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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]

Presents research which demonstrated that phytoplankton are iron-limited in parts of the California coastal upwelling region. Phytoplankton growth limited by iron availability; Addition of iron to high-nitrate, low-chlorophyll (HNLC) regimes; Silicic acid:nitrate (Si:N) uptake ratios; Diatoms stressed by lack of iron; Si:cell, Si:C and Si:pigment ratios in diatoms; Implications of research.

Abstract: Distributions of iron and nitrate in the central California Current System upwelling regime (cCCS) from 34 to 41°N were determined during cruises in May 2010 and August 2011. High spatial and temporal resolution data for dissolved Fe and (nitrate+nitrite) in the cCCS from this study greatly expands upon previous studies that were narrower in scope (e.g., focused on just the Monterey Bay region). Shelf sediments from mid-shelf mud belts in this region provide the dominant source of Fe, and there are areas in the cCCS where insufficient Fe is upwelled to accompany elevated levels of other macronutrients (nitrate, phosphate, silicate) to fuel extensive diatom blooms. Surface dissolved Fe concentrations were related to continental shelf width and upwelling strength, and surface Fe concentrations tended to be lower in the late summer than early spring. We present extensive benthic boundary layer (BBL) dissolved and leachable particulate Fe data from both seasons in the mid-shelf region along the central California coast. Leachable particulate Fe concentrations were strongly related to the width of the mid-shelf mud belts (i.e., the continental shelf between the 50 and 90m isobaths). Dissolved Fe concentrations in the BBL over the mid-shelf were generally highest in wide mud belt areas as well as in areas with very low dissolved oxygen concentrations but did not show a clear seasonal trend. Evidence for probable Fe limitation in upwelled waters was found by using surface dissolved Fe: ratios and the estimated specific growth rate of coastal diatoms based on either Fe or concentrations. Several coastal upwelling regions with only moderate to narrow continental shelves (Pt. Arena to Cape Mendocino and the Big Sur Coast) exhibited evidence for Fe limitation in both the spring and summer upwelling seasons. [Copyright &y& Elsevier]

Abstract: Following basin-wide contamination from industrial emissions and urban development, total dissolved copper concentrations in some regions of San Francisco Bay have exceeded national and state guidelines for water quality. In the face of dramatic improvements in wastewater treatment and point source control, persisting elevated dissolved copper concentrations in the Bay have prompted multiple studies and extensive monitoring of this estuary since 1989. Statistical analyses of monitoring data show that total dissolved copper concentrations have declined in the North (by 17%) and South (29%) San Francisco Bay as well as in the Southern Sloughs (44%) from 1993 to 2001. Concentrations remain elevated in the farthest reaches of the Bay (Delta and Estuary Interface), and in the Central Bay. Dissolved copper concentrations throughout the Bay have also been positively correlated (, , ) with dissolved organic matter, supporting results from complimentary chemical speciation studies which indicate that high-affinity copper-binding organic ligands dominate the chemical speciation of dissolved copper in the Bay. These organic ligands typically bind>99.9% of the dissolved copper, effectively buffering the system against small changes in dissolved copper concentrations, and maintaining free Cu2+ concentrations well below the toxicity threshold of ambient aquatic microorganisms. In response to these findings, site-specific water quality criteria for dissolved copper concentrations are now being developed by the Regional Water Quality Board to provide a more appropriate standard for copper toxicity in the Bay—one based on its chemical speciation and bioavailability. [Copyright &y& Elsevier]