The lack of available iron (Fe) in seawater is widely accepted as a factor that limits phytoplankton growth in extensive high nutrient, low chlorophyll (HNLC) ocean areas, as well as some coastal upwelling regions. More recently, iron has been shown to impact the ecology and species distribution of stratified oligotrophic regimes as well. Productivity (or lack thereof) at the scale of these iron limited areas is significant to the global marine carbon budget. The availability of a reliable, ship-deployable Fe sensor would permit high resolution datasets to be obtained on a routine basis, resulting in improved understanding of global biogeochemical interactions. This proposal is designed to make concrete steps toward improving measurement coverage by developing a field instrument that could be used to greatly expand the data available to modelers. This project will provide training for graduate and undergraduate students and an undergraduate engineering class in the newly opened Scripps Makerspace at Scripps.

This project will integrate the chalcogenide Fe3+ ion selective electrode (Fe-ISE) into underway and in situ autonomous measuring systems. The researchers will calibrate and test these systems through: 1) comparison of the Fe3+ ion activity measured by the Fe-ISE to the concentration of soluble inorganic iron determined independently by competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV), and 2) calibration of the Fe-ISE in an artificial seawater medium with a well-understood dissolved organic ligand background serving as a mimetic calibration system. A secondary objective of this proposal is to enhance our understanding of the complex chemistry that exists at the surface of the chalcogenide ISE in the presence of a heterogeneous dissolved organic matter pool, such as seawater. It is expected that this project will yield an improved Fe-ISE methodology that is suitable for long term autonomous use. It is also expected that this project will describe/develop an instrument package suitable for long term monitoring of oceanographic variables at pier locations, shipboard underway systems, and potentially autonomous moored and profiling systems.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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Kandace Binkley
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University of California-San Diego Scripps Inst of Oceanography
La Jolla
United States
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