In-Situ Determination of Iron Limitation in the Peruvian Upwelling System

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Mesoscale iron fertilization experiments are somewhat controversial, prohibitively expensive, logistically difficult to perform in many open ocean environments and not suitable for fine scale ecological ocean studies. In situ diagnostic indicators of iron limitation can circumvent the above stated problems. The investigators will collaborate with trace metal chemists and biologists to explore the applicability of utilizing in situ biochemical and biophysical indicators to assess their usefulness and validity. In so doing, the scientists will also participate in investigating the hypothesis that the Peru coastal upwelling system is iron-limited. The two in situ indicators that will be investigated include (1) photochemical efficiency measurements using a fast repetition rate fluorometer and (2) quantitative measurements (using a combined high performance liquid chromatography and capillary electrophoresis method) of ferredoxin and flavodoxin concentrations in algae as an indicator of iron-nutritional status. These two methods will provide complimentary evidence regarding algal iron-limitation in the macro-nutrient replete Peru upwelling region. In addition, taxon-specific growth rates of algae will be measured using 14C pigment labeling to help interpret and support measurements by other investigators of the ambient iron concentration as well as the results from iron-addition experiments that will be run concomitantly on a transect across the Peru upwelling region.