. Following the cruise in February 2004, a further series of experiments will be conducted in the laboratory to determine what role organic complexing agents may play in controlling Fe(II) speciation under conditions typical of high latitude waters. By contrasting extreme HNLC areas with naturally Fe-enriched, higher chlorophyll regimes, the research outlined here will answer many basic questions about the production and persistence of Fe(II) in Antarctic waters under conditions of sustained iron enrichment.