Description: Our study followed the seasonal cycling of soluble (SFe), colloidal (CFe), dissolved (DFe), total dissolvable (TDFe), labile particulate (LPFe) and total particulate (TPFe) iron in the Celtic Sea (NE Atlantic Ocean). Preferential uptake of SFe occurred during the spring bloom, preceding the removal of CFe. Uptake and export of Fe during the spring bloom, coupled with a reduction in vertical exchange, led to Fe deplete surface waters (〈0.2 nM DFe; 0.11 nM LPFe, 0.45 nM TDFe, 1.84 nM TPFe) during summer stratification. Below the seasonal thermocline, DFe concentrations increased from spring to autumn, mirroring NO3- and consistent with supply from remineralised sinking organic material, and cycled independently of particulate Fe over seasonal timescales. These results demonstrate that summer Fe availability is comparable to the seasonally Fe limited Ross Sea shelf, and therefore is likely low enough to affect phytoplankton growth and species composition.

Description: The questions that chemical oceanographers prioritize over the coming decades, and the methods we use to address these questions, will define our field's contribution to 21st century science. In recognition of this, the U.S. National Science Foundation and National Oceanic and Atmospheric Administration galvanized a community effort (the Chemical Oceanography MEeting: A BOttom-up Approach to Research Directions, or COME ABOARD) to synthesize bottom-up perspectives on selected areas of research in Chemical Oceanography. Representing only a small subset of the community, COME ABOARD participants did not attempt to identify targeted research directions for the field. Instead, we focused on how best to foster diverse research in Chemical Oceanography, placing emphasis on the following themes: strengthening our core chemical skillset; expanding our tools through collaboration with chemists, engineers, and computer scientists; considering new roles for large programs; enhancing interface research through interdisciplinary collaboration; and expanding ocean literacy by engaging with the public. For each theme, COME ABOARD participants reflected on the present state of Chemical Oceanography, where the community hopes to go and why, and actionable pathways to get there. A unifying concept among the discussions was that dissimilar funding structures and metrics of success may be required to accommodate the various levels of readiness and stages of knowledge development found throughout our community. In addition to the science, participants of the concurrent Dissertations Symposium in Chemical Oceanography (DISCO) XXV, a meeting of recent and forthcoming Ph.D. graduates in Chemical Oceanography, provided perspectives on how our field could show leadership in addressing long-standing diversity and early-career challenges that are pervasive throughout science. Here we summarize the COME ABOARD Meeting discussions, providing a synthesis of reflections and perspectives on the field.

Description: Iron (Fe), cobalt (Co), and vitamin B12 addition experiments were performed in the eastern Equatorial Pacific/Peruvian upwelling zone during the 2015 El Niño event. Near the Peruvian coastline, apparent photosystem II photochemical efficiencies (Fv/Fm) were unchanged by nutrient addition and chlorophyll‐a tripled in untreated controls over two days, indicating nutrient replete conditions. Conversely, Fe amendment further away from the coastline in the high nitrate, low Fe zone significantly increased Fv/Fm and chlorophyll‐a concentrations. Mean chlorophyll‐a was further enhanced following supply of Fe+Co and Fe+B12 relative to Fe alone, but this was not statistically significant; further offshore, reported Co depletion relative to Fe could enhance responses. The persistence of Fe limitation in this system under a developing El Niño, as previously demonstrated under non‐El Niño conditions, suggests that diminished upwelled Fe is likely an important factor driving reductions in offshore phytoplankton productivity during these events.

Description: Anthropogenic activities have resulted in enhanced lead (Pb) emissions to the environment over the past century, mainly through the combustion of leaded gasoline. Here, we present the first combined dissolved (DPb), labile (LpPb) and particulate (PPb) Pb dataset from the Northeast Atlantic (Celtic Sea) since the phasing out of leaded gasoline in Europe. Concentrations of DPb in surface waters have decreased by 4-fold over the last four decades. We demonstrate that anthropogenic Pb is transported from the Mediterranean Sea over long distances (〉2500 km). Benthic DPb fluxes exceeded the atmospheric Pb flux in the region, indicating the importance of sediments as a contemporary Pb source. A strong positive correlation between DPb, PPb and LpPb indicates a dynamic equilibrium between the phases and the potential for particles to ‘buffer’ the DPb pool. This study provides insights into Pb biogeochemical cycling and demonstrates the potential of Pb in constraining ocean circulation patterns.

Description: Here we demonstrate the use of reverse titration - competitive ligand exchange-adsorptive cathodic stripping voltammetry (RT-CLE-ACSV) for the analysis of iron (Fe) binding ligands in seawater. In contrast to the forward titration, which examines excess ligands in solution, RT-CLE-ACSV examines the existing Fe-ligand complexes by increasing the concentration of added (electroactive) ligand (1-nitroso-2-naphthol) and analysis of the proportion of Fe bound to the added ligand. The data manipulation allows the accurate characterisation of ligands at equal or lower concentrations than Fe in seawater, and disregards electrochemically inert dissolved Fe such as some colloidal phases. The method is thus superior to the forward titration in environments with high Fe and low ligand concentrations or high concentrations of inert Fe.We validated the technique using the siderophore ligand ferrioxamine B, and observed a stability constant K'Fe3+FoB of 0.74-4.37×1021mol-1, in agreement with previous results. We also successfully analysed samples from coastal waters and a deep ocean hydrothermal plume. Samples from these environments could not be analysed with confidence using the forward titration, highlighting the effectiveness of the RT-CLE-ACSV technique in waters with high concentrations of inert Fe. © 2013 Elsevier B.V.

Description: On voyages in the Iceland Basin in 2007 and 2009, we observed low (ca. 0.1nM) total dissolved iron concentrations dFe in surface waters (〈150m), which increased with depth to ca. 0.2-0.9nM. The surface water dFe was low due to low atmospheric Fe inputs combined with biological uptake, with Fe regeneration from microbial degradation of settling biogenic particles supplying dFe at depth. The organic ligand concentrations LT in the surface waters ranged between 0.4 and 0.5nM, with conditional stability constants (logK'FeL) between 22.6 and 22.7. Furthermore, LT was in excess of dFe throughout the water column, and dFe was therefore largely complexed by organic ligands (>99%). The ratio of LT/dFe was used to analyse trends in Fe speciation. Enhanced and variable LT/dFe ratios ranging between 1.6 and 5.8 were observed in surface waters; the ratio decreased with depth to a more constant LT/dFe ratio in deep waters. In the Iceland Basin and Rockall Trough, enhanced LT/dFe ratios in surface waters resulted from decreases in dFe, likely reflecting the conditions of Fe limitation of the phytoplankton community in the surface waters of the Iceland Basin and the high productivity in the Rockall Trough.Below the surface mixed layer, the observed increase in dFe resulted in a decrease of the LT/dFe ratios (1.2-2.6) with depth. This indicated that the Fe binding ligand sites became occupied and even almost saturated at enhanced dFe in the deeper waters. Furthermore, our results showed a quasi-steady state in deep waters between dissolved organic Fe ligands and dFe, reflecting a balance between Fe removal by scavenging and Fe supply by remineralisation of biogenic particles with stabilisation through ligands. © 2011 Elsevier Ltd.

Description: Siderophore type chelates were detected in nutrient enriched, incubated seawater collected from different biogeographical regions of the Atlantic Ocean. Seawater was enriched with glucose and ammonium, glycine (as a source of carbon and nitrogen) or chitin and ammonium at different concentrations and was incubated for up to 3-4. days in the dark. Siderophore type chelates were detected using high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS) after complexation with Ga. Samples were subsequently analysed by HPLC-electrospray ionisation mass spectrometry (HPLC-ESI-MS) in order to confirm the identity of the known siderophores, and to obtain the pseudo-molecular ions of unknown siderophore type chelates. A total of 22 different siderophore type chelates were resolved in the HPLC-ICP-MS chromatograms. Ten different siderophore type chelates were identified by HPLC-ESI-MS, 3 of which had not previously been identified in nutrient enriched seawater incubations. The concentration and diversity of siderophore type chelates was highest in seawater amended with glucose. The concentrations and diversity of siderophore type chelates also varied with biogeographical area in the Atlantic Ocean, with the North Atlantic Sub-tropical Gyre yielding highest concentrations in incubations, and the South Atlantic Sub-tropical Gyre and Western Tropical Atlantic yielding the highest diversity

Description: Phytochelatins (PCs) and glutathione (GSH) are -SH-containing compounds produced by a range of organisms for intracellular functions, such as protection against oxidative stress, metal detoxification and regulation of intracellular metal concentrations. These compounds, particularly PCs, have a potential use as metal-stress indicators for phytoplankton in natural waters. Despite their important roles, there is a paucity of data on intracellular GSH and PCs produced by natural phytoplankton assemblages. Current analytical methods for the determination of these compounds in phytoplankton from natural waters are based on high-performance liquid chromatography (HPLC) with detection of fluorescent derivatives, and comprise multi-step protocols. In this article, we discuss the analytical methods for HPLC determination of PCs and GSH, as there are limitations and practical challenges when they are applied to environmental studies. © 2005 Elsevier Ltd. All rights reserved.

Description: A novel automated metal monitor was optimised and validated for high temporal resolution (every 45 s to 5 min) measurements of dissolved Cu by adsorptive cathodic stripping voltammetry (AdCSV), Pb and Zn by anodic stripping voltammetry (ASV). The system was designed to allow the determination of both total (with UV digestion) and labile (without UV digestion) dissolved trace metal concentrations in seawater equilibrated with aerosol particles. There was negligible contamination or adsorption of trace metals from the experimental system and reaction vessel. Observed recoveries from certified reference materials for Cu, Pb and Zn were within the certified values; detection limits for total Cu, Pb and Zn were 28, 4 and 63 nM, respectively. The system was applied to the investigation of the desorption of trace metals from an urban aerosol end-member (Liverpool Urban Particulate Material; LUPM, 50 mg l -1) in seawater. Carefully controlled and optimised experimental conditions were implemented. The analytical limits of detection of Cu, Pb and Zn were 〈25 of the mean desorbed metal concentrations from LUPM. Contamination from reagents were 〈0.1 of the mean sample concentration. Separate experimental runs measuring the desorption of the dissolved trace metals from the aerosol sample had good repeatability (e.g. for labile determinations mean R.S.D. 〈5 for Zn; 〈10 for Cu and Pb). The high temporal resolution datasets generated by the metal monitor were used to calculate model desorption rate constants. The following range of constants were calculated 0.0047-0.015 min-1 (Cu); 0.049-0.056 min-1 (Zn) and 0.039-0.052 min-1 (Pb)

Description: Siderophore type chelates were isolated from nutrient enriched seawater collected from coastal and near shore environments and detected using a novel high performance liquid chromatography-electrospray ionisation-mass spectrometric technique. Seawater was enriched with added glucose, ammonia and phosphate, and incubated for four days. Seven different siderophore type compounds were detected in the extracted supernatants and tentatively identified based on mass numbers and spectra. The compounds comprised two groups, the ferrioxamines and the amphibactins. They were produced at typical coastal iron concentrations (total dissolved iron=2.9±1.4 and 2.2±0.1 nM) both in the presence and absence of the iron chelating ligand ethylene diamine-N,N′-diacetic acid. © 2004 Elsevier B.V. All rights reserved.