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Iron distribution and phytoplankton iron limitation in the southern California Current System

  • Author(s): King, Andrew Luke
  • et al.
Abstract

The research presented in this dissertation focuses on the distribution of dissolved iron (<0.4 [mu]m) and its biogeochemical consequences in the southern California Current System (sCCS). Trace metal clean oceanographic techniques were used to conduct iron addition bottle experiments and collect samples for dissolved iron on ten research cruises between 2002 and 2007. The concentration of dissolved iron from both mixed layer and water column samples was determined using a new and improved flow injection method with preconcentration of iron(II) on nitriloacetic acid and luminol chemiluminescence detection (detection limit of 0.02 nM iron). Spatially and temporally, elevated dissolved iron concentrations were found to be generally associated with coastal upwelling processes in the northern coastal domain of the study area, and thus corresponded with elevated macronutrient and chlorophyll a concentrations. However, at the fringes and outside of the northern coastal domain (1\̃0-100 km from the coast) during April 2003, April 2004, July 2003, July 2004, and April 2007, dissolved iron concentrations dropped rapidly below 0\̃.5 nM and were found to be lower relative to macronutrients, especially nitrate. This was supported by regional and mesoscale synoptic observations during California Cooperative Oceanic Fisheries Investigations (CalCOFI) survey cruises and mesoscale Lagrangian drifter studies during California Current Ecosystem-Long Term Ecological Research (CCE-LTER) cruises. The spatial extent of the nitrate-dissolved iron decoupling was as far as 1\̃00 km offshore in April 2003 and 2004 and as far as 2\̃50 km offshore in July 2003 and 2004. Iron addition bottle experiments conducted in relatively high nitrate-low dissolved iron mixed-layer water masses in July 2003 and 2004 indicated that phytoplankton nitrate-utilization, and therefore growth, was limited by iron availability. Somewhat analogous to the spatial decoupling between dissolved iron and nitrate in the mixed layer, the ferricline (defined as the depth where dissolved iron is > 0.2 nM) was found to be deeper than the nitracline (defined as the depth where nitrate is >1 [mu]M) on several occasions in July 2007. Based on these findings and the results of other studies in nearby systems, the distribution of dissolved iron has important biological and geochemical implications for the sCCS

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