ABSTRACT

High nitrate levels observed offshore in the California Current (CC) transition zone filament waters originate from coastal upwelled waters that have become iron-limited according to a research at the University of California-Santa Cruz. This scientist further proposes that iron-limitation in the CC transition zone results in nitrate drawdown and biological responses on time scales of a few weeks to months. This slow drawdown of nitrate differs from near-shore regions located over a relatively broad continental shelf with an adequate supply of iron allowing a rapid phytoplankton bloom and drawdown of nitrate on time scales of a few days to a week. To determine the role of Fe limitation in controlling phytoplankton biomass in the California Current (CC) transition zone off northern and central California, a research cruise, proposed to take place in 2010 on the RV Point Sur, would be carried out to determine the following: (1) the sources of nutrients, micronutrients, and trace metals from various upwelling regions along the northern and central coasts of California; (2) whether elevated macronutrients in the CC transition zone are due to coastal upwelling and subsequent advection and mixing offshore versus upwelling off the shelf due to curl of the wind stress or eddy dynamics; (3) Fe limitation in the CC transition zone; (4) nutrient consumption patterns in the CC system relative to Fe availability; and (5) remineralization/solubilization and assimilation of leachable particulate Fe by the phytoplankton community using low abundance stable isotopes of Fe as tracers.

As regards broader impact, this study would further our knowledge on what controls phytoplankton biomass and ecosystem productivity in eastern boundary current regions, an economically important area. In regards to educational impacts, this research would provide scientific training for a graduate student and a postdoc.

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