Mixing of Iron-Rich Coastal Waters with Nutrient-Rich HNLC Waters Leading to Enhanced Phytoplankton Biomass: a Focus on the Northwest Gulf of Alaska

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A scientist from the University of California, Santa Cruz proposes to examine high-chlorophyll regions that develop at the boundaries of high-nitrate, iron-deplete, offshore waters and iron-rich, nitrate-poor, coastal water. Specifically, the researcher proposes to test the hypothesis that high biomass observed in satellite imagery in the northwestern Gulf of Alaska (GoA) during mid-summer months results from high river runoff into the Alaskan Coastal Current during this time of year, and mixing of this coastal water rich in dissolved and leachable particulate iron with the HNLC waters of the adjacent GoA via mesoscale eddies. To test the hypothesis, the PI will determine the distribution of dissolved and particulate iron (and other micronutrient trace metals) versus the distribution of macronutrients to assess the supply and demand of micro- and macronutrient elements in the northwestern GoA. In addition, the degree to which particulate iron is solubilized and becomes bioavailable will be determined using a series of grow out experiments with stable isotopes of iron. This data will also serve to fill in gaps for iron distributions in coastal regions. Another high chlorophyll region off Point Conception, CA will also be studied. In terms of broader impacts, this study will not only further our understanding of iron cycling in the northern GoA and off Point Conception, California, but provide much needed information on ecosystem productivity in these economically important coastal regions. Results from this project will be presented at local service clubs and in a display for K-12 students at the Seymour Discover Center of the Long Marine Lab. Training of graduate students and post-docs is included in the study.