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Date Permissions Signed


Date of Award

Spring 2020

Document Type

Masters Thesis

Department or Program Affiliation


Degree Name

Master of Science (MS)



First Advisor

Strom, Suzanne L., 1959-

Second Advisor

Bingham, Brian L., 1960-

Third Advisor

Olson, M. Brady (Michael Brady)


Episodic iron input from natural sources (e.g., riverine input, dust deposition, and mesoscale eddies) plays an important role in dictating phytoplankton growth, physiology, and community structure in the high-nitrate low-chlorophyll (HNLC) waters of the Northern Gulf of Alaska (NGA). Iron addition experiments utilizing the synthetic iron source, FeCl3, have been performed in all major HNLC regions and have resulted in diatom blooms with significant implications for ecosystem productivity and resilience. If FeCl3 and natural iron sources differ in bioavailability, and hence potential phytoplankton production, re-interpretation of these results is warranted. To test the hypothesis that natural and synthetic iron sources are differentially bioavailable, we performed a deck-board iron addition experiment in the summer of 2019. We exposed the NGA HNLC phytoplankton community to three iron sources: FeCl3, the Copper River plume, and an HNLC control and assessed net growth, photosynthetic efficiency, community composition, and nutrient use over a 5 d incubation. Addition of the FeCl3 and Copper River plume iron sources alleviated iron stress for the total phytoplankton community, yet the bioavailability of these two iron sources was size-dependent. Cells > 20 µm responded differently to all three iron sources, with net growth rates and photosynthetic efficiency being highest in the FeCl3 treatment and intermediate in the Copper River plume treatment. In contrast to cells > 20 µm, phytoplankton < 20 µm responded similarly to the Copper River plume and FeCl3 treatments. Consistent with previous experiments, FeCl3 addition promoted diatom growth. However, the Copper River plume iron source primarily increased the production and turnover of cells < 20 µm. We conclude that diatom growth and physiology measured in previous iron addition experiments in response to FeCl3 do not directly translate to fluvial iron sources. We also suggest that fluvial iron input is critical to maintaining ultraplankton in NGA HNLC waters and that it may aid the rapid transport of biomass into secondary production with the addition of more highly bioavailable iron sources.




Western Washington University

OCLC Number


Subject – LCSH

Marine productivity--Alaska--Alaska, Gulf of; Iron--Bioavailability--Alaska--Alaska, Gulf of; Phytoplankton--Effect of iron on--Alaska--Alaska, Gulf of

Geographic Coverage

Alaska, Gulf of (Alaska)




masters theses




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