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  • 1
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    Spatial heterogeneity in particle-associated, light-independent superoxide production within productive coastal waters (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sutherland, K. M., Grabb, K. C., Karolewski, J. S., Plummer, S., Farfan, G. A., Wankel, S. D., Diaz, J. M., Lamborg, C. H., & Hansel, C. M. Spatial heterogeneity in particle-associated, light-independent superoxide production within productive coastal waters. Journal of Geophysical Research: Oceans, 125(10), (2020): e2020JC016747, https://doi.org/10.1029/2020JC016747.
    Description: In the marine environment, the reactive oxygen species (ROS) superoxide is produced through a diverse array of light‐dependent and light‐independent reactions, the latter of which is thought to be primarily controlled by microorganisms. Marine superoxide production influences organic matter remineralization, metal redox cycling, and dissolved oxygen concentrations, yet the relative contributions of different sources to total superoxide production remain poorly constrained. Here we investigate the production, steady‐state concentration, and particle‐associated nature of light‐independent superoxide in productive waters off the northeast coast of North America. We find exceptionally high levels of light‐independent superoxide in the marine water column, with concentrations ranging from 10 pM to in excess of 2,000 pM. The highest superoxide concentrations were particle associated in surface seawater and in aphotic seawater collected meters off the seafloor. Filtration of seawater overlying the continental shelf lowered the light‐independent, steady‐state superoxide concentration by an average of 84%. We identify eukaryotic phytoplankton as the dominant particle‐associated source of superoxide to these coastal waters. We contrast these measurements with those collected at an off‐shelf station, where superoxide concentrations did not exceed 100 pM, and particles account for an average of 40% of the steady‐state superoxide concentration. This study demonstrates the primary role of particles in the production of superoxide in seawater overlying the continental shelf and highlights the importance of light‐independent, dissolved‐phase reactions in marine ROS production.
    Description: This work was funded by grants from the Chemical Oceanography program of the National Science Foundation (OCE‐1355720 to C. M. H. and C. H. L.), NASA Earth and Space Science Fellowship (Grant NNX15AR62H to K. M. S.), Agouron Institute Postdoctoral Fellowship (K. M. S.), NSF GRFPs (2016230268 to K. C. G. and 2017250547 to S. P.), and a Sloan Research Fellowship (J. M. D.). The Guava flow cytometer was purchased through an NSF equipment improvement grant (1624593).
    Keywords: reactive oxygen species ; Extracellular superoxide ; Light‐independent ROS
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Substantial oxygen consumption by aerobic nitrite oxidation in oceanic oxygen minimum zones (2022)
    Nature Research
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    Publication Date: 2022-05-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Beman, J. M., Vargas, S. M., Wilson, J. M., Perez-Coronel, E., Karolewski, J. S., Vazquez, S., Yu, A., Cairo, A. E., White, M. E., Koester, I., Aluwihare, L. I., & Wankel, S. D. Substantial oxygen consumption by aerobic nitrite oxidation in oceanic oxygen minimum zones. Nature Communications, 12(1), (2021): 7043, https://doi.org/10.1038/s41467-021-27381-7.
    Description: Oceanic oxygen minimum zones (OMZs) are globally significant sites of biogeochemical cycling where microorganisms deplete dissolved oxygen (DO) to concentrations 〈20 µM. Amid intense competition for DO in these metabolically challenging environments, aerobic nitrite oxidation may consume significant amounts of DO and help maintain low DO concentrations, but this remains unquantified. Using parallel measurements of oxygen consumption rates and 15N-nitrite oxidation rates applied to both water column profiles and oxygen manipulation experiments, we show that the contribution of nitrite oxidation to overall DO consumption systematically increases as DO declines below 2 µM. Nitrite oxidation can account for all DO consumption only under DO concentrations 〈393 nM found in and below the secondary chlorophyll maximum. These patterns are consistent across sampling stations and experiments, reflecting coupling between nitrate reduction and nitrite-oxidizing Nitrospina with high oxygen affinity (based on isotopic and omic data). Collectively our results demonstrate that nitrite oxidation plays a pivotal role in the maintenance and biogeochemical dynamics of OMZs.
    Description: This work was supported by NSF CAREER Grant OCE-1555375 to J.M.B. Metagenome sequencing was supported by the UCMEXUS-CONACyT Collaborative Grants Program (joint awards to J.M.B. and José García Maldonado).
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Isotopic constraints on nitrogen transformation rates in the deep sedimentary marine biosphere (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-06-10
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Isotopic constraints on nitrogen transformation rates in the deep sedimentary marine biosphere. Global Biogeochemical Cycles, 32, (2018):1688–1702., doi: 10.1029/2018GB005948.
    Description: Little is known about the nature of microbial community activity contributing to the cycling of nitrogen in organic-poor sediments underlying the expansive oligotrophic ocean gyres. Here we use pore water concentrations and stable N and O isotope measurements of nitrate and nitrite to constrain rates of nitrogen cycling processes over a 34-m profile from the deep North Atlantic spanning fully oxic to anoxic conditions. Using a 1-D reaction-diffusion model to predict the distribution of nitrogen cycling rates, results converge on two distinct scenarios: (1) an exceptionally high degree of coupling between nitrite oxidation and nitrate reduction near the top of the anoxic zone or (2) an unusually large N isotope effect (~60‰) for nitrate reduction that is decoupled from the corresponding O isotope effect, which is possibly explained by enzyme-level interconversion between nitrite and nitrate.
    Description: Samples analyzed for this study were collected during the final expedition of the RV Knorr, KN223. The expedition would not have been possible without the captain and crew of the RV Knorr and the efforts of the shipboard science party. We would like to acknowledge Robert Pockalny for planning and facilitating the expedition. Inorganic geochemistry sample collection, processing, and analysis were performed shipboard by Arthur Spivack,Dennis Graham, Chloe Anderson, Emily Estes, Kira Homola, Claire McKinley, Theodore Present, and Justine Sauvage. Coring capabilities were provided by the Oregon State University and Woods Hole Oceanographic Institute Coring Facilities, directed and funded by the U. S. National Science Foundation (NSF) Ship Facilities Program. The cored materials and discrete samples from the expedition are curated and stored by the Marine Geological Samples Laboratory at the University of Rhode Island, codirected by Rebecca Robinson and Katherine Kelly and funded by the NSF Ocean Sciences Division. The nutrient and isotope data from pore waters in this study will be available at The Biological and Chemical Data Management Office (https://www.bcodmo.org/project/567401). This project was partially funded by an NSF CDEBI postdoctoral fellowship to C. Buchwald. Portions of this material are based upon work supported while R. W. M. was serving at the National Science Foundation.
    Description: 2019-04-18
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Recent increases in water column denitrification in the seasonally suboxic bottom waters of the Santa Barbara Basin (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46(12), (2019): 6786-6795, doi:10.1029/2019GL082075.
    Description: Denitrification in the anoxic sediments of the Santa Barbara Basin has been well documented in the historic and modern record, but the regulation of and frequency with which denitrification occurs in the overlying water column are less understood. Since 2004, the magnitude and speciation of redox active nitrogen species in bottom waters have changed markedly. Most notable are periods of decreased nitrate and increased nitrite concentrations. Here we examine these changes in nitrogen cycling as recorded by the stable isotopes of dissolved nitrate from 2010–2016. When compared to previous studies, our data identify an increase in water column denitrification in the bottom waters of the basin. Observations from inside the basin as well as data from the wider California Current Ecosystem implicate a long‐term trend of decreasing oxygen concentrations as the driver for these observed changes, with ramifications for local benthic communities and regional nitrogen loss.
    Description: We thank CalCOFI and Shonna Dovel for sample collection and two anonymous reviewers for improving the manuscript. Thanks also to Daniel Sigman for useful discussions, and Zoe Sandwith and Jen Karolewski for help with sample analysis. Data sets presented here were supported in part by CCE‐LTER augmented funding (NSF grant OCE‐1026607). Additional funding came from the Edna Bailey Sussman Foundation and the San Diego Foundation Blasker Environment grant. All data can be accessed at http://calcofi.org and https://oceaninformatics.ucsd.edu/datazoo/catalogs/ccelter/datasets. SDW acknowledges the support of a fellowship through the Hanse‐Wissenschaftskolleg (Institute for Advanced Studies).
    Description: 2019-12-11
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    Oxygen isotopes (delta O-18) trace photochemical hydrocarbon oxidation at the sea surface (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46(12), (2019): 6745-6754, doi:10.1029/2019GL082867.
    Description: Although photochemical oxidation is an environmental process that drives organic carbon (OC) cycling, its quantitative detection remains analytically challenging. Here, we use samples from the Deepwater Horizon oil spill to test the hypothesis that the stable oxygen isotope composition of oil (δ18OOil) is a sensitive marker for photochemical oxidation. In less than one‐week, δ18OOil increased from −0.6 to 7.2‰, a shift representing ~25% of the δ18OOC dynamic range observed in nature. By accounting for different oxygen sources (H2O or O2) and kinetic isotopic fractionation of photochemically incorporated O2, which was −9‰ for a wide range of OC sources, a mass balance was established for the surface oil's elemental oxygen content and δ18O. This δ18O‐based approach provides novel insights into the sources and pathways of hydrocarbon photo‐oxidation, thereby improving our understanding of the fate and transport of petroleum hydrocarbons in sunlit waters, and our capacity to respond effectively to future spills.
    Description: We thank Robert Ricker and Greg Baker (NOAA) for helping secure the oil residues, James Payne (Payne Environmental Consultants, Inc.) for collecting many of the surface oil residues, Joy Matthews (UC Davis) for exceptional assistance in preparing and analyzing the oil residues for oxygen content and isotopes, Hank Levi and Art Gatenby at CSC Scientific Company for assistance with the water content measurements, Robyn Comny (US EPA) for providing the Alaska North Slope oil, and Rose Cory (UMich) for discussions about our findings. Special thanks to John Hayes who provided constructive feedback on a preliminary version of this dataset prior to his passing in February of 2017. We thank Alex Sessions (CalTech) for his constructive feedback during the review process. This work was supported, in part, by National Science Foundation grants RAPID OCE‐1043976 (CMR), OCE‐1333148 (CMR), OCE‐1333026 (CMS), OCE‐1333162 (DLV), OCE‐1841092 (CPW), NASA NESSF NNX15AR62H (KMS), the Gulf of Mexico Research Initiative grants ‐ 015, SA 16‐30, and DEEP‐C consortium, a fellowship through the Hansewissenschaftskolleg (Institute for Advanced Studies) to SDW, and assistant scientist salary support from the Frank and Lisina Hoch Endowed Fund (CPW).
    Description: 2019-11-30
    Keywords: Petroleum hydrocarbons ; Photochemical oxidation ; Deepwater Horizon ; Stable oxygen isotopes ; Organic carbon
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Spectroscopic insights into ferromanganese crust formation and diagenesis (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 21(11), (2020): e2020GC009074, doi:10.1029/2020GC009074.
    Description: Marine ferromanganese deposits, often called the scavengers of the sea, adsorb and coprecipitate with a wide range of metals of great interest for paleo‐environmental reconstructions and economic geology. The long (up to ∼75 Ma), near‐continuous record of seawater chemistry afforded by ferromanganese deposits offers much historical information about the global ocean and surface earth including crustal processes, mantle processes, ocean circulation, and biogeochemical cycles. The extent to which the ferromanganese deposits hosting these geochemical proxies undergo diagenesis on the seafloor, however, remains an important and challenging factor in assessing the fidelity of such records. In this study, we employ multiple X‐ray techniques including micro–X‐ray fluorescence, bulk and micro–X‐ray absorption spectroscopy, and X‐ray powder diffraction to probe the structural, compositional, redox, and mineral changes within a single ferromanganese crust. These techniques illuminate a complex two‐dimensional structure characterized by crust growth controlled by the availability of manganese (Mn), a dynamic range in Mn oxidation state from +3.4 to +4.0, changes in Mn mineralogy over time, and recrystallization in the lower phosphatized portions of the crust. Iron (Fe) similarly demonstrates spatial complexity with respect to concentration and mineralogy, but lacks the dynamic range of oxidation state seen for Mn. Micrometer‐scale measurements of metal abundances reveal complex element associations between trace elements and the two major oxide phases, which are not typically resolvable via bulk analytical methods. These findings provide evidence of post‐depositional processes altering chemistry and mineralogy, and provide important geochemical context for the interpretation of element and isotopic records in ferromanganese crusts.
    Description: This research is supported by NASA Exobiology NNX15AM046 to Scott D. Wankel and Colleen M. Hansel, NASA NESSF NNX15AR62H to Kevin M. Sutherland, and WHOI Ocean Exploration Institute to Colleen M. Hansel. The Stanford Synchrotron Radiation Lightsource was utilized in this study. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE‐AC02‐76SF00515.
    Description: 2021-04-26
    Keywords: Diagenesis ; Ferromanganese crust ; Manganese oxide minerals ; X‐ray absorption spectroscopy
    Repository Name: Woods Hole Open Access Server
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