Iron in the Equatorial Undercurrent: Data and Models

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ABSTRACTOCE-0425721One of the principle new findings from the US JGOFS EqPac Process study in the central equatorial Pacific was that iron in the equatorial undercurrent (EUC) is the most important source of iron for driving biological new production and thus carbon cycling in this region. It has been hypothesized that the source of the iron is from terriginous sources in the vicinity of New Guinea. If that is the case, what is happening downstream from New Guinea? How far eastward can a New Guinea iron source be traced? There is a critical lack of data from this region that is needed to test this source hypothesis. This is a major lingering question that needs to be answered.In this project an international team of US and French ocean scientists, under the leadership of a marine geochemist at the University of Washington, will determine the distributions of iron, manganese, aluminum and neodymium in a zonal section along the equatorial Pacific. They will be seeking answers to four major questions: 1. Is there really a maximum of iron in the equatorial undercurrent? 2. What is its zonal gradient? 3. What is its origin? 4. How do the distributions constrain model derived fluxes? The team will use a 4-year integrated field, analytical and modeling approach. They will conduct a zonal cruise along the equator from 143'E to 140'W to measure dissolved, colloidal and total acid soluble Fe, Mn and Al. Laboratory studies will be carried out to measure dissolved and particulate neodymium isotopes and particulate Fe, Mn and Al. A coupled dynamical-biogeochemical model will be run to predict iron distributions before the cruise. They will also the model approach to estimate the relative importance of physical versus biogeochemical fluxes in the central (cold tongue) and western (warm pool) equatorial Pacific.The broader impacts of the science are that because iron has been shown to be an element limiting carbon cycling in this region, understanding its source will lead to greater understanding of past and future changes in biological productivity and carbon fluxes and provide a basis for predicting the response to climate change. New observations are required so that iron can be effectively incorporated into models of carbon cycling in this region. This project will feature major international collaboration with several foreign scientists from different disciplines. This will include scientists from Noumea, New Caledonia (biological analyses), Paris, France (modeling) and Toulouse, France (Nd analyses). It will also include training of graduate students in a wide range of state-of-the-art analytical and modeling techniques and interdisciplinary oceanography.