Effects of Rainwater Iron and Hydrogen Peroxide on Iron Speciation and Phytoplankton Growth in Seawater near Bermuda |
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Authors: | Joan D Willey Robert J Kieber G Brooks Avery Jr |
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Institution: | (1) Department of Chemistry and Marine Science Program, University of North Carolina at Wilmington, 601 S. College Road, Wilmington, NC, 28403-5932, U.S.A. |
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Abstract: | Rainwater is a major source of dissolved iron to much of the world's oceans, including regions where iron may be a limiting
nutrient for marine phytoplankton primary production. Rainwater iron is therefore potentially important in regulating global
photosynthetic uptake of CO2, and hence climate. Two rainwater addition bioassay experiments (2% rain) conducted at the Bermuda Atlantic Time-series Station
(BATS) during March 2000 using 50 or 100 nM FeCl2 or FeCl3 in synthetic rain (pH 4.5 H2SO4) showed an increase in chlorophyll a 50% greater than controls after three days. Addition of 20 μM hydrogen peroxide, a typical rainwater concentration at BATS,
completely removed the chlorophyll a increase with both forms of iron additions, suggesting stimulation of phytoplankton growth by rainwater iron can be limited
by rainwater H2O2. In laboratory experiments using Gulf Stream seawater, iron-enriched (100 nM Fe(III)) synthetic rain was mixed with seawater
in a 5% rain 95% seawater ratio. Dissolved iron concentrations increased two times above concentrations predicted based on
dilution alone. The increase in soluble iron probably resulted from release from seawater particles and was maintained for
more than 24 hours. No increase was observed in controls that did not have iron added to the synthetic rain, or with synthetic
rainwater containing both added iron and H2O2. The increase in iron concentration above that predicted by dilution indicates rain may have a larger effect on seawater
iron concentrations than that calculated for rainwater iron addition alone. |
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Keywords: | rain iron hydrogen peroxide seawater chlorophyll a |
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