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Abstract: Coastal upwelling in the central California Current System (cCCS) delivers macro and micronutrients to the surface ocean that fuel biological productivity. Variations in upwelling strength and continental shelf width affect trace metal sources seasonally. The purpose of this study was to investigate various sources and distributions for a suite of dissolved trace metals (Mn, Fe, Co, Ni, Cu, Zn, and Cd) in the cCCS (34–41°N) as well as to determine the effects of biological uptake, physical advection, and mixing processes on trace metal concentrations during the spring and summer upwelling season. Continental shelf sediments did not substantially affect upwelled concentrations of Ni, Zn, and Cd — three typical nutrient-type trace metals. However, shelf sediments provided a significant external source for Mn, Fe, Co, and Cu — scavenged and hybrid-type trace metals. There was no clear seasonal trend in benthic boundary layer (BBL) Fe concentrations; however, higher concentrations of Mn and Co together with lower O2 concentrations were found in the BBL in the late summer compared to early spring. Conversely, there was a higher sedimentary Cu source to the BBL in the early spring before O2 concentrations dropped. Surface transect samples along the Big Sur Coast (May, 2010) and North Coast (August, 2011) demonstrated both mixing and biological assimilation of NO3 − and trace metals. Iron and Zn showed accelerated drawdown relative to NO3 − during both seasons suggesting an increased metal to nitrogen drawdown ratio at higher dissolved metal concentrations. Surface Mn and Co concentrations were higher in the late summer and both showed evidence for accelerated drawdown relative to NO3 −. Cadmium and Ni were strongly correlated with NO3 − indicating that both are affected by a combination of assimilation and regeneration at a constant rate relative to NO3 −; however, Cd showed slightly increased drawdown in aged upwelled waters during the late summer when Zn and Fe concentrations were low. This study provides field trace metal and macronutrient data supporting past laboratory studies suggesting that complex biological interactions are a key control on trace metal distributions and marine biogeochemical cycles. [Copyright &y& Elsevier]

Abstract: Dissolved copper speciation and total dissolved copper concentrations were determined at six San Francisco Bay sites in January and March of 2003. Multiple analytical windows were incorporated into an established competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) method, which employs salicylaldoxime (SA) as the added competitive ligand for speciation analyses. The titration results were integrated into [CuT *] versus log [Cu2+] plots, combining data from each of the different competing ligand concentrations and providing a powerful approach to visually interpret the variation in [Cu2+] as the natural Cu-binding ligands in the sample are titrated over a wide range of [CuT]. In addition, the data for different analytical windows were interpreted with Langmuir and Scatchard linearization techniques to estimate natural Cu-binding ligand concentrations [L i ] and conditional stability constants K CuLi,Cu2+ cond. All results indicate that ambient ligand concentrations exceed total dissolved copper concentrations at each site, with dissolved copper greater than 99.9% complexed by the strong copper-binding L 1 ligand class. The [Cu2+] does not exceed 10−13 M at any site, a concentration sufficiently below the toxicity threshold for microorganisms. Thus, the excess of strong Cu-binding ligands appears to effectively buffer free Cu2+ at low concentrations and the existing levels of copper do not impair San Francisco Bay. [Copyright &y& Elsevier]