The Marine Biogeochemistry of Selenium: A Re-Evaluation

Vertical and horizontal profiles from the North and South Pacific Oceans demonstrate the existence of three species of dissolved selenium: selenite, selenate, and organic selenide (operationally defined). In surface waters, organic selenide makes up about 80% of the total dissolved selenium, selenite concentrations are uniformly low, and selenate concentrations rise with increased vertical mixing. The organic selenide maximum (thought to consist of seleno-amino acids in peptides) coincides with the maxima of primary productivity, pigments, bioluminescence, and dissolved free amino acids. Deep ocean waters are enriched in selenite and selenate, while organic selenide is nondetectable. In suboxic waters of the tropical northeastern Pacific, organic selenide concentrations rise, while selenite values decrease. The downward flux of particulate selenium generally decreases with depth, and fluxing particulate selenium is found to be primarily in the (-2) oxidation state. These data allow a re-evaluation of the internal biogeochemical cycle of selenium. This cycle includes selective uptake, reductive incorporation, particulate transport, a multistep regeneration, and kinetic stabilization of thermodynamically unstable species

Rapid and Noncontaminating Sampling System For Trace Elements in Global Ocean Surveys

A system for the rapid and noncontaminating sampling of trace elements with volumes of up to 36 L per depth and including the dissolved and particulate phases has been developed for ocean sections that are a crucial part of programs such as International GEOTRACES. The system uses commercially available components, including an aluminum Seabird Carousel with all titanium pressure housings for electronics and sensors to eliminate zinc sacrificial anodes and holding twenty-four 12 L GO-FLO bottles, and a 7500 m, 14 mm Vectran conducting cable (passing over an A-frame with nonmetallic sheave) spooled onto a traction winch. The GO-FLO bottles are stored and processed in a clean lab built into a 20\u27 ISO container. To minimize contamination, the GO-FLO bottles are triggered when the carousel is moving upward into clean water at 3 m min super(-1. Analyses of salinity and nutrients in bottle samples from the stopped versus moving carousel show no detectable smearing, whereas the contamination-prone trace elements show the samples are uncontaminated when compared with other clean sampling methods. Based on the use of this system on three major cruises, the launch-sample-recover time for the carousel (2 bottles triggered per depth) is 1 h per 1000 m, and dissolved and particulate sampling time averages 6 h per hydrocast. Thus, the system described here meets all the requirements for ocean basin sampling for trace elements: rapid, good hydrographic fidelity, and noncontaminating

The Distribution of Nickel in the West-Atlantic Ocean, Its Relationship With Phosphate and a Comparison to Cadmium and Zinc

Nickel (Ni) is a bio-essential element required for the growth of phytoplankton. It is the least studied bio-essential element, mainly because surface ocean Ni concentrations are never fully depleted and Ni is not generally considered to be a limiting factor. However, stimulation of growth after Ni addition has been observed in past experiments when seemingly ample ambient dissolved Ni was present, suggesting not all dissolved Ni is bio-available. This study details the distribution of Ni along the GEOTRACES GA02 Atlantic Meridional section. Concentrations of Ni were lowest in the surface ocean and the lowest observed concentration of 1.7 nmol kg(-1) was found in the northern hemisphere (NH). The generally lower surface concentrations in the NH subtropical gyre compared to the southern hemisphere (SH), might be related to a greater Ni uptake by nitrogen fixers that are stimulated by iron (Fe) deposition. The distribution of Ni resembles the distribution of cadmium (Cd) and also features a so called kink (change in the steepness of slope) in the Ni-PO4 relationship. Like for Cd, this is caused by the mixing of Nordic and Antarctic origin water masses. The overall distribution of Ni is driven by mixing with an influence of regional remineralization. This influence of remineralization is, with a maximum remineralization contribution of 13% of the highest observed concentration, smaller than for Cd (30%), but larger than for zinc (Zn; 6%). The uptake pattern in the formation regions of Antarctic origin water masses is suggested to be more similar to Zn than to Cd, however, the surface concentrations of Ni are never fully depleted. This results in a North Atlantic concentration distribution of Ni where the trends of increasing and decreasing concentrations between water masses are similar to those observed for Cd, but the actual concentrations as well as the uptake and remineralization patterns are different between these elements

Different iron storage strategies among bloom-forming diatoms

Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 115(52), (2018): E12275-E12284. doi: 10.1073/pnas.1805243115.Diatoms are prominent eukaryotic phytoplankton despite being limited by the micronutrient iron in vast expanses of the ocean. As iron inputs are often sporadic, diatoms have evolved mechanisms such as the ability to store iron that enable them to bloom when iron is resupplied and then persist when low iron levels are reinstated. Two iron storage mechanisms have been previously described: the protein ferritin and vacuolar storage. To investigate the ecological role of these mechanisms among diatoms, iron addition and removal incubations were conducted using natural phytoplankton communities from varying iron environments. We show that among the predominant diatoms, Pseudo-nitzschia were favored by iron removal and displayed unique ferritin expression consistent with a long-term storage function. Meanwhile, Chaetoceros and Thalassiosira gene expression aligned with vacuolar storage mechanisms. Pseudo-nitzschia also showed exceptionally high iron storage under steady-state high and low iron conditions, as well as following iron resupply to iron-limited cells. We propose that bloom-forming diatoms use different iron storage mechanisms and that ferritin utilization may provide an advantage in areas of prolonged iron limitation with pulsed iron inputs. As iron distributions and availability change, this speculated ferritin-linked advantage may result in shifts in diatom community composition that can alter marine ecosystems and biogeochemical cycles.We thank the captain and crew of the R/V Melville and the CCGS J. P. Tully as well as the participants of the IRNBRU (MV1405) cruise for the California-based data, particularly K. Ellis [University of North Carolina (UNC)], T. Coale (University of California, San Diego), F. Kuzminov (Rutgers), H. McNair [University of California, Santa Barbara (UCSB)], and J. Jones (UCSB). W. Burns (UNC), S. Haines (UNC), and S. Bargu (Louisiana State University) assisted with sample processing and analysis. This work was funded by the National Science Foundation Grants OCE-1334935 (to A.M.), OCE-1334632 (to B.S.T.), OCE-1333929 (to K.T.), OCE-1334387 (to M.A.B.), OCE-1259776 (to K.W.B), and DGE-1650116 (Graduate Research Fellowship to R.H.L).2019-06-1

Demonstration of a microelectromechanical tunable F-P cavity based on graphene-bonded fiber devices

Taking advantage of the high thermal conductivity of graphene, this paper demonstrates a microelectromechanical (MEM) tunable Fabry-Perot (F-P) cavity, based on a graphene-bonded fiber device (GFD) which acts as a microheater. By increasing the electric current from 0 mA to 8 mA in the heater, the temperature of the GFD can rise and approach a value of 760 K theoretically. This high temperature will cause a deformation of the fiber, allowing the graphene-bonded fiber end to forma gap adjustable F-P cavity with a cleaved single mode fiber. The gap in the cavity can be reduced by increasing the current applied, leading the transmittance of the cavity to change. In this work, a highly sensitive current sensor (5.9x10⁵nm/A²) and a tunable modelocked fiber laser (1.2x10⁴nm/A²) are created based on the MEM tunable F-P cavity

Structural characterization of natural nickel and copper binding ligands along the US GEOTRACES Eastern Pacific Zonal Transect

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Frontiers in Marine Science 3 (2016): 243, doi:10.3389/fmars.2016.00243.Organic ligands form strong complexes with many trace elements in seawater. Various metals can compete for the same ligand chelation sites, and the final speciation of bound metals is determined by relative binding affinities, concentrations of binding sites, uncomplexed metal concentrations, and association/dissociation kinetics. Different ligands have a wide range of metal affinities and specificities. However, the chemical composition of these ligands in the marine environment remains poorly constrained, which has hindered progress in modeling marine metal speciation. In this study, we detected and characterized natural ligands that bind copper (Cu) and nickel (Ni) in the eastern South Pacific Ocean with liquid chromatography tandem inductively coupled plasma mass spectrometry (LC-ICPMS), and high-resolution electrospray ionization mass spectrometry (ESIMS). Dissolved Cu, Ni, and ligand concentrations were highest near the coast. Chromatographically unresolved polar compounds dominated ligands isolated near the coast by solid phase extraction. Offshore, metal and ligand concentrations decreased, but several new ligands appeared. One major ligand was detected that bound both Cu2+ and Ni2+. Based on accurate mass and fragmentation measurements, this compound has a molecular formula of [C20H21N4O8S2+M]+ (M = metal isotope) and contains several azole-like metal binding groups. Additional lipophilic Ni complexes were also present only in oligotrophic waters, with masses of 649, 698, and 712 m/z (corresponding to the 58Ni metal complex). Molecular formulae of [C32H54N3O6S2Ni]+ and [C33H56N3O6S2Ni]+ were determined for two of these compounds. Addition of Cu and Ni to the samples also revealed the presence of additional compounds that can bind both Ni and Cu. Although these specific compounds represent a small fraction of the total dissolved Cu and Ni pool, they highlight the compositional diversity and spatial heterogeneity of marine Ni and Cu ligands, as well as variability in the extent to which different metals in the same environment compete for ligand binding.Support was provided by the National Science Foundation (NSF) program in Chemical Oceanography (OCE-1356747, OCE-1233261, OCE-1233733, OCE-1233502, and OCE-1237034), the NSF Science and Technology Center for Microbial Oceanography Research and Education (C-MORE; DBI-0424599), the Gordon and Betty Moore Foundation (#3298 and 3934), and the Simons Foundation (#329108, DR)

The GEOTRACES Intermediate Data Product 2014

The GEOTRACES Intermediate Data Product 2014 (IDP2014) is the first publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2013. It consists of two parts: (1) a compilation of digital data for more than 200 trace elements and isotopes (TEIs) as well as classical hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing a strongly inter-linked on-line atlas including more than 300 section plots and 90 animated 3D scenes. The IDP2014 covers the Atlantic, Arctic, and Indian oceans, exhibiting highest data density in the Atlantic. The TEI data in the IDP2014 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at cross-over stations. The digital data are provided in several formats, including ASCII spreadsheet, Excel spreadsheet, netCDF, and Ocean Data View collection. In addition to the actual data values the IDP2014 also contains data quality flags and 1-? data error values where available. Quality flags and error values are useful for data filtering. Metadata about data originators, analytical methods and original publications related to the data are linked to the data in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2014 data providing section plots and a new kind of animated 3D scenes. The basin-wide 3D scenes allow for viewing of data from many cruises at the same time, thereby providing quick overviews of large-scale tracer distributions. In addition, the 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of observed tracer plumes, as well as for making inferences about controlling processes

Development of a liquid membrane technique to measure the temporal variation in “bioavailable” copper and nickel in the South San Francisco Bay

A supported liquid membrane (SLM) technique for the determination of free and labile copper in estuarine and coastal water was developed. The SLM consisted of 10 mM Lasalocid, a naturally occurring carboxylic polyether ionophore, dissolved in o-nitrophenyl octyl ether (NPOE), immobilized on a thin microporous solid membrane. The solid membrane was sandwiched between two aqueous phases: (1) a source or sample solution containing the analyte (in this case free/labile copper) to be extracted and (2) a strip or acceptor solution into which the analyte(s) is trapped. The membrane support was clamped between two circular Teflon blocks each with circular groves like an Archimedes spiral.The SLM was used to extract free and labile copper from water samples collected from two sampling stations, Dumbarton Bridge and San Bruno Shoals in South San Francisco Bay The copper concentration in the SLM extracts was determined off-line by GFAAS.Between 90-97% of the total dissolved copper was bound to organic ligands, and therefore not “bioavailable” to phytoplankton. Thus only about 5-10% of the total dissolved copper existed as inorganic and/or labile organic copper species. The measurements were consistent with earlier copper speciation measurements that were made in South San Francisco Bay using electrochemical methods

Dissolved trace metal concentrations from a GO-FLO rosette collected during the R/V Thomas G. Thompson cruise TN303 from Peru to Tahiti in 2013 (U.S. GEOTRACES EPZT project)

Dataset: GP16 Trace Metals DissolvedDissolved trace metal concentrations from a GO-FLO rosette collected during the R/V Thomas G. Thompson cruise TN303 from Peru to Tahiti in 2013. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/643423NSF Division of Ocean Sciences (NSF OCE) OCE-123350