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In order to establish the status of metal contamination in surface waters in the coastal ocean off Los Angeles, California, we determined their dissolved and particulate pools and compared them with levels reported in the 1970s prior the implementation of the Clean Water Act. These measurements revealed a significant reduction in particulate toxic metal concentrations in the last 33 years with decreases of ∼100-fold for Pb and ∼400-fold for Cu and Cd. Despite these reductions, the source of particulate metals appears to be primarily anthropogenic as enrichment factors were orders of magnitude above what is considered background crustal levels. Overall, dissolved trace metal concentrations in the Los Angeles coastal waters were remarkably low with values in the same range as those measured in a pristine coastal environment off Mexico's Baja California peninsula. In order to estimate the impact of metal contamination on regional phytoplankton, the internalization rate of trace metals in a locally isolated phytoplankton model organism (Synechococcus sp. CC9311) was also determined showing a rapid internalization (in the order of a few hours) for many trace metals (e.g., Ag, Cd, Cu, Pb) suggesting that those metals could potentially be incorporated into the local food webs.

Near-surface waters ranging from the Pacific subarctic (58°N) to the Southern Ocean (66°S) contain the neurotoxin domoic acid (DA), associated with the diatom Pseudo-nitzschia. Of the 35 stations sampled, including ones from historic iron fertilization experiments (SOFeX, IronEx II), we found Pseudo-nitzschia at 34 stations and DA measurable at 14 of the 26 stations analyzed for DA. Toxin ranged from 0.3 fg·cell(-1) to 2 pg·cell(-1), comparable with levels found in similar-sized cells from coastal waters. In the western subarctic, descent of intact Pseudo-nitzschia likely delivered significant amounts of toxin (up to 4 μg of DA·m(-2)·d(-1)) to underlying mesopelagic waters (150-500 m). By reexamining phytoplankton samples from SOFeX and IronEx II, we found substantial amounts of DA associated with Pseudo-nitzschia. Indeed, at SOFeX in the Antarctic Pacific, DA reached 220 ng·L(-1), levels at which animal mortalities have occurred on continental shelves. Iron ocean fertilization also occurs naturally and may have promoted blooms of these ubiquitous algae over previous glacial cycles during deposition of iron-rich aerosols. Thus, the neurotoxin DA occurs both in coastal and oceanic waters, and its concentration, associated with changes in Pseudo-nitzschia abundance, likely varies naturally with climate cycles, as well as with artificial iron fertilization. Given that iron fertilization in iron-depleted regions of the sea has been proposed to enhance phytoplankton growth and, thereby, both reduce atmospheric CO(2) and moderate ocean acidification in surface waters, consideration of the potentially serious ecosystem impacts associated with DA is prudent.

There has been a growing interest in the cause and impact of hypoxic regions known as "dead zones" that have increasingly appeared along the west coast of the United States and have caused widespread destruction to the crab and fishing industry in this upwelling region. Here, we present results that demonstrate that the hypoxic conditions in the water column over the continental shelf result in a marked increase in iron(II) concentrations, which contribute to elevated dissolved and labile particulate iron concentrations. These elevated dissolved iron(II) concentrations result from two factors: (1) the hypoxic water column allows extremely elevated iron(II) concentrations in reducing porewaters to exist close to the sediment water interface, leading to an increased flux of iron(II) from the sediments; (2) the low oxygen, low pH, and low temperatures within the bottom boundary layer act in concert to markedly slow down the oxidation rate of Fe(ll). During upwelling conditions, this process can result in a greatly enhanced source of Fe available to upwell to surface waters, potentially increasing phytoplankton productivity, which can, in turn, lead to enhanced export flux, driving the system further into hypoxic or suboxic conditions.

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 (r = 0.632, P < 0.0005, n = 598) 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 Cu(2+) 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.

Abstract: A method was developed using the chelating resin Nobias-chelate PA1 in an off-line pre-concentration manifold with magnetic sector inductively coupled plasma mass spectrometry (ICP-MS) detection for analysis of Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb. This multi-element method allows for the simultaneous extraction of eight samples in a closed column manifold. Standard additions to seawater demonstrated quantitative recovery and eliminated the need to use isotope dilution to account for non-quantitative recoveries of the metals on the resin. UV-oxidation of seawater samples before extraction was necessary to provide accurate total dissolved concentrations of Co and Cu. Samples (40mL) were loaded onto the chelating resin column at a pH of 6.2±0.3 after pH adjustment with a basic ammonium acetate (NH4Ac) solution. The columns were rinsed after sample loading with a weak (0.05M) NH4Ac solution to remove the bulk of the major ions in seawater. The trace metals were eluted with 3 to 4mL of 1N Q-HNO3 and analyzed on a magnetic sector ICP-MS. This multi-element method is ideal for high sample throughput and quantification over a broad range of element concentrations with low blanks and detection limits. We report results here from the SAFe and GEOTRACES reference samples as well as the U.S. GEOTRACES Atlantic and Pacific Baseline profiles. [Copyright &y& Elsevier]

Abstract: Trace elements in seawater can be limiting factors of biological productivity, tracers of ocean circulation and biogeochemical processes, and proxies for paleoceanography. The global status of trace elements and their isotopes (TEIs) in the ocean is being explored this decade through an international study of the global marine biogeochemical cycles of TEIs (GEOTRACES). Such an international study has become possible due to recent methodological developments in sampling, preconcentration, and measurement of TEIs. Here, we present an overview of recent methodological developments and initial GEOTRACES intercalibration activities for obtaining data about TEIs that are accurate, precise, and intercomparable. [Copyright &y& Elsevier]

Abstract: A vertical mixing event was simulated in shipboard incubation experiments on the mid-continental shelf of the eastern Bering Sea to investigate Fe and Zn cycling between the soluble (<0.03 μm or 200 kDa), colloidal (0.03–0.2 μm), and particulate (0.2–10 μm, >10 μm) size-fractions. The particulate Fe and Zn were further separated into chemically labile (25% acetic acid-leachable) and refractory pools. The experiment employed 57Fe (+0.90 nM) and 68Zn (+0.99 nM) as stable, low-abundance isotope amendments to the soluble fraction, and the exchange of Fe and Zn between the different physico-chemical fractions was measured using high resolution-inductively coupled plasma-mass spectrometry (HR-ICP-MS). More than 50% of the added 57Fe partitioned to the colloidal fraction within 45 min of adding the tracer. Both the 57Fe and 56Fe colloidal fraction were removed from the dissolved phase at a faster rate than the soluble Fe fraction. In contrast, the colloidal 66Zn and 68Zn concentrations remained constant over the 5-day experiment, suggesting a unique removal mechanism for colloidal Fe. The net removal of dissolved 57Fe was observed to be 3 to 4 times more rapid than dissolved 56Fe, which can be attributed to the regeneration of particulate Fe. Using a simple first-order model, it was determined that the net removal of 2.0 nM of dissolved Fe during the experiment was a consequence of dynamic cycling, whereby 2.9 nM of particulate Fe was regenerated and contributed to an overall removal of 4.9 nM of Fe from the dissolved phase. The amended 68Zn tracer resided in the soluble fraction and was assimilated by the diatom biomass (>10 μm size-fraction) at the same rate as 66Zn. This similarity in rates suggests that nearly all of the net removal of Zn was due to assimilation and that regeneration did not play a significant role in Zn cycling within the incubation experiment. This research demonstrates the advantage of using low-abundance isotopes as tracers and the importance of particulate and colloidal Fe in the overall biogeochemical cycling of Fe in ocean surface waters. [Copyright &y& Elsevier]

A flow injection inductively coupled plasma magnetic sector mass spectrometry (FI-ICP-MS) method was developed for the analysis of Cd, Cu, Ni, Zn, and Mn in estuarine waters. The method uses just greater than 3 ml sample, and employs an automated on-line preconcentration step using a metal chelating resin (Toyopearl AF-Chelate 650 M). Acidified samples for the analysis of Cd, Cu, Ni, and Zn were buffered on-line to pH of 5.6±0.2 with ammonia acetate just prior to loading onto the chelating resin, while samples for Mn analysis were adjusted to pH of 9.0±0.2 prior to concentration. Limits of detection were: Cd=1.4 ng l−1 (0.013 nM), Cu=17 ng l−1 (0.27 nM), Ni=28 ng l−1 (0.48 nM), Zn=46 ng l−1 (0.70 nM), and Mn=86 ng l−1 (1.6 nM). The blank concentrations were less than 1.5% of the SLEW-2 concentrations for each element analyzed, except Ni, which had a significant, but very constant blank from the Ni cones used. The detection limits were less than 5% of the concentrations observed in the San Francisco Bay estuarine samples, with the exception of Zn where the detection limit was 10% of the concentration of lowest San Francisco Bay sample analyzed. Using the FI preconcentration technique, we conducted medium resolution scans of potential isobaric interferences (mass units 55–66) using a magnetic sector ICP-MS to identify a number of interferent complications with evaluating certain isotopes, especially, 59Co, and 60Ni. Investigations of potential interferents illustrate the importance of appropriate isotope selection and, in some instances, the need to perform blank corrections with both an instrumental and a matrix blank. The method was verified by the analysis of an estuarine water standard reference materials (SLEW-2), and San Francisco Bay samples with previously reported values. Six estuarine samples run in triplicate generated the following average precision (presented as % R.S.D.); Cd=4.2%, Cu=3.2%, Ni=3.3%, Zn=4.4%, and Mn=2.2%. [Copyright &y& Elsevier]

Precise and accurate quantification of Ag and platinum group elements in marine, estuarine and riverine waters is challenging due to the complex matrices and ultra-low concentrations in the pmol kg − 1 and fmol kg − 1 range. A methodological approach has been developed for the analysis of Ag and Pt in seawater based on the extraction of their anionic chloro-complexes utilizing the strong anion exchange resin Dowex™ 1-× 8 in an off-line matrix separation and pre-concentration approach prior to determination by ICP-SFMS. The method allows simultaneous processing of four 100 mL samples at a flow rate of up to 2 mL min − 1 in an ultra-clean manifold. Enrichment factors of 40 could be achieved with elution into 2.5 g of a mixture of HNO 3 /HCl, yielding adequately low detection limits to obtain open ocean profiles. Quantification was performed by matrix-matched calibration and internal standardization. To validate the accuracy of this approach, isotope dilution analysis was also used. The applicability of the method was demonstrated on a suite of reference samples and depth profiles collected during the 2009 2nd U.S. GEOTRACES Intercalibration cruise in the eastern North Pacific. [ABSTRACT FROM AUTHOR]