An official website of the United States government
Dissolved iron (dFe) is an essential micronutrient for phytoplankton, with vanishingly low oceanic dissolved concentrations (pico- to nanomoles per kg) known to limit growth—and thus influence primary productivity and carbon cycling—over much of the surface ocean. However, because of the considerable challenges associated with contamination-free sample collection and accurate analysis of such low dFe concentrations, the first reliable dFe measurements came only in the 1980s. Further, by 2003, despite several decades of research, there were only ~25 full-depth oceanic dFe profiles worldwide, with dust considered to be the main oceanic dFe source. Since 2008, facilitated by the extensive field campaign and rigorous intercalibration of the international GEOTRACES program, there has been an “explosion” in the availability of oceanic dFe data, with hundreds of profiles now available. Concurrently, there has been a paradigm shift to a view of the marine Fe cycle where multiple sources contribute, and some forms of dFe can be transported great distances through the intermediate and deep ocean. Here, we showcase the GEOTRACES dFe datasets across the different ocean basins, synthesize our current multi-source view of the oceanic Fe cycle, spotlight sediments as an important dFe source, and look to future directions for constraining oceanic dFe boundary exchange.
more »
« less
Spectroscopic models of CO2 microsolvation: Bringing data analytics techniques to undergraduate physical chemistry research
Broadband microwave spectra have been recorded for weakly bound clusters formed from mixtures containing fluoroethylene (FE) or 1,1-difluoroethylene (DFE) and varying percentages of CO2. These clusters serve as simple models for behavior of supercritical CO2 as a solvent. Analysis of changes in rotational transition intensities as CO2 concentration is systematically varied allows identification and assignment of spectra for a multitude of different clusters from within a single data set, with at least 15 species identified in FE/CO2 mixtures, and 4 species so far identified in DFE/CO2 mixtures. Several analysis approaches have been implemented, ranging from simple correlation of intensity variations between two spectra recorded with different sample concentrations, to more sophisticated principal component analysis based representations of the spectroscopic data from multiple scans. These techniques provide a range of tools that, in addition to facilitating assignment of spectra of complex mixtures, also assist in identifying the chemical species that give rise to the spectra within each mixture. The visual aspects of the research process, and the accessibility of coding tools such as Python, Excel and Mathcad, make this work particularly appropriate to undergraduate students, including those with little or no previous physical chemistry experience.
more »
« less
- Award ID(s):
- 1664900
- PAR ID:
- 10290645
- Date Published:
- Journal Name:
- American Chemical Society National Meeting Fall 2021
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The method of competitive ligand exchange followed by adsorptive cathodic stripping voltammetry (CLEAdCSV) allows for the determination of dissolved iron (DFe) organic speciation parameters, i.e., ligand concentration (LFe) and conditional stability constant (log Kcond Fe′L ). Investigation of DFe organic speciation by CLEAdCSV has been conducted in a wide range of marine systems, but aspects of its application pose challenges that have yet to be explicitly addressed. Here, we present a set of observations and recommendations to work toward establishing best practice for DFe organic speciation measurements using the added ligand salicylaldoxime (SA). We detail conditioning procedures to ensure a stable AdCSV signal and discuss the processes at play during conditioning. We also present step-by-step guidelines to simplify CLE-AdCSV data treatment and interpretation using the softwares ECDSoft and ProMCC and a custom spreadsheet. We validate our application and interpretation methodology with the model siderophore deferoxamine B (DFO-B) in a natural seawater sample. The reproducibility of our application and interpretation methodology was evaluated by running duplicate titrations on 19 samples, many of which had been refrozen prior to the duplicate analysis. Nevertheless, 50% of the duplicate analyses agreed within 10% of their relative standard deviation (RSD), and up to 80% within 25% RSD, for both LFe and log Kcond Fe′L . Finally, we compared the sequential addition and equilibration of DFe and SA with overnight equilibration after simultaneous addition of DFe and SA on 24 samples. We found a rather good agreement between both procedures, with 60% of samples within 25% RSD for LFe (and 43% of samples for log KcondFe′L ), and it was not possible to predict differences in LFe or log KcondFe′L based on the method applied, suggesting specific association/dissociation kinetics for different ligand assemblages. Further investigation of the equilibration kinetics against SA may be helpful as a potential way to distinguish natural ligand assemblages.more » « less
-
Abstract Open clusters are key chemical and age tracers of Milky Way evolution. While open clusters provide significant constraints on galaxy evolution, their use has been limited due to discrepancies in measuring abundances from different studies. We analyze medium-resolution (R∼ 19,000) Cerro Tololo Inter-American Observatory/Hydra spectra of giant stars in 58 open clusters using The Cannon to determine [Fe/H], [Mg/Fe], [Si/Fe], [Al/Fe], and [O/Fe]. This work adds an additional 55 primarily southern hemisphere open clusters calibrated to the Sloan Digital Sky Survey/Apache Point Observatory Galactic Evolution Experiment DR16 metallicity system. This uniform analysis is compared to previous studies [Fe/H] measurements for 23 clusters and we present spectroscopic metallicities for the first time for 35 open clusters.more » « less
-
Abstract We present a new approach for quantifying the bioavailability of dissolved iron (dFe) to oceanic phytoplankton. Bioavailability is defined using an uptake rate constant (kin‐app) computed by combining data on: (a) Fe content of individual in situ phytoplankton cells; (b) concurrently determined seawater dFe concentrations; and (c) growth rates estimated from the PISCES model. We examined 930 phytoplankton cells, collected between 2002 and 2016 from 45 surface stations during 11 research cruises. This approach is only valid for cells that have upregulated their high‐affinity Fe uptake system, so data were screened, yielding 560 single cellkin‐appvalues from 31 low‐Fe stations. We normalizedkin‐appto cell surface area (S.A.) to account for cell‐size differences. The resulting bioavailability proxy (kin‐app/S.A.) varies among cells, but all values are within bioavailability limits predicted from defined Fe complexes. In situ dFe bioavailability is higher than model Fe‐siderophore complexes and often approaches that of highly available inorganic Fe′. Station averagedkin‐app/S.A. are also variable but show no systematic changes across location, temperature, dFe, and phytoplankton taxa. Given the relative consistency ofkin‐app/S.A. among stations (ca. five‐fold variation), we computed a grand‐averaged dFe availability, which upon normalization to cell carbon (C) yieldskin‐app/C of 42,200 ± 11,000 L mol C−1 d−1. We utilizekin‐app/C to calculate dFe uptake rates and residence times in low Fe oceanic regions. Finally, we demonstrate the applicability ofkin‐app/C for constraining Fe uptake rates in earth system models, such as those predicting climate mediated changes in net primary production in the Fe‐limited Equatorial Pacific.more » « less
-
null (Ed.)The incorporation of substitutional Co2+ impurities in [Cd10S4(SPh)16]4– (Cd10) molecular clusters prepared by the self-assembly method where Na2S is the sulfur precursor and a redox method where elemental S is the sulfur precursor is studied. The Co2+ ions provide unique spectroscopic and chemical handles to monitor dopant speciation during cluster formation and determine what role, if any, other cluster species play during Cd10 cluster formation. In contrast to the redox method that produces exclusively surface-exchanged Co2+-doped Cd10 (Co:Cd10), the preparation of Cd10 by the self-assembly method in the presence of Co2+ ions results in Co2+ incorporation at both the surface and core sites of the Cd10 cluster. Electrospray ionization mass spectrometry (ESI–MS) analysis of the dopant distribution for the self-assembly synthesis of Co:Cd10 is consistent with a near-Poissonian distribution for all nominal dopant concentrations albeit with reduced actual Co2+ incorporation. At a nominal Co2+ concentration of 50%, we observe incorporation of up to seven Co2+ ions within the Cd10 self-assembled cluster compared to a maximum of only four Co2+ dopants in the Cd10 redox clusters. The observation of up to seven Co2+ dopants must involve substitution of at least three core sites within the Cd10 cluster. Electronic absorption spectra of the Co2+ ligand field transition in the heavily doped Co:Cd10 clusters display clear deviation with the surface-doped Co2+-doped Cd10 clusters prepared by the redox method. We hypothesize that the coordination of Co2+ and S2– ions in solution prior to cluster formation, which is possible only with the self-assembly method, is critical to the doping of Co2+ ions within the Cd10 cores.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- The DOI is not currently available.
